Background Rhabdomyosarcoma (RMS) is the most common soft-tissue tumor in children and adolescents but is rare in adults. RMS has three main subtypes: alveolar, embryonal, and pleomorphic. The embryonal subtype includes sarcoma botryoides, anaplastic type, and spindle cell type. Spindle cell rhabdomyosarcoma(SCR), comprising 5%-10% of RMS cases, is considered a distinct entity related to embryonal RMS. These tumors resemble leiomyomas histologically. With a 5-year survival rate of only 27% in adults, further research is needed. We report a case of a 21-year-old female with spindle cell rhabdomyosarcoma in the left frontal region.

Case Presentation A 21-year-old female presented with a left frontal extracranial mass and intermittent headaches for the past year. Initial CT imaging revealed a 3.2 x 2.3 x 2.9 cm mass extending from the subcutaneous tissue through the bone intracranially. Initially suspected as a meningioma, MRI and angiogram later confirmed its growth and hypervascularity. Surgical resection was performed, and the pathology identified spindle cell rhabdomyosarcoma with FUS:TFCP2 fusion and positive IMHC markers (MYOD1, CKAE/AE, desmin, CD9, SSX-C, myogenin). Postoperatively, she developed a pulmonary embolism and was treated with apixaban. Subsequent visits for nausea, vomiting, and headaches led to observations of intracranial bleeding. Apixaban reversal was administered, and a six-week chemotherapy regimen (vincristine, adriamycin, cyclophosphamide) was initiated. A chest X-ray suggested possible pulmonary metastasis. Remaining treatment was continued at another facility.

Discussion Sarcomas represent 1% of adult solid malignancies, with SCR being exceptionally rare (0.041 per 100,000). Predominantly found in the paratesticular region and head/neck of children, it is rarer in adults, especially in females. Diagnosis relies on histology, with MYOD1 as a primary marker, indicating poor prognosis when mutated. PIK3CA, involved in the mTOR pathway and also associated with SCR, was negative in this case. Spindle cell rhabdomyosarcoma in adults presents unpredictably, often forming in the lower extremities, abdomen, or inguinal region. Therefore, the frontal lobe tumor in this case demonstrates a distinct, uncommon location. Treatment follows general rhabdomyosarcoma guidelines, including cyclophosphamide and vincristine, with additional monitoring needed for metastasis and recurrence.

Spindle cell rhabdomyosarcoma in adults is a rare and complex malignancy. This case highlights the importance of recognizing its distinct pathological and immunohistochemical characteristics and demonstrates the effectiveness of surgical intervention followed by targeted chemotherapy. Understanding these nuances is crucial for enhancing diagnostic accuracy, optimizing treatment plans, and improving patient outcomes.