Ancient Schwannoma of the Thumb Pulp Presenting as a Cystic, Non-enhancing Lesion on MRI: A Diagnostic Pitfall

Schwannomas are benign peripheral nerve sheath tumors that rarely occur in the digits, with the ancient (degenerative) variant being even more uncommon.We describe the case of a 59-year-old male with a recurrent, painless thumb pulp mass.Preoperative magnetic resonance imaging (MRI) demonstrated a cystic-appearing lesion without significant postcontrast enhancement, interpreted as an epidermal inclusion cyst (EIC).Intraoperatively, the lesion was larger than expected and extended to the periosteum of the distal phalanx.Complete excision revealed a schwannoma with degenerative ("ancient") changes, confirmed by diffuse S100 and SOX10 immunoreactivity.This case provides MRI characterization of an ancient schwannoma of the thumb, demonstrating an atypical cystic, non-enhancing appearance.In this case, the lesion demonstrated atypical imaging features, leading to diagnostic confusion with an EIC.This report highlights a potential diagnostic pitfall of imaging and the importance of histopathology for definitive diagnosis, while expanding the spectrum of reported radiologic appearances of digital ancient schwannomas.