The oculomotor-tentorial triangle. Part 1: microsurgical anatomy and techniques to enhance exposure

Abstract

OBJECTIVE Access to the ventrolateral pontomesencephalic area may be required for resecting cavernous malformations, performing revascularization of the upper posterior circulation, and treating vascular lesions such as aneurysms. However, such access is challenging because of nearby eloquent structures. Commonly used corridors to this surgical area include the optico-carotid, supracarotid, and carotid-oculomotor triangles. However, the window lateral to the oculomotor nerve can also be used and has not been studied. The authors describe the anatomical window formed between the oculomotor nerve and the medial tentorial edge (the oculomotor-tentorial triangle [OTT]) to the ventrolateral pontomesencephalic area, and assess techniques to expand it. METHODS Four cadaveric heads (8 sides) underwent orbitozygomatic craniotomy. The OTT was exposed via a pretemporal approach. The contents of the OTT were determined and their anatomical features were recorded. Also, dimensions of the brainstem surface exposed lateral and inferior to the oculomotor nerve were measured. Measurements were repeated after completing a transcavernous approach (TcA), and after resection of temporal lobe uncus (UnR). RESULTS The s segment and proximal s segment of the superior cerebellar artery (SCA) and P segment of the posterior cerebral artery (PCA) were the main contents of the OTT, with average exposed lengths of 6.4 ± 1.3 mm and 5.5 ± 1.6 mm for the SCA and PCA, respectively. The exposed length of the SCA increased to 9.6 ± 2.7 mm after TcA (p = 0.002), and reached 11.6 ± 2.4 mm following UnR (p = 0.004). The exposed PCA length increased to 6.2 ± 1.6 mm after TcA (p = 0.04), and reached 10.4 ± 1.8 mm following UnR (p < 0.001). The brainstem surface was exposed 7.1 ± 0.5 mm inferior and 5.6 ± 0.9 mm lateral to the oculomotor nerve initially. The exposure inferior to the oculomotor nerve increased to 9.3 ± 1.7 mm after TcA (p = 0.003), and to 9.9 ± 2.5 mm after UnR (p = 0.21). The exposure lateral to the oculomotor nerve increased to 8.0 ± 1.7 mm after TcA (p = 0.001), and to 10.4 ± 2.4 mm after UnR (p = 0.002). CONCLUSIONS The OTT is an anatomical window that provides generous access to the upper ventrolateral pontomesencephalic area, s- and s-SCA, and P-PCA. This window may be efficiently used to address various pathologies in the region and is considerably expandable by TcA and/or UnR.

Unveiling the vulnerability of the human abducens nerve: insights from comparative cranial base anatomy in mammals and primates

“…The pathways of these cranial nerves are included on a transverse plane, situated above the planes of other cranial nerves, such that they do not encounter any bony elements of the cranial base along their path ( Tubbs and Oakes, 1998 ; Joo and Rhoton, 2015 ; Park et al, 2017 ; Standring, 2021 ). In addition, both nerves gain a special relation to the cavernous sinus, reaching it at the level of the free margin of the tentorium cerebelli and the posterior clinoid process ( Meybodi et al, 2018 ). The meeting point with the tentorial margin introduces the oculomotor and trochlear nerves directly into the lateral wall of the cavernous sinus, which secures their course into the superior orbital fissure ( Joo and Rhoton, 2015 ; Tubbs and Loukas, 2016 ; Park et al, 2017 ; Standring, 2021 ) (see Figures 3N , 11 ).…”

Epidural Pretemporal Transcavernous Approach Double-Barrel Superficial Temporal Artery-Posterior Cerebral Artery/Superior Cerebellar Artery Bypass for a Ruptured Anterior Spinal Artery Aneurysm

“…When doing a rostral posterior circulation bypass, it has been argued that the oculomotor-tentorial triangle is superior to the carotid-oculomotor triangle not only for the recipient exposure but also for the bypass manipulation. 3,11 The reported approaches for bypass using lateral oculomotor space include pretemporal, 3 subtemporal, 1 or transpetrosal 9 approaches. A pretemporal approach is less invasive and provides better temporal lobe protection compared with a subtemporal approach.…”

“…2 However, veins converging into the cavernous sinus at the temporal pole need to be sacrificed to facilitate a sufficient temporal lobe lateral retraction. 11,12 An epidural pretemporal transcavernous approach was reported to be able to provide an extended lateral oculomotor space for the upper basilar artery manipulation. 15,16 In addition, the temporal lobe was retracted under dura protection.…”

“…2,[7][8][9] Although the Drake subtemporal exposure is widely accepted, 1,[5][6][7]10 it is noted that symptomatic temporal lobe contusion caused by brain retraction in that approach cannot be neglected. 1,2,5 Therefore, a subdural pretemporal approach has been used for the bypass within the oculomotor-tentorial triangle, 2,3,11 which has been advocated to decrease temporal lobe retraction and extend recipient exposure. 2 However, one concern of the subdural pretemporal approach is that the superficial Sylvian veins at the temporal pole usually need to be sacrificed to facilitate a posterolateral temporal lobe retraction.…”

“…2 However, one concern of the subdural pretemporal approach is that the superficial Sylvian veins at the temporal pole usually need to be sacrificed to facilitate a posterolateral temporal lobe retraction. 11,12 The author used an epidural pretemporal transcavernous approach with bridging veins preservation to perform a double-barrel STA-SCA/PCA bypass. The surgical nuances are illustrated in the current report.…”