Case Number : Case 1534 - 11 May Posted By: Guest

Mixed pattern, spindle cell lipoma-like and sclerotic fibroma-like...so my first thought is "Sclerotic Lipoma", of the scalp ( unusual site ). 

Spindle cell proliferations with scattered typical adipocytes, few hyaline collagen bundles and many mast cells. This is a case of Spindle cell lipoma.

Spindle cell lipoma.

My differential is between a neurofibroma maybe a diffuse type or circumscribed (the latter because of the weird clinical diagnosis) vs spindle cell lipoma (rare at this age and location, usually has some myxoid areas) in my differential I also considered fibroblastic connective tissue nevus and even desmoid fibromatosis but this lesión is usually Deep seated, infiltrative and lacks mast cells. So to sum up I would do a panel of immunos including Desmin, SMA, S-100 and CD34.

Spindle cell lipoma.

I think this needs special stains. See a few mast cells. How about a neurofibroma?

the presence of adnexal entrapment is also a weird finding in spindle cell lipoma http://www.ncbi.nlm.nih.gov/pubmed/20559119 If this lesión was more cellular, with alternating cellularity and lacked mast cells even solitary fibrous tumor could be considered (I read in the last edition of Weedon that spindle cell lipoma and SFT are considered by some an spectrum of entities and to my astonishment in the book they say that clinically some cases are interpreted as cysts). To sum up immunos are mandatory in this case

I believe that the adipocytes are part of the lesion, not just entrapped cells. Mast cells are very common in Spindle cell lipomas as well.