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Pilomatricoma (ultrasound and MRI)

Case contributed by Andrei Dumitrescu
Diagnosis almost certain

Presentation

Mildly painful, reddened bump at the antero-lateral aspect of the left thigh's middle to distal third, reportedly there for about 3 years.

Patient Data

Age: 40 years
Gender: Male

Ultrasound of the left thigh

ultrasound

Well-defined, ovoid, solid subcutaneous mass measuring 26 x 14 x 24 mm. Prominent blood vessels in Doppler mode. No discernible perifocal changes and no significant mass effect.

MRI

mri

Subcutaneous, solid, well-defined ovoid mass at the antero-lateral aspect of the left thigh with intermediate signal intensity on both T1 and T2 weighted non-contrast scans. Strong, slightly inhomogeneous contrast uptake. Subcutaneous perifocal changes with increased contrast uptake of the surrounding fatty tissue. There is no invasion of the underlying vastus lateralis muscle.

Case Discussion

Pilomatricomas (or pilomatrixomas) are some of the most frequent subcutaneous incidental findings encountered by general and musculoskeletal radiologists. The well-defined ovoid shape with only mild surrounding edema is suggestive of a benign lesion. However, relatively strong contrast uptake on CT or MRI, and the prominent blood supply visible on Doppler ultrasound, may raise suspicions of malignancy.

Differential diagnosis should include dermatofibrosarcoma or, more generally, soft tissue sarcoma until histologically proven otherwise.

In this case, the biopsy proved the lesion to be a pilomatrixoma, and it was subsequently excised at the patient's request.

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