Spiradenocarcinoma in Brooke–Spiegler syndrome: radiology-pathology correlation of synchronous benign and malignant dermal adnexal tumors

Abstract Spiradenocarcinoma is a rare dermal adnexal malignancy often arising from a pre-existing benign spiradenoma and may occur sporadically or in the setting of the autosomal dominant genodermatosis Brooke–Spiegler Syndrome (BSS). Imaging descriptions of spiradenoma and spiradenocarcinoma are scant, with no literature to date describing comparative imaging features of benign and malignant tumors to the best of our knowledge. We report a case of a 64-year-old patient with a rapidly enlarging right frontal scalp mass and a relatively indolent left parietal scalp mass in addition to innumerable small head and neck nodules. MRI for preoperative planning demonstrated heterogeneous enhancement and markedly reduced diffusion in both lesions, while 18 F-FDG PET-CT showed marked FDG avidity (SUVmax = 16.3) in the frontal mass but mild uptake in the parietal mass (SUVmax = 2.1). Histopathology confirmed the frontal mass to be a low-grade spiradenocarcinoma and the left parietal lesion a benign spiradenoma. Genetic testing confirmed BSS. This case illustrates the clinical-radiologic-pathologic correlation of spiradenocarcinoma in the context of BSS, a rare clinical and radiologic mimic of NF1, and highlights that rapid growth and FDG avidity may help the reporting radiologist to differentiate spiradenocarcinoma from spiradenoma in patients with BSS.