A Progressively Enlarging Cystic Renal Mass in a Previously Healthy 48-Year-Old Woman

Vernon M. Chapman, BS, and Todd R. Hazelton, MD

Disclosures

November 27, 2001

Discussion

Renal cell carcinoma (RCC) accounts for 80% to 85% of primary malignant neoplasms of the kidney.[2] It usually presents as a solid mass; however, in 10% to 22% of cases, RCC appears as a unilocular or multilocular cystic mass on imaging studies.[3,4] Four mechanisms have been described to account for renal cell carcinomas with cystic features: intrinsic unilocular cystic growth (papillary cystic adenocarcinoma), intrinsic multilocular cystic growth, tumor necrosis resulting in cyst formation (pseudocyst), and tumor arising in a preexisting simple renal cyst.[4] Some investigators have proposed that multilocular cystic RCC be recognized as a distinct subtype of RCC based on its characteristic microscopic features and improved prognosis. Histologically, multilocular cystic RCC demonstrates multilocular cysts lined by a single layer of cuboidal clear cell epithelium, and most show grade 1 nuclear atypia with rare or absent mitoses.[5]

The classic symptoms of RCC include hematuria, abdominal pain, and a flank or abdominal mass. The complete triad has been found historically in up to 10% of patients.[2] With the widespread use of ultrasound and CT, the majority of RCCs are now being found incidentally in asymptomatic individuals. The tumor stage in incidentally discovered cases is similar to that in symptomatic cases.[6] The initial evaluation of a symptomatic renal mass often includes a renal ultrasound followed by a contrast-enhanced CT of the abdomen and pelvis for masses suspicious for malignancy.

Cystic renal masses are categorized based on radiographic features according to the Bosniak classification system.[1] Class I lesions are simple, benign cysts that are nonenhancing and well marginated with thin, smooth walls. Class II lesions are mildly complicated, benign cysts that are nonenhancing and may be hyperdense or multiloculated with thin septa. Small amounts of calcium may be present in the cyst wall or septa. Class III lesions are considered 'indeterminate lesions' and may have thick, irregular calcifications, irregular margins, or thickened enhancing septa. Class IV lesions are highly suspicious for malignancy. Lesions in this class exhibit thickened, irregular, and enhancing areas with adjacent tumor mass or tumor within the wall of the cyst. Most cystic RCCs present as Bosniak class III or class IV cystic masses.[1] On contrast-enhanced CT, cystic RCCs typically exhibit unilocular or multilocular cystic growth with areas of wall thickening and contrast enhancement.

The differential diagnosis of a multilocular cystic renal mass includes numerous cystic diseases of the kidney, most of which are easily excluded based on CT findings.[7] However, multilocular cystic nephroma, a rare benign tumor of the kidney, frequently cannot be distinguished from multilocular cystic RCC by imaging. Microscopic examination of surgically resected tissue is often necessary to distinguish between these two neoplasms. Microscopically, multilocular cystic nephroma demonstrates multilocular cysts lined by a single layer of epithelium without nuclear atypia.[8]

RCC is staged according to the American Joint Committee on Cancer.[9] The traditional treatment of RCC is radical nephrectomy with regional lymphadenectomy. More recently, nephron-sparing or partial nephrectomy has been proposed for patients with tumors less than 4 cm in size. In such cases, partial nephrectomy has resulted in a recurrence rate similar to that obtained by radical nephrectomy.[10,11] The role of lymphadenectomy in the treatment of RCC is controversial. Though clinical studies[12] have demonstrated an improved prognosis following regional lymphadenectomy, a recent study found that 94% of patients with autopsy diagnosed RCC with lymphatic spread had additional distant metastases.[13]

Multilocular cystic renal cell carcinoma is distinguished from the other subtypes of RCC based on the high incidence of stage I disease at initial presentation (83% to 88%), infrequent metastases, and an extremely high cure rate following surgical resection of the tumor.[12,13] Corica et al[13] recently reported the outcomes of 24 patients with cystic RCC treated by radical nephrectomy (46%), simple nephrectomy (17%), partial nephrectomy (12%), or tumor enucleation (25%). Most patients (87%) presented with stage I or stage II tumors. After a mean follow-up of 77.6 months, 22 patients (92%) had no evidence of disease.

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