Sparing a Craniotomy: The Role of Intraoperative Methylene Blue in Management of Midline Dermoid Cysts

Background: Midline nasal dermoid cysts are rare congenital anomalies that extend intracranially in approximately 10 percent of cases. Cysts with intracranial extension require a craniotomy to avoid long-term complications, including meningitis, abscesses, and cavernous sinus thrombosis. Current guidelines recommend preoperative imaging with either magnetic resonance imaging or computed tomography to determine appropriate management. Methods: Patients who underwent excision of a midline nasal dermoid cyst between January 1995 and September 2016 were identified using Current Procedural Terminology codes. In cases with equivocal imaging findings or uncertain stalk extent during surgical dissection, methylene blue was used intraoperatively. Demographics, preoperative imaging findings, intraoperative dye findings, surgical approach, and complications were collected. Results: A total of 66 midline dermoid cyst excisions were identified; 17 (25.8 percent) had intracranial extension requiring craniotomy. Preoperative imaging showed a subcutaneous cyst in 41 (62.1 percent), intraosseous tracking in three (4.5 percent), and intracranial extension in 15 (22.7 percent). Twelve patients (18.2 percent) had preoperative imaging that was inconsistent with intraoperative findings. Methylene blue was used in 17 cases and indigo carmine was used in one case. Intraoperative dye findings changed management in five cases, and in three cases a craniotomy was avoided without evidence of cyst recurrence. Conclusions: This report is the largest published series of midline dermoid cysts with intracranial extension. In almost 20 percent of cases, preoperative imaging was not consistent with intraoperative findings. Given disparate radiographic and intraoperative findings, methylene blue is a valuable tool that can facilitate appropriate, morbidity-sparing management of midline dermoid cysts.