Validity Of CT/MRI Diagnosis Of Intracranial Extension Of Midline Nasal Dermoids: Implications In Surgical Approach
M. Jason Hancey, MD, T. Shane Johnson, MD, A. Mark Boustred, MD, Mark S. Dias, MD, Donald R. Mackay, MD.
Penn State Hershey, Hershey, PA, USA.
BACKGROUND: Midline nasal dermoids are rare congenital anomalies possibly resulting from incomplete separation of neural and cutaneous ectoderm or from faulty involution of the dural tract. Untreated, intracranial extension can lead to increased risk for facial and cranial growth disturbances as well as CNS infection. Pre-operative CT/MRI evaluation is the current gold standard determining the type of surgical technique required for complete resection. Using our institutional experience, we evaluated the validity of this approach.
METHODS: We performed an IRB approved retrospective review of 30 consecutive dermoid excisions performed at our institution between January 1995 and January 2006. Patients were identified based on billing codes. Exclusion criteria were non-midline lesions and incomplete data. Characteristics of the lesions, pre-operative imaging results, surgical approach, and complications were reviewed.
RESULTS: Eighteen patients were identified as having undergone midline nasal dermoid excision meeting the above criteria. Mean age at diagnosis was 26.4 months (range 0-101) and mean age at surgery was 29.4 months (range 2-103) with a mean delay to surgery of 3 months. Eight patients were female (44%) and 10 were male (56%). Sixteen patients were Caucasian (89%) and 2 were Hispanic (11%). Ten patients (56%) had other associated congenital malformations, including agenesis of the corpus callosum (n=4, 22%), hydrocephalus (n=3, 17%), midline facial cleft (n=2, 11%), cardiac anomalies (n=2, 11%) and craniosynostosis (n=1, 6%). There was no history of meningitis in any of the patients. Two patients who were siblings had a family history of a midline nasal abnormality. Eleven (61%) patients presented with an external sinus, 13 (72%) with a nasal tip/dorsal mass, and 4 (22%) with a nasoglabellar mass. All patients had pre-operative radiographic assessment consisting of CT, MRI or both, demonstrating probable intracranial extension in 10 patients (56%). In these 10 cases, a staged extracranial/intracranial approach was planned; in 2 of these cases, the intracranial approach was abandoned due to lack of intracranial extension seen during the extracranial portion of the excision. Surgical approaches included staged extracranial/intracranial (n=8, 44%), direct extracranial (n=9, 50%) and endoscopic (n=1, 6%). Complications included nasal growth disturbances (n=2, 11%) and recurrence of the dermoid (n=4, 22%). Mean follow-up was 31.4 months (range 1-119), with 2 subjects lost to follow-up.
CONCLUSIONS: Despite modern radiographic techniques, difficulty of accurate diagnosis regarding intracranial extension of midline nasal dermoids exists. Treatment algorithms should account for this uncertainty by incorporating a staged excision allowing for intraoperative conversion to an intracranial procedure if intracranial extension is confirmed during the initial extracranial approach.