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Ali Tayebi Meybodi, Michael T. Lawton, Halima Tabani and Arnau Benet

OBJECTIVE

Surgical access to the lateral recess of the fourth ventricle (LR) is suboptimal with existing transvermian and telovelar approaches because of limited lateral exposure, significant retraction of the cerebellar tonsil, and steep trajectories near brainstem perforator arteries. The goal in this study was to assess surgical exposure of the tonsillobiventral fissure approach to the LR, and to describe the relevant anatomy.

METHODS

Two formaldehyde-fixed cerebella were used to study the anatomical relationships of the LR. Also, the tonsillobiventral fissure approach was simulated in 8 specimens through a lateral suboccipital craniotomy.

RESULTS

The pattern of the cerebellar folia and the cortical branches of the posterior inferior cerebellar artery were key landmarks to identifying the tonsillobiventral fissure. Splitting the tonsillobiventral fissure allowed a direct and safe surgical trajectory to the LR and into the cerebellopontine cistern. The proposed approach reduces cervical flexion and optimizes the surgical angle of attack.

CONCLUSIONS

The tonsillobiventral fissure approach is a feasible and effective option for exposing the LR. This approach has more favorable trajectories and positions for the patient and the surgeon, and it should be added to the armamentarium for lesions in this location.

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Brian P. Walcott, Jae Seung Bang, Omar Choudhri, Sirin Gandhi, Halima Tabani, Arnau Benet and Michael T. Lawton

A 46-year-old male presented with an incidentally discovered left ventricular body arteriovenous malformation (AVM). It measured 2 cm in diameter and had drainage via an atrial vein into the internal cerebral vein (Spetzler-Martin Grade III, Supplementary Grade 4). Preoperative embolization of the posterior medial choroidal artery reduced nidus size by 50%. Subsequently, he underwent a right-sided craniotomy for a contralateral transcallosal approach to resect the AVM. This case demonstrates strategic circumferential disconnection of feeding arteries (FAs) to the nidus, the use of aneurysm clips to control large FAs, and the use of dynamic retraction and importance of a generous callosotomy. Postoperatively, he was neurologically intact, and angiogram confirmed complete resection.

The video can be found here: https://youtu.be/j0778LfS3MI.

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Ali Tayebi Meybodi, Michael T. Lawton, Dylan Griswold, Pooneh Mokhtari, Andre Payman, Halima Tabani, Sonia Yousef and Arnau Benet

OBJECTIVE

In various disease processes, including unclippable aneurysms, a bypass to the upper posterior circulation (UPC) including the superior cerebellar artery (SCA) and posterior cerebral artery (PCA) may be needed. Various revascularization options exist, but the role of intracranial (IC) donors has not been scrutinized. The objective of this study was to evaluate the anatomical feasibility of utilizing the anterior temporal artery (ATA) for revascularization of the UPC.

METHODS

ATA-SCA and ATA-PCA bypasses were performed on 14 cadaver specimens. After performing an orbitozygomatic craniotomy and opening the basal cisterns, the ATA was divided at the M3-M4 junction and mobilized to the crural cistern to complete an end-to-side bypass to the SCA and PCA. The length of the recipient artery between the anastomosis and origin was measured.

RESULTS

Seventeen ATAs were found. Successful anastomosis was performed in 14 (82%) of the ATAs. The anastomosis point on the PCA was 14.2 mm from its origin on the basilar artery. The SCA anastomosis point was 10.1 mm from its origin. Three ATAs did not reach the UPC region due to a common opercular origin with the middle temporal artery. The ATA-SCA bypass was also applied to the management of an incompletely coiled SCA aneurysm.

CONCLUSIONS

The ATA is a promising IC donor for UPC revascularization. The ATA is exposed en route to the proximal SCA and PCA through the pterional-orbitozygomatic approach. Also, the end-to-side anastomosis provides an efficient and straightforward bypass without the need to harvest a graft or perform multiple or difficult anastomoses.

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Tomoya Kamide, Halima Tabani, Michael M. Safaee, Jan-Karl Burkhardt and Michael T. Lawton

OBJECTIVE

While most paraclinoid aneurysms can be clipped with excellent results, new postoperative visual deficits are a concern. New technology, including flow diverters, has increased the popularity of endovascular therapy. However, endovascular treatment of paraclinoid aneurysms is not without procedural risks, is associated with higher rates of incomplete aneurysm occlusion and recurrence, and may not address optic nerve compression symptoms that surgical debulking can. The increasing endovascular management of paraclinoid aneurysms should be justified by comparisons to surgical benchmarks. The authors, therefore, undertook this study to define patient, visual, and aneurysm outcomes in the most common type of paraclinoid aneurysm: ophthalmic artery (OphA) aneurysms.

METHODS

Results from microsurgical clipping of 208 OphA aneurysms in 198 patients were retrospectively reviewed. Patient demographics, aneurysm morphology (size, calcification, etc.), clinical characteristics, and patient outcomes were recorded and analyzed.

RESULTS

Despite 20% of these aneurysms being large or giant in size, complete aneurysm occlusion was accomplished in 91% of 208 cases, with OphA patency preserved in 99.5%. The aneurysm recurrence rate was 3.1% and the retreatment rate was 0%. Good outcomes (modified Rankin Scale score 0–2) were observed in 96.2% of patients overall and in all 156 patients with unruptured aneurysms. New visual field defects (hemianopsia or quadrantanopsia) were observed in 8 patients (3.8%), decreased visual acuity in 5 (2.4%), and monocular blindness in 9 (4.3%). Vision improved in 9 (52.9%) of the 17 patients with preoperative visual deficits.

CONCLUSIONS

The most important risk associated with clipping OphA aneurysms is a new visual deficit. Meticulous microsurgical technique is necessary during anterior clinoidectomy, aneurysm dissection, and clip application to optimize visual outcomes, and aggressive medical management postoperatively might potentially decrease the incidence of delayed visual deficits. As the results of endovascular therapy and specifically flow diverters become known, they warrant comparison with these surgical benchmarks to determine best practices.

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Arnau Benet, Halima Tabani, Xinmin Ding, Jan-Karl Burkhardt, Roberto Rodriguez Rubio, Ali Tayebi Meybodi, Peyton Nisson, Olivia Kola, Sirin Gandhi, Sonia Yousef and Michael T. Lawton

OBJECTIVE

The occipital artery (OA) is a frequently used donor vessel for posterior circulation bypass procedures due to its proximity to the recipient vessels and its optimal caliber, length, and flow rate. However, its tortuous course through multiple layers of suboccipital muscles necessitates layer-by-layer dissection. The authors of this cadaveric study aimed to describe a landmark-based novel anterograde approach to harvest OA in a proximal-to-distal “inside-out” fashion, which avoids multilayer dissection.

METHODS

Sixteen cadaveric specimens were prepared for surgical simulation, and the OA was harvested using the classic (n = 2) and novel (n = 14) techniques. The specimens were positioned three-quarters prone, with 45° contralateral head rotation. An inverted hockey-stick incision was made from the spinous process of C-2 to the mastoid tip, and the distal part of the OA was divided to lift up a myocutaneous flap, including the nuchal muscles. The OA was identified using the occipital groove (OG), the digastric muscle (DM) and its groove (DG), and the superior oblique muscle (SOM) as key landmarks. The OA was harvested anterogradely from the OG and within the flap until the skin incision was reached (proximal-to-distal technique). In addition, 35 dry skulls were assessed bilaterally (n = 70) to study additional craniometric landmarks to infer the course of the OA in the OG.

RESULTS

The OA was consistently found running in the OG, which was found between the posterior belly of the DM and the SOM. The mean total length of the mobilized OA was 12.8 ± 1.2 cm, with a diameter of 1.3 ± 0.1 mm at the suboccipital segment and 1.1 ± 0.1 mm at the skin incision. On dry skulls, the occipitomastoid suture (OMS) was found to be medial to the OG in the majority of the cases (68.6%), making it a useful landmark to locate the OG and thus the proximal OA.

CONCLUSIONS

The anterograde transperiosteal inside-out approach for harvesting the OA is a fast and easy technique. It requires only superficial dissection because the OA is found directly under the periosteum throughout its course, obviating tedious layer-by-layer muscle dissection. This approach avoids critical neurovascular structures like the vertebral artery. The key landmarks needed to localize the OA using this technique include the OMS, OG, DM and DG, and SOM.

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Ali Tayebi Meybodi, Michael T. Lawton, Sonia Yousef, Xiaoming Guo, Jose Juan González Sánchez, Halima Tabani, Sergio García, Jan-Karl Burkhardt and Arnau Benet

Anterior clinoidectomy is a difficult yet essential technique in skull base surgery. Two main techniques (extradural and intradural) with multiple modifications have been proposed to increase efficiency and avoid complications. In this study, the authors sought to develop a hybrid technique based on localization of the optic strut (OS) to combine the advantages and avoid the disadvantages of both techniques.

Ten cadaveric specimens were prepared for surgical simulation. After a standard pterional craniotomy, the anterior clinoid process (ACP) was resected in 2 steps. The segment anterior to the OS was resected extradurally, while the segment posterior to the OS was resected intradurally. The proposed technique was performed in 6 clinical cases to evaluate its safety and efficiency.

Anterior clinoidectomy was successfully performed in all cadaveric specimens and all 6 patients by using the proposed technique. The extradural phase enabled early decompression of the optic nerve while avoiding the adjacent internal carotid artery. The OS was drilled intradurally under direct visualization of the adjacent neurovascular structures. The described landmarks were easily identifiable and applicable in the surgically treated patients. No operative complication was encountered.

A proposed 2-step hybrid technique combines the advantages of the extradural and intradural techniques while avoiding their disadvantages. This technique allows reduced intradural drilling and subarachnoid bone dust deposition. Moreover, the most critical part of the clinoidectomy—that is, drilling of the OS and removal of the body of the ACP—is left for the intradural phase, when critical neurovascular structures can be directly viewed.