Pilomatricoma, also known as calcifying epithelioma of Malherbe, is a benign tumor that arises from hair follicle matrix cells. These lesions were formerly known as "pilomatrixoma," a term introduced in 1961. The typical history provided by the patient is a slow-growing, rock-hard mass that occasionally involves pain and tenderness. There may be a blue discoloration as well as ulceration of the skin overlying the mass. The prevalence of these lesions is slightly increased in females, and they usually present in the first decade of life, with a second peak in the sixth to seventh decades.[2,3] Pilomatricomas usually present in the head and neck region as single lesions. On occasion, lesions arise in areas of previous trauma or infection. Multiple lesions have been reported in conjunction with myotonic dystrophy.
Pilomatricoma is typically diagnosed on the basis of history and physical examination alone, without the need for imaging or biopsy. If the mass is located in an area that suggests another diagnosis -- for example, overlying the parotid gland or in the paraspinal region -- then CT or MRI may be indicated. In addition, fine-needle aspiration biopsy may be indicated to rule out suspected cancer.
Pilomatricomas are often misdiagnosed as epidermoid cysts, dermoid cysts, hemangiomas, and other tumors. One study examining 346 cases of pilomatricoma determined that the preoperative diagnosis was correct in only 28.9% of cases. The diagnosis of pilomatricoma can be confirmed by palpation of an irregular nodular surface that moves freely underneath the skin. The "tent sign" -- stretching the skin overlying the mass to better observe underlying nodularity -- may be used as well.
Medscape Plastic Surgery © 2012
Cite this: Ian C. Hoppe, Mark S. Granick. A Boy With a Subcutaneous Mass - Medscape - Feb 14, 2012.