A RARE CASE OF ALVEOLAR RHABDOMYOSARCOMA OF PERINEAL REGION

Abstract

The term "rhabdomyosarcoma" (RMS) dates back to Weber's description in 1854 and is characterized by two primary subtypes: Alveolar Rhabdomyosarcoma (ARMS) and Embryonal Rhabdomyosarcoma (ERMS). A 23-year-old male with complaints of mass and bleeding per rectum since a month was referred for Contrast Enhanced Computerized Tomography (CECT) Abdomen and Pelvis. The CECT revealed a mildly lobulated heterogeneously enhancing soft tissue mass arising from the perianal region with infiltration of bilateral ischioanal, ischiorectal fossae extending to anterior perineum and infiltrating to right side of prostate. Histopathological findings revealed small round cells showing round nucleus, coarse chromatin having high N:C ratio and scant cytoplasm. The tumor cells were immune positive for vimentin, desmin, myogenin and myoD1 with a leading differential diagnosis of Rhabdomyosarcoma. Imaging is required for both the initial diagnosis and the assessment of the tumor's response to treatment. Ultrasonography (US) of the mass is frequently the first imaging modality used in the diagnostic work-up whereas Magnetic resonance imaging (MRI) is the preferred modality for assessing primary rhabdomyosarcoma. Advanced multiparametric MRI may be useful in predicting prognosis. Both immunohistochemistry and histology are always used to confirm the diagnosis.