Three-year-old develops ‘pebble’ on her cheek

Issue: August 2011

A mother brings her 3-year-old daughter to your office for evaluation of a firm nodule on her cheek. The mother reports the nodule has been there for several months and does not appear to bother her daughter. The daughter describes it as, “a pebble on my cheek.” On physical examination, you note a discrete 9 mm, extremely firm, mobile, white to slightly bluish, superficial nodule on her cheek. A complete skin examination is otherwise normal.

What is the most likely etiology?

Diagnosis: Pilomatricoma

A pilomatricoma, also known as a pilomatrixoma, trichomatricoma or calcifying epithelioma of Malherbe, is an uncommon benign neoplasm usually found on the head and neck. Pilomatricomas most commonly present in childhood during the first 2 decades and are more commonly seen in females. It is the most common tumor of the head and neck in this age group. Pilomatricomas derive from the hair follicle matrix, hence the name (“pilo-” meaning hair and “matric-” or “matrix-” referring to the hair matrical cells, a collection of epithelial cells that form the hair follicle and inner root sheath).

A pilomatricoma is an uncommon benign neoplasm usually found on the head and neck

Clinically, pilomatricomas often present as 5 mm to 15 mm hard, dermal or subcutaneous, mobile, skin-colored nodules and may occasionally demonstrate a slightly tender, blue, white or reddish hue of the overlying skin when located more superficially. A firm, deep red, protruding nodule is occasionally seen. Pilomatricomas uncommonly ulcerate, which may be due to transepidermal elimination of the calcified contents. The head and neck are the most common location, followed by the extremities and trunk.

Mutations in CTNNB1, the gene encoding for beta-catenin, are found in matrical neoplasms, including pilomatricomas. Beta-catenin is part of the Wnt signaling pathway and is involved in cell proliferation, differentiation and adhesion. In most cases, pilomatricomas are solitary. However, familial cases and multiple lesions in a single patient have been reported either as a normal variant or in association with Steinert’s disease (myotonic muscular dystrophy), Gardner’s syndrome, Turner’s syndrome and 21-hydroxylase deficiency, among others.

On histopathologic examination, the neoplasm appears as a well-circumscribed cystic structure with a fibrous capsule and islands of epithelial cells. The periphery of the islands consists of nucleated basaloid cells, whereas the central aspect contains enucleate eosinophilic shadow cells. The shadow or “ghost” cells represent keratinization of the basaloid cells. Focal calcification is common, and ossification may also be present, representing the firm nature of pilomatricoma.

The differential diagnosis includes epidermoid cyst, brachial cleft cyst, osteoma cutis, pyogenic granuloma (if more superficial and bright red), dermoid cyst, foreign body reaction, basal cell carcinoma (in adults) and other adnexal neoplasms, including trichilemmoma cyst, trichoepithelioma and eccrine spiradenoma. Malignant transformation is rare.

Pilomatricomas are asymptomatic but usually do not regress. Because they tend to enlarge, they are therefore often referred for surgical excision. The recurrence rate is low with enucleation or, if attached to the surrounding skin, en-bloc excision with clear margins. It is important to recognize pilomatricomas in children to reassure families of their benign nature and recommend elective surgical excision in most cases.

For more information:

Demircan M. Pediatr Dermatol. 1997;14:430-432.

Guinot-Moya R. Med Oral Patol Oral Cir Bucal. 2011; 16: 552-555.

Yencha MW. Int J Pediatr Otorhinolaryngol. 2001;57:123-128.

Marissa J. Perman, MD, is a pediatric dermatology fellow at The Children’s Hospital of Philadelphia. Disclosure: Dr. Perman reports no relevant financial disclosures.

Follow the PediatricSuperSite.com on Twitter.