Proliferating trichilemmal tumors: CT and MR imaging findings in two cases, one with malignant transformation

Abstract

We report the imaging findings in two patients with proliferating trichilemmal tumors. In the first patient, the tumor arose on the lower lip, a very unusual location for this type of tumor, and showed malignant transformation with metastasis to a regional lymph node. It was seen as a poorly marginated soft-tissue mass with isointense signal on T1-weighted MR images and hyperintense signal on T2-weighted images. Large areas of high signal intensity caused by necrosis were also found within the tumor on T2-weighted images. After i.v. administration of contrast material, the mass showed significant enhancement, with considerable portions remaining unenhanced. In the second patient, the tumor originated from a preexisting trichilemmal cyst and occurred in the hair-bearing area of the posterior part of the neck. CT scans showed a well-encapsulated cystic mass that contained multiple speckled calcifications in a wall of variable thickness. There were several foci of smooth soft-tissue elevations from the inner wall of the mass, which corresponded histologically to proliferating portions of trichilemmal cyst.

fig 1.

Case 1: 75-year-old man with malignant proliferating trichilemmal tumor. A, Axial T1-weighted MR image shows a poorly defined soft-tissue mass in the central portion of the lower lip. The signal intensity of the mass is comparable to that of the adjacent muscles. B, On axial T2-weighted MR image, the mass becomes hyperintense with some portions being much higher in signal intensity. The irregular margin of the mass and its infiltrating nature through the orbicularis oris muscle are better seen on the T2-weighted image. C, Axial contrast-enhanced T1-weighted MR image shows significant enhancement of the mass, with considerable portions remaining unenhanced (fig 1C and D). The areas of the tumor showing no enhancement appear larger on the contrast-enhanced image than on the T2-weighted image. D, Photograph of a cut section shows partially poorly defined, lobulated, soft-tissue mass, which has a large irregular central cavity. The continuity of the mass with the overlying epidermis (arrow) is a general feature of a tumor of hair sheath origin. E, Photomicrograph shows numerous proliferating lobules of reserve cells with extensive trichilemmal keratinization (hematoxylin-eosin, original magnification ×20). F, Higher-magnification photomicrograph shows dysplastic cells with high nuclear-to-cytoplasmic ratios, nuclear pleomorphisms, and frequent mitoses. There is no evidence of a granular layer associated with keratinization, which is a useful feature for distinguishing PTT from squamous cell carcinoma (hematoxylin-eosin, original magnification ×200).

fig 2.

Case 2: 54-year-old woman with coexistent proliferating trichilemmal tumor and trichilemmal cyst. A, Axial contrast-enhanced CT scan at level of the submandibular glands shows a large, well-encapsulated, cystic mass located in the subcutaneous fat of the left posterior part of the neck. It has a well-enhancing wall of variable thickness, which contains numerous speckled calcifications. Note a focal area of smooth soft-tissue elevation (arrow) from the anterior wall of the mass. There were several similar foci of soft-tissue elevations in the inner wall of the mass (not shown). The outer portions of the mass abut the overlying skin. Although the lesion apparently reveals a mass effect on the adjacent paravertebral muscles, the fatty interface is seen to be well preserved. B, Photograph of a cut section corresponding to A shows a well-encapsulated, unilocular, cystic mass continuous with the overlying epidermis (arrowhead). There is a focal, smooth excrescence of soft-tissue (arrow) in the deep portion of the inner wall. C, Photomicrograph of soft-tissue portion of the mass shows extensive areas of trichilemmal keratinization without formation of a granular layer. The reserve cells reveal differentiation toward large polygonal keratinocytes (hematoxylin-eosin, original magnification ×200).