Meningothelial hamartoma of the scalp.

Meningothelial hamartoma is a benign tumor composed of ectopic meningothelial elements in the dermis and subcutaneous tissue. It mainly occurs in the scalp; however, the incidence is extremely low. The origin of meningothelial hamartoma has not been elucidated; nevertheless, it has been theorized that it derives from ectopic meningothelial rests displaced during embryologic development. It can be diagnosed histologically as proliferation of connective tissue elements and cells arranged in solid nests, resembling vascular tumors. On immunohistochemistry, it stains positively for epithelial membrane antigen and vimentin. At least 17 cases have been reported, verifying the rarity of the lesion. We present the case of a 16-year-old male patient with a soft scalp mass which was thought to be a lipoma, but turned out to be a meningothelial hamartoma on histology.