Utility of Intraoperative MRI Assessing Nasoseptal Flap Vascularity in Predicting Postoperative CSF Leak After Endoscopic Endonasal Approaches to Anterior Skull Base Lesions

Robust reconstruction of the skull base after endoscopic endonasal approaches (EEA) for parasellar lesions is paramount to preventing postoperative cerebrospinal fluid (CSF) leak. Traditionally, multilayer closure is performed, composed of a fat graft, subdural underlay with adjunct bony substitutes, followed by biologic glues. Recently, nasoseptal flaps perfused by a vascularized pedicle have been utilized and may decrease the rate of post-operative CSF leaks. Flap viability measured by vascularity has been hypothesized to correlate with decreased CSF leak rates. Radiographic enhancement of the nasoseptal flap on MRI may be a proxy for flap viability and correlate with reduced CSF leak rates. Intraoperative MRI has previously been studied in improving extent of resection after EEA, but its role in assessing nasoseptal flap viability has not been described.

A single-institution retrospective chart review was conducted in patients undergoing EEA for resection of sellar/suprasellar pathologies between January 2017 and March 2021. Patients with intraoperative contrasted MRI after nasoseptal flap placement were included. Fisher's exact tests were used for statistical analysis.

Out of 193 patients, 59 met inclusion criteria. Pathologies composed of 44 pituitary adenomas, 9 craniopharyngiomas, 3 meningiomas, 1 metastasis, 1 epidermoid, and 1 nondiagnostic sample. Thirty-nine of 59 patients demonstrated nasoseptal flap enhancement on intraoperative MRI. There were two cases of postoperative CSF leak, requiring revision surgery. The first case demonstrated nasoseptal flap enhancement on intraoperative MRI after craniopharyngioma resection ([Fig. 1]) but demonstrated displacement of the underlay AlloDerm on repeat surgery for CSF leak correction. The second case for tuberculum sella meningioma resection did not show nasoseptal flap enhancement ([Fig. 2]) but at time of repeat surgery, showed displacement of the nasoseptal flap where the CSF leak was emanating from.

There were 15 patients with noted intraoperative CSF leak but without postoperative clinical leak, of whom 13/15 exhibited nasoseptal flap enhancement on intra-operative MRI. The two patients who did not have nasoseptal flap enhancement were managed with lumbar drainage in the postoperative period. Fisher's exact tests did not reveal any significant correlations between nasoseptal flap enhancement with postoperative CSF leak in the overall population (p = 0.99) or in the subset of patients with intraoperative CSF leak (p = 0.28).

Nasoseptal flap enhancement as a predictor of postoperative CSF leak has not been well-characterized with the only one study of 19 patients who underwent EEA for skull base lesions, which did not find significance between nasoseptal flap enhancement and postoperative CSF leaks. Although we did not find statistical significance in part limited by small sample size, our experience suggests in cases of significant intra-operative CSF leak, confirmation of nasoseptal flap enhancement with intra-operative MRI may be an important consideration prior to closure. That said, there are a number of factors in skull base reconstruction that can jeopardize the integrity of the closure and lead to CSF leak despite MRI evidence of adequate perfusion (i.e., AlloDerm placement, high vs low flow leak, BMI, suspected intracranial hypertension). Additional studies are needed to determine whether nasoseptal flap enhancement is an important predictor of postoperative CSF leaks after EEA for sellar/suprasellar pathologies.

Fig. 1 (A) Pre-operatve MRI of craniopharyngioma. (B) Intra-operative MRI after resection demonstrating nasoseptal flap enhancement (white arrow).

Fig. 2 (A) Pre-operative MRI of tuberculum sella meningioma. (B) Intra-operative MRI after resection without evidence of nasoseptal flap enhancement.

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Artikel online veröffentlicht:
15. Februar 2022