[Pilomatrixoma: ultrasound diagnosis]

Pilomatrixoma is a benign tumor of the skin, preferentially found in children. The final diagnosis is made by biopsy. High resolution ultrasound (US) is a non invasive method for its diagnosis.

To describe the US findings in children with pilomatrixoma.

Fifty five patients with 62 clinically suspected pilomatrixomas were studied by US. All examinations were done with an ATL HDI 5000, linear 5-12 MHz transducer. Pathological study confirmed the diagnosis pilomatrixoma in 52 cases.

Fifty of 52 pilomatrixomas were diagnosed by US, with a sensitivity of 96%. The mean age of patients was 7.5 years. Forty seven lesions (90%) were located in the head, neck or upper extremities and their mean size was 8.5 mm. Thirty two lesions were hypodermal, 14 were dermohypodermal and 6 were dermal. In 44 lesions the contour was regular and non delineated, 44 lesions were oval, 41 lesions had an acoustic shadow, 36 were echogenic or hyperechogenic, 31 had a peripheral halo (60%), 55 had calcifications (98%), nine had perilesional vessels, 2 had intratumoral vessels and 7 had inflammatory changes. US excluded the diagnosis of pilomatrixoma in 10 lesions formulating a correct differential diagnosis in eight, with a specificity of 80%.

Pilomatrixomas had two US types of presentation. The first is a well defined nodule with peripheral halo partially calcified or with microcalcifications. The second is a completely calcified nodule without peripheral halo and with a strong acoustic shadow. US is a useful, sensitive and specific diagnostic method for pilomatrixoma.