= PILOMATRIXOMA (former name)

= CALCIFYING EPITHELIOMA OF MALHERBE

= benign calcifying subcutaneous tumor arising from primitive cells of skin appendage that normally differentiate into hair matrix cells

Frequency:<1% of all skin tumors;

◊Most common solid cutaneous tumor in patients <20 years

Histo: epithelial cells with basophilic cytoplasm arranged in arclike fashion at periphery (basaloid cells) → centrally transformed into shadow cells (= ghost cells); eosinophilic cells without nuclei + filled with keratin

Age: two peaks of <20 years and 50–65 years

• slowly growing tumor confined to subcutis

Location: head & neck (68%), trunk (29%), extremities (17%)

• typically centrally calcified (in 85%)

MR:

• homogeneous intermediate signal intensity on T1WI
• heterogeneous intermediate signal intensity on T2WI
• peritumoral edema / inflammation
• enhancement of connective tissue capsule but not center

DDx: calcified lymph node, ossifying hematoma, hemangioma with phlebolith, granuloma annulare, dermatofibrosarcoma protuberans