Managing the positive periosteal margin after Mohs excision of scalp dermatofibrosarcoma protuberans in children with underlying calvarial bone thinning and resorption: The value of multidisciplinary treatment

Accuracy of Preoperative Imaging in Assessing the Positivity of the Deep Periosteal Margin in Dermatofibrosarcoma Protuberans of the Scalp

The locally aggressive nature and high recurrence rate of dermatofibrosarcoma protuberans (DFSP) make it challenging to manage, especially when present on the scalp, owing to its ability to invade the underlying periosteum, bone, dura, or brain. Preoperative imaging is used to plan resection, but the true correlation between periosteal or osseous changes on imaging and the presence of tumor within the periosteum is unclear. We present our institutional experience of managing DFSP of the scalp with emphasis on the imaging used. A retrospective review of 33 patients with DFSP of the scalp treated at a tertiary center was conducted. Data on demographics, tumor characteristics, preoperative imaging (magnetic resonance imaging or computed tomography), and surgical outcomes were analyzed. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of each imaging modality were calculated. Patients underwent surgical resection at a mean age of 37.11 years and had a median follow-up of 28.34 months. Preoperative imaging was available for 26 patients (CT only: 5, MRI only: 12, CT and MRI: 9). Calvarial abnormalities were seen in 3 patients. Treatment included Mohs surgery (66.7%) and wide local excision (33.3%). In 10 patients with positive periosteal margins, bone involvement was managed by burring (7) or craniectomy (3). The sensitivity and PPV of CT for periosteal margin positivity were 25% and 100%, and for MRI were 33% and 100%, respectively. The specificity and NPV were 100% and 50% for CT, and 100% and 66% for MRI. Preoperative CT and MRI have low sensitivity and NPV but high specificity and PPV in determining depth of involvement and are essential to guiding reconstruction in DFSP of the scalp.