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Ali Tayebi Meybodi, Arnau Benet, Vera Vigo, Roberto Rodriguez Rubio, Sonia Yousef, Pooneh Mokhtari, Flavia Dones, Sofia Kakaizada and Michael T. Lawton

OBJECTIVE

The expanded endoscopic endonasal approach (EEA) has shown promising results in treatment of midline skull base lesions. Several case reports exist on the utilization of the EEA for treatment of aneurysms. However, a comparison of this approach with the classic transcranial orbitozygomatic approach to the basilar apex (BAX) region is missing.

The present study summarizes the results of a series of cadaveric surgical simulations for assessment of the EEA to the BAX region for aneurysm clipping and its comparison with the transcranial orbitozygomatic approach as one of the most common approaches used to treat BAX aneurysms.

METHODS

Fifteen cadaveric specimens underwent bilateral orbitozygomatic craniotomies as well as an EEA (first without a pituitary transposition [PT] and then with a PT) to expose the BAX. The following variables were measured, recorded, and compared between the orbitozygomatic approach and the EEA: 1) number of perforating arteries counted on bilateral posterior cerebral arteries (PCAs); 2) exposure and clipping lengths of the PCAs, superior cerebellar arteries (SCAs), and proximal basilar artery; and 3) surgical area of exposure in the BAX region.

RESULTS

Except for the proximal basilar artery exposure and clipping, the orbitozygomatic approach provided statistically significantly greater values for vascular exposure and control in the BAX region (i.e., exposure and clipping of ipsilateral and contralateral SCAs and PCAs). The EEA with PT was significantly better in exposing and clipping bilateral PCAs compared to EEA without a PT, but not in terms of other measured variables. The surgical area of exposure and PCA perforator counts were not significantly different between the 3 approaches. The EEA provided better exposure and control if the BAX was located ≥ 4 mm inferior to the dorsum sellae.

CONCLUSIONS

For BAX aneurysms located in the retrosellar area, PT is usually required to obtain improved exposure and control for the bilateral PCAs. However, the transcranial approach is generally superior to both endoscopic approaches for accessing the BAX region. Considering the superior exposure of the proximal basilar artery obtained with the EEA, it could be a viable option when surgical treatment is considered for a low-lying BAX or mid–basilar trunk aneurysms (≥ 4 mm inferior to dorsum sellae).

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Ali Tayebi Meybodi, Andrew S. Little, Vera Vigo, Arnau Benet, Sofia Kakaizada and Michael T. Lawton

OBJECTIVE

The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel’s cave, paraclival area, and the infratemporal fossa. Safe and efficient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel landmark for localization of the lacerum ICA.

METHODS

Ten cadaveric heads were prepared for transnasal endoscopic dissection. The floor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid floor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament.

RESULTS

The pterygoclival ligament was identified bilaterally during drilling of the sphenoid floor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolaterally and superiorly to blend into the fibrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identified at the confluence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the anteromedial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided.

CONCLUSIONS

The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery.

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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.

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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, Arnau Benet and Michael T. Lawton

The V3 segment of the vertebral artery (VA) has been studied in various clinical scenarios, such as in tumors of the craniovertebral junction and dissecting aneurysms. However, its use as a donor artery in cerebral revascularization procedures has not been extensively studied. In this report, the authors summarize their clinical experience in cerebral revascularization procedures using the V3 segment as a donor. A brief anatomical description of the relevant techniques is also provided.

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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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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 and Arnau Benet

OBJECTIVE

The anterior temporal artery (ATA) supplies an area of the brain that, if sacrificed, does not cause a noticeable loss of function. Therefore, the ATA may be used as a donor in intracranial-intracranial (IC-IC) bypass procedures. The capacities of the ATA as a donor have not been studied previously. In this study, the authors assessed the feasibility of using the ATA as a donor for revascularization of different segments of the distal middle cerebral artery (MCA).

METHODS

The ATA was studied in 15 cadaveric specimens (8 heads, excluding 1 side). First, the cisternal segment of the artery was untethered from arachnoid adhesions and small branches feeding the anterior temporal lobe and insular cortex, to evaluate its capacity for a side-to-side bypass to insular, opercular, and cortical segments of the MCA. Any branch entering the anterior perforated substance was preserved. Then, the ATA was cut at the opercular-cortical junction and the capacity for an end-to-side bypass was assessed.

RESULTS

From a total of 17 ATAs, 4 (23.5%) arose as an early MCA branch. The anterior insular zone and the frontal parasylvian cortical arteries were the best targets (in terms of mobility and caliber match) for a side-to-side bypass. Most of the insula was accessible for end-to-side bypass, but anterior zones of the insula were more accessible than posterior zones. End-to-side bypass was feasible for most recipient cortical arteries along the opercula, except for posterior temporal and parietal regions. Early ATAs reached significantly farther on the insular MCA recipients than non-early ATAs for both side-to-side and end-to-side bypasses.

CONCLUSIONS

The ATA is a robust arterial donor for IC-IC bypass procedures, including side-to-side and end-to-side techniques. The evidence provided in this work supports the use of the ATA as a donor for distal MCA revascularization in well-selected patients.

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Ali Tayebi Meybodi, Wendy Huang, Arnau Benet, Olivia Kola and Michael T. Lawton

OBJECT

Management of complex aneurysms of the middle cerebral artery (MCA) can be challenging. Lesions not amenable to endovascular techniques or direct clipping might require a bypass procedure with aneurysm obliteration. Various bypass techniques are available, but an algorithmic approach to classifying these lesions and determining the optimal bypass strategy has not been developed. The objective of this study was to propose a comprehensive and flexible algorithm based on MCA aneurysm location for selecting the best of multiple bypass options.

METHODS

Aneurysms of the MCA that required bypass as part of treatment were identified from a large prospectively maintained database of vascular neurosurgeries. According to its location relative to the bifurcation, each aneurysm was classified as a prebifurcation, bifurcation, or postbifurcation aneurysm.

RESULTS

Between 1998 and 2015, 30 patients were treated for 30 complex MCA aneurysms in 8 (27%) prebifurcation, 5 (17%) bifurcation, and 17 (56%) postbifurcation locations. Bypasses included 8 superficial temporal artery–MCA bypasses, 4 high-flow extracranial-to-intracranial (EC-IC) bypasses, 13 IC-IC bypasses (6 reanastomoses, 3 reimplantations, 3 interpositional grafts, and 1 in situ bypass), and 5 combination bypasses. The bypass strategy for prebifurcation aneurysms was determined by the involvement of lenticulostriate arteries, whereas the bypass strategy for bifurcation aneurysms was determined by rupture status. The location of the MCA aneurysm in the candelabra (Sylvian, insular, or opercular) determined the bypass strategy for postbifurcation aneurysms. No deaths that resulted from surgery were found, bypass patency was 90%, and the condition of 90% of the patients was improved or unchanged at the most recent follow-up.

CONCLUSIONS

The bypass strategy used for an MCA aneurysm depends on the aneurysm location, lenticulostriate anatomy, and rupture status. A uniform bypass strategy for all MCA aneurysms does not exist, but the algorithm proposed here might guide selection of the optimal EC-IC or IC-IC bypass technique.

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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.