Renal Neoplasia: Diagnostic Problems and Recently Recognized Entities
Case 9 -
Metanephric Stromal Tumor
John N Eble, M.D.
Holger Moch, M.D.
While bathing her son, the mother of a 29-month-old boy
found an abdominal mass. Physical examination disclosed slight flank pain and microscopic hematuria.
Radiographic evaluation disclosed a large mass in his right kidney and a nephrectomy was done.
Macroscopic findings: The diameter of the tumor was 5 cm. The tumor was well circumscribed but not
encapsulated. The cut surface was gray.
Metanephric stromal tumor
Metanephric stromal tumor is approximately one-tenth as common as congenital mesoblastic nephroma.
These tumors often present as abdominal masses or with hematuria. The mean age at diagnosis is 24
months, but metanephric stromal tumor also has been observed in an adult. So far, all of the tumors have
been cured by surgery.
Metanephric stromal tumors usually form a tan, lobulated mass centrally located in the
kidney. With a mean diameter of 5 cm, they often are large compared to the kidney. Approximately 50% of
tumors are grossly cystic and 15% are multifocal.
The border with the surrounding kidney lacks a capsule and is delicately infiltrative. It
is composed of spindle and stellate cells with hyperchromatic skinny nuclei, and fine cytoplasmic
processes. Metanephric stromal tumor often entraps renal tubules and blood vessels, creating "onionskin"
collarettes around them in a myxoid background. More cellular areas at the periphery of the impart a
striking image of variable cellularity. Epithelioid transformation of medial smooth muscle of entrapped
blood vessels is common and may result in aneurysms. IN roughly 25% of metanephric stromal tumors, there
is hyperplasia of juxtaglomerular cell associated with entrapped glomeruli. Approximately 20%
metanephric stromal tumors contain foci of glia or cartilage. Necrosis is unusual. Metanephric stromal
tumors often are immunoreactive for CD34, but this can be patchy. Reactions for desmin, cytokeratins,
and S-100 protein are negative.
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clinicopathologic study of 25 cases from the National Wilms Tumor Study Group Pathology Center. Am J
Surg Pathol 25: 433-444, 2001
- Bluebond-Langner R, Pinto PA, et al. Adult presentation of metanephric stromal tumor. J Urol 168: