24 - Kidney Tumors

Authors: Macfarlane, Michael T.

Title: Urology, 4th Edition

Copyright 2006 Lippincott Williams & Wilkins

> Table of Contents > Part Two - Selected Topics > Chapter 24 - Kidney Tumors

Chapter 24

Kidney Tumors

Benign Solid Tumors

Renal Cortical Adenomas

Renal cortical adenomas are benign tumors of the renal cortex that are generally discovered incidentally. They have been distinguished from renal cell carcinomas (RCCs) in the past primarily by their small size: less than 3 cm in diameter. The designation of these tumors as benign adenomas has been questioned because they are histologically indistinguishable from RCCs. It has been reasoned that all tubular cell adenomas are malignant and simply represent an early stage of renal carcinoma growth. These tumors should be treated as small RCCs.

Renal Oncocytoma

Renal oncocytoma is generally a benign, unifocal renal tumor that averages 5 to 8 cm in diameter; however, the presence of malignant elements has been known to occur. Its presentation is usually asymptomatic, with the majority being discovered incidentally. It can have a somewhat typical spoke-wheel appearance on angiogram, but this is uncertain. Partial or radical nephrectomy is the safest method of treatment because of the unreliability of differentiating it from RCC preoperatively.

Angiomyolipomas (Renal Hamartoma)

Angiomyolipomas are generally benign tumors, are frequently bilateral or multiple, and are often associated with tuberous sclerosis. Histologically, they are composed of fat cells, blood vessels, and sheets of smooth muscle cells. Profuse internal hemorrhage can occur. Its angiographic pattern is not characteristic; however, it has a distinctive fat content on computed tomography (CT) that is usually diagnostic. Asymptomatic lesions smaller than 4 cm

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should be followed with yearly ultrasound examinations. Larger tumors should be considered for embolization or renal-sparing surgery. Conservative surgical therapy is necessary because of frequent bilaterality and multiplicity.

Other Rare Benign Renal Tumors

Fibroma, lipoma, leiomyoma, angioma, rhabdomyoma, neurofibroma, dermoid tumors, and tumors of endometriosis are other rare benign renal tumors.

Pseudotumors

Pseudotumors are normal variants of functioning renal tissue that can occasionally appear as a questionable renal mass on intravenous urography (IVU) or ultrasound. They include fetal lobulations, column of Bertin, dromedary hump, hilar lip or uncus, and nodular compensatory hypertrophy. A CT scan will generally differentiate a true tumor from a pseudotumor. However, if one suspects an equivocal renal mass to be a pseudotumor, then a dimercaptosuccinic acid (DMSA) renal scan may be helpful. A pseudotumor will appear as normal homogeneous functioning kidney, whereas a true renal mass will appear as a focal defect within the renal parenchyma (sensitivity 95%).

Malignant Tumors

Renal Cell Carcinoma (Hypernephroma, Renal Adenocarcinoma)

RCC is the most common solid renal tumor (90%). It is primarily a tumor of adults (age 40 60 years), with a 2:1 male predominance. Approximately 30,000 new diagnoses are made each year in the United States, and 12,000 deaths from it are recorded. It arises from cells of the proximal convoluted tubule with no known cause. These are typically round tumors of varying size with a pseudocapsule and areas of hemorrhage and necrosis, and they often displace or invade the collecting system. Local extension occasionally occurs despite Gerota's fascia. Tumor thrombus into the renal vein is frequent and may extend into the vena cava. Metastatic spread is to lung, liver, bone, brain, and subcutaneous tissues.

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Presentation

Because of its retroperitoneal location, symptoms such as the classic triad of pain, hematuria, and flank mass occur only rarely today and generally indicate advanced disease. More than 50% of these tumors are presenting as asymptomatic incidental findings on IVU, abdominal ultrasound, or CT scans. Nevertheless, the more frequent findings are pain (41%), hematuria (36%), weight loss (36%), flank mass (24%), hypertension (20%), hypercalcemia (13%), and erythrocytosis (3%). Some paraneoplastic syndromes may occur as a result of renal tumor production of 1,25 dihydroxycholecalciferol, rennin, erythropoietin, and other hormone substances. Hepatic dysfunction without evidence of hepatic metastasis (Stauffer's syndrome) can occur in up to 20% of patients. Epidemiologic studies suggest tobacco smoking as a likely cause.

Patients with Von Hippel Lindau disease frequently get RCC in addition to pheochromocytomas, retinal angiomas, and hemangioblastomas of the brain and spinal cord.

Diagnosis

The renal tumor must first be differentiated from the more common benign renal cysts. Ultrasound and CT scan can effectively define the solid or cystic nature of the mass. Complete evaluation of the cystic renal mass is described in Chapter 15. Fine-needle aspiration or biopsy of a solid renal mass has little value except when lymphoma or metastases to the kidney is suspected from another primary. These biopsies have a high false-negative rate.

Intravenous Urography

IVU should be performed to fully evaluate the upper and lower urinary tract.

Abdominal Computed Tomography

A CT scan without and with intravenous (IV) contrast (renal protocol) is the method of choice to evaluate a renal mass. Any mass that enhances with IV contrast should be considered an RCC until proven otherwise. CT also provides accurate information on renal vein and inferior vena cava involvement, lymph node metastases, and perirenal extension to adjacent organs.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) can help differentiate solid and cystic renal masses and is particularly useful in patients who cannot receive IV contrast agents. Enhancement following IV gadolinium diethylenetriamine pentaacetic acid (GDPA) on T1 images of an MRI indicates vascularity and helps identify RCC.

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MRI has become the best study to evaluate the IVC for tumor thrombus.

Selective Renal Arteriography

Selective renal arteriography was the standard diagnostic test for RCC because of its classic angiographic picture of neovascularity, venous pooling, arteriovenous fistulae, and capsular vessels. Even hypovascular renal cell tumors could be differentiated by infusion of epinephrine that will constrict normal but not tumor vessels. However, arteriography is primarily reserved for patients with solitary kidneys to gain knowledge of the vascular anatomy for planning conservative surgical excision.

Metastatic Workup

Metastatic workup should include routine chest radiograph, IVU, CT, liver function tests, and serum calcium. A bone scan should be obtained in any patient with skeletal pain or other evidence of metastatic disease.

Staging Systems

Staging systems used in the United States include the simpler, but less accurate, Robson's classification, and the more complicated, but precise, TNM system. Both are included here.

Robson's Classification

Stage I tumor within renal capsule

Stage II outside capsule but within Gerota's fascia

Stage III involvement of regional lymph nodes, renal vein, or vena cava

Stage IV adjacent organs or distant metastases

TNM Staging Classification American Joint Committee on Cancer

	Description	Robson's Stage
T	Primary tumor
T1	Tumor 7 cm limited to kidney	I
T2	Tumor >7 cm limited to kidney	I
T3	Tumor extends into major veins, adrenal, or perirenal fat
T3a	Tumor invades adrenal or perirenal fat but within Gerota's fascia	II
T3b	Tumor grossly into renal vein or vena cava	III
T3c	Tumor into vena cava above diaphragm	III
T4	Tumor invades beyond Gerota's fascia	IV
N	Lymph nodes

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Treatment

Surgery

Surgery is the most effective treatment for primary RCC. Traditionally, radical nephrectomy with early ligation of the renal artery and vein and removal of the entire kidney including Gerota's fascia and the accompanying adrenal gland has been standard treatment. However, the increasing number of incidental small renal tumors diagnosed by ultrasound and CT scans has led to greater use of nephron-sparing surgery. Partial nephrectomy had generally been reserved for tumors in solitary kidneys. Nephron-sparing surgery is now acceptable with single, small, peripheral tumors less than 4 cm and a normal contralateral kidney.

In addition to standard surgical approaches, increasing use of laparoscopy and cryoablation is now common.

• T1 to T3a radical nephrectomy (excision of the kidney and adrenal including Gerota's fascia) with a limited regional lymphadenectomy and early ligation of the artery and vein is standard therapy. Nephron-sparing surgery is used with appropriate indications (small peripheral T1a tumors).

• T3b to T4 patients with only renal vein or inferior vena cava thrombus appear to benefit from radical nephrectomy. Regional lymph node or adjacent organ involvement is a dire prognostic sign. However, because radical nephrectomy is the most effective therapy for renal cell cancer, extended radical surgery may be appropriate if complete excision is contemplated.

• Metastatic disease distant metastatic disease is present in 30% of patients at the time of diagnosis. These patients have an average survival of only 4 months, and only 10% survive 1 year. The use of the term adjunctive nephrectomy in this group was adopted in the past because of the rare cases of spontaneous regression of metastases that had occurred after nephrectomy. However, regression can be expected in less than 1% of patients, which advises against such therapy. Palliative nephrectomy is reserved for patients with severe hemorrhage, pain, or paraneoplastic syndromes.

Radiation Therapy

Preoperative or postoperative irradiation has not been shown to influence overall survival.

Chemotherapy

RCC remains resistant to currently available chemotherapeutic agents.

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Hormonal Therapy

No report has proved the efficacy of progesterone therapy in the treatment of RCC.

Immunotherapy

Both active and passive immunotherapy has shown promise in the treatment of advanced RCC. Immunotherapeutic protocols using interferon- or interleukin (IL)-2 in patients with nonbulky metastatic disease after nephrectomy have had favorable responses.

Observation

Observation of small renal tumors less than 3 cm in the elderly or poor surgical risk patient with serial renal imaging at 6-month or 1-year intervals is reasonable management in this setting.

Renal Sarcomas

Renal sarcomas account for only 2% of malignant renal tumors, and 60% of these are leiomyosarcomas. Differentiation from RCC is difficult or impossible until surgery. Radical nephrectomy is the treatment. Prognosis is poor without adjuvant chemotherapy.

Hemangiopericytomas

Hemangiopericytomas are highly vascular tumors that often secrete renin and may grow to a large size. Some 15% are malignant. Radical nephrectomy is the appropriate treatment.

Metastatic Renal Tumors

Usually cancers metastatic to the kidney are discovered at autopsy except for lymphoblastomas. Because they are a metastasis, removal is not indicated.

Lymphoblastomas

Lymphoid malignancies of the kidney are generally a manifestation of the systemic disease and should be treated as such. Nephrectomy is not indicated.

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Wilms' Tumor

Nephroblastoma or Wilms' tumor accounts for 95% of all urinary tract malignancies occurring in childhood, followed by RCC representing only 3%. Approximately 450 new cases occur in the United States each year. Ninety percent of these occur in children younger than 7 years, with a median age at diagnosis of 3 years. Nephroblastoma, also referred to as renal embryoma, is believed to arise from abnormal proliferation of remnants of immature kidney (metanephric blastema) within the kidney. It appears to have little familial tendency (1% 2%); however, it has been associated with other anomalies, including aniridia (1%), hemihypertrophy (3%), and genitourinary defects (4%).

Pathology

Wilms' tumor is characteristically a solitary, unilateral mass with a fleshy tan cut surface and variable areas of hemorrhage and necrosis. Venous invasion occurs in up to 20% of cases. Histologically it is composed of primitive tubules and glomerular structures in a background of stromal components and undifferentiated blastemal tissue. Three unfavorable histologic types comprise about 10% of all cases: (a) anaplasia, (b) rhabdoid tumor, and (c) clear cell sarcoma (also known as bone-metastasizing Wilms' tumor).

Major indicators of poor prognosis include unfavorable histology, distant metastases (lung, liver, bone, brain), and lymph node involvement at time of diagnosis. Other less clear prognostic factors include age (>2 years), tumor weight (>250 g), extrarenal vessel extension, direct abdominal extension, and operative spillage.

Presentation

Children appearing otherwise well will present with an enlarging, smooth abdominal mass confined to one side of the abdomen with hypertension (60%) or microscopic hematuria (25%). The differential diagnosis for an abdominal mass in a child includes hydronephrosis, multicystic kidney diseases, neuroblastoma, Wilms' tumor, splenomegaly, lymphoma, and mesenteric cysts (see Chapter 15).

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Diagnosis

The diagnosis of Wilms' tumor is made radiologically by ultrasound and confirmed by CT scan or MRI. It must be differentiated from hydronephrosis, polycystic kidney, and neuroblastoma.

Treatment

Because of effective, modern multimodal therapies including surgery, radiation, and chemotherapy, survivals approaching 100% can be expected with Wilms' tumor. Protocols for managing Wilms' tumor have been extensively studied by the National Wilms' Tumor Study (NWTS) group. The latest recommendations of the NWTS (presently NWTS-5) should be reviewed.

Surgery

A nephrectomy is initial therapy for most children with Wilms' tumor. The contralateral kidney must be inspected for bilaterality before proceeding with nephrectomy. Large tumors should be shrunk with chemotherapy and/or radiotherapy preoperatively. A regional lymph node sampling should be performed for staging purposes.

Radiotherapy

Preoperative radiotherapy decreases the incidence of intraoperative tumor rupture but does not affect survival. Postoperative radiotherapy to the flank is routinely given to all children with unfavorable histology.

Chemotherapy

Chemotherapeutic regimens include dactinomycin, vincristine, doxorubicin, and cyclophosphamide and should begin almost immediately postoperatively.