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BENIGN TUMORS OF THE KIDNEY

What is the most common benign renal mass lesion?
A simple cyst, which may be single or multiple, unilateral or bilateral, and typically ranges from a few millimeters to several centimeters in diameter. Most simple cysts are found incidentally on abdominal or renal imaging studies, are asymptomatic, and require no treatment. Occasionally, a cyst may become very large and cause pain or obstruction of the collecting system.
 
. Describe the radiographic characteristics of simple cy!.ts.
On renal ultrasound, simple cysts are smooth-walled, sh :ply demarcated from surrounding parenchyma, and anechoic and exhibit posterior acoustic s ~.dowing. On intravenous urography, cysts usually show a mass effect and may distort the renal outline or collecting system. On computed tomography (CT), cysts are thin-walled, sharply demarcated, and fluid-filled with a tissue attenuation similar to water. On angiography, simple cysts are avascular.
 

. What is a renal cortical adenoma?

As originally described by Bell, these are small «3 em), well-circumscribed solid tumors comprising uniform clear or acidophilic cells with uniform histology. Adenomas are almost always asymptomatic, found incidentally, and often multifocal.
 
How can a renal adenoma be distinguished from a smaU renal cell carcinoma?
In clinical practice, these lesions are indistinguishable. Both adenomas and small renal cell carcinomas appear radiographically as solid tumors, but even benign-appearing renal cortical tumors < 3 em can metastasize. The diagnosis of adenoma is therefore based solely on pathologic examination. Molecular and cytogenetic studies suggest that adenomas of papillary histology are characterized by a loss of the Y chromosome and trisomy of chromosomes 7 and 17, as compared with renal cell carcinoma which is characterized by a deletion of the short arm of chromosome 3.
 
Describe the appearance and behavior of renal oncocytoma

Oncocytomas are usually round, well-circumscribed, and brown or tan and may contain a central stellate scar. Histologically they comprise nests, cysts, or tubular aggregates of polygonal cells with granular eosinophilic cytoplasm. Mitoses are rare. Electron microscopy demonstrates an abundance of mitochrondria. Oncocytomas show no tendency to invade surrounding structures or metastasize.
 
Can renal oncocytoma be distinguished clinically or radiographically from renal cell carcinoma?

No. Although increasingly diagnosed as incidental radiographic findings, both tumors may present with hematuria or other symptoms and appear radiographically as solid mass lesions which distort the renatcontour and/or collecting system. It has been suggested that the appearance of a central stellate scar on CT or a spoke-wheel pattern of tumor vessels on angiography is suggestiv~ of oncocytoma, but these patterns are rare and nonspecific. Both oncocytoma and renal cell carcinoma can present with multiple and bilateral synchronous tumors, and oncocytoma can occur simultaneously with renal cell carcinoma in the same or contralateral kidney in up to one-third of cases.
 

Can renal oncocytoma be distinguished pathologically from renal cell carcinoma?
Yes. True oncocytomas are low grade, have a characteristically uniform histologic appearance, typically have diploid DNA histograms, lack expression of HLA A,B, and C antigens, and are characterized by loss of the Y chromosome and translocations involving the long arm of chromosome I I. However, many renal cell carcinomas contain "oncocytic" features on histologic examination that could be misleading if the tumor is not adequately sampled. This fact, Along with the frequent coexistence of oncocytoma and renal cell carcinoma in the same or opposite kidney, limits the preoperative use of percutaneous needle biopsy of solid renal masses to establish the diagnosis of oncocytoma.
 
What are the clinical features of tuberous sclerosis?

Tuberous sclerosis is a hereditary syndrome characterized by mental retardation, epilepsy, and adenoma sebaceum. Hamartomas may be found in the brain, eye, heart, lung, and bone. Because of the high incidence and potential morbidity of renal hamartomas, all patients with tuberous sclerosis should be screened with renal ultrasonography or CT scans.
 

How do the renal hamartomas of tuberous sclerosis differ from sporadic angiomyolipomas?
The angiomyolipomas of tuberous sclerosis occur at a younger age, are bilateral in 80% of cases, and tend to be larger at the time of diagnosis. The symptomatic presentations and histologic appearances are similar.
 
 

How is renal oncocytoma treated?
Surgical excision, by partial or total nephrectomy.
 
 

Describe the histologic appearance of angiomyolipoma (renal hamartoma).
These tumors are composed of variable amounts of blood vessels (angio-), smooth muscle (myo-), and fat (lipoma).
 
 

In what clinical scenarios are angiomyolipomas encountered?
Angiomyolipomas occur sporadically or in association with tuberous sclerosis. Sporadic angiomyolipomas are more commonly right-sided (two-thirds of cases), occur almost exclusively in adult females, and are usually smaller and less frequently bilateral than those seen with tuberous sclerosis. Although increasingly diagnosed incidentally, both types occur with similar symptoms, including abdominal or flank pain, palpable mass, intratumoral hemorrhage, hematuria, anemia, and hypertension.

 
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