Pontine Encephalocele and Abnormalities of the Posterior Fossa following Transclival Endoscopic Endonasal Surgery

Object : Transclival endoscopic endonasal surgery (EES) has recently been employed for the treatment of posterior fossa tumors. The optimal method of reconstruction of large clival defects following EES has not been established. Methods : A morphometric analysis of the posterior fossa was performed in patients who underwent transclival EES to compare those with observed postoperative anatomic changes (study group) to 50 normal individuals (anatomic control group) and 41 matched transclival cases with preserved posterior fossa anatomy (case control group) using the same parameters. Given the absence of clival bone following transclival EES, we used the line between the anterior commissure (AC) and the basion (B) as an equivalent to the clival plane to evaluate the location of the pons. Four parameters were studied and compared in the two populations: the pontine location/displacement, the maximum anterior-posterior (AP) diameter of the pons, the maximum AP diameter of the 4th ventricle and the cervico-medullary angle (CMA). All measurements were performed on mid-sagittal 3 month postoperative MRI in the study group. Results : Among 103 posterior fossa tumors treated with transclival EES, 14 cases (13.6%) with postoperative posterior fossa anatomy changes were identified. The most significant change was anterior displacement of the pons (transclival pontine encephalocele) compared with the normal location in the anatomic control group ( p 25kg/m2). An association between BMI and the degree of pontine encephalocele was observed, but did not reach statistical significance. The use of fat graft as part of the reconstruction following transclival EES with dural opening was significant in preventing pontine displacement ( p = 0.02) with 91% lower odds of encephalocele (OR = 0.09, 95% CI: 0.01–0.77). The effect of fat graft reconstruction was more pronounced in overweight/obese individuals ( p = 0.04). In addition, younger adults were more likely to develop pontine encephalocele ( p = 0.05) and postoperative meningitis was associated with the development of posterior fossa deformities ( p = 0.05). One patient