An Unusual Schwannoma in the Proximal Part of the Left Arm – A Case Report

Background: Schwannomas are the most common benign tumors of peripheral nerves, originating from Schwann cells and accounting for 90% of all peripheral neural tumors. However, their occurrence along the musculocutaneous nerve in the upper extremity is rare. Due to their slow growth and nonspecific symptoms, diagnosis can often be delayed or challenging. Imaging modalities such as ultrasonography (USG) and magnetic resonance imaging (MRI) play a crucial role in preoperative diagnosis, though definitive confirmation requires histopathological analysis. Case Presentation: We present the case of a 22-year-old female who presented with swelling, numbness, weakness, and paresthesia in the left arm. Clinical examination revealed a mobile, round, firm mass on the volar aspect of the proximal part of the left arm with a positive Tinel’s sign but no neurological deficits. Laboratory findings showed mild anemia, but other parameters were within normal limits. Imaging studies suggested an intramuscular peripheral nerve sheath tumor. USG revealed a fusiform hypoechoic mass with characteristic “split fat sign” and increased vascularity, while MRI demonstrated an encapsulated lesion with hyperintense T2 signal, fascicular sign, and intense post-contrast enhancement, consistent with schwannoma. Histopathological examination confirmed the diagnosis, revealing spindle-shaped cells with wavy nuclei and Verocay bodies, without evidence of malignancy. Conclusion: This case report highlights the importance of integrating clinical, radiological, and histopathological findings to achieve an accurate diagnosis of schwannomas, particularly in atypical locations such as the upper extremities. Early identification and appropriate management are crucial in preventing complications and preserving nerve function.