Chapter 13 Skin and Subcutaneous Tissue
Principles of Surgery Companion Handbook
SKIN AND SUBCUTANEOUS TISSUE
|Functions of Skin|
Tension and elasticity are the primary physical properties of the skin. Tension is the characteristic that accounts for the fact that skin can resist stretching. Tension is most marked where the skin contains very dense elastic fibers, particularly if the skin is thin. Anatomic lines of tension are called Langer's lines. Elasticity refers to the skin's ability to resume its original shape after an external force has been applied. As with tension, elasticity decreases in the elderly.
Tensile strength is the resistance of skin to tearing under tension. The average strength is 1.8 kg/m2. Abnormally low values of tensile strength are found in diseases such as Ehlers-Danlos syndrome, in which a defective form of collagen is produced. Also, tensile strength is reduced in patients taking high doses of cortisone for a prolonged period of time.
FUNCTIONS OF SKIN
Functions of skin include (1) percutaneous absorption, (2) circulatory vasoregulation, (3) serving as an organ of sense, (4) secretion of sweat, (5) providing an avenue for the insensible loss of water, and (6) contributing to thermal regulation.
Percutaneous Absorption This function of skin permits entry of substances into the bloodstream. The stratum corneum is the major barrier to diffusion. Water and lipid-soluble substances diffuse rapidly across the skin. Most electrolytes, including sodium and calcium, cannot penetrate the skin.
Percutaneous absorption of phenol and carbolic acid is rapid and may cause fatal poisoning. Estrogenic hormones and hydrocortisone also absorb rapidly and can be therapeutically effective with percutaneous application.
Substances in gas form, with the exception of carbon monoxide, penetrate the skin easily. This method has been employed pharmaceutically with the use of dimethylsulfoxide (DMSO) as a vehicle.
Circulation and Vascular Reactions The cutaneous vascular system is extremely complex. Changes in skin circulation contribute significantly to general vascular and circulatory physiology. Skin blood flow can be visualized directly through the beds of the nails. The color of skin depends on the quantity of blood in the subdermal plexus as much as on melanin and keratin pigments. In addition, skin temperature depends on the rate of blood flow.
Local vascular response may result from direct action on the vessel wall or its contractile elements. A red local reaction can develop after dilatation of small vessels. A skin wheal is a circumscribed area of skin edema secondary to dilated blood vessels and leakage of plasma into the extracellular space. Conversely, stimulation of sympathetic nerve fibers causes vasoconstriction of these cutaneous vessels. In addition, the cutaneous vessels respond to various chemical agents such as acetylcholine and nitrites, which cause vasodilatation, whereas norepinephrine, epinephrine, and vasopressin cause vasoconstriction. Although nitrites cause a sensation of flushing and increased blood flow, smoking paradoxically decreases blood flow through the skin.
Sensory Function Many specific sensory functions are facilitated by the skin. The Krause end bulbs mediate cold sensitivity. Ruffini's endings are the receptors for warmth. Meissner's corpuscles provide tactile sensation, and pacinian corpuscles are involved in the sensation of pressure. Pain is mediated by nonmyelinated nerve endings.
Causalgia is a syndrome of pain and vasodilatation that occurs after injury of major nerves. This syndrome also is called reflex sympathetic dystrophy. The most common cause is a prior operation with transection of minor nerve branches. Treatment of this condition is difficult and requires physical and occupational therapeutic resources. Active use of the involved extremity is important. For advanced cases, blockade of the contributing sympathetic ganglion with neurolytic agents is used. If ganglion blocks are transiently successful, a surgical sympathectomy may be curative.
Sweat Secretion Sweat glands in skin are eccrine glands or apocrine glands. The eccrine glands are distributed all over the body and are primarily responsible for heat regulation. The apocrine glands are similar to sebaceous glands and develop mostly during puberty. Their activity is in response to autonomic nervous stimulation rather than thermal conditions.
Sweating is a response to local application of heat or to nervous impulses. Sympathetic nerve fibers liberate acetylcholine to stimulate sweat glands. Atropine and other anticholinergic drugs can block these receptors and interfere with sweat secretion. Hyperhidrosis results from an abnormal increase in nerve impulses or emotional states.
The content of sweat is primarily water with small amounts of sodium chloride. Potassium also is lost through sweat. Nitrogen compounds are secreted in sweat as well. The concentration of urea in sweat is twice as high as that in blood. Sweat also contains large amounts of lactic acid and ammonia.
Insensible Water Loss Besides sweat secretion, water is lost through the epidermis by continuous evaporation. In contrast to sweat, water lost through evaporation does not contain electrolytes or other solutes. Approximately 700 mL total water loss occurs through the skin each day. Hypothyroidism decreases the daily amount of water loss, whereas thyrotoxicosis greatly increases this amount.
Thermoregulation Regulation of body temperature is an important function of the skin. Heat escapes through skin under the processes of radiation, convection, conduction, and evaporation. Sweating is a primary process for heat evaporation. Increased humidity markedly decreases the efficiency of sweating for thermoregulation because of the impairment of evaporation.
Thermoregulation is accomplished in skin also by shifting blood flow from the interior to the skin. Cold stimuli result in pallor of the skin by relative vasoconstriction. After the stimulus has ceased, there is a reactive arterial vasodilatation. This results in a reddish discoloration of skin. In contrast, prolonged cold stimulus causes paresis of the venous limbs of capillaries. A reddish discoloration also may result from this condition, which is not associated with increased blood flow, and skin temperature does not rise. This condition leads to frostbite. Prolonged exposure of skin to cold temperature should be treated by immersion of the involved portion into water at a temperature of 40°C.
Heat exhaustion is a syndrome of excessive loss of salt and water during exposure to high temperatures. The clinical symptoms are exhaustion, headache, palpitation, dizziness, and confusion. Treatment is immediate cooling by evaporation or application of ice. Simultaneously, intravascular volume replacement of fluids is indicated.
Pressure on an area of skin for 2 h or more may result in ischemia sufficient to cause a pressure sore. Factors contributing to pressure sores include skin over bony prominence, anemia, malnutrition, and immobilization. Surgical therapy requires sharp debridement to excise the ulcer and underlying fascia and necrotic material. Frequently, a bony prominence must be modified to prevent subsequent pressure. The remaining wound often must be covered with a myocutaneous flap.
Hidradenitis suppurativa is a chronic infection of the cutaneous apocrine glands, subcutaneous tissue, and fascia. This disease occurs in the axilla, areola of the nipple, groin, or perineum. Commonly, there is slight induration and subsequent inflammation of the skin. Eventually, suppuration develops and cellulitis surrounds the abscess. Initial treatment is incision and drainage, but frequently this produces only a few drops of purulent material. Then the chronic stage develops, with multiple painful cutaneous nodules. Culture of these abscesses reveals a preponderance of staphylococci and streptococci.
Definitive treatment requires complete excision of the involved area and improved hygiene to prevent recurrence. Myocutaneous flaps or advancement flaps provide wound coverage.
Epidermal Inclusion Cysts An epidermal inclusion cyst results from epithelium of skin that is trapped subdermally because of trauma or other reasons and begins to grow and desquamate. The cyst is filled with keratin and desquamated cells. These cysts can occur anywhere on the body. They generally are cured by complete removal. If the cyst is infected secondarily, incision and drainage are indicated first.
Sebaceous Cysts Sebaceous glands are associated with hair follicles and are generally found on the midline of the trunk and on the face. A cyst is formed from a sebaceous gland when the exit of sebum is blocked. True sebaceous cysts are very rare and usually represent epidermal cysts that have been incorrectly diagnosed. The presence of glandular epithelium lining is necessary for the diagnosis.
Dermoid Cysts Dermoid cysts are congenital lesions that arise in early childhood. They generally occur in the midline of the body, on the lateral eyebrow, on the scalp, or in the abdominal and sacral regions. There have been no reports of malignant degeneration of these cysts. Dermoid cysts in the nasal region have a remote possibility of communication with the central nervous system. A computed tomographic (CT) scan should be obtained before excising nasal dermoids.
Pilonidal Cysts Pilonidal cysts are malformations of the neuroenteric canal that occur in the sacrococcygeal region. The ingrowth of hair in the coccygeal region sets the stage for cyst formation and repeated infections. This disease has been referred to as jeep driver's disease because long hours of sitting and bumpy driving aggravate the congenital condition. Chronic infection and drainage are the usual presentation. Treatment includes incision and drainage followed by secondary removal of the cyst or sinus when infection has subsided. Excision of the entire sinus is essential for successful treatment. This may be facilitated by injection of methylene blue to determine the extent of arborization of the sinus tract. A skin graft or muscle advancement flap may be necessary to close the defect. Some surgeons prefer to allow closure by secondary intention, particularly if there is residual infection.
Ganglia Ganglia are areas of mucoid degeneration in retinacular structures. They are cystic masses frequently found over the dorsum of the wrist and over tendon sheaths of hands or feet. These cysts contain clear fluid similar to joint fluid. Aspiration alone of the ganglion yields a 75 percent recurrence rate. Surgical excision of the entire ganglion is the recommended treatment. This may require excision of part of the joint capsule.
Warts Verruca vulgaris, the common wart, is caused by a contagious virus. Warts usually occur on the hand or soles of the feet. They are quite tender and painful.
Treatment of verruca vulgaris can be accomplished with liquid nitrogen freezing or electrodesiccation under local anesthesia. Caustic agents also have been used but result in a higher recurrence rate.
Keratosis Keratosis is a precancerous lesion manifested by hypertrophy of the epidermis. Senile keratoses occur in older individuals with a fair complexion. They should be treated by surgical excision if the lesion is large and the suspicion of malignancy is low. Topical treatment with 5-fluorouracil or liquid nitrogen may be done.
Seborrheic keratosis is a thickened area of skin that may appear brown, gray, or black. Occasionally these lesions are mistaken for melanoma. Electrocoagulation is adequate treatment.
Keloids Keloids are dense accumulations of fibrous tissue that extend above the surface of the skin from traumatic wounds or surgical incisions. They are the result of a failure of collagen breakdown and occur most commonly in blacks. Recurrence is common after simple excision.
First-line treatment of keloids is steroid injection. This method is effective in relieving the burning and itching, as well as in producing actual shrinkage of the lesion. Radiation therapy is not effective in treating keloids. Subcuticular sutures should be avoided in patients with a history of keloid formation.
Capillary Malformation Capillary malformations are commonly known as port-wine stains of the skin. They represent dilated abnormal capillaries in the subdermal plexus. They are smooth lesions with reddish or purplish patchy distribution. Excision of small lesions is appropriate. The larger lesions are now being treated with laser. This is reserved, however, for patients over 14 years of age.
Hemangioma Hemangiomas appear in infancy and may enlarge over the first year of life but usually regress thereafter. They are bright red, raised, and irregular skin lesions. Episodes of ulceration or superficial infection actually hasten spontaneous resolution of these lesions. Spontaneous resolution usually occurs by age 7 years.
Arteriovenous Malformation Arteriovenous malformations are also called cavernous hemangiomas. These lesions are evident at birth and do not change during growth of the child. Occasionally, they involve deep structures such as the central nervous system or muscles. Nonetheless, wide excision is the treatment of choice. Occasionally, preoperative embolization of feeding vessels can assist wide excision.
Glomus Tumor Glomus tumor is a rare benign neoplasm of the skin that usually occurs in the nail beds of the hands and feet. These lesions are extremely painful because they are derived from the glomic end organ, a nerve apparatus that normally functions to regulate blood flow in the extremity. These lesions are also called angiomyoneuroma and generally are benign. The malignant counterpart to this tumor is called hemangiopericytoma.
Neural Tumors Neurofibromas and Schwann cell tumors can occur in the skin. Their treatment is surgical excision. Neurofibromas are associated with von Recklinghausen's disease. Approximately 10 percent of patients with neurofibromatosis will have sarcomatous degeneration of these tumors.
Skin cancer is associated with exposure. Ultraviolet light, ionizing radiation, and chemicals are causative factors. Skin cancer usually is manifested by a low-grade malignant tumor that metastasizes late. Therefore, cure rates of carcinoma of the skin are high.
Basal Cell Carcinoma Basal cell carcinoma is a skin malignancy that grows slowly and accounts for at least three-fourths of cancers in most clinical series. These lesions are waxy and grayish yellow and often have telangiectasia below the surface. Most basal cell cancers are located on the head and neck. They tend to invade and erode into deep structures including the skull, orbit, and brain if left untreated.
Squamous Cell Carcinoma Squamous cell carcinoma usually presents as an ulcerated skin lesion that tends to grow more rapidly than basal cell cancer. Biopsy is necessary to differentiate this lesion from other types of skin cancer. Again, most occur on the head and neck. The typical appearance is an ulcer with rolled margins resembling a small volcanic crater. Squamous cell carcinoma is more aggressive than basal cell carcinoma and will metastasize to regional nodes more rapidly.
Squamous cell cancers are found in areas of frequent irritation such as the vermilion border of the lip, areas of postirradiation dermatitis, or ulcerations in old burn scars. Bowen's disease is a slowly growing squamous cell carcinoma in situ for which excision is recommended.
Sweat Gland Carcinoma This rare tumor usually occurs in the sixth and seventh decades of life. Therapy consists of wide local excision and consideration of lymphadenectomy. Regional lymph nodes will be involved in approximately 50 percent of patients.
Options for treatment of skin cancer include electrodesiccation, cryosurgery, chemosurgery, radiation therapy, and surgical therapy. Biopsy of the skin lesion and relevant history determine the choice of therapy. Electrodesiccation and curettage are applicable for superficial, nonrecurrent basal cell carcinomas. Chemosurgery is described as the Mohs technique. The lesion is excised under local anesthesia, and frozen sections are taken of the entire surface of the resection. Four or five resections may be necessary to completely excise the lesion. The advantage of this method is the possibility of eradicating small extensions of the central lesion with greater certainty than conventional excision provides. This technique is particularly useful in recurrent basal cell or squamous cell carcinomas. Radiation therapy can be used to cure basal or squamous cell carcinomas. In some instances, a good result with less effort can be accomplished. Surgical therapy is conventional treatment for most skin cancers. Controversy continues regarding an adequate margin of normal tissue. Most physicians recommend 0.5-cm margins around basal cell carcinomas and 1-cm margins around squamous cell carcinomas. In recurrent lesions, frozen-section or permanent-section determination of tumor-free margins should precede definitive reconstruction. Regional lymph node dissection is performed only for clinical evidence of node involvement.
Approximately one-third of patients with positive margins after resection of basal cell carcinoma will develop recurrence. If the patient is reliable, simple observation may be all that is indicated. Repeat surgical excision is the best treatment for recurrence.
Eighty percent of squamous cell carcinomas are cured by surgical excision. Mohs has reported about a 95 percent cure rate for recurrent basal cell carcinoma and a 75 percent cure rate for recurrent squamous cell carcinoma.
Fibrosarcoma This tumor occurs commonly in women in the thigh, buttock, or inguinal region. It usually is a relatively low-grade malignancy and is radioresistant. Wide surgical excision is the treatment of choice. Local recurrence is common.
Hemangiopericytoma This is a malignant tumor of angioblastic origin and is probably a variant of the glomus tumor. Prognosis is distinctly poor, with only 27 percent 5-year disease-free survival. Radiation therapy is considered the treatment of choice, especially for larger tumors.
Kaposi's Sarcoma This tumor has a markedly increased incidence in homosexuals. Acquired immune-deficiency syndrome (AIDS) is commonly associated with Kaposi's sarcoma. Usually, the tumor begins in the hands or feet as multiple plaques that are reddish to purple and may be flat, ulcerated, or polypoid. Lymph node involvement is common. Radiation can retard the growth of Kaposi's sarcoma, but surgical excision is also helpful. Actinomycin D has produced some positive responses. Overall, the prognosis is poor.
Dermatofibrosarcoma Protuberans This tumor is a relatively low-grade malignancy that generally occurs on the trunk. It is radioresistant but responds to surgical excision with a 70 percent 5-year disease-free survival.
Intradermal nevus, junctional nevus, and compound nevus are examples of benign pigmented lesions; however, they have variable degrees of malignant potential. The intradermal nevus is a nest of melanoblasts confined to the dermis. Frequently, these nevi contain hair. The junctional nevus is a proliferation of melanoblasts that originates in the basal layer of the epidermis and extends down into the dermis. These lesions occur around the genitalia, palms, nail beds, and mucous membranes. The compound nevus has both junctional and intradermal elements. These lesions are benign but have some malignant potential. Juvenile melanomas are nevi that occur before puberty. Most occur in the face and enlarge slowly.
The differential diagnosis between benign pigmented skin lesions and melanoma can be difficult. Changes in various characteristics of pigmented lesions are indications for excision. These include change in color or pigment distribution, development of erythema, change in size or consistency, and change in the surface characteristic, such as oozing, bleeding, or erosion.
The Hutchinson freckle (lentigo maligna) is a precancerous melanosis of the face that usually occurs in elderly people. Approximately one-third of these lesions will become malignant melanoma. Prognosis is excellent, however, especially when the lesion is excised from the face. Any suspicious lesions should be excised completely with a margin of normal skin.
Melanoma is a malignant lesion originating in the melanoblast of the skin. Mucous membranes and pigmented regions of the eye also can harbor primary melanoma. The lesion is usually darkly pigmented, smooth, firm, and nonhairy. At some phases of development the melanoma cells do not contain melanin and are referred to as amelanotic melanoma.
TNM Classification for Staging of Melanoma The T classification refers to primary tumor thickness. T1 includes lesions 0.75 mm or less in thickness. T2 lesions are 0.761.5 mm thick. T3 indicates tumors that are 1.54.0 mm thick. T4 tumors are greater than 4.0 mm thick or invade the subcutaneous tissue. N0 designates regional lymph nodes negative for metastasis. N1 indicates positive regional lymph nodes 3 cm or less in size. N2 indicates positive regional lymph nodes greater than 3 cm in size or the presence of intransit lesions.
The stage grouping is divided by involvement of nodes. Stage I is smaller tumors (T1 and T2) with negative lymph nodes, Stage II is larger tumors (T3 and T4) with negative lymph nodes, Stage III is any tumor size with positive lymph nodes, and Stage IV is any tumor with positive distant metastases.
The incidence of melanoma is increased by exposure to solar radiation in light-skinned people. The presence of melanin in the skin has a protective effect against ultraviolet light acting as a stimulus. Melanoma is much more common in patients with xeroderma pigmentosum, a genetic disorder associated with hypersensitivity to ultraviolet light.
Pathology Melanomas usually arise in nevi that have junctional activity. Nevi of the palms, soles, nail beds, genitalia, and mucous membranes have functional elements that make them more prone to be the source of melanoma than moles at other sites. Malignant melanoma rarely occurs in prepubertal children.
Four types of melanoma are described: superficial spreading melanoma, nodular melanoma, lentigo maligna melanoma, and acral lentiginous melanoma. Superficial spreading melanoma is characterized by intradermal spreading and accounts for almost 70 percent of all cutaneous melanomas. Nodular melanoma is less common and is characterized by little radial growth but more invasive growth. The prognosis for nodular melanoma is significantly worse. Lentigo maligna melanoma is the most indolent of all and occurs mostly in older individuals. Acral lentiginous melanoma occurs in the palms, soles, and subungual regions; its histology is similar to that of lentigo maligna melanoma.
Surgical Treatment Surgical excision is the primary therapy for melanoma. For most pigmented lesions, an excisional biopsy with a margin of 25 mm is indicated. However, extremely large lesions may require an incisional biopsy, which is appropriate prior to planning definitive therapy.
The acceptable margins for definitive excision of melanomas depend on the thickness of the lesion. A margin of 0.5 cm is adequate for lesions less than 0.75 mm thick. Lesions between 0.76 and 1.5 mm thick require a 2-cm margin. Thicker lesions require a 4-cm margin. Amputation of a digit is indicated for acral lentiginous melanomas.
Removal of regional lymph nodes should be performed when there is clinical evidence of adenopathy and no distant metastases. Prophylactic dissection of regional lymph nodes is more controversial. The choice between a prophylactic lymph node dissection versus waiting for clinical evidence of node involvement may be based on the probability of occult lymph node metastases with a given stage of primary tumor. Sentinel node biopsy and lymphoscintigraphy aid in planning regional lymph node dissection. Tumors less than 1.5 mm have about a 15 percent association with positive lymph nodes. Thicker lesions between 1.6 and 3.7 mm have a 35 percent association with positive lymph nodes. Tumors thicker than 3.7 mm have a 50 percent association with positive lymph nodes.
Some retrospective studies show a survival advantage for immediate lymph node dissection of clinical Stage I melanoma. A prospective, randomized study by the World Health Organization, however, showed no survival improvement for patients in this category. A prospective, multi-institutional trial is proceeding in North America to confirm or refute these results. Nonetheless, immediate lymph node dissection should be used when the melanoma originates in the skin covering a lymph node basin because the changes after excision of the primary tumor may complicate the clinical evaluation of lymph nodes.
Adjunctive Treatment Regional Chemotherapy and Hyperthermia Isolated regional perfusion has been tested for melanoma. The involved extremity is perfused with a solution at approximately 40°C. The chemotherapeutic agent most commonly used is melphalan. This therapy is probably beneficial only in those patients whose primary tumor is thicker than 3.7 mm. Also, patients with numerous satellite and transit metastases may benefit from isolated regional perfusion.
Immunotherapy A number of agents have temporarily controlled cutaneous metastases of melanoma. Local intralesional injections of bacille Calmette-Guérin provided remission in approximately 20 percent of patients in one study. Systemic treatment with biologic response modifiers has begun to show some impact on disseminated melanoma. Interferon has proved to be effective in a small percentage of patients.
Prognosis Prognosis for patients with melanoma depends on the staging. The 5-year cure rate for Stage I lesions smaller than 0.76 mm is almost 95 percent. Lesions between 0.76 and 1.5 mm have an 85 percent 5-year cure rate. Stage II lesions are less favorable, with a 60 percent 5-year survival rate. Patients who are Stage III (positive lymph node involvement) have approximately 35 percent 5-year survival.
For a more detailed discussion, see Young DM, Mathes SJ: Skin and Subcutaneous Tissue, chap. 13 in Principles of Surgery, 7th ed.
Copyright © 1998 McGraw-Hill
Seymour I. Schwartz
Principles of Surgery Companion Handbook