Optic Canal Decompression: Comparing the Endonasal Endoscopic and Transcranial Approaches

Introduction: Several pathologies can affect the optic canal (OC) and the optic nerve (ON) and ophthalmic artery. Tumors, vascular abnormalities, bony dysplasia, connective tissue disease, and trauma are examples. The compression of the ON, leading to visual impairment, is an indication for decompression OC. The OC decompression is usually recommended through a transcranial approach. Recently, the advances in endoscopic skull base surgery techniques allowed achieving the decompression through an endoscopic endonasal approach (EEA), because of the straightforward access to the OC in the sphenoid sinus.

Objectives: The objective of this study is to quantitatively compare the two different options to perform OC decompression, in regard of amount of bony resection and opening of the dural sheath.

Methods: A total of 10 cadaveric specimens were prepared for dissection at the anatomy laboratory of the department of Otolaryngology and Neurosurgery in the Ohio State University in Columbus, Ohio. Each specimen was submitted to computed tomography (CT) scans, with coronal, sagittal, and axial 0.5 mm slices, through a bony window.

The endonasal transsphenoidal approach was used, with a binostril access. The right OC was drilled, from the medial aspect, all the way to the orbital apex and the dural sheath opened. We performed direct measurement of the bone resected through this method, as well as the dural opening. The transcranial approach was performed on the left side, through a frontolateral craniotomy and subfrontal corridor. The left OC was drilled initially in an extradural fashion, going intradural at the end, to complement the decompression, and to open the dural sheath. Direct measurement was also performed.

The specimens were submitted again to the same CT scan protocol, measuring the amount of bony resection and comparing with the previous examination.

Results: Adequate OC decompression was achieved through an EEA, especially in the inferior and medial aspect of the canal. The superior and lateral margins of the OC were adequately decompressed through the transcranial access.

Conclusion: The EEA to the OC allows adequate decompression of the canal and the structures located inside of it. This is an effective method, complementary to the standard approach. It is particularly useful for decisions based on the location of the pathology to be treated and the pattern of OC invasion.