The oculomotor-tentorial triangle. Part 2: a microsurgical workspace for vascular lesions in the crural and ambient cisterns

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OBJECTIVE

Pathology in the region of the basilar quadrifurcation, anterolateral midbrain, medial tentorium, and interpeduncular and ambient cisterns may be accessed anteriorly via an orbitozygomatic (OZ) craniotomy. In Part 1 of this series, the authors explored the anatomy of the oculomotor-tentorial triangle (OTT). In Part 2, the versatility of the OTT as a surgical workspace for treating vascular pathology is demonstrated.

METHODS

Sixty patients with 61 vascular pathologies treated within or via the OTT from 1998 to 2017 by the senior author were retrospectively reviewed. Patients were grouped together based on pathology/surgical procedure and included 1) aneurysms (n = 19); 2) posterior cerebral artery (PCA)/superior cerebellar artery (SCA) bypasses (n = 24); 3) brainstem cavernous malformations (CMs; n = 14); and 4) tentorial region dural arteriovenous fistulas (dAVFs; n = 4). The majority of patients were approached via an OZ craniotomy, wide sylvian fissure split, and temporal lobe mobilization to widen the OTT.

RESULTS

Aneurysm locations included the P1-P2 junction (n = 7), P2A segment (n = 9), P2/3 (n = 2), and basilar quadrification (n = 1). Aneurysm treatments included clip reconstruction (n = 12), wrapping (n = 3), proximal occlusion (n = 2), and trapping with (n = 1) or without (n = 1) bypass. Pathologies in the bypass group included vertebrobasilar insufficiency (VBI; n = 3) and aneurysms of the basilar trunk (n = 13), basilar apex (n = 4), P1 PCA (n = 2), and s1 SCA (n = 2). Bypasses included M2 middle cerebral artery (MCA)–radial artery graft (RAG)–P2 PCA (n = 8), M2 MCA–saphenous vein graft (SVG)–P2 PCA (n = 3), superficial temporal artery (STA)–P2 PCA (n = 5) or STA–s1 SCA (n = 3), s1 SCA–P2 PCA (n = 1), V3 vertebral artery (VA)–RAG–s1 SCA (n = 1), V3 VA–SVG–P2 PCA (n = 1), anterior temporal artery–s1 SCA (n = 1), and external carotid artery (ECA)–SVG–s1 SCA (n = 1). CMs were located in the midbrain (n = 10) or pontomesencephalic junction (n = 4). dAVFs drained into the tentorial, superior petrosal, cavernous, and sphenobasal sinuses. High rates of aneurysm occlusion (79%), bypass patency (100%), complete CM resection (86%), and dAVF obliteration (100%) were obtained. The overall rate of permanent oculomotor nerve palsy was 8.3%. The majority of patients in the aneurysm (94%), CM (93%), and dAVF (100%) groups had stable or improved modified Rankin Scale scores.

CONCLUSIONS

The OTT is an important anatomical triangle and surgical workspace for vascular lesions in and around the crural and ambient cisterns. The OTT can be used to approach a wide variety of vascular pathologies in the region of the basilar quadrifurcation and anterolateral midbrain.

ABBREVIATIONS ACA = anterior cerebral artery; AChA = anterior choroidal artery; ATA = anterior temporal artery; CM = cavernous malformation; CN = cranial nerve; COT = carotid-oculomotor triangle; CS = cavernous sinus; CTA = CT angiography; dAVF = dural arteriovenous fistula; DSA = digital subtraction angiography; ECA = external carotid artery; ICA = internal carotid artery; ICG = indocyanine green; MCA = middle cerebral artery; mRS = modified Rankin Scale; ONP = oculomotor nerve palsy; OTT = oculomotor-tentorial triangle; OZ = orbitozygomatic; PCA = posterior cerebral artery; PCoA = posterior communicating artery; PCP = posterior clinoid process; PIA = posterior interhemispheric approach; RAG = radial artery graft; SAH = subarachnoid hemorrhage; SBS = sphenobasal sinus; SCA = superior cerebellar artery; SCIT = supracerebellar infratentorial; SPS = superior petrosal sinus; STA = superficial temporal artery; SVG = saphenous vein graft; TS = tentorial sinus; VA = vertebral artery; VBI = vertebrobasilar insufficiency.

Article Information

Correspondence Michael T. Lawton: Barrow Neurological Institute, Phoenix, AZ. michael.lawton@barrowbrainandspine.com.

INCLUDE WHEN CITING Published online June 29, 2018; DOI: 10.3171/2018.2.JNS173141.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    Illustration of the OTT. The OTT is bordered medially by CN III, laterally by the tentorium, and posteriorly by the retracted temporal lobe. The contents of the triangle include the anterolateral midbrain (including the cerebral peduncle), the P2 segment of the PCA, and the lateral pontomesencephalic segment (s2) of the SCA. BA = basilar artery; TPA = temporal polar artery. Copyright Michael T. Lawton. Published with permission. Figure is available in color online only.

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    PCA aneurysm. A 73-year-old woman presented with a large dolichoectatic left P2 PCA aneurysm and a smaller basilar bifurcation aneurysm detected incidentally (A). She was referred for surgery after a failed attempt at endovascular therapy. The aneurysms were exposed through an OZ-pretemporal approach, and posterior retraction on the temporal lobe (TL) exposed the fetal PCA (fPCA) and aneurysms (B). The PCA aneurysm (An1) can be seen within the OTT (blue outline) and the basilar apex aneurysm (An2) can be seen within the COT (green outline). Note the large thalamoperforator at the proximal end of the aneurysm. Both aneurysms were treated with clip reconstruction (C). The basilar aneurysm was clipped successfully with two clips. Note the large circumflex perforator (arrow) originating from the lateral wall of the aneurysm. The P2A segment was reconstructed with straight fenestrated clips stacked around the circumflex perforator laterally and a bayoneted fenestrated clip around the thalamoperforator medially. Aneurysm occlusion and patency of parent and perforating arteries was confirmed intraoperatively with ICG videoangiography (D) and postoperatively with DSA (E). The patient had an uneventful postoperative course and made a full recovery. FL = frontal lobe; T = tentorium. Figure is available in color online only.

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    Basilar blister aneurysm. This 44-year-old man presented in a coma with SAH and a history of intravenous drug abuse. Angiography revealed two aneurysmal lesions involving the left P2 PCA and basilar quadrifurcation (A). The OTT was opened through a left OZ craniotomy and a blister aneurysm (An) was found within the OTT (blue outline) arising from the posterior wall of the quadrification, covered with a thrombus cap (B). The OTT was the optimal working space for wrapping the blister aneurysm by passing a muslin sling behind the aneurysm (C). The tails of the sling were pulled snuggly and secured with 3 stacked clips. Despite the lesion’s location in the midline, the OTT provided the best visualization and access. The P2 PCA dilation was also wrapped, although it did not appear to be the rupture site. Figure is available in color online only.

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    MCA-PCA bypass. This 69-year-old man presented with mass effect symptoms from this giant, dolichoectatic, thrombotic basilar trunk aneurysm shown on axial MRI (A). MR angiography demonstrated an irregular intraaneurysmal lumen with minimal saccular dilation, indicating its thrombotic core (B). An M2 MCA–SVG–P2 PCA bypass with distal aneurysm occlusion was planned. He failed his preoperative Allen test and the radial arteries could not be used. A right OZ craniotomy and transsylvian-pretemporal approach exposed the OTT (blue outline), which was filled with atherosclerotic distal basilar artery aneurysm (An) and the P2A recipient vessel (C). The distal end-to-side anastomosis to P2A was completed in the OTT (D), and the proximal end-to-side anastomosis to the M2 MCA was competed in the sylvian fissure (E). The distal basilar trunk was followed through the OTT and the aneurysm was distally occluded with 3 clips (F). Postoperative angiography (right ICA anteroposterior, lateral, and left VA anteroposterior) showed a patent bypass that filled the basilar apex retrograde and stagnant flow into the basilar trunk aneurysm (G). Despite administering clopidogrel in the immediate postoperative period to slow the aneurysm thrombosis, he suffered midbrain perforator infarcts, remained comatose, and his family withdrew support. Figure is available in color online only.

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    Midbrain CM. A 49-year-old woman presented with sudden onset of left hemiparesis and left facial droop. MRI of the brain demonstrated a hemorrhagic lesion within the right midbrain displacing the right cerebral peduncle laterally (A). The CM was exposed through a right OZ-pretemporal approach, with opening of the OTT with temporal lobe retraction (B). The lesion protruded into the interpeduncular cistern with access between CN III, the tentorium, and the medial edge of the cerebral peduncle (C). The CM was removed completely though the working space of the OTT (D). The resection cavity was clean visually at surgery (E) and on postoperative MRI (F). The patient had an uncomplicated hospital course and her hemiparesis has improved at late follow-up. Figure is available in color online only.

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    Tentorial dAVF. This 8-year-old girl had a right carotid-cavernous fistula that embolized multiple times with incomplete obliteration. Coils filled the right CS and expanded its lateral wall, as noted on coronal MRI (A). She was referred for surgical treatment when angiography (right ICA angiogram, lateral view) revealed persistent retrograde cortical venous drainage to the basal vein of Rosenthal and cortical veins, including the vein of Labbe and Trolard (B). A right OZ-pretemporal approach exposed the coils in the lateral wall of the CS (C). Dissection into the OTT (blue outline) identified the arterialized incisural vein leading to a venous varix (V) in the basal vein just above the P2 PCA (D). ICG videoangiography confirmed the site of shunt flow out of the CS through this vein (E). The vein was clip-occluded, cauterized, and divided within the OTT (F). The varix turned dark blue after clipping. Postoperative angiography demonstrated no residual filling of the carotid-cavernous fistula (G). Figure is available in color online only.

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