Challenging diagnosis of superficial acral fibromyxoma: cellular atypia and unusual imaging findings

Introduction: Superficial acralfibromyxoma (SAF) is a rare benign soft tissue tumor typically occurring in acral regions, particularly the peri- and subungual areas. Submatrix localization is exceedingly uncommon and poses diagnostic and therapeutic challenges. Case Presentation: We report the case of a 21-year-old female presenting with a painful, progressively enlarging swelling of the left fourth toe over three years. Clinical examination revealed a subungual mass measuring 2.5 cm, firm and minimally mobile, with nail widening and pseudo-clubbing. Radiological findings demonstrated a well-defined lytic lesion in the distal phalanx, suggestive of a mucous or epidermoid cyst. Histopathological and immunohistochemical evaluation confirmed the diagnosis of SAF with cellular atypia and moderate mitotic activity. Given the rapid progression and significant bone involvement, a trans-phalangeal amputation was performed. Discussion: SAF typically exhibits slow growth and a benign course. However, in cases with atypical histological features and extensive bone involvement, as presented here, aggressive surgical management may be necessary to prevent recurrence. This case also highlights the importance of including SAF in the differential diagnosis of acral lesions with lytic bone involvement. Conclusion: This case underscores the rarity of SAF with submatrix localization and cellular atypia. Early diagnosis and adequate surgical margins are crucial to achieving favorable outcomes while minimizing recurrence risk.