Fine Needle Aspiration Cytology of Adult Perineal Rhabdomyosarcoma

Background Adult perineal soft tissue sarcomas are rare. Fewer than 30 cases have been reported, and all were diagnosed after surgical resection by histologic examination. Below we report a case in which the diagnosis was established preoperatively by fine needle aspiration (FNA). Case A 27-year-old man presented with a firm, midline, perineal mass. Magnetic resonance imaging showed a 3-cm, enhancing mass that was considered neoplastic. FNA biopsy, followed by cytologic examination, revealed moderately cellular aspirates composed of discohesive, small, blue cells with scant cytoplasm, high nuclear/cytoplasmic ratios and pleomorphic nuclei with irregular nuclear contours; uniform, hyperchromatic chromatin; and occasional mitotic figures. Frequent naked nuclei and scattered cells with more abundant, dense cytoplasm and eccentric nuclei were also noted. The diagnosis of rhahdomyosarconia was favored on FNA and was corroborated by immunohistochemical stains for desmin, myogenin and CD 56. Upon surgical resection, the diagnosis of alveolar rhabdomyosarcoma was confirmed histologically and immunophenotypically. Conclusion FNA is a useful tool in diagnosing soft tissue lesions of the perineum, including rare primary tumors, such as adult rhabdomyosarcoma. In this case, early identification avoided incisional biopsy and directed appropriate extirpative surgery and reconstruction considerations.