Dermpedia

Sharing dermatology and dermatopathology knowledge

Pilomatrixoma presents as a slow growing, firm to hard nodule (0.5- 3 cm) appearing, in decreasing frequency, on the head (cheek most common), upper limbs, neck, trunk, lower limbs.

Its pathogenesis is associated with the Wnt/wingless signal transduction pathway and mutated B-catenin protein, which plays a structural role in cell-cell formation between adherens junctions and the actin cytoskeleton.

There have been rare reports of pilomatrix carcinoma arising out of benign pilomatrixomas, and sites treated for pilomatricoma.

Who is affected: young (<20 years old, many before10 years old) with second peak in 6-7th decades of life.

Treatment: surgery is curative. Local recurrence in 2-3% of cases.

Microscopic features: 

- Lobules of basaloid and ghost cells (biphasic cell population

- Early lesions show brisk mitoses (indicating rapid growth and not a malignancy) and sheets of germinative basaloid cells with uniform nuclei and small nucleoli.

- As cells mature, they become larger with abundant eosinophilic cytoplasm, and pyknotic nuclei

- Melanin pigment in basaloid and tumor cells

- Foreign body giant cell reaction common

- Calcification, granular and basophilic, may be seen

- Atypical features in the elderly such as basloid cell pleomorphism, loss of polarity, nuclear hyperchromatism, and marked mitotic activity.

Differential diagnosis: infundibular cysts, trichoepithelioma.