 | Note: Large images and tables on this page may necessitate printing in landscape mode.
Copyright 2007 The McGraw-Hill Companies. All rights reserved.
Current Otolaryngology > XIV. Skull Base > Chapter 60. Lesions of the Anterior Skull Base >
| Lesions of the Anterior Skull Base: Introduction Although it remains a formidable problem, the anterior skull base is no longer an absolute barrier to the effective management of tumors that encroach on it. The otolaryngologisthead and neck surgeon involved in the multidisciplinary team that approaches this area will necessarily have an in-depth knowledge of surgical anatomy and tumor pathology, familiarity with radiologic assessment and the roles of interventional radiology , and experience with the various surgical approaches that have been used to access this area. Most of the problems the surgical team encounters in anterior skull base surgery are either malignant tumors of the paranasal sinuses that extend superiorly to involve the anterior skull base, or benign or malignant processes such as meningiomas, which extend inferiorly from above. In addition, benign lesions of the paranasal sinuses, such as extensive inverted papillomas, extensive mucoceles, and selected benign fibro-osseous lesions, occasionally require these approaches to skull base surgery. | | Anatomy The anterior skull base is the skull base superior to the orbit and the ethmoid and sphenoid sinuses. It includes the posterior wall of the frontal sinus, the ethmoid roof and cribriform plate, and the orbital roof. More posteriorly, it includes parts of the sphenoid bone, including the lesser wing of the sphenoid, the planum sphenoidale, and the roof of the sphenoid sinus. Orbit A thin fascial layer surrounds the orbital fat that lies just within the orbital periosteum. Preserving this layer allows for the resection of the orbital periosteum, when needed, while maintaining the integrity of the orbital contents. The significance of this layer is that the orbit is generally able to be preserved if the extraocular muscles , which are inside this fascial plane, are uninvolved. This is generally true when the patient has full extraocular motility preoperatively, and it may be true at times even when there is some diplopia secondary to mass effect. The actual invasion of orbit fat deep to this fascial plane usually suggests the need for orbital exenteration. The optic canal transmits the optic nerve and the ophthalmic artery. The ophthalmic artery originates superiorly to superomedially from the internal carotid artery (ICA), but then courses laterally such that it is found lateral to the optic nerve at the anterior optic canal. The significance of this anatomy is that dissection of the medial surface of the optic nerves to the optic chiasm is generally safe with respect to its blood supply. The optic nerve, contained within a thin sheath of bone, is usually seen within the sphenoid sinus just superior to the ICA, which also is generally separated from the sphenoid sinus by bone. The optic nerve (and ophthalmic artery) borders the posterior ethmoidal air cells in about 1015% of cases. Imola MJ, Schramm VL Jr. Orbital preservation in surgical management of sinonasal malignancy. Laryngoscope. 2002;112:1357. (Orbital preservation is sound in selected cases. Although 30% of the 66 reviewed cases recurred locally, this was at the site of the initial orbit involvement in only 8% of these cases.) [PMID: 12172245]
| Rhoton AL Jr. The anterior and middle cranial base. Neurosurgery. 2002;51:273. (Overview of the anterior and middle cranial base.) [PMID: 12234451]
| Tiwari R, van der Wal J, van der Waal I, Snow G. Studies of the anatomy and pathology of the orbit in carcinoma of the maxillary sinus and their impact on preservation of the eye in maxillectomy. Head Neck. 1998;20(3):193. (Periocular fat is surrounded by a thin distinct fascial layer and is not in direct contact with the periorbita.) [PMID: 9570623]
| Paranasal Sinuses The variability in individual anatomy is such that a preoperative evaluation using magnetic resonance imaging (MRI) is essential in planning operative approaches. Sometimes, for example, tumor has eroded bone such that a particular approach becomes ideal. Although the sphenoid sinus septum is usually midline anteriorly at the sphenoid rostrum, it almost always deviates laterally as it courses posteriorly. In addition, additional septa within the sphenoid sinus are common and can confuse an unwary surgeon. Intraoperative navigation can be useful so that the surgeon can be sure that the lateral limit of the sphenoid sinus has been accessed. Traditionally, access to the sphenoid sinus is via the ethmoid sinuses from the front. However, if access to the skull base from above is needed for an individual, superb access to the sphenoid sinus, as well as the ethmoids and maxillary sinus, is possible from above. Brain, Dura, Olfactory Nerves, & Frontal Bone The cribriform plate is medial to the ethmoid roof and is separated from it by the superior attachment of the middle turbinate. Anatomically, the cribriform plate is usually 13 mm more inferior than the ethmoid roof and is perforated by the olfactory system. Dura at the cribriform plate is closely adherent to bone, unlike at the ethmoid roof where it can be separated more easily. The crista galli lies in the midline, directly above the superior extent of the nasal septum. The crista galli and nasal septum separate the left and right cribriform plates. Occasionally, the physician can consider saving the contralateral olfactory system when resecting a tumor that penetrates the skull base unilaterally in this area. The involvement of the dura and the brain by malignant neoplasms of the paranasal sinuses is prognostically unfavorable. Dura is often resected in this area. The effective repair and subsequent segregation of brain and frontal bone plate from underlying sinuses is critical in preventing both cerebrospinal fluid (CSF) leaks and osteomyelitis of the bone flap. | | Limits of Resection The limits of modern resection have changed in the past 25 years . A generation ago, it was generally felt that the skull base was unresectable, as was the pterygomaxillary space, the nasopharynx, and the ICA. Tumors that extend to the pterygomaxillary space, involve the orbital periosteum, or infiltrate the dura have a worse prognosis than those that do not. However, all three of these anatomic areas are technically resectable. A unilateral ICA can be resected with some degree of safety. A unilateral ICA can be resected with about a 5% risk of a cerebrovascular accident when a patient has successfully passed a balloon test occlusion . In this test, a transarterial balloon is placed by an interventional neuroradiologist into the ICA and inflated to occlude proximal blood flow to the brain. A patient is considered to have "passed" when he remains symptom-free and maintains adequate back pressures in the ICA distal to the ballooneven when, pharmacologically, the systemic blood pressure has been reduced 20 mm Hg. Most surgeons feel that the optic chiasm is not resectable. Most surgeons also agree that patients with a malignant tumor that extends to involve the cavernous sinus are rarely helped by surgery. Similarly, surgery is unlikely to improve the prognosis when a malignant neoplasm extends from paranasal sinuses to beyond the mucosa and cartilage in the nasopharynx. The limits of resection today are posterior and superolateral: the osseous components of the nasopharynx, the cavernous sinus, and the optic chiasm. | | Malignant Neoplasms Malignant tumors of the paranasal sinuses are fortunately rare, accounting for about 1:1,000,000 cases overall and representing < 23% of head and neck cancers. Most of these malignant tumors do not extend to the skull base, but skull base resection should be considered for the minority of tumors that do. In addition, benign processes that may also require anterior skull base resections include some angiofibromas, some fibro-osseous benign tumors, occasional inverted papillomas, and occasional sequelae of chronic sinusitis (eg, mucoceles). Squamous Cell Carcinoma The most common malignant tumor of the paranasal sinuses is squamous cell carcinoma (SCC). The antrum, the largest sinus, is the most common site of SCC, but extension posteriorly and superiorly may lead to the necessity of including a skull base resection in the overall management. About 10% of tumors present with neck nodes, and about 20% of patients develop cervical nodes if no elective neck irradiation is included in the treatment plan. The radiologic assessment of the course of V2 is important to exclude perineural spread before surgery and as a baseline for future evaluation. For tumors that extend to the skull base, combining skull base surgery with postoperative irradiation has improved the overall local control and cure rates from < 50% to about 60%. Le QT, Fu KK, Kaplan MJ, Terris DJ, Fee WE, Goffinet DR. Lymph node metastasis in maxillary sinus carcinoma. Int J Radiat Oncol Biol Phys. 20001;46(3):541. (The overall risk of developing cervical metastases from squamous cell carcinoma of the maxillary sinus was 28%; no patients who received elective neck irradiation subsequently developed nodal metastases.) [PMID: 10701732]
| Paulino AC, Fisher SG, Marks JE. Is prophylactic neck irradiation indicated in patients with squamous cell carcinoma of the maxillary sinus? Int J Radiat Oncol Biol Phys. 1997;39(2):283. (Four of 42 patients presented with nodal metastases. Eleven [29%] of 42 patients with nodal metastases subsequently developed neck metastases, and because of this, the authors recommended prophylactic neck irradiation.) [PMID: 9308929]
| Adenocarcinoma Adenocarcinoma represents approximately 1015% of paranasal sinus tumors. Involvement in the woodworking and leather industries is a causative factor in the development of adenocarcinoma, especially in Europe. Since distant spread is uncommon, local control is the goal. Results of surgery and postoperative irradiation suggest cure rates between 45% and 85%, with a meta-analysis suggesting that about two thirds of patients are cured. Adenoid Cystic Carcinoma Adenoid cystic carcinoma (ACC) represents about 1015% of paranasal sinus tumors and tends to recur locally, despite surgery and irradiation. Approximately 1520% of patients with ACC develop hematogenous metastases, especially to the lungs; therefore, an initial metastatic evaluation is important. Because it is advisable to resect isolated lung metastases, periodic metastatic evaluations remain an important part of post-treatment tumor follow-up. A baseline computed tomography (CT) scan of the chest followed by a chest scan repeated at least annually is recommended. When the initial tumor is bright on positron emission tomography (PET) scanning, it is logical to use PET as a total body screen; however, the use of periodic PET scans has not been established for this histology. Recent reviews suggest that the 5-year local control rate is as high as 60%, with a sizable number of patientsperhaps 1520%experiencing local recurrences but living with tumor. Like SCC, perineural spread should be specifically investigated by MRI, both initially and in follow-ups because there is evidence that gamma knife radiosurgery for perineural spread along the fifth cranial nerve is effective in both reducing pain and in controlling disease progression. Pitman KT, Prokopakis EP, Aydogan B et al. The role of skull base surgery for the treatment of adenoid cystic carcinoma of the sinonasal tract . Head Neck. 1999;21(5):402. (Following surgery and radiation therapy , 36% recurred locally, 14% regionally , and 21% developed distant metastases. Skull base surgery facilitated gross total resection of lesions once deemed inoperable, but has not resulted in an overall improvement in the disease-free survival rate of 46%.) [PMID: 10402519]
| Esthesioneuroblastoma (Olfactory Neuroblastoma) A tumor of neuroendocrine origin, esthesioneuroblastomas are tumors of the olfactory nerve and are seen above and below the cribriform plate. An MRI evaluation is essential to determine the extent of intracranial involvement. At times, no involvement appears to exist superior to the cribriform plate, suggesting that resection of the dura around the olfactory groove would fully encompass the superior extent of the tumor. Occasionally, there is extensive involvement of dura and even brain. Nodal or distant metastases are rare at presentation. Eventually, about 10% of patients develop neck metastases. Several staging classifications have been suggested based on the anatomic extent of tumor or based on the assessment of histologic parameters. Tumors that appear histologically aggressive and those with extension to the orbit or dura appear to do somewhat worse to the extent that the analysis of few cases can generalize. The rarity of this tumor makes the comparison of different treatment regimens difficult. In most centers, surgery and radiation therapy are the mainstays of treatment, with 5-year cure rates frequently reported in the range of 74% to 86%. The role of chemotherapy remains unclear: some centers routinely include cisplatin-based treatment whenever there is bone erosion superiorly through the cribriform plate, whereas others reserve this for only the most advanced tumors. In addition, there are reports of chemotherapy and radiation therapy alone being used with initially good results, although the follow-up has been relatively brief. Lund VJ, Howard D, Wei W, Spittle M. Olfactory neuroblastoma: past, present, and future? Laryngoscope. 2003;113(3):502. (A combination of skull base resection and irradiation, which was superior to surgery alone, is the standard to which other approaches must be judged. The 5- and 10-year disease-free actuarial survival was 77% and 53%, respectively, among the 24 patients so treated.) [PMID: 12616204]
| Melanoma Melanomas of the nose and paranasal sinuses portend a poor prognosis, with high rates of both local recurrence and distant metastases. When there are already metastases, participation in chemotherapy protocols is available. If disease appears to be locally confined, then surgical resection and irradiation are often plausible, despite the prognosis, as long as the morbidity is minimal. Whether radiation fractionation should be standard1.82.0 Gy daily for 5 d/wk to a dose of 6066 Gyor provided as 6 Gy twice weekly to a total dose of 30 Gy is not definitively known. The 5-year survival rate of melanoma of the nose and paranasal sinuses has been reported to be in the range of 14% to 47%, with most reports citing 2025%. When recurrences can be surgically resected with a minimum of morbidity, then a nasal airway may be maintained and epistaxis reduced. Medina JE, Ferlito A, Pellitteri PK et al. Current management of mucosal melanoma of the head and neck. J Surg Oncol. 2003;83(2):116. (Reviews current management of this rare tumor that portends a poor prognosis.) [PMID: 12772206]
| Patel SG, Prasad ML, Escrig M et al. Primary mucosal malignant melanoma of the head and neck. Head Neck. 2002;24(3):247. (Significant prognostic factors include advanced clinical stage, tumor thickness > 5 mm, the presence of vascular invasion, and the development of distant metastases.) [PMID: 11891956]
| Thompson LD, Wieneke JA, Miettinen M. Sinonasal tract and nasopharyngeal melanomas: a clinicopathologic study of 115 cases with a proposed staging system. Am J Surg Pathol. 2003;27(5):594. (Reviews histologic and immunohistochemical parameters of sinonasal tract and nasopharyngeal melanomas.) [PMID: 12717245]
| Sinonasal Undifferentiated Carcinoma Sinonasal undifferentiated carcinoma is a rare and highly aggressive malignant tumor that is distinct from other apparently poorly differentiated small, round-cell tumors. At presentation, the tumor is invariably extensive, commonly involving the orbit and extending to or through the skull base. Neck metastases are seen in 20% of patients. The prognosis is very poor. An optimal treatment modality has not evolved; multimodality therapy is generally used. The goal of treatment should be the control of local disease, including the preservation of vision as long as possible and the prevention or at least delay of intracranial extension and its sequelae. Mills SE. Neuroectodermal neoplasms of the head and neck with emphasis on neuroendocrine carcinomas. Mod Pathol. 2002; 15(3):264. (Clarifies the confusion in the literature regarding neuroendocrine carcinomas in the head and neck; suggests that sinonasal undifferentiated carcinoma is likely of neuroectodermal origin.) [PMID: 11904342]
| Miyamoto RC, Gleich LL, Biddinger PW, Gluckman JL. Esthesioneuroblastoma and sinonasal undifferentiated carcinoma: impact of histological grading and clinical staging on survival and prognosis. Laryngoscope. 2000;110(8):1262. (Reviews Kadish clinical and Hyams histopathologic grading systems for sinonasal undifferentiated carcinoma [and esthesioneuroblastomas]. Although the prognosis for sinonasal undifferentiated carcinomas is poor, 2 of 14 patients had long- term survival, even with advanced disease.) [PMID: 10942123]
| Musy PY, Reibel JF, Levine PA. Sinonasal undifferentiated carcinoma: the search for a better outcome. Laryngoscope. 2002;112:1450. (Reviews experience with chemotherapy, followed by skull base resection in 10 patients, with a 2-year survival rate of 64%.) [PMID: 12172261]
| Chordoma Chordomas are rare tumors of notochord origin that may be seen at the craniocervical junction. About 35% of these tumors are found in this sphenoclival area, with about 15% occurring in vertebrae and the rest in the region of the sacrum and coccyx. Although chordomas have been seen in infants and the elderly, the usual age at presentation is 3550 years. These tumors are usually large at presentation but without evidence of metastases, and they may abut or encase the ICA in the cavernous sinus or the basilar artery. The typical symptoms are headache and diplopia secondary to paresis of cranial nerve VI (the abducens nerve). At times there may be numbness of the face via involvement of sensory branches of the trigeminal nerve. Evaluation by MRI is critical in evaluating the extent of tumor involvement. Chordomas are usually bright on T2-weighted images and enhance heterogeneously with gadolinium. The goal of treatment is as complete a resection as possible by an appropriate approach, followed by irradiation. Although the appearance on MRI of a heterogeneously gadolinium-enhancing lesion that is also bright on T2-weighted images at the craniocervical junction is highly suggestive of a chordoma, this appearance is not pathognomonic. Other entities, such as nasopharyngeal carcinoma, meningioma, metastases, plasmacytoma, and pituitary adenoma, are included in the differential diagnosis. Frozen-section confirmation at the beginning of a resection is therefore recommended. A classic pathologic finding shows physaliphorous cells with abundant mucus or glycogen-rich vacuoles, mucoid microcysts, fibrovascular strands, and cords of eosinophilic syncytial cells. The results of surgery plus charged particle irradiation have demonstrated a 5-year survival rate of 7680% for smaller tumors that had not been previously treated (see Radiation Therapy later in this chapter). At the skull base, about 90% of tumors fall into this favorable category. Larger tumors (> 75 cm 3 ) and recurrent tumors did noticeably worse, with a 5-year cure rate of approximately 33%. Lymphoma Lymphomas represent about 10% of nonepithelial malignant tumors of the paranasal sinuses. The most common lymphoma is diffuse large cell B-cell lymphoma, with patients most often presenting in Stage 1E. Approximately 67% of these patients survive with modern multimodality therapy. CD56+ NK/T-cell lymphomas, especially with a positive finding of the Epstein-Barr virus, represent about 30% of lymphomas when only nasal involvement is seen. Although some Asian studies suggest a poorer prognosis compared with apparently similar patients in the United States, most patients survive. The role of surgery is generally limited to obtaining tissue for diagnosis if a fine-needle aspiration (FNA) of a lymph node is either not available or is insufficient for a definitive diagnosis. | | Benign Neoplasms Juvenile Angiofibroma Juvenile angiofibromas are rare, benign but locally invasive, and highly vascular tumors that occur in male adolescents. They invariably originate at the level of the sphenopalatine foramen on the posterolateral nasal wall at the junction with the nasopharynx and may extend laterally into the pterygopalatine fossa, posteriorly to the sphenoid sinus, or superiorly to and through the skull base. As they extend anteriorly, they lead to nasal obstruction. Because of their high vascularity, recurrent epistaxis is typical. Their appearance on MRI is so typical that the diagnosis can be presumed . Angiography is indicated for preoperative embolization of the tumor and the ipsilateral internal maxillary artery. Treatment is interventional radiologic embolization followed by surgical excision . The approach used should be appropriate for the individual. Usually, a trans-sphenoethmoidal approach is sufficient to remove an angiofibroma completely. Some surgeons prefer a transpalatal approach (or a maxillotomy approach), which offers the advantage of avoiding even a small, well-camouflaged facial incision; however, this approach may either affect palate function or provide suboptimal exposure for larger tumors. If the tumor extends to the greater wing of the sphenoid, then a preauricular orbitozygomatic approach (sometimes combined with a middle cranial fossa approach) is necessary. | | Patient Evaluation Because of the often poor prognosis and the possibility of significant surgical complications, it is important for the physician managing skull base problems to obtain a complete knowledge of the patient's comorbidities and to weigh different options based on the individual. This begins with a thorough history and physical examination. Although the symptoms of lesions of the anterior skull base often mimic those of chronic sinusitis, which is far more common, certain signs and symptoms suggest that the presenting disorder may be far more serious. These include unilateral, persistent lesions (especially if the onset occurs after the age of 50); bleeding; pain; diplopia, epiphora, and numbness (eg, V2). The signs that suggest a possible malignant neoplasm include a visible mass that is either palpable subcutaneously or visible via an endoscopic exam, abnormal extraocular motility, facial dysesthesia or numbness (ie, V13), and a neck mass. If the patient has a history of a malignant tumor, then metastasis should be considered in the differential diagnosis. If there is a history of tobacco use, SCC is a more likely finding; SCC is the most common malignant tumor of the paranasal sinuses, accounting for more than 50% of cases. When the patient history and physical exam are suggestive of a malignant neoplasm, a radiologic evaluation is indicated before obtaining a biopsy. A high-quality MRI is always the examination of choice. T1-weighted images with and without gadolinium, T1-weighted images with fat suppression, and T2-weighted images are indicated. In addition to axial images, invasion through the cribriform area is best evaluated with coronal images, which are sometimes supplemented with sagittal images. Multiplanar images greatly assist the surgeon in visualizing a three-dimensional image of the tumor extent. MRI assesses the vascularity of the tumor and may, at times, strongly suggest a particular diagnosis, such as angiofibroma or lymphoma. Assessing the neck is usually indicated because a number of histologies have the potential to metastasize to the neck. Radiologic assessment is reviewed in more detail in Chapter 3, Radiology. How extensive a metastatic evaluation should be completed before obtaining tissue for pathologic review depends on a number of factors. For example, if lymphoma is suspected, it might be more reasonable at times to pursue the noninvasive aspect of the evaluation as the physician may find an easily accessible node to biopsy. FNA of a neck node, when present, may yield a diagnosis of SCC, thus precluding the need for a nasal biopsy. However, the paranasal sinuses are frequently the sole site of involvement, however extensive, and establishing the diagnosis requires a biopsy. Depending on the individual circumstances, the biopsy may be done in advance of further planning; at times it may be performed at the beginning of a major resection, with the surgeon intending to proceed only if the frozen section diagnosis is definitive. Both a thorough, detailed discussion with the patient and coordination with the primary care and referring physicians are imperative in planning the optimum treatment plan. The primary care physician may have considerable insight about how the patient reacts to bad news as well as how to best establish rapport with the patient and create a treatment plan. Where metastatic evaluations and medical evaluations will be done and how post-treatment follow-up is to be coordinated should all be discussed at this time. The patient must fully comprehend the treatment alternatives, the realistic goals and likelihood of the success of these alternatives, and the potential side effects and complications of each aspect of intervention. The surgeon, who is likely to lead the treatment team both for surgery and for long-term follow-up, must also understand how intervention is likely to affect the particular patient's daily life. He must respect the patient's own goals for treatment and recognize that what he thinks he might choose for himself may be different from what his patient chooses. Plans for follow-up begin preoperatively. If PET scans are to be used in long-term follow-up, it may be helpful to obtain one preoperatively so that any areas that unexpectedly enhance can be evaluated. This approach occasionally also reveals unexpected metastases, which would make a curative surgical approach futile. The need for long-term radiologic and clinical follow-up should be discussed with the patient, the primary care physician and referring physician, and at times the patient's insurance carrier. A high-quality MRI obtained 23 months after the completion of all treatment is valuable as a baseline and is strongly recommended. This is the most sensitive way to detect subtle perineural spread, changes that suggest a possible recurrence, or possible radionecrosis. | | Radiology, Interventional Radiology, & Intraoperative Navigation Improved radiologic imaging, both preoperatively and for intraoperative guidance, has significantly enhanced accurate surgical planning; this allows the physicians to consider combining several low-morbidity approaches, resulting in adequate resection and reduced functional loss. High-quality MRI is imperative. Occasionally, CT scanning is complementary in assessing bone at the cribriform plate, the anterior clinoid process, or the posterior wall of the sphenoid bone. Imaging is reviewed in Chapter 3, Radiology. For highly vascular tumors, the preoperative embolization of both the tumor and the distal internal maxillary artery is helpful in reducing blood loss. A common example of this is the treatment of juvenile angiofibromas. The anterior and posterior ethmoid arteries are branches of the ophthalmic artery. As such, they cannot be safely embolized; therefore, when indicated, they are controlled surgically, usually by a metallic clip. Intraoperative navigation is frequently unnecessary because there are numerous adequate bony landmarks available to the surgeon. However, if important landmarks have been eroded by tumor or removed in a prior surgery or if a structure has been displaced by tumor, then intraoperative navigation may be invaluable. This is especially so if a critical structure within soft tissue cannot be easily found, despite adjacent landmarks . Dissection near the ICA and optic chiasm may often be aided in this manner. | | Treatment Preoperative Considerations Before planning surgery, a metastatic evaluation, as indicated by the histology, is completed. The treatment goals, alternatives, risks, and expected postoperative course are thoroughly discussed with the patient. Follow-up strategies are also discussed with the patient and the referring physician. It is essential for the patient to clearly understand the limitations of surgery, the prognosis, and the alternatives, including palliative measures, even when a reasonably high possibility of a cure is anticipated. The poorer the prognosis, the more the physician should consider a PET scan to screen for metastatic disease; doing so may allow the physician to avoid surgery in patients for whom such an approach would prove futile. If a PET scan is to be considered as part of subsequent tumor surveillance, the physician should consider obtaining it initially to be sure the tumor is detected by the PET scan and to evaluate, in advance of the proposed surgery, any areas that are highlighted by the scan. Surgical Measures The surgical measures discussed here concentrate on the approaches appropriate for paranasal sinus tumors that extend superiorly to the anterior skull base. Such approaches can be expanded to the anterolateral skull base to access the middle cranial fossa floor and cavernous sinus. Similarly, an orbitozygomatic approach can be added if access to the superior infratemporal fossa is required. Access to the central skull base and the craniocervical junction for petroclival chordomas, chondrosarcomas, and meningiomas is also excluded. The four major goals of the multidisciplinary surgical team that approaches a tumor of any part of the skull base are (1) safety; (2) adequate access for three-dimensional tumor resection, with negative surgical margins; (3) minimal brain retraction; and (4) reconstruction that preserves function and aesthetics. How best to accomplish these goals, as well as to succinctly coordinate the overlapping approaches required to do so, has led to the development of several classification schemes. Approaches to the anterior skull base have evolved since their introduction 4050 years ago. Initial approaches to the anterior skull base usually combined a bifrontal craniotomy with modifications of common otolaryngologic approaches, including lateral rhinotomy and external sphenoethmoidectomy. Current skull base surgery uses many complementary approaches to expose the tumor for resection while minimizing morbidity. Frontal brain retraction and edema are reduced by using lumbar subarachnoid drains and by adjusting the angle of approach, such as resecting and later replating the orbital rim when a tumor extends posteriorly to the planum sphenoidale. Facial skin incisions can often be eliminated by accessing the paranasal sinuses either via a bicoronal incision behind the hairline or by adding transoral, transmucosal incisions. For example, a combined glabellar and extended subcranial approach that provides adequate access to the sphenoethmoid and medial maxillary areas may eliminate an external ethmoidectomy incision. Often, all of the paranasal tumor resection can be done through a standard low bifrontal craniotomy, supplemented with a supraorbital rim approach, if needed, without a complete extended subcranial approach. Degloving approaches may be used to supplement the tumor resection. Endoscopic guidance for the paranasal sinus component of the resection may also be used. Many surgeons favor minimizing central facial incisions for anterior skull base lesions. A low bifrontal craniotomy, supplemented as needed by a supraorbital rim approach, provides sufficient access to resect most paranasal sinus tumors that extend through the skull base. The supraorbital rim approach is added, when necessary, either to expose an orbital tumor or to reduce brain retraction when a far posterior exposure is required. When tumor involves bone in the glabellar area, requiring the resection of bone in this area, the extended subfrontal approach, in which the dural component is initially explored from below, provides excellent anterior dural exposure. Postoperative MRI has confirmed the clinical impression of excellent resections and shown only a modest incidence of encephalomalacia, with very few patients experiencing clinical symptoms. When needed, a limited facial incision (ie, a slightly extended external ethmoidectomy) results in good cosmesis. Bicoronal Craniotomy If it is anticipated that the tumor can be resected without a facial incision, then the bifrontal craniotomy with or without a supraorbital rim approach is planned initially. A lumbar subarachnoid drain is usually placed. In contrast, when it is anticipated that resection can be accomplished extradurally or with the resection and repair of dura without a craniotomy, the transfacial approach is initially performed. If intraoperative navigation is to be used, the patient is placed in fixation and the navigation system calibrated. Appropriate perioperative antibiotics are begun. The anesthesiologist monitors end-tidal CO 2 . The bicoronal skin incision from the top of one ear to the top of the other is placed approximately 1 cm posterior to the hairline. The hairline should be marked before shaving, with the patient choosing either a complete or anterior shave. If more skin reflection is needed, the incision can be extended inferiorly to just anterior to the root of the helix , toward the incision usually used for a parotidectomy. This incision incorporates the superficial temporal arteries into the skin flap. A pericranial-galeal flap is separated from the skin flap for later use. Its blood supply is from vessels coursing to it in the superomedial brow. At the end of the procedure, this flap is used to reinforce the dural closure and segregate the dura from the paranasal sinus cavity below it. No bone graft or skin graft is necessary or indicated for a skull base repair, except perhaps in an infant . If the pericranial flap is unavailable because of either tumor involvement or prior surgery, then a microvascular free flap is often used instead, with superficial temporal vessels as the most convenient , correct-caliber vascular access to which to connect the vasculature of the flap. Olfactory Bulb Preservation If the tumor extends across the anterior midline, both olfactory bulbs are sacrificed. Invariably, this is necessary except in the smallest of tumors, such as a very small esthesioneuroblastoma. Orbit Preservation If the extraocular motion is clinically normal, the orbit rarely needs to be sacrificed. Although MRI is the most effective evaluative tool to delineate tumor extent preoperatively, the radiologist and surgeon can misinterpret a film that suggests that orbital fat is medially invaded when, in fact, it is the periosteum and fat that are medially displaced; however, the fat is not involved per se. If the eye is functioning, the decision to preserve the eye or to do an orbit exenteration is likely to be an operative decision by the surgeon, based on whether the surgeon can remove the periosteum with negative margins while noting the fat is uninvolved. If this decision appears to be a close one, it is often wise to leave it until the end of the case. If equally close margins are necessary elsewhere, as in the pterygomaxillary space or at the lateral sphenoid sinus, then it is unlikely that doing an orbit exenteration would substantially (if at all) improve the likelihood of local tumor control. The same holds true if the closest margin is the far posterior orbit where orbit exenteration would not materially improve the likelihood of overall tumor control. Preservation of the orbit but partial resection of the orbit periosteum may make planning subsequent radiation fields difficult, requiring close cooperation of the radiation oncologist, neuroradiologist, and surgeon. Intensity-modulated radiation therapy (IMRT) would likely play an important role in planning radiation in this situation. Optic Nerve and Chiasm Tumors of the anterior skull base may extend to the optic nerves from an inferior and inferomedial direction. Occasionally, the optic nerve may be surrounded by tumor, in which case the overlying ICA may also be involved. Since the blood supply to the optic nerve does not run along its medial surface, the physician can generally dissect gently along the nerve without affecting the patient's vision. This is also true along the chiasm anteriorly. If the optic nerve or chiasm has been dissected, it is important that the placement of the pericranial-galeal flap at the conclusion of the procedure does not lead to pressure against the nerve. Occasionally, the optic nerve is nearly surrounded by tumor. If that is true, then particular attention must first be directed to the ICA, lying just above the optic nerve, to determine to what extent the tumor can be resected. Although the adjacent ICA will have been carefully examined on the preoperative MRI, the surgeon, intraoperatively, will need to closely inspect and confirm to what extent the tumor is resectable. For a tumor to be resectable there must be approximately 1 cm of uninvolved optic nerve anterior to the chiasm, as well as an uninvolved ICA. Dural Repair and Pericranial-Galeal Flap After tumor resection, the dura is repaired. This can be done using preserved bovine pericardium, fascia lata, or other materials. This repair is buttressed by the pericranial flap, or, if that is unavailable or in extensive skull base defects, by a microvascular free flap ( rectus muscle or radial forearm myofascial flap). After hemostasis is achieved, pieces of absorbable gelatin sponge (ie, Gelfoam) are placed against the orbit periosteum and raw bone. Merocel sponges 810 cm in length are placed through the nostrils along the floor of the nasal cavity. A layer of small pieces of absorbable gelatin are then placed superior to the Merocel sponges, up to the axial plane of the skull base, to help support the pericranial flap. This layer also serves to segregate the Merocel sponges from the pericranial flap so that removal of these sponges 10 days later is unlikely to disturb the pericranial flap. The pericranial flap is then reflected over the central orbital rims and glabellas into the skull base defect and posteriorly rests on a shelf of remaining planum sphenoidale anterior to the chiasm. Care must be taken to ensure that there is sufficient redundancy (ie, the flap should not be stretched ) so that the flap does not subsequently retract anteriorly. It may be helpful to tack the flap to the dura to prevent anterior displacement. Suctioning the air from beneath the flap while the flap is set may help the surgeon ensure an adequate length of flap on the bony defect. Any redundant flap may be reflected anterosuperiorly over the frontal dura. The Merocel sponge is left in place for approximately 10 days, and antibiotics are administered until the pack is removed. In tumors that invade the sphenoid roof, there may be no remaining planum sphenoidale posteriorly (anterior to the chiasm) and therefore no bony shelf for the pericranial-galeal flap to rest on. In such cases, the skull base can be successfully sealed by placing the pericranial flap over the skull base defect where the ethmoidal roof, cribriform plates, and planum sphenoidale have been resected, and then turning it inferiorly to rest against sella and the posterior wall of the sphenoid sinus, which has been completely stripped of its mucosa. Gelfoam pledgets are placed in the sphenoid sinus first so that the Gelfoam is against the flap. The Merocel sponge is then placed through the nostril into the front of the sphenoid sinus and as the sponge expands, it presses the flap against bone. The pack is kept in place for 10 days. Craniotomy Closure and Frontal Sinus Management Subsequent closure of the craniotomy is routine; however, care should be taken at the end of the procedure to ensure there is no remaining mucosa in any frontal sinus that may have been part of the bone flap and is now superior to the pericranial-galeal flap. If there is any portion of frontal sinus within the bone flap, a diamond bur should be used to bur down the frontal sinus 12 mm in the same manner as the frontal sinus is prepared before obliteration of sinus by fat in an osteoplastic frontal sinus procedure. Some surgeons also prefer an active drain beneath the skin closure, depending in part on concern for some postoperative bleeding or oozing. Transfacial Approaches When necessary, a trans-sphenoethmoidal incision is planned. As mentioned earlier, this may supplement the craniotomy incision, or it may be performed as the sole approach. An example of its being performed as the sole approach is to access the craniocervical junction from the sphenoid sinus through the clivus to the foramen magnum and the arch of C1, the first cervical vertebrae. This incision is the same as for an external ethmoidectomy, but extends more inferiorly. It extends toward the medial ala but stops at the axial plane of the inferior limit of the nasal bone. A lateral rhinotomy at the ala and Weber-Ferguson incision is rarely needed. This extended external sphenoethmoidectomy provides access from the inferior clivus upward through the sphenoid sinus, the sella, the medial cavernous sinus, the ethmoid sinuses, and the frontal sinus. In the sphenoid sinus, the physician can access the area posterolateral to the carotid artery and, if needed, the area as far lateral as the abducens nerve. In addition, lateral access to the pterygomaxillary space, the lateral antrum, and the orbit is provided when the medial maxilla is removed. The preservation of the inferior turbinate reduces postoperative nasal crusting and discomfort and is possible unless tumor extirpation requires its removal. Transoral-Transpharyngeal Approach Additional routes to the skull base are available as needed, depending on the extent of tumor. A common approach for chordomas and for decompression of the cervical spinal cord at the craniocervical junction secondary to degenerative or inflammatory processes is a transoral-transpharyngeal approach. Whether this approach, a trans-sphenoethmoidal approach, or, occasionally, a combination of both approaches is best is determined on an individual basis by evaluating the sagittal images on MRI and determining the superior and inferior access afforded by each approach. If the patient has a small mouth or trismus, the exposure afforded by a transoral approach may be reduced. Perioperative antibiotics are begun, an intraoral endotracheal tube, as small as is tolerable, is positioned and taped to the lower midline, and lidocaine with epinephrine (1:200,000) is infiltrated into both the midline soft palate and the posterior pharyngeal wall laterally. The soft palate is divided in the midline (heading to one side or the other of the uvula posteriorly) and retracted laterally. Specialized intraoral retractors are available that keep the mouth open , retract the tongue inferiorly, and retract the soft palate laterally and also anteriorly, if needed. One way to access the inferior clivus, the dens (the body of the second cervical vertebra), and the arch of C1 is by creating an inferiorly based myomucosal flap that incorporates the longus colli muscle and superior constrictor muscles. The superior transverse part of the mucosal incision is placed as superiorly as needed, keeping in mind the following: (1) the surgeon can see more superiorly as he or she removes the posterosuperior odontoid and clival bone, and (2) closure of this superior incision can be difficult, even with specialized needles with a large radius of curvature (eg, C-type needles and absorbable suture materials). The advantage of an inferiorly based flap is that it preserves maximal soft tissue, thus minimizing the risk of velopharyngeal insufficiency inherent in removing bone in this area, which posteriorly displaces the Passavant ridge. Depending on the individual, the physician can usually reach superiorly to the lower to mid-clivus and inferiorly to the junction of C2C3. The exposure can be made greater or lesser, depending on the specific need of each case. The arch of C1 is preserved or not, as needed. Laterally, this approach is limited by the vertebral arteries. Evaluation of the preoperative MRI demonstrates the distance from the midline of the left and right vertebral arteries. Usually, this distance is 1215 mm, which provides an adequate 2.5- to 3.0-cm wide access to the central skull base. The odontoid and clivus can be removed as needed with long-handled narrow drills, with intraoperative spinal cord monitoring (in the case of serious spinal cord compression) or intraoperative anatomic monitoring (in the case of tumor resection), as indicated. Additional soft tissue at the posterior longitudinal ligament can also be removed as needed. With this approach, entry into the dura is highly unusual. If it occurs, the direct repair of the CSF leak should be supplemented with the interposition of nearby muscle, along with the placement of a lumbar subarachnoid drain for 45 days. If there is no tongue edema, patients should be extubated at the end of the procedure, keeping a 32F (ie, 10 mm in diameter) nasal trumpet in place for 48 hours. If there is concern about the development of tongue edema from the retractor, then the patient may be intubated in the ICU for 23 days while the edema is monitored . In selected patients, a temporary tracheotomy may be performed at the beginning of the procedure, and decannulation may be planned before discharge . After repairing the posterior pharyngeal wall in one layer using absorbable sutures, a small-diameter nasogastric feeding tube is placed, taking care not to disrupt the pharyngeal suture line. The soft palate is then repaired in three layers , also using absorbable sutures. Orbitozygomatic Approach Access to the superior parapharyngeal space and access along the floor of the middle cranial fossa can be gained by a temporary removal, en bloc, of the zygomatic arch, the lateral orbit, and the part of the maxilla where they intersect. Care should be taken to avoid injury to the temporal branch of the facial nerve. The temporalis muscle can be separated from the temporal bone squama and reflected inferiorly, with some of the fibrous attachment left for resuturing at the conclusion of the procedure. Using this approach, the foramen ovale, posterolateral antrum, pterygomaxillary space, and lateral orbit are all in view, and the dura can be retracted as necessary. In addition, the floor of the middle cranial fossa can be resected. Lalwani AK, Kaplan MJ, Gutin PH. The trans-sphenoethmoid approach to the sphenoid sinus and clivus. Neurosurgery. 1992;31:1008. (Reviews transfacial approach to sphenoid sinus and clivus, with diagrams showing the extent of exposure and discussing limitations.) [PMID: 1470312]
| Van Buren JM, Ommaya AK, Ketcham AS. Ten years' experience with radical combined craniofacial resection of malignant tumors of the paranasal sinuses. J Neurosurg. 1968;28:341. (Reviews the early pioneering experience with this approach.) [PMID: 5643926]
| Surgery-Related Complications With a surgeon's increased surgical experience, complications have become less common. In the past decade , operative mortality has, in most US institutions, been reduced from about 2% to nearly 0%. The incidence of CSF leaks has similarly decreased from 1015% to less than 2%. Serious central nervous system deficits (including cerebrovascular accidents, unanticipated blindness, and autonomic dysfunction) have remained constant at approximately 3%. Complications of intracranial infections, such as meningitis or brain abscess, have also remained at approximately 2%. The loss of the anterior bone flap secondary to osteomyelitis has been reduced from 813% to 0%. Pericranial-galeal flaps and, for larger defects and patients who have undergone prior irradiation, microvascular free flaps have reduced the incidence of postoperative CSF leaks as well as wound or bone infection. The incidence of intracranial hematoma has decreased from 2% to 0% as a result of tailoring approaches to minimize the need for brain retraction, thus reducing encephalomalacia as well as the risk of hematoma. Finally, nonlethal medical complications such as pneumonia, arrhythmias, and occasional myocardial infarction have been steady at 10%, sometimes extending the length of hospitalization. Clayman GL, DeMonte F, Jaffe DM et al. Outcome and complications of extended cranial-base resection requiring microvascular free-tissue transfer. Arch Otolaryngol Head Neck Surg. 1995;121(11):1253. (Review of MD Anderson's outcomes and complications when microvascular flaps are needed in extensive skull base resections.) [PMID: 7576471]
| Nonsurgical Measures Radiation Therapy In the past 25 years, numerous series have demonstrated that radiation therapy alone results in a survival rate no better than 50%, and, in most series, 2535% for the more common malignant epithelial neoplasms of the paranasal sinuses. This poor prognosis has been the major impetus for developing anterior skull base surgery. However, most physicians agree that a multimodality approach for most malignant tumors in this area is superior to either surgery or radiation alone. Most centers plan surgery with postoperative radiation for resectable tumors. The dilemma in planning radiation ports lies in the need to give a tumoricidal dose to the tumor volume while limiting the dose to adjacent critical structures such as the brain, optic nerve and chiasm, and the lens. The tolerance of the lens is about 50 Gy; above this dose, cataracts may develop. The optic nerve well tolerates doses below 50 Gy. There is approximately a 10% incidence of optic neuritis when the dose is 5055 Gy, and above 65 Gy, this incidence is > 20%. Fortunately, a patient can often tolerate minimal radionecrosis of the inferior portions of the frontal lobe with a minimum of long-term symptoms. Although there is variation in the literature as to how much radiation should be given as the target volume, most centers aim for a minimum of 60 Gy, with many centers advocating a minimum of 65 Gy. Before the development of intensity-modulated radiation therapy (IMRT), charged particles were often used when irradiating the anterior skull base. The rapid falloff in dose afforded by protons permitted, for example, a dose of 6080 Gy to be administered to chordomas of the sphenoclival area without undue risk to the optic nerves and chiasm. At Harvard a 160-MEV proton beam was generated from their cyclotron. At the Lawrence Berkeley Laboratory, in conjunction with UCSF, a helium-neon beam was used until about 1991. Protons are also currently available at Loma Linda University in southern California. In the last 5 years, IMRT has been applied to the anterior skull base. With IMRT, the radiation oncologist conceptually plots the target volume using CT scanning, often with additional diagnostic information provided by an MRI, and inputs this information into a computer. The computer then generates a plan for multifield conformal radiation, using as many ports as needed and with the ability to use as many as 55 fields. Machines are now increasingly available to implement this strategy. It is likely that with IMRT, there will be better uniformity of the dose to the target volume and therefore a reduction in damage to adjacent tissue. Chemotherapy As in SCC encountered elsewhere in the head and neck, the role of chemotherapy in the treatment of malignant neoplasms of the paranasal sinuses continues to be investigated. During the 1980s and early 1990s, neoadjuvant chemotherapy for SCC, usually using cisplatin and 5-fluorouracil, was widely studied. Except for nasopharyngeal carcinoma, no improvement in the overall survival rate was found, despite good response rates. These disappointing results led to a more intense investigation of concomitant chemotherapy-radiation strategies in which the chemotherapy agent was predominantly used as a radiosensitizer. The results of concomitant radiation therapy plus cisplatin in the initial treatment of SCC at a number of head and neck sites, including the paranasal sinuses, have been encouraging, with a meta-analysis suggesting a 58% improvement compared with radiation alone. Postoperatively, although the rationale remains sound, there is much less data comparing radiation alone with concomitant radiation therapy plus chemotherapy. The role of chemotherapy for specific histologies, such as esthesioneuroblastoma and lymphoma, was discussed earlier in this chapter. Chemotherapy for metastases is also usually appropriate; the specific regimen chosen depends on the histology and the health and tolerance of the patient. Adams EJ, Nutting CM, Convery DJ et al. Potential role of intensity-modulated radiotherapy in the treatment of tumors of the maxillary sinus. Int J Radiat Oncol Biol Phys. 2001;51 (3):579. (Reviews intensity-modulated radiation therapy with respect to paranasal sinus tumors.) [PMID: 11597796]
| Diaz EM Jr, Kies MS. Chemotherapy for skull base cancers. Otolaryngol Clin North Am. 2001;34(6):1079. (Review of the indications and results of chemotherapy for malignant tumors that affect the skull base.) [PMID: 11728933]
| Rasch C, Eisbruch A, Remeijer P et al. Irradiation of paranasal sinus tumors, a delineation and dose comparison study. Int J Radiat Oncol Biol Phys. 2002;52(1):120. (Reviews details of radiation planning.) [PMID: 11777629]
| Remouchamps V, Van Duyse B, Vakaet L, Lemmerling M, Vermeersch H, De Neve W. An implementation strategy for IMRT of ethmoid sinus cancer with bilateral sparing of the optic pathways . Int J Radiat Oncol Biol Phys. 2001;51(2):318. (Intensity-modulated radiation therapy is used to minimize the radiation dose to critical structures while retaining the adequacy and homogeneity of dose-to-tumor volume.) [PMID: 11567805]
| Waldron JN, O'Sullivan B, Gullane P et al. Carcinoma of the maxillary antrum: a retrospective analysis of 110 cases. Radiother Oncol. 2000;57(2):167.. (Reviews the extensive experience of a single institution.) [PMID: 11054520]
| Combined Surgery & Irradiation Many series have documented that a combination of anterior skull base surgery and postoperative irradiation has improved the rates of local control for a number of malignant histologies, including esthesioneuroblastoma, adenoid cystic carcinoma, and adenocarcinoma. A review of the 5-year survival rate is summarized in Table 601. The survival rate is highest for esthesioneuroblastomas and adenocarcinomas. A number of tumors are associated with a fair prognosis, with 5-year survival rates that are approximately 50%. Melanoma and sinonasal undifferentiated tumors portend a poor prognosis, and treatment strategies for patients with these two histologies should stress the preservation of function; how best to incorporate chemotherapy protocols into the management of these tumors continues to be discussed. | Table 601. Five-Year Survival Rate with a Combination of Surgery and Radiation Therapy for Malignant Disorders of the Anterior Skull Base.
| | | Histology | 5-year Survival Rate | Comment | | Esthesioneuroblastoma | 6295% | Most: 8095% | | Adenocarcinoma | 4585% | Meta-analysis 78% | | Adenoid cystic carcinoma | 4060% | AWD: + 1520 | | Sarcomas | 5060% | AWD: + 20 | | Squamous cell carcinoma | 3065% | Meta-analysis 60% | | Melanoma | <1545% | Meta-analysis 23% | | Sinonasal undifferentiated carcinoma and undifferentiated carcinoma | <1015% | | |
AWD, alive with disease (ie, disease has recurred, but patient is alive ). | Boyle JO, Shah KC, Shah JP. Craniofacial resection for malignant neoplasms of the skull base: an overview. J Surg Oncol. 1998;69:275. (Reviews the improvements in cure and the reduction in morbidity of Memorial Sloan-Kettering.) [PMID: 9881946]
| Dulguerov P, Jacobsen MS, Allal AS, Lehmann W, Calcaterra T. Nasal and paranasal sinus carcinoma: are we making progress? A series of 220 patients and a systematic review. Cancer. 2001;92(12):3012. (Review of the UCLA experience; includes a good systemic literature review.) [PMID: 11753979]
| Harbo G, Grau C, Bundgaard T et al. Cancer of the nasal cavity and paranasal sinuses. A clinico-pathological study of 277 patients. Acta Oncol. 1997;36(1):45. (Reviews the 28-year experience from the Aarhus University Hospital in Denmark.) [PMID: 9090965]
| Irish JC, Gullane PJ, Gentili F et al. Tumors of the skull base: outcome and survival analysis of 77 cases. Head Neck. 1994;16(1):3. (Reviews the outcomes from an experienced center in Toronto.) [PMID: 8125786]
| Janecka IP, Sen C, Sekhar LN et al. Cranial base surgery: results in 183 patients. Otolaryngol Head Neck Surg. 1994;110(6):539. (Review of outcomes by a premier team.) [PMID: 8208569]
| Janecka IP, Sen C, Sekhar L, Curtin H. Treatment of paranasal sinus cancer with cranial base surgery: results. Laryngoscope. 1994;104(5 Pt 1):553. (Review of outcomes by the same premier team as noted in the previous reference.) [PMID: 8189985]
| Kraus DH, Shah JP, Arbit E, Galicich JH, Strong EW. Complications of craniofacial resection for tumors involving the anterior skull base. Head Neck. 1994;16(4):307. (Reviews and updates.) [PMID: 8056574]
| Lund VJ, Howard DJ, Wei WI, Cheesman AD. Craniofacial resection for tumors of the nasal cavity and paranasal sinusesa 17-year experience. Head Neck. 1998;20(2):97. (Reviews the outcomes and complications of a highly experienced team in England.) [PMID: 9484939]
| McCaffrey TV, Olsen KD, Yohanan JM, Lewis JE, Ebersold MJ, Piepgras DG. Factors affecting survival of patients with tumors of the anterior skull base. Laryngoscope. 1994;104:940. (From the Mayo Clinic, a review of the prognostic factors in 54 patients, 24 of whom had esthesioneuroblastoma.) [PMID: 8052078]
| O'Malley BW Jr, Janecka IP. Evolution of outcomes in cranial base surgery. Semin Surg Oncol. 1995;11(3):221. (Discusses methods used to decrease complications and improve overall results.) [PMID: 7638509]
| Treatment of Recurrent Disease Perineural Spread Perineural spread along V2 and less commonly along V1 is especially common in squamous cell and adenoid cystic carcinomas. It is suspected when there is a new onset of dysesthesias or when the patient experiences pain above the eye (V1) or along the lateral nasal area and the maxillary alveolar ridge (V2). MRI with gadolinium enhancement is diagnostic, especially if there have been serial MRIs indicating changes that correspond to patient symptoms. Gamma-knife radiosurgery has been used in such instances, with the control of pain usually achieved in approximately 6 months, and a 40% rate of disease control, with no progression radiologically or clinically, in 5 years. Neck Metastases Neck metastases occur in approximately 20% of cases of SCC and in about 10% of cases of esthesioneuroblastoma. In both disorders, if the primary site is disease-free, it is likely that a neck dissection is indicated. If there has been no prior neck irradiation, then postoperative neck irradiation is also indicated. When there has been prior neck irradiation, then there may be a role for intraoperative radiation therapy. Local Recurrences The local recurrence of malignant tumors of the paranasal sinuses portends a worse prognosis than the initial disease. There are usually limitations in the treatment of local recurrences owing to the prior use of irradiation and the scarring associated with prior surgery, which make subsequent surgery more difficult, if such surgery is even possible. In addition, a tumor that has recurred after prior postoperative irradiation is likely to have grown from a clonal population that is resistant to radiation. Because of some cross-resistance, it may also be resistant to chemotherapy. If a metastatic evaluation demonstrates no regional or distant disease, then the next step should be a thorough discussion with the patient of all the available modalities. Depending on the histology, chemotherapy protocols may be of some value. Protocols for subsequent treatment are useful for some patients. Depending on the patient's current symptoms and the extent of the recurrence, there may be a role for surgery that is palliative or, occasionally, even curative, although this latter is unlikely. | | Special Considerations In the past 30 years, surgery at the anterior skull base has evolved from a desperate attempt to improve dismal control rates fraught with daunting perioperative complications to a developed multidisciplinary subspecialty with proven results. Clearly, local control is now likely to be improved for the more common malignant tumors that occur in this area. Approaches have evolved that select an angle of approach that minimizes brain retraction while optimizing accessibility to structures requiring resection, and that simultaneously limit esthetic and functional side effects. Initially, the approach that was routinely used was a transcutaneous transfacial approach via an extended external ethmoidectomy incision in association with a low bifrontal craniotomy, with or without a supraorbital rim approach. This allowed the exposure of an area from the frontal sinuses superiorly to the mid-clivus inferiorly, reaching laterally to the cavernous sinus and the carotid artery, orbit, and lateral antrum. This is an extension of an approach highly familiar to all otolaryngologists and requires no central facial plating . Its disadvantage is a facial incision, although one that heals with a generally well-camouflaged scar. With subsequent surgical experience, it was found that the transfacial incision could often be avoided, instead providing access solely from above. A subfrontal approach without brain retraction at all was occasionally possible when frontal bone and nasal bone necessarily needed to be removed because of tumor involvement. At each institution where skull base surgery is performed, a multidisciplinary team has grown that involves, among others, otolaryngologisthead and neck surgeons, neurosurgeons, plastic surgeons, neuroradiologists, medical oncologists, radiation oncologists, and prosthodontists. Each team determines what classification schemes they find useful as an organizing and teaching tool, and with which sets of approaches, with variations, they are the most comfortable. This judgment may also be based on prior irradiation or surgical intervention as well as the patient's evaluation of the risks and alternatives. | | | |
Print Close Window 
