pilomatricoma

School ager

with a lump on the forearm. AP radiograph of the forearm (left) shows a round faintly calcified lesion lateral to the diaphysis of the radius. Transverse (above right) and sagittal (below right) US images of the lesion show it to be in the subcutaneous tissues and to have a heterogenous speckled appearance.The diagnosis was pilomatricoma.

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A pilomatricoma is an uncommon, benign neoplasm thought to arise from hair cortex cells. It was formerly referred to as pilomatrixoma or calcifying epithelioma of Malherbe.

Epidemiology

the reported incidence ranges between 1 in 500-2000
they make up 0.12% of cutaneous neoplasms and 20% of all hair follicle related tumors
more common in females; F:M ratio = 3:2
more common in the Caucasian population
more common in children, but occurrence in adults is increasingly being recognized
there is a developmental bi-modal peak during the first and sixth decades of life
usually develops within the first two decades of life with 40% of cases occurring before the age of 10 years and 60% before the age of 20 years
usually solitary but up to 3% are multiple

Clinical presentation

painless
slow-growing
superficial
mobile
hard mass
ranges in size from 0.5 to 5 cm in diameter
overlying skin has a bluish-red discolouration

Pathology

Location

Approximately 50% of cases occur in the head and neck region. This is followed by the upper extremities, trunk and the lower extremities. Less commonly seen in the frontal, temporal, cheek, periorbital and preauricular areas.

Macroscopic appearance

Well-circumscribed nodulocystic tan colored mass containing irregularly shaped, lobulated islands of cells separated by fine, fibrovascular connective tissue stroma.

Microscopic appearance

peripheral basaloid cells are darkly stained, round or elongated, with indistinct cell borders and minimal cytoplasm; they contain round to ovoid deeply basophilic nuclei with most showing prominent nucleoli
central ghost cells have abundant, pale, eosinophilic cytoplasm with well defined cell borders and central clear area

Associations

Recognized associations include:

sarcoidosis
Turner syndrome
Gardner syndrome
Steinert disease
Rubinstein-Taybi syndrome
myotonic muscular dystrophy (associated with multiple and recurring lesions)
skull dysostosis

Familial forms may be present.

Variants

Pilomatrix carcinoma = malignant pilomatricoma (rare)

Radiographic features

Plain radiograph

there may be non-specific soft tissue calcification

Ultrasound

ovoid complex mass, often with calcification, at the junction of the dermis and subcutaneous fat with focal thinning of the overlying dermis
appear as target lesions with a hyporeflective connective tissue capsule and central hyper-reflective epithelial cells

CT

well-defined, subcutaneous tumors with microcalcifications

MRI

T1: uniform, homogeneously low to intermediate to high signal
T2: variable appearance either inhomogeneous with multiple areas of intermediate signal or homogeneous with either intermediate signal intensity or high signal radiating from the center
T1 C+ (Gd): variable post contrast T1 appearance, where some only enhance peripherally

Treatment and prognosis

Surgical resection is often curative.

History and etymology

It was first described by Malherbe and Chenantias in 1880, as a subcutaneous tumor, and was shown to be a derivative from hair cortex cells in 1942 by Turhan and Krainer.

The root of the term pilomatricoma is derived from the Latin word pilus meaning hair.