Intradermal spindle cell/pleomorphic lipoma: a distinct subset.

Spindle cell/pleomorphic lipomas are a group of benign lipogenic tumors composed of primitive spindle cells, multinucleated giant cells, and mature adipocytes. These tumors have rarely been reported to arise in the dermis and may be misdiagnosed in this location. Twenty (12.7%) intradermal lesions identified among 157 spindle cell/pleomorphic lipomas in the authors' files were studied clinicopathologically and immunohistochemically. The patients' ages ranged from 20 to 85 years (median: 42 years); 14 of 20 patients were female (70%). Anatomical sites were the head/neck region (7 cases, 4 of which arose on the face), shoulder/upper back (4 cases), lower limbs (4 cases), trunk (3 cases), and upper limbs (2 cases). Most lesions presented as a soft and slowly enlarging cutaneous nodule, usually measuring less than 2.5 cm. Histologically, these dermal lesions differed from usual spindle cell/pleomorphic lipoma, being unencapsulated with poorly defined infiltrative margins, although the cytomorphologic findings, ropy collagen, and mast cells were as seen in usual subcutaneous lesions. Six cases showed features of pleomorphic lipoma. Immunohistochemically, lesional cells stained positively for CD34 and were negative for S-100 protein. One case recurred locally after 21 years. Dermal spindle cell/pleomorphic lipomas are distinctive in their apparent female predilection, wider anatomical distribution than subcutaneous lesions, and lack of circumscription. These unusual features can cause problems in differential diagnosis.