7 May 2009 – Case of the Week #145
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Thanks to Debra L. Zynger, MD and Jeffrey A. McDavit, MD, University of Pittsburgh Medical Center, Pittsburgh, PA, for contributing this case. To contribute a Case of the Week, email [email protected] with the clinical history, your diagnosis and diagnostic microscopic images (textbook quality) in JPG, GIF or TIFF format (send as attachments, we will shrink if necessary). Please include any other images (gross, immunostains, etc.) that may be helpful or interesting. We will write the discussion (unless you want to), list you as the contributor, and send you $35 (US dollars) by check or PayPal for your time after we send out the case. Please only send cases with high quality images and a diagnosis that is somewhat unusual (or a case with unusual features).
Case of the Week #145
A 15-year-old boy presented with a paratesticular mass.
What is your diagnosis?
Spindle Cell Embryonal Rhabdomyosarcoma
Rhabdomyosarcomas are classified into embryonal, alveolar and pleomorphic types. Embryonal rhabdomyosarcoma can be further classified as spindle cell or botryoid subtypes.
Spindle cell rhabdomyosarcoma, first described in 1992, is most commonly found in the paratesticular region of young boys (Am J Surg Pathol 1992;16:229), although cases have also been described in adults (Am J Surg Pathol 2005:29:1106, Virchows Arch 2006;449:554). Grossly, the tumors are firm and fibrous, with a whorled cut surface resembling leiomyoma. Fine needle aspiration reveals numerous spindle cells and large fragments of cytoplasmic processes with cross-striations (Acta Cytol 2005;49:331). At excision, they are composed of a uniform proliferation of relatively bland, elongated spindle cells (at least 50% of tumor cells) with eosinophilic and fibrillar cytoplasm mimicking smooth muscle fibers. Nuclei are often elongated and vesicular. Scattered spindled or polygonal rhabdomyoblasts with brightly eosinophilic cytoplasm and pleomorphic nuclei are also present. Stains for desmin, myogenin, vimentin, myoD1, and smooth muscle actin are positive (Arch Pathol Lab Med 2006;130:1454). The tumor cells are negative for S100, keratin and caldesmon.
The differential diagnosis includes:
● fibrosarcoma - herringbone pattern, may have similar morphology but no rhabdomyoblasts, negative for skeletal muscle markers
● infantile fibromatosis - deep location, fascicles of spindle cells, no cross striations, no undifferentiated cells
● leiomyosarcoma - usually high grade, cigar shaped nuclei, no rhabdomyoblasts, often positive for caldesmon, negative for myoglobin
● neuromuscular hamartoma of soft tissue - usually age < 2 years, affects brachial plexus or sciatic nerve, multinodular growth with connective tissue separating nodules, no rhabdomyoblasts, muscular component is positive for desmin and muscle specific actin, neural component is positive for S100
● rhabdomyoma - benign tumor of skeletal muscle differentiation, no rhabdomyoblasts, no pleomorphism, no necrosis
Excision typically results in a good prognosis in children, but tumors in adults have a more aggressive course.
Additional references: Soft Tissue Tumor chapter of PathologyOutlines.com
Nat Pernick, M.D., President
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