Spindle cell lipoma with predominant nerve sheath tumor-like areas: A potential diagnostic pitfall on aspiration cytology.

Spindle cell lipoma (SCL) is an uncommon variant of lipoma that usually is present in subcutaneous fat of adult men. This tumor has a low rate of local recurrence and no risk of malignant behavior. Although histological features of SCL are well documented, cytological descriptions have been few. We present the case of a 41-year man with a right arm swelling, which on fine-needle aspiration cytology showed adipose tissue fragments, spindle cell areas mimicking benign nerve sheath tumor, and bundles of ropy collagen in a myxoid background, suggesting a diagnosis of SCL. SCL with predominant spindle cell component may mimic benign nerve sheath tumor on aspiration cytology. Subtle cytological features like presence of adipose tissue, ropy collagen, and mast cells help in accurate diagnosis.