Introduction: Repair of middle fossa meningoencephalocele (MFE) with tegmen defect (TD) involves craniotomy and moderate temporal lobe retraction to visualize the skull base defect. Endoscopy with a keyhole approach should considerably reduce this risk and improve other procedural aspects.

Methods: Endoscopy for MFE/TD repair was employed in a 5-case series. All patients were diagnosed with MFE/TD on MRI/CT imaging. Surgery was conducted jointly between neurosurgery and otolaryngology. Intraoperative image guidance was used to localize the defect and perform a keyhole craniotomy. We utilized both the endoscope and the operative microscope to elevate the encephalocele while TD repair was done only with endoscopic assistance. Zero and thirty degree scopes were utilized for dissection while thirty and seventy degree scopes were employed for the defect repair.

Results: A number of benefits are noted. This technique allows for a small targeted keyhole craniotomy-- minimizing incision size, muscle dissection, and bone work. Increased viewing angles on the endoscope significantly reduce the amount of temporal lobe displacement required, allows for close examination of the bony TD, visual inspection of the middle ear, and improves the view for direct bony repair. It improves visualization of the dural tears, but it is less easy to directly repair them due to the smaller working corridor. Additionally, there were no recurrent leaks or hearing loss after repair in the series.

Conclusions: Initial evaluation suggests the endoscope is a beneficial tool for MFE/TD repairs. It reduces risk of brain retraction injury and allows better working views without compromising repair integrity. The craniotomy is also of sufficient size to place a vascularized rotational temporalis flap. Further development of technique and a larger patient series is needed to delineate additional benefits beyond those discussed and define nuances of technique.

Patient Care: Use of the endoscope can help reduce brain retraction injury and improve quality of skull base repair.

Learning Objectives: By the conclusion of this section, participants should be able to: 1. Describe technique for keyhole craniotomy and approach for tegmen repair 2. Understand advantages of use of the endoscope during MFE/tegmen defect repair

References: Endoscopic extradural subtemporal approach to lateral and central skull base: a cadaveric study. Komatsu F, Komatsu M, Di Ieva A, Tschabitscher M. World Neurosurg. 2013 Nov;80(5):591-7. doi: 10.1016/j.wneu.2012.12.018. Epub 2012 Dec 13. Endoscopic reconstruction of the middle cranial fossa through a subtemporal keyhole using a pedicled deep temporal fascial flap: a cadaveric study. Komatsu M, Komatsu F, Di Ieva A, Inoue T, Tschabitscher M. Neurosurgery. 2012 Mar;70(1 Suppl Operative):157-61; discussion 162. doi: 10.1227/NEU.0b013e31822fedbb.