Metastatic malignant proliferating trichilemmal tumor detected by positron emission tomography

BACKGROUND. Whole-body 18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) was introduced in 1990s, and its efficacy for cerebral mapping and for selective detection of various malignancies is now being recognized. OBJECTIVE. To report on the usefulness of whole-body 18F-FDG-PET for detecting a metastatic lesion in a rare case of malignant proliferating trichilemmal tumor. METHODS. A malignant proliferating trichilemmal tumor on the occipital scalp of a 69-year-old female recurred on the margin of the surgical scar after an initial wide excision, and it was removed by Mohs micrographic surgery. 18F-FDG-PET was done to detect any remaining tumor tissue, and it showed a hot uptake on the lower left occipital area, where a pea-sized nodule formed 2 months later. Dissection and wide excision of the nodule showed metastatic malignant proliferating trichilemmal tumor cells in the lymph nodes. RESULTS. We were able to take advantage of the high resolution of the 18F-FDG-PET in detecting a metastatic lesion despite its proximity to the central nervous system. CONCLUSION. The 18F-FDG-PET can be used in future malignant proliferating trichilemmal tumor cases to study the metastatic characteristics of this rare tumor.