IS Case 252: Pilomatrixoma
Imaging Sciences URMC 2008
Publication Date: 2009-05-26
Pilomatrixomas are uncommon benign tumors that develop in the subcutaneous tissue arising from the matrix cells of the hair bulb. The lesion was originally described by Dr. Chenantals Malherbe and had been previously named calcifying epithelioma of Malherbe. Most tumors are found in the head and neck region of children but less frequently they can be found in adults as well as trunk and upper and lower extremities. Patients present with a solitary hard skin nodule and are usually asymptomatic otherwise. There are reports of lesions up to 15 cm but most are under 3 cm. Multiple pilomatrixomas can be seen in association with myotonic dystrophy.
Usual imaging findings for pilomatrixoma include a well circumscribed round or ovid nodule. The lesion typically contains calcifications radiographically and is isodense to skeletal muscle with slight enhancement on CT. On ultrasound, pilomatrixomas are typically heterogeneously hyperechoic when compared to muscle and calcifications appear as hyperechoic foci. Posterior acoustic shadowing is common. The lesion on MR shows T1 signal isointense to muscle with patching increased signal on T2. Peritumoral edema is also best visualized with water sensitive sequences. There is internal reticular patchy enhancement on post contrast T1 imaging.
Differential considerations can include epidermoid cyst, lymph node, neurofibroma, schwannoma, sebaceous cyst, and post-traumatic cyst or hematoma. In the case above the lesion had many benign features, but given the man’s strong family history of breast cancer a biopsy was performed which showed pilomatrixoma.
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