A 12-year-old girl was referred for evaluation of a solitary red lesion on her upper right arm (see images above). It was first noted several months earlier. The lesion has been growing and recently became red on the surface. There is no history of preceding trauma to the area. She is otherwise healthy and takes no medications. Medical and family history are unremarkable.
On palpation, the lesion, located on her right arm, is approximately 15 mm in size, mobile, very firm, and nontender. There is a subcutaneous portion that is larger than the red area on the surface. There are no other skin findings on physical examination.
A pilomatricoma (calcifying epithelioma of Malherbe) is a benign tumor originating from hair follicle matrix cells. ì It is more common in children and occurs in higher frequency in girls. The most common location are the head and neck (50%), but lesions can be found on any hair-bearing body site.
Clinically, pilomatricoma presents as solitary subcutaneous tumors. The overlying skin is normal in the early stages of growth. Lesions are calcified and have a rock-hard, angular and lobular consistency. Typical lesions measure 5 mm to several centimeters.2 Stretching of the skin overlying a pilomatricoma can result in "tenting" or an indentation of the skin on the surface of the lesion due to attachment of the tumor to the overlying epidermis. Pressing on one edge of the lesion can cause the opposite edge to protrude from the skin like a "teetertotter." The "tent sign" and "teeter-totter sign" can be helpful clinical clues to the diagnosis of these lesions.
Figure. Stretching the skin over a pilomatricoma can illustrate that there is a larger tumor underlying the cutaneous red lesion.
Pilomatricomas grow slowly and typically attain their full size over 6 to 12 months. The area may become discolored with a reddish blue tint as small blood vessels grow into the skin overlying the surface of these lesions. Often, lesions are not noted until this surface change appears, due to their asymptomatic nature. Periodic swelling can be seen, infrequently, in association with granulomatous inflammation. Occasionally, pilomatricomas may perforate through the skin, discharging a chalky white material containing calcium.3
Cystic-appearing pilomatricomas occur, in which hemorrhage results in bluered or purple translucent nodules that rapidly enlarge, probably in association with trauma. Other rare forms of pilomatricoma include a malignant form that demonstrates rapid growth and aggressive malignant behavior with metastasis.4 The latter form is very rare in childhood.
Although most lesions are solitary, multiple lesions have been reported. These are typically familial and can occur without any underlying associations5 or in association with Gardner's syndrome, a dominantiy inherited disorder characterized by multiple epidermoid and adnexal cysts, premalignant colonie and rectal polyps, and osseous and dental lesions, and Steinert's disease, a rare, dominantiy inherited disorder characterized by myotonic dystrophy, hypotonia, muscle wasting, cataracts, hypogonadism, and progressive mental retardation.6
The differential diagnosis of pilomatricoma includes other benign cysts, foreign body granulomas, calcinosis cutis, and even vascular malformations when the overlying skin has prominent vascularity or has undergone hemorrhage. The rock-hard consistency, "tent sign" and "teeter-totter sign" are very helpful diagnostic clues.
Most facial pilomatricomas are excised. Early excision is recommended because even facial lesions can attain several centimeters in size and have significant cosmetic consequences. Any rapidly enlarging lesion or recurrent lesion should be excised because of the risk of malignancy. Small lesions on the trunk or extremities often are left untreated unless they become large or symptomatic.
The only treatment for pilomatricoma is incision of the overlying skin and dissection of the tumor with suture closure. Incision and drainage of the contents of these lesions, even in the setting of perforating pilomatricomas, is not recommended because of the highly inflammatory nature of the calcified material that can cause a severe foreign body reaction in the skin. Lavage of the subcutaneous tissue with saline during dissection is recommended to avoid leaving any calcified material in the skin.
Calcification of these tumors lends a distinctive gross morphology that is eggshell-like in consistency. Histology usually is diagnostic, demonstrating sheets of epitheliod cells with adjacent cells devoid of basophilic material that are ghost or shadow cells. Frequently, there is pathognomonic calcification, either as fine granules within the shadow cells or as large sheets that replace these cells.
1. Lan MY, Lan MC, Ho CY, Li WY, Lin CZ. Pilomatricoma of the head and neck: a retrospective review of 179 cases. Arch Otolaryngol Head Neck Surg. 2003;129(12): 1327-1330.
2. Pirouzmanesh A, Reìnìsch JF, Gonzalez-Gomez I, Smith EM, Meara JG. Pilomatrixoma: a review of 346 cases. Plast Recensir Surg. 2003;112(7):1784-1789.
3. Ohnishi T, Nakamura Y, Watanabe S. Perforating pilomatricoma in a process of total elimination. JAm Acad Dermatol. 2003;49(2 Suppl Case Reports): S 146-S 147.
4. Sable D, Snow SN. Pilomatrix carcinoma of the back treated by mohs micrographie surgery. Dermatol Surg. 2004;30(8):1174-1176.
5. Hubbard VG, Whittaker SJ. Multiple familial pilomatricomas: an unusual case. J Cutan Pathol. 2004;31(3):281-283.
6. Urabe K, Xia J, Masuda T, Moroi Y, Fume M, Matsumoto T. Pilomatricoma-like changes in the epidermoid cysts of Gardner syndrome with an APC gene mutation. J Dermatol. 2004;31(3):255-257.