Presentation
Incidental renal mass identified on CT abdomen
Patient Data
Unfixed, bivalved right kidney specimen. Circumscribed, pale, rubbery, 100mm in diameter, in the upper pole of the right kidney. The tumor has a 'whorled' cut surface, reminiscent of a uterine fibroid.
Intersecting fascicles of smooth muscle cells with relatively uniform, 'cigar' shaped nuclei, eosinophilic cytoplasm and indistinct cell boundaries. Malignant features including mitotic activity, pleomorphism and necrosis are not seen.
There is strong cytoplasmic staining for the intermediate filament Desmin. The staining also demonstrates the intersecting fascicles.
Case Discussion
Leiomyoma is a benign tumor of smooth muscle. It is seen most commonly in the uterus (uterine 'fibroid'), gut and skin, but it is recognized to occur wherever smooth muscle is present... which is virtually everywhere as smooth muscle is present in the walls of arterial and venous vessels.
Renal leiomyoma is an uncommon condition. Most present as small capsular/subcapsular tumors, with only rare lesions presenting as a clinically relevant mass. There is an even more uncommon malignant counterpart, renal leiomyosarcoma.
Despite the characteristic macroscopic appearance, the diagnosis of leiomyoma is determined histologically, with intersecting fascicles of smooth muscle cells often with interspersed blood vessels. The tumor cells have uniform, spindled nuclei and the tumor lacks significant mitotic activity or necrosis.
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