FINAL DIAGNOSIS: EMBRYONAL RHABDOMYOSARCOMA IN THE SELLA TURCICA.
Rhabdomyosarcomas are malignant mesenchymal tumors composed of striated muscle cells (1). They represent the most frequent soft tissue sarcoma in children less than 15 years of age. Less commonly they may occur in young adults and also in the older age group. It is difficult to assess the real incidence of rhabdomyosarcoma because of differences in diagnostic criteria. Mahour et al (2) reported that among 2,000 soft tissue tumors examined at the Mayo Clinic, 379 tumors (19%) were diagnosed as rhabdomyosarcomas. According to Young and Miller (3) at least 350 new cases of rhabdomyosarcoma occur in the USA every year. Rhabdomyosarcomas may originate anywhere in the body, most frequently in the head and neck region, the extremeties, the genitourinary tract and the retroperitoneum. Histologically the tumors can be divided in various types: embryonal, botryoid, alveolar and pleomorphic tumors.
Embryonal rhabdomyosarcoma, the most commonly occurring variant, develops mainly in children, rarely in the older age group. By light microscopy rhabdomyosarcomas are poorly differentiated, cellular tumors exhibiting cellular and nuclear pleomorphism and spreading to adjacent tissues. Mitotic figures are frequent and hemorrhagic areas and necrotic foci are often noticeable. The tumor cells are elongated, spindle-shaped and are embedded in a loose edematous myxoid stroma. Depending on the extent of differentiation they may resemble striated muscle cells. In many cases scattered cells with hyperchromatic nuclei and acidophilic cytoplasm can be recognized. These cells are regarded as rhabdomyoblasts and their presence can assure the diagnosis. The presence of cross striations in the tumor cell cytoplasm is diagnostic. This feature is, however, frequently not apparent by light microscopy. The use of immunocytochemical markers such as vimentin, desmin, myosin, myoglobin and actin, as well as nestin (4) or MyoD1 (myogenic regulatory protein) (5), can confirm the diagnosis. The most valuable method is transmission electron microscopy. The ultrastructural observation of sarcomeres demonstrates myogenesis.
From the clinical point of view our case is exceptional because the tumor was located within the sella turcica and posed as a pituitary adenoma. The patient was a 49 year old woman who presented with visual defects, developed hypopituitarism and was not cured by repeated surgeries. The cytogenesis of the tumor has not been clarified. It may originate in myocytes adjacent to the pituitary or alternatively derive from pluripotential mesenchymal cells capable of myogenesis. Primary intracranial rhabdomyosarcomas have been reported but they are extremely rare (6, 7). The intracranial spread of head and neck rhabdomyosarcoma may also occur.
Although rare, rhabdomyosarcomas should be included into the differential diagnosis of tumors of the sella turcica. Detailed histologic study including immunocytochemistry and primarily transmission electron microscopy are needed to reach a conclusive diagnosis because sellar rhabdomyosarcoma can mimic adenohypophysial tumors.