Malherbe's Calcifying Epithelioma (Pilomatrixoma): An Uncommon Periocular Tumor.

Benign calcifying epithelioma of Malherbe or pilomatrixoma or pilomatricoma is an uncommon lesion of the periocular tissues, arising from the matrix cells at the base of the hair. In the periocular area, it usually arises from the lids and eyebrows. Pilomatrixoma has certain characteristic clinical and histopathologic features, but since it is not commonly suspected preoperatively, certain distinctive clinical features of tumor should suggest clinical diagnosis followed by histopathologic confirmation.

INTRODUCTION

Benign calcifying epithelioma of Malherbe or pilomatrixoma or pilomatricoma is an uncommon lesion of the periocular tissues, arising from the matrix cells at the base of the hair.[1] In the periocular area, it usually arises from the lids and eyebrows. Since it is not commonly suspected preoperatively, certain distinctive clinical features of tumor should suggest clinical diagnosis followed by histopathologic confirmation.

CASE REPORT

A 25-year-old male presented with a small nodule in the right brow since the past 2 years. His best-corrected visual acuity was 20/20, N6 in both eyes and ocular examination was within normal limits.

The nodular lesion measuring 8×6 mm was present within the brow, subcutaneous in location, well-circumscribed, non-tender, freely movable and firm with a gritty surface on palpation. Skin over the swelling could not be well-visualized because of the dense overlying brow hair [Figure 1]. Since the patient was keen on surgical removal, an excision biopsy was performed through a small incision taken just over the lesion so that the scar could well be hidden within the brow hair.

Figure 1

External clinical photograph. The slight elevation and boundaries of the subcutaneous nodular lesion are marked by a circle

Histopathology

Gross examination showed a well-circumscribed single grayish-white mass measuring 7×5×5 mm. Cut section showed grayish areas, firm and gritty. Microscopic examination showed numerous lobules with basophilic cells in the periphery and of ghost-like squamous cells toward the center with a few anucleated cells [Figure 2]. Various stages of maturation of the basaloid cells into shadow cells could be seen [Figure 3]. These islands are surrounded by foreign body giant cells with a few lymphoplasmacytic infiltrates [Figure 4]. There were numerous foci of calcification more so in the necrotic areas and in the periphery of cellular islands [Figures 2 and 3]. The histopathologic features were consistent with a diagnosis of pilomatrixoma (benign calcifying epithelioma of Malherbe).

Figure 2

Photomicrograph showing central area of calcification surrounded by shadow cells. Basaloid cells can be seen in the periphery (H and E, ×100)

Figure 3

Various stages of maturation of basaloid cells into shadow cells seen (H and E, ×400)

Figure 4

Photomicrograph showing numerous islands of basaloid cells and few foreign body giant cells (H and E, ×100)

DISCUSSION

Pilomatrixoma is an uncommon lesion that arises from the matrix cells at the base of the hair. It was first described by Malherbe as benign calcifying epithelioma.[2] Subsequently numerous ultrastructural and electron microscopic studies[34] provided strong evidence of its origin from the matrix cells and the term “pilomatrixoma” was then coined by Forbis and Helwig keeping the histogenesis into consideration.[1]

Pilomatrixoma is usually a solitary lesion affecting young individuals. Forty percent of them develop in the first decade of life and another 20% in the second decade.[5] They most commonly involve the head and neck region followed by upper extremities, trunk, and lower extremities.[6] Periocular tissues are involved in 10–17% of cases and 5% of cases are multifocal.[6-8]

Pilomatrixoma generally presents with subcutaneous red to blue mass that is fairly well circumscribed, freely movable and firm to gritty on palpation.[9] Clinical features as documented by Duran et al.[10] and later also by Perez and Nicholson.[11] should arise clinical suspicion and they include onset in childhood or early adulthood, average size of 10 mm or less, consistency ranging from firm to cystic, moderate pattern of growth, pink to purple hue with subepithelial yellowish tinge, and intact overlying skin with telangiectatic vessels.

Clinical differential diagnosis includes epidermoid cysts, dermoid cyst, sebaceous adenoma or carcinoma, juvenile xanthogranuloma, capillary hemangioma, chalazion, and rhabdomyosarcoma.[6911] Although they grow slowly, they occasionally demonstrate rapid growth and may resemble keratoacanthoma.[12] They can rarely undergo malignant transformation into pilomatrix carcinoma.[13]

Histopathologic examination reveals the tumor to be grossly well circumscribed and firm to gritty in consistency. Microscopic examination shows numerous islands of epithelial cells with characteristic arrangement of basophilic cells in the periphery and shadow cells in the center. As the tumor matures the number of basophilic cells looses their nuclei and becomes shadow cells. Calcification is seen in 75% of the cases. Sheets of intensely eosinophilic keratinous material is seen within necrotic areas, and this may induce a foreign body giant cell reaction.[7914] Histopathologic differential diagnosis include basal or squamous cell epitheliomas as well as a variety of skin and subcutaneous cysts.[15]

Management includes a complete excision biopsy if there is any clinical suspicion of pilomatrixoma based on the clinical features described since this tumor is often confined to the soft tissues. Various aesthetic approaches can be used for excision. A sub-brow approach using a small incision close the hairline is ideal in such lesions. A superior lid crease approach as for blepharoplasty can also be used but preferable if the brow lesion is larger.

Although pilomatrixoma is an uncommon benign tumor and frequently misdiagnosed as epidermoid or dermoid cyst, it has some distinctive clinical features that suggest the correct diagnosis.