Nervus intermedius: Microsurgical and anatomic relationships to the cerebellopontine angle neurovascular complex.

Background: The nervus intermedius (NI) comprises fibers originating from the trigeminal, superior salivary, and solitary tract nuclei, which join the facial nerve (cranial nerve [CN] VII). Neighboring structures include the vestibulocochlear nerve (CN VIII), the anterior inferior cerebellar artery (AICA), and its branches. Microsurgical procedures at the cerebellopontine angle (CPA) benefit from understanding NI anatomy and relationships, especially for the microsurgical treatment of geniculate neuralgia, where the NI is transected. This study sought to characterize common relationships between the NI rootlets, CN VII, CN VIII, and the meatal loop of AICA at the internal auditory canal (IAC). Methods: Seventeen cadaveric heads underwent retrosigmoid craniectomy. Following complete unroofing of the IAC, the NI rootlets were individually exposed to identify their origins and insertion points. The AICA and its meatal loop were traced to assess their relationship with the NI rootlets. Results: Thirty-three NIs were identified. The median number of NI rootlets was 4 per NI (interquartile range, 3-5). The rootlets mainly originated from the proximal premeatal segment of CN VIII (81 of 141, 57%) and inserted onto CN VII at the IAC fundus (89 of 141, 63%). When crossing the acoustic-facial bundle, the AICA most frequently passed between the NI and CN VIII (14 of 33, 42%). Five composite patterns of neurovascular relationships were identified regarding NI. Conclusion: Although certain anatomical trends can be identified, the NI has a variable relationship with the adjacent neurovascular complex at the IAC. Therefore, anatomical relationships should not be used as the sole method of NI identification during CPA surgery.

Tailoring the surgical corridor to the basilar apex in the pretemporal transcavernous approach: morphometric analyses of different neurovascular mobilization maneuvers.

BACKGROUND: The pretemporal transcavernous approach (PTA) provides optimal exposure and access to the basilar artery (BA); however, the PTA can be invasive when vital neurovascular structures are mobilized. The goal of this study was to evaluate mobilization strategies to tailor approaches to the BA. METHODS: After an orbitozygomatic craniotomy, 10 sides of 5 cadaveric heads were used to assess the surgical access to the BA via the opticocarotid triangle (OCT), carotid-oculomotor triangle (COT), and oculomotor-tentorial triangle (OTT). Measurements were obtained, and morphometric analyses were performed for natural neurovascular positions and after each stepwise expansion maneuver. An imaginary line connecting the midpoints of the limbus sphenoidale and dorsum sellae was used as a reference to normalize the measurements of BA exposure and to facilitate the clinical applicability of this technique. RESULTS: In the OCT, the exposed BA segment ranged from - 1 ± 3.9 to + 6 ± 2.0 mm in length in its natural position. In the COT, the accessible BA segment ranged from - 4 ± 2.3 to - 2 ± 3.0 mm in length in its natural position. Via the OTT, the accessible BA segment ranged from - 7 ± 2.6 to - 5 ± 2.8 mm in length in its natural position. In the OCT, COT, and OTT, a posterior clinoidectomy extended the exposure down to - 6 ± 2.7, - 8 ± 2.5, and - 9 ± 2.9 mm, respectively. CONCLUSIONS: This study quantitatively evaluated the need for the expansion maneuvers in the PTA to reach BA aneurysms according to the patient's anatomical characteristics.

Using the Post-Descendens Hypoglossal Nerve in Hypoglossal-Facial Anastomosis: An Anatomic and Histologic Feasibility Study.

BACKGROUND: Hypoglossal-facial anastomosis (HFA) is a popular facial reanimation technique. Mobilizing the intratemporal segment of the facial nerve and using the post-descendens hypoglossal nerve (ie, the segment distal to the take-off of descendens hypoglossi) have been proposed to improve results. However, no anatomic study has verified the feasibility of this technique. OBJECTIVE: To assess the anatomic feasibility of HFA and the structural compatibility between the 2 nerves when the intratemporal facial and post-descendens hypoglossal nerves are used. METHODS: The facial and hypoglossal nerves were exposed bilaterally in 10 sides of 5 cadaveric heads. The feasibility of a side-to-end (ie, partial end-to-end) HFA with partial sectioning of the post-descendens hypoglossal nerve and the mobilized intratemporal facial nerve was assessed. The axonal count and cross-sectional area of the facial and hypoglossal nerves at the point of anastomosis were assessed. RESULTS: The HFA was feasible in all specimens with a mean (standard deviation) 9.3 (5.5) mm of extra length on the facial nerve. The axonal counts and cross-sectional areas of the hypoglossal and facial nerves matched well. Considering the reduction in the facial nerve cross-sectional area after paralysis, the post-descendens hypoglossal nerve can provide adequate axonal count and area to accommodate the facial nerve stump. CONCLUSION: Using the post-descendens hypoglossal nerve for side-to-end anastomosis with the mobilized intratemporal facial nerve is anatomically feasible and provides adequate axonal count for facial reanimation. When compared with use of the pre-descendens hypoglossal nerve, this technique preserves C1 fibers and has a potential to reduce glottic complications.

Posterior Inferior Cerebellar Artery (PICA) Reanastomosis After Excision of a Ruptured p2-PICA Aneurysm: 2-Dimensional Operative Video.

Posterior inferior cerebellar artery (PICA) aneurysms have an increased tendency towards a fusiform morphology precluding primary clip reconstruction. The management of these complex aneurysms might require cerebral revascularization to preserve flow in a distal PICA territory. This video illustrates a case of a ruptured p2-PICA aneurysm excision followed by a PICA reanastomosis. A 54-yr-old male presented with a sudden-onset severe headache, diplopia, and complete left cranial nerve six (CN VI) palsy. Neuroimaging demonstrated diffuse subarachnoid hemorrhage in basal cisterns. A catheter angiogram shows a ruptured small fusiform aneurysm in the p2-PICA segment. After obtaining consent for surgery, the patient was placed in a three-quarter prone position. After a hockey stick skin incision and C1 laminectomy, a lateral suboccipital craniotomy was performed. The aneurysm was identified within the vagoaccessory triangle. Cerebral protection consisted of propofol-induced electroencephalography burst suppression during the clamp time for the bypass, without hypothermia or hypertension. After trapping the aneurysm and excising the diseased arterial segment, the distal end of the p2-PICA was reanastomosed to the proximal parent vessel in an end-to-end fashion. Indocyanine green angiography confirmed patency of the anastomosis. Postoperatively, the patient was neurologically at his baseline. The CN VI palsy had completely resolved at a follow-up visit. Reanastomosis is an effective modality for reconstructing PICA following the excision of the fusiform aneurysm. The redundancy of the tonsillomedullary segment of PICA allows for easier distal segment reapproximation in the inferior hypoglossal triangle. An intracranial-intracranial revascularization technique eliminates the need for harvesting the occipital artery. Additionally, it prevents iatrogenic ischemic injury to contralateral PICA, if used for a PICA-PICA bypass.1 © Barrow Neurological Institute, used with permission.

Fluorescence Image Histology Pattern Transformation Using Image Style Transfer.

Confocal laser endomicroscopy (CLE) allow on-the-fly in vivo intraoperative imaging in a discreet field of view, especially for brain tumors, rather than extracting tissue for examination ex vivo with conventional light microscopy. Fluorescein sodium-driven CLE imaging is more interactive, rapid, and portable than conventional hematoxylin and eosin (H&E)-staining. However, it has several limitations: CLE images may be contaminated with artifacts (motion, red blood cells, noise), and neuropathologists are mainly trained on colorful stained histology slides like H&E while the CLE images are gray. To improve the diagnostic quality of CLE, we used a micrograph of an H&E slide from a glioma tumor biopsy and image style transfer, a neural network method for integrating the content and style of two images. This was done through minimizing the deviation of the target image from both the content (CLE) and style (H&E) images. The style transferred images were assessed and compared to conventional H&E histology by neurosurgeons and a neuropathologist who then validated the quality enhancement in 100 pairs of original and transformed images. Average reviewers' score on test images showed 84 out of 100 transformed images had fewer artifacts and more noticeable critical structures compared to their original CLE form. By providing images that are more interpretable than the original CLE images and more rapidly acquired than H&E slides, the style transfer method allows a real-time, cellular-level tissue examination using CLE technology that closely resembles the conventional appearance of H&E staining and may yield better diagnostic recognition than original CLE grayscale images.

Retromastoid-transmuscular identification and harvest of the occipital artery during retrosigmoid craniotomy.

OBJECTIVE: Harvesting the occipital artery (OA) is challenging. The subcutaneous OA is usually found near the superior nuchal line and followed proximally, requiring a large incision and risking damage to the superficially located OA. The authors assessed the anatomical feasibility and safety of exposing the OA through a retromastoid-transmuscular approach. METHODS: Using 10 cadaveric heads, 20 OAs were harvested though a 5-cm retroauricular incision placed 5 cm posterior to the external auditory meatus. The underlying muscle layers were sequentially cut and recorded before exposing the OA. Changes in the orientation of muscle fibers were used as a roadmap to expose the OA without damaging it. RESULTS: The suboccipital segment of the OA was exposed without damage after incising two consecutive layers of muscles and their investing fasciae. These muscles displayed different fiber directions: the superficially located sternocleidomastoid muscle with vertically oriented fibers, and the underlying splenius capitis with anteroposteriorly (and mediolaterally) oriented fibers. The OA could be harvested along the entire length of the skin incision in all specimens. If needed, the incision can be extended proximally and/or distally to follow the OA and harvest greater lengths. CONCLUSIONS: This transmuscular technique for identification of the OA is a reliable method and may facilitate exposure and protection of the OA during a retrosigmoid approach. This technique may obviate the need for larger incisions when planning a bypass to nearby arteries in the posterior circulation via a retrosigmoid craniotomy. Additionally, the small skin incision can be enlarged when a different craniotomy and/or bypass is planned or when a greater length of the OA is needed to be harvested.

Styloidogenic Jugular Venous Compression Syndrome: Clinical Features and Case Series.

BACKGROUND: Styloidogenic jugular venous compression syndrome (SJVCS) is a rare cause of idiopathic intracranial hypertension (IIH). OBJECTIVE: To elucidate the pathophysiology and the hemodynamics of SJVCS. METHODS: We conducted a retrospective review of medical records, clinical images, dynamic venography, and manometry for consecutive patients with SJVCS undergoing microsurgical decompression from April 2009 to October 2017. Patients with IIH with normal venography and manometry findings served as controls. RESULTS: Data were analyzed for 10 patients with SJVCS who presented with headaches. Neck flexion exacerbated headaches in 7 patients. Eleven patients with IIH provided control data for normal intracranial venous pressure and styloid process anatomy. Patients with SJVCS had bilateral osseous compression of venous outflow. The styloid processes were significantly longer in patients with SJVCS than in those with IIH (mean [standard deviation (SD)] distance, 31.0 [10.6] vs 19.0 [14.1] mm; P < .01). The styloid process-C1 lateral tubercle distance was shorter in patients with SJVCS than in those with IIH (mean [SD] distance, 2.9 [1.0] vs 9.9 [2.8] mm; P < .01). Patients with SJVCS had significantly higher global venous pressure and a higher pressure gradient across the stenosis site than controls (mean [SD] pressure, 2.86 [2.61] vs 0.13 [1.09] cm H2O; P = .09). All 10 patients with SJVCS experienced venous pressure elevation during contralateral neck turning (mean [SD] pressure, 4.29 [2.50] cm H2O). All 10 patients with SJVCS underwent transcervical microsurgical decompression, and 9 experienced postoperative improvement or resolution of symptoms. One patient had transient postoperative dysphagia and facial drooping, and another patient reported jaw numbness. CONCLUSION: SJVCS is a novel clinical entity causing IIH. Patients should be evaluated with dynamic venography with manometry. Surgical decompression with removal of osseous overgrowth is an effective treatment in select patients.

Travels to the tropics: Deutschtum and Fedor Krause's visits to Brazil.

Fedor Krause, the father of German neurosurgery, traveled to Latin America twice in the final years of his career (in 1920 and 1922). The associations and motivations for his travels to South America and his work there have not been well chronicled. In this paper, based on a review of historical official documents and publications, the authors describe Krause's activities in South America (focusing on Brazil) within the context of the Germanism doctrine and, most importantly, the professional enjoyment Krause reaped from his trips as well as his lasting influence on neurosurgery in South America. Fedor Krause's visits to Brazil occurred soon after World War I, when Germany sought to reestablish economic, political, cultural, and scientific power and influence. Science, particularly medicine, had been chosen as a field capable of meeting these needs. The advanced German system of academic organization and instruction, which included connections and collaborations with industry, was an optimal means to reestablish the economic viability of not only Germany but also Brazil. Krause, as a de facto ambassador, helped rebuild the German image and reconstruct diplomatic relations between Germany and Brazil. Krause's interactions during his visits helped put Brazilian neurosurgery on a firm foundation, and he left an indelible legacy of advancing professionalism and specialization in neurosurgery in Brazil.

Exposure of the External Carotid Artery Through the Posterior Neck Triangle, Cadaveric Surgical Simulation: 2-Dimensional Operative Video.

The external carotid artery (ECA) is a robust extracranial donor used for high-flow cerebrovascular bypass procedures. It is usually exposed through the anterior triangle of the neck and may be used to revascularize recipients in the anterior or upper posterior cerebral circulations. However, when a high-flow bypass to the posterior circulation is indicated, oftentimes the patient needs to be put in the prone position (or variants thereof). In such situations, accessing the ECA through the anterior triangle of the neck can be challenging. Therefore, using a technique that enables the surgeon to expose the ECA through a posterior approach could be helpful.1 Although we have not yet encountered a case requiring this type of exposure and bypass, this cadaveric surgical simulation video demonstrates the surgical technique of exposing the ECA through the posterior triangle of the neck (as a cadaveric video, no patient consent was necessary). Briefly, this technique involves an inferolateral extension of the muscular stage of the far-lateral approach and exposing the ECA through a plane developed between the parotid gland and the posterior belly of the digastric muscle. The technical details of this technique are described. Also, relevant anatomic information regarding the safety measures taken to protect adjacent neurovascular structures are discussed.

Microvascular anastomosis under 3D exoscope or endoscope magnification: A proof-of-concept study.

BACKGROUND: Extracranial-intracranial bypass is a challenging procedure that requires special microsurgical skills and an operative microscope. The exoscope is a tool for neurosurgical visualization that provides view on a heads-up display similar to an endoscope, but positioned external to the operating field, like a microscope. The authors carried out a proof-of-concept study evaluating the feasibility and effectiveness of performing microvascular bypass using various new exoscopic tools. METHODS: We evaluated microsurgical procedures using a three-dimensional (3D) endoscope, hands-free robotic automated positioning two-dimensional (2D) exoscope, and an ocular-free 3D exoscope, including surgical gauze knot tying, surgical glove cutting, placental vessel anastomoses, and rat vessel anastomoses. Image quality, effectiveness, and feasibility of each technique were compared among different visualization tools and to a standard operative microscope. RESULTS: 3D endoscopy produced relatively unsatisfactory resolution imaging. It was shown to be sufficient for knot tying and anastomosis of a placental artery, but was not suitable for anastomosis in rats. The 2D exoscope provided higher resolution imaging, but was not adequate for all maneuvers because of lack of depth perception. The 3D exoscope was shown to be functional to complete all maneuvers because of its depth perception and higher resolution. CONCLUSION: Depth perception and high resolution at highest magnification are required for microvascular bypass procedures. Execution of standard microanastomosis techniques was unsuccessful using 2D imaging modalities because of depth-perception-related constraints. Microvascular anastomosis is feasible under 3D exoscopic visualization; however, at highest magnification, the depth perception is inferior to that provided by a standard operative microscope, which impedes the procedure.