Distal Vascular Compression (Beyond the Obersteiner Redlich Zone) during Fully Endoscopic Microvascular Decompression for Trigeminal Neuralgia

Objective: Proximal vascular decompression of the trigeminal nerve at the Obersteiner Redlich zone has become the neurosurgical standard of care since Dr. Jannetta introduced microvascular decompression in 1967. Fifty years later, the introduction of the endoscope into the CP angle provides the surgeon the ability to identify distal vascular compression at the entrance into Meckel’s cave. In this study, we catalog the incidence of distal (beyond the Obersteiner Redlich zone) vascular compression during endoscopic MVD.

Methods: A retrospective review and analysis of operative videos of endoscopic microvascular decompression (E-MVD) for TN. A 6-year interval review, from 2013 to 2019, yielded 233 consecutive patients undergoing E-MVD by a single surgeon for TN. Start date of 2013 chosen because of institution of centralized server for surgical video backup. Patients undergoing E-MVD for neoplasia or E-MVD for hemifacial spasm/glossopharyngeal neuralgia were excluded. Patients without recorded operative videos were excluded. Trigeminal nerve was always visualized in full from pontine exit zone to its entry into Meckel’s cave, and then divided into anatomic half. Vascular compression was categorized into one of four groups: (1) proximal (majority of compression from dorsal root entry zone (DREZ) to midpoint of the trigeminal nerve), (2) distal (majority of compression from midpoint of trigeminal nerve to Meckle’s cave), (3) both proximal and distal (separate and distinct proximal and distal compression), and 4) no discernable compression. Additionally, petrosal tubercle (PT) bone anatomy was analyzed and determined as either obstructive (obstructing visualization of >50% of trigeminal nerve during surgical approach when 0-degree endoscope is in view of both PT and trigeminal nerve) or non-obstructive (obstructing <50% of trigeminal nerve during surgical approach when 0-degree endoscope is in view of both PT and trigeminal nerve).

Results: Proximal vascular compression of the trigeminal nerve was noted in 143/233 (61%) of patients. Distal vascular compression of the trigeminal nerve was noted in 36/233 (15%) of patients ([Fig. 1]). Proximal and distal vascular compression of the trigeminal nerve was noted in 50/233 (21%). No discernable compression was noted in 4/233 (2%) of patients. Petrosal tubercle anatomy noted to be obstructive in 42/233 (18%) of patients ([Fig. 2]) and non-obstructive in 191/233 (82%) of patients.

Conclusion: E-MVD offers benefits compared with conventional microscopic microvascular decompression by way of enhanced visualization, particularly with distal structures and around corners. Two factors directly related to decreased visualization of vascular compression are an obstructive PT and distal compression of the trigeminal nerve near Meckle’s cave. This study demonstrates the rate of subsets of patients with obstructive PT and with distal/proximal and distal vascular compression that would have greater difficulty with visualization in a microscopic versus endoscopic approach. Future work will correlate anatomic findings with outcome.