A 10-year-old girl is bought in for evaluation after her parents recently noted a growth located on her right cheek. The child has no discomfort and palpation does not elicit tenderness. She is of average height and weight and has no overt developmental abnormalities. Examination reveals a firm nodule with off-white coloration when squeezed. No other lesions are noted elsewhere.
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Pilomatricoma, also referred to as calcifying epithelioma of Malherbe, is a benign neoplasm of the skin that originates within hair follicles. Although uncommon in adults, pilomatricoma is one of the most common tumors in children and adolescents.1,2 The growth most frequently occurs in hair-bearing regions such as the head, neck, and upper extremities.
Lesions present as flesh-colored to bluish, firm, slowly enlarging, subcutaneous nodules measuring 0.5 cm to 3.0 cm in diameter.2 The majority of these tumors are asymptomatic. Multiple pilomatricomas are associated with myotonic dystrophy and the Rubinstein-Taybi syndrome.3,4
Definitive diagnosis is made by biopsy. Histologic findings reveal a well-demarcated lesion that extends into the lower dermis and subcutaneous fat. Tumors consist of islands of epithelial cells comprised of both basophilic cells and so-called ghost cells that have a central unstained area indicative of a lost nucleus.5 Calcium deposition is frequently noted. In some cases, imaging studies may be recommended to help exclude a diagnosis of malignancy or to determine depth of a lesion.6
Approximately 75% of pilomatricomas have somatic mutations in the CTNNB1 gene, which encodes a protein involved with regulation of cell growth and attachment.7 This mutation does not portend malignancy and malignant degeneration is exceptionally rare.8 By contrast, metastasis occurs in 13% of cases of pilomatrix carcinoma, the malignant counterpart of pilomatricoma that occurs most commonly in adults.8
- Schwarz Y, Pitaro J, Waissbluth S, Daniel SJ. Review of pediatric head and neck pilomatrixoma. Int J Pediatr Otorhinolaryngol. 2016;85:148-153. doi:10.1016/j.ijporl.2016.03.026
- Kondo RN, Pontello Junior R, Belinetti FM, Cilião C, Vasconcellos VR, Grimaldi DM. Proliferating pilomatricoma—case report. An Bras Dermatol. 2015;90(3 Suppl 1):94-96. doi:10.1590/abd1806-4841.20153972
- Geh JL, Moss AL. Multiple pilomatrixomata and myotonic dystrophy: a familial association. Br J Plast Surg. 1999;52(2):143-145. doi:10.1054/bjps.1998.3036
- Aslan G, Erdogan B, Akoz T, Gorgu M, Seckin S, Terzioglu A. Multiple occurrence of pilomatrixoma. Plast Reconstr Surg. 1996;98(3):510-513. doi:10.1097/00006534-199609000-00024
- DeRosa DC, Lin-Hurtubise K. Pilomatricoma: an unusual dermatologic neoplasm. Hawaii J Med Public Health. 2012;71(10):282-286.
- Li L, Xu J, Wang S, Yang J. Ultra-high-frequency ultrasound in the evaluation of paediatric pilomatricoma based on the histopathologic classification. Front Med (Lausanne). 2021;8:673861. doi:10.3389/fmed.2021.673861
- Genetic and Rare Diseases Information Center. Pilomatrixoma. Accessed July 21, 2021. https://rarediseases.info.nih.gov/diseases/9452/pilomatrixoma
- Eckhoff MD, Tadlock J, Kafchinski LA. Pilomatrix carcinoma of the antecubitum. Cureus. 2020;12(1):e6821. doi:10.7759/cureus.6821