Pilomatricoma: Sonographic features

Abstract

Pilomatricomas (also known as calcifying epitheliomas of Malherbe) are benign subcutaneous tumors that arise from the cutaneous adnexa and usually affect young subjects. They typically present as solitary asymptomatic nodules located in most cases on the face or neck. On ultrasonography, pilomatricomas appear as hypoechoic lesions with inhomogeneous echo structures, well-defined margins, and posterior shadowing. Color Doppler generally reveals a single artery that penetrates the lesion and gives rise to multiple intralesional branches. Diagnosis is based on clinical and histological findings. The authors present a typical case of pilomatricoma diagnosed on the basis of clinical and sonographic findings that were subsequently confirmed by histology.

Introduction

Pilomatricomas (also known as calcifying epitheliomas of Malherbe) are benign subcutaneous tumors that arise from the cutaneous adnexa. They typically present as solitary asymptomatic nodules located in most cases on the face or neck. Their size generally ranges from 0.5 to 3.0 cm although pilomatricomas over 10 cm in diameter have been reported in the literature. Occasionally, they are associated with signs of inflammation. They generally arise in young subjects (first or second decade of life) and are more frequent among females. Multiple forms have also been described [1,2].

Histologically, the tumor appears as a well-defined dermal or subcutaneous lesion composed of epithelial cells surrounded by stromal cells. Basophilic cells are seen in the peripheral regions of the tumor whereas the central region contains mummified ghost (or shadow) cells, which have lost their nuclei and are filled with keratin and often calcium deposits as well. The transitional cells located between the basophilic and ghost-cell populations seem to be cells that have undergone apoptosis and are on their way to becoming ghost cells. The stroma is composed of collagen and contains blood vessels [3].

Pilomatricomas are not aggressive tumors, and they are generally treated with surgical excision with margins of at least 1–2 cm to prevent recurrence, which is frequent following cases of incomplete resection [4].

The diagnosis of pilomatricoma is histological, but ultrasonography can be an aid in the interpretation of clinical findings.

Case report

The patient was a 7-year-old girl who presented with a firm, nontender swelling on the outer aspect of the distal third of the right arm. Sonographic examination of the lesion revealed a solid, oval, hypoechoic mass approximately 2 cm in diameter containing multiple millimeter-sized calcifications (Fig. 1). The color Doppler examination revealed a single artery that penetrated the parenchyma of the mass and gave rise to multiple intralesional branches (Fig. 2). Based on clinical and sonographic findings, the mass was diagnosed as a pilomatricoma. The tumor was excised, and the preoperative diagnosis was confirmed by the histological examination.

Fig. 1.

Sonography reveals a solid, oval-shaped mass with well-demarcated borders and a diameter of approximately 2 cm (A: panoramic imaging). The lesion is hypoechoic with multiple small calcifications (B).

Fig. 2.

Color Doppler reveals an artery that penetrates the parenchyma of the lesion and gives rise to multiple intralesional branches.

Ethical approval for this study was granted by the Medical Research Ethics Committee of our Institute, and informed consent was obtained from the patient's relatives.

Conclusions

On ultrasonography, pilomatricomas appear as well-demarcated lesions, generally oval in shape, with inhomogeneous echo structures characterized by anechoic areas representing cystic degeneration and punctate hyperechoic images corresponding to calcification. They exhibit posterior shadowing and a hypoechoic border that represents the connective-tissue capsule [1–3].

The differential diagnosis includes the following: epidermal cysts (which appear as hypoechoic masses with no detectable vascularization on color Doppler); hemangiomas, softer, lobulated masses which may or may not contain calcifications; when present, the latter are usually roundish; hyperplastic lymph nodes, which generally exhibit hilar vascularization and are uniformly hyperechoic; ossifying hematomas, which are nonvascularized lesions that are markedly hyperechoic with posterior shadowing; and dermatofibrosarcomas, which do not usually contain calcifications [3–5].

Pilomatricoma is a relatively rare tumor that is diagnosed on the basis of clinical and histological findings. Ultrasonographic findings serve as a support for the clinical and histological diagnosis. The sonographic examination can also rule out other types of pathology with similar presentations and reveal the relations between the tumor and the anatomical structures surrounding it.

Conflict of interest statement

None declared.