D19. Accuracy of Preoperative Imaging in Assessing the Involvement of the Deep Periosteal Margin in Dermatofibrosarcoma Protuberans of the Scalp: The Mayo Clinic Experience

PURPOSE: Dermatofibrosarcoma protuberans (DFSP) of the scalp may infiltrate the periosteum, calvarium, dura or brain. We sought to examine whether preoperative calvarial bone abnormalities on imaging correlate with the involvement of the deep periosteal margin. METHODS: A retrospective medical record and image review was done of all patients with DFSP of the scalp treated at our institution. RESULTS: A total of 33 (19 male) patients were diagnosed with DFSP of the scalp at a mean age of 37 years (range: 6-88 years). Preoperative imaging was done in 26 (78.8%) patients (CT only in 5, MRI only in 12, both in 9). Calvarial bone abnormalities were detected in 3 (11.5%) patients (CT = 2, MRI = 3). Complete resection with negative deep margins through Mohs micrograohic surgery (n=22) or wide local excision (n=11) was achieved above the periosteum in 11 patients. Out of the remaining patients, information related to the status of periosteal involvement was available in 19 (57.6 %) patients, of which the deep periosteal margin was positive in 10 (52.6%) patients. CONCLUSION: Calvarial bone abnormalities detected on preoperative CT and MRI are highly predictive of the involvement of the periosteal margin at surgical excision with a 100% specificity and PPV.