Orbital Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma Masquerading as Pleomorphic Lipoma: A Diagnostic Challenge.

Atypical lipomatous tumor/well-differentiated liposarcoma is a common neoplasm of the superficial and deep soft tissues of the extremities, trunk, and retroperitoneum. Atypical lipomatous tumor/well-differentiated liposarcoma is very rare in the orbit, with only 19 previously reported cases. The authors describe a 22-year-old woman who presented with an 8-month history of diplopia and was found to have an orbital mass on MRI. The excised tumor initially was interpreted as spindle cell/pleomorphic lipoma based on its morphologic and immunohistochemical features. Nine years later, the patient returned with a recurrence that required surgical debulking. Histopathologic and molecular cytogenetic evaluation of both primary and recurrent lesions disclosed Atypical lipomatous tumor/well-differentiated liposarcoma. This case highlights the diagnostic challenges and the importance of molecular genetic studies in evaluation of fatty orbital tumors.