Answer to Image of the Month April 2013

Submitted by I S Reddy and G Swarnalata

 

Pilomatricoma

A 28-year old male presented with an asymptomatic, firm nodule over the back of right arm since 8 months.

pilomatricomaFirm nodule on the arm

The histology showed two types of cells, basophilic cells and eosinophilic shadow cells. The basophilic cells are at the periphery and have scanty cytoplasm, indistinct cell borders, hyperchromatic nuclei, which resemble cells of basal cell carcinoma. Eosinophilic shadow cells are seen towards the centre of the tumour. The shadow cells have more cytoplasm, distinct cell borders but no nuclear staining. The basophilic cells transform into shadow cells. The transformation is abrupt in some areas and gradual in other areas of the tumour. The shadow cells represent terminal differentiation towards the matrical cells of the hair follicle. The clinical features and histology correlate with that of pilomatricoma.

Pilomatricoma is a benign, appendageal tumour, which shows differentiation towards the matrical cells of the hair follicle. It presents as a firm nodule, 0.5 to 2 centimetres in size, slow growing, mostly solitary, distributed over the head, neck and upper limbs. Multiple lesions may be associated with myotonic dystrophy. The malignant variant of pilomatricoma is termed as pilomatrical carcinoma.