Category: anatomy

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The endoscopic transpterional port approach: anatomy, technique, and initial clinical experience

J Neurosurg 132:884–894, 2020

The evolution of microsurgical and endoscopic techniques has allowed the development of less invasive transcranial approaches. The authors describe a purely endoscopic transpterional port craniotomy to access lesions involving the cavernous sinus and the anterolateral skull base.

METHODS Through single- or dual-port incisions and with direct endoscopic visualization, the authors performed an endoscopic transpterional port approach (ETPA) using a 4-mm straight endoscope in 8 sides of 4 formalin-fixed cadaveric heads injected with colored latex. A main working port incision is made just below the superior temporal line and behind the hairline. An optional 0.5- to 1-cm second skin port incision is made on the lateral supraorbital region, allowing multiangle endoscopic visualization and maneuverability. A 1.5- to 2-cm craniotomy centered over the pterion is done through the main port, which allows an extradural exposure of the cavernous sinus region and extra/intradural exposure of the frontal and temporal cranial fossae. The authors present a pilot surgical series of 17 ETPA procedures and analyze the surgical indications and clinical outcomes retrospectively.

RESULTS The initial stage of this work on cadavers provided familiarity with the technique, standardized its steps, and showed its anatomical limits. The clinical ETPA was applied to gain access into the cavernous sinus, as well as for aneurysm clipping and meningioma resection. Overall, perioperative complications occurred in 1 patient (6%), there was no mortality, and at last follow-up all patients had a modified Rankin Scale score of 0 or 1.

CONCLUSIONS The ETPA provides a less invasive, focused, and direct route to the cavernous sinus, and to the frontal and temporal cranial fossae, and it is feasible in clinical practice for selected indications with good results.

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The temporoinsular projection system: an anatomical study

J Neurosurg 132:615–623, 2020

Connections between the insular cortex and the amygdaloid complex have been demonstrated using various techniques. Although functionally well connected, the precise anatomical substrate through which the amygdaloid complex and the insula are wired remains unknown. In 1960, Klingler briefly described the “fasciculus amygdaloinsularis,” a white matter tract connecting the posterior insula with the amygdala. The existence of such a fasciculus seems likely but has not been firmly established, and the reported literature does not include a thorough description and documentation of its anatomy. In this fiber dissection study the authors sought to elucidate the pathway connecting the insular cortex and the mesial temporal lobe.

METHODS Fourteen brain specimens obtained at routine autopsy were dissected according to Klingler’s fiber dissection technique. After fixation and freezing, anatomical dissections were performed in a stepwise progressive fashion.

RESULTS The insula is connected with the opercula of the frontal, parietal, and temporal lobes through the extreme capsule, which represents a network of short association fibers. At the limen insulae, white matter fibers from the extreme capsule converge and loop around the uncinate fasciculus toward the temporal pole and the mesial temporal lobe, including the amygdaloid complex.

CONCLUSIONS The insula and the mesial temporal lobe are directly connected through white matter fibers in the extreme capsule, resulting in the appearance of a single amygdaloinsular fasciculus. This apparent fasciculus is part of the broader network of short association fibers of the extreme capsule, which connects the entire insular cortex with the temporal pole and the amygdaloid complex. The authors propose the term “temporoinsular projection system” (TIPS) for this complex.

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Individual variations of the superior petrosal vein complex and their microsurgical relevance in 50 cases of trigeminal microvascular decompression

Acta Neurochirurgica (2020) 162:197–209

We investigated the understudied anatomical variations of the superior petrosal vein (SPV) complex (SPVC), which may play some role in dictating the individual complication risk following SPVC injury.

Methods Microvascular decompressions of the trigeminal nerve between September 2012 and July 2016. All operations utilized an SPVC preserving technique. Preoperative balanced fast field echo (bFFE) magnetic resonance imaging, or equivalent sequences, and operative videos were studied for individual SPVC anatomical features.

Results Applied imaging and operative SPVC anatomy were described for fifty patients (mean age, 67.18 years; female sex and right-sided operations, 58% each). An SPVC component was sacrificed intentionally in 6 and unintentionally in only 7 cases. Twenty-nine different individual variations were observed; 80% of SPVCs had either 2 SPVs with 3 or 1 SPV with 2, 3, or 4 direct tributaries. Most SPVCs had 1 SPV (64%) and 2 SPVs (32%). The SPV drainage point into the superior petrosal sinus was predominantly between the internal auditory meatus and Meckel cave (85.7% of cases). The vein of the cerebellopontine fissure was the most frequent direct tributary (86%), followed by the pontotrigeminal vein in 80% of SPVCs. Petrosal-galenic anastomosis was detected in at least 38%of cases. At least 1 SPVin 54%of the cases and at least 1 direct tributary in 90%disturbed the operative field. The tributaries were more commonly sacrificed.

Conclusions The extensive anatomical variation of SPVC is depicted. Most SPVCs fall into 4 common general configurations and can usually be preserved. BFFE or equivalent sequences remarkably facilitated the intraoperative understanding of the individual SPVC in most cases.

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Disruption of Frontal Aslant Tract Is Not Associated with Long-Term Postoperative Language Deficits

World Neurosurg. (2020) 133:192-195

The frontal aslant tract (FAT) is a white matter fiber pathway connecting the superior frontal gyrus to the Broca area. This tract in the dominant hemisphere has been shown to play a role in speech initiation and production, and direct subcortical stimulation can induce stuttering and speech arrest in a patient. However, controversy remains as to whether disruption of this pathway will lead to a permanent language deficit and if it is even necessary to map this tract during tumor resections of the dominant frontal lobe.

CASE DESCRIPTION: Here, we report a case of a patient with a lower-grade diffuse glioma invading the dominant FAT that was removed with an asleep craniotomy. In the immediate postoperative state, the patient had a transcortical motor dysphasia and was unable to initiate speech. These immediate language deficits quickly recovered, and the patient was neurologically intact at the time of discharge a few days after surgery.

CONCLUSIONS: Given the high likelihood for a complete neurologic recovery including transient aphasia, we propose that awake mapping for the purpose of identifying the dominant FAT is unnecessary during tumor resection and that disruption of this tract is not associated with any long-term language deficits.

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The foramen lacerum: surgical anatomy and relevance for endoscopic endonasal approaches

J Neurosurg 131:1571–1582, 2019

The foramen lacerum is a relevant skull base structure that has been neglected for many years. From the endoscopic endonasal perspective, the foramen lacerum is a key structure due to its location at the crossroad between the sagittal and coronal planes. The objective of this study was to provide a detailed investigation of the surgical anatomy of the foramen lacerum and its adjacent structures based on anatomical dissections and imaging studies, propose several relevant key surgical landmarks, and demonstrate the surgical technique for its full exposure with several illustrative cases.

METHODS Ten colored silicone-injected anatomical specimens were dissected using a transpterygoid approach to the foramen lacerum region in a stepwise manner. Five similar specimens were used for a comparative transcranial approach. The osseous anatomy was examined in 32 high-resolution multislice CT studies and 1 disarticulated skull. Representative cases were selected to illustrate the application of the findings.

RESULTS The pterygosphenoidal fissure is the synchondrosis between the lacerum process of the pterygoid bone and the floor of the sphenoid bone. It constantly converges with the posterior end of the vidian canal at a 45° angle, and its posterolateral end points directly to the lacerum foramen. The pterygoid tubercle separates the vidian canal from the pterygosphenoidal fissure, and forms the anterior wall of the lower part of the foramen lacerum. The lingual process, which forms the lateral wall of the foramen lacerum, was identified in 53 of 64 sides and featured an average height of 5 mm. The mandibular strut separates the foramen lacerum from the foramen ovale and had an average width of 5 mm.

CONCLUSIONS This study provides relevant surgical landmarks and a systematic approach to the foramen lacerum by defining anterior, medial, lateral, and inferior walls that may facilitate its safe exposure for effective removal of lesions while minimizing the risk of injury to the internal carotid artery.

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Key anatomical landmarks for middle fossa surgery: a surgical anatomy study

J Neurosurg 131:1561–1570, 2019

Middle fossa surgery is challenging, and reliable surgical landmarks are essential to perform accurate and safe surgery. Although many descriptions of the middle fossa components have been published, a clinically practical description of this very complex anatomical region is lacking. Small structure arrangements in this area are often not well visualized or accurately demarcated with neuronavigation systems. The objective is to describe a “roadmap” of key surgical reference points and landmarks during middle fossa surgery to help the surgeon predict where critical structures will be located.

METHODS The authors studied 40 dry skulls (80 sides) obtained from the anatomical board at their institution. Measurements of anatomical structures in the middle fossa were made with a digital caliper and a protractor, taking as reference the middle point of the external auditory canal (MEAC). The results were statistically analyzed.

RESULTS The petrous part of the temporal bone was found at a mean of 16 mm anterior and 24 mm posterior to the MEAC. In 87% and 99% of the sides, the foramen ovale and foramen spinosum, respectively, were encountered deep to the zygomatic root. The posterior aspect of the greater superficial petrosal nerve (GSPN) groove was a mean of 6 mm anterior and 25 mm medial to the MEAC, nearly parallel to the petrous ridge. The main axis of the IAC projected to the root of the zygoma in all cases. The internal auditory canal (IAC) porus was found 5.5 mm lateral and 4.5 mm deep to the lateral aspect of the trigeminal impression along the petrous ridge (mean measurement values). A projection from this point to the middle aspect of the root of the zygoma, being posterior to the GSPN groove, could estimate the orientation of the IAC.

CONCLUSIONS In middle fossa approaches, the external acoustic canal is a reliable reference before skin incision, whereas the zygomatic root becomes important after the skin incision. Deep structures can be related to these 2 anatomical structures. An easy method to predict the location of the IAC in surgery is described. Careful study of the preoperative imaging is essential to adapt this knowledge to the individual anatomy of the patient.

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Microsurgical anatomy of the sagittal stratum

Acta Neurochirurgica (2019) 161:2319–2327

The sagittal stratum (SS) is a critical neural crossroad traversed by several white matter tracts that connect multiple areas of the ipsilateral hemisphere. Scant information about the anatomical organization of this structure is available in literature. The goal of this study was to provide a detailed anatomical description of the SS and to discuss the functional implications of the findings when a surgical approach through this structure is planned.

Methods Five formalin-fixed human brains were dissected under the operating microscope by using the fiber dissection technique originally described by Ludwig and Klingler.

Results The SS is a polygonal crossroad of associational fibers situated deep on the lateral surface of the hemisphere, medial to the arcuate/superior longitudinal fascicle complex, and laterally to the tapetal fibers of the atrium. It is organized in three layers: a superficial layer formed by the middle and inferior longitudinal fascicles, a middle layer corresponding to the inferior frontooccipital fascicle, and a deep layer formed by the optic radiation, intermingled with fibers of the anterior commissure. It originates posteroinferiorly to the inferior limiting sulcus of the insula, contiguous with the fibers of the temporal stem, and ends into the posterior temporo-occipito-parietal cortex.

Conclusion The white matter fiber dissection reveals the tridimensional architecture of the SS and the relationship between its fibers. A detailed understanding of the anatomy of the SS is essential to decrease the operative risks when a surgical approach within this area is undertaken.

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Microsurgical dissection of Sylvian fissure—short technical videos of third generation cerebrovascular neurosurgeons

Acta Neurochirurgica (2019) 161:1743–1746

Multiple intracranial pathologies, including aneurysms of the middle cerebral artery, distal basilar artery, and suprasellar pathologies require the microsurgical opening of the Sylvian fissure. Delicate splitting of the arachnoid and safe microdissection of the veins, arteries, and brain parenchyma is the key to successful surgery through the Sylvian fissure corridor. We hypothesize that the geographical and historical environment in which neurosurgeons learn their operative skills is subject to a number of extrinsic influences, including cultural nuances of surgical techniques. Here we try to illustrate some cultural differences and technical aspects of the opening of the Sylvian fissure by four “third generation” cerebrovascular neurosurgeons from three different continents.

Methods In the video analysis, various microsurgical aspects, including the opening style of the Sylvian fissure, handedness, use of sharp or blunt microinstruments, use of retractors, use of high magnification, and handling of bridging veins are presented. Results The video illustrates the two distinct Sylvian fissure opening styles, namely sharp and blunt microdissection, as well as the extent of the opening namely a wide and focal splitting.

Conclusion The edited video underlines nuances and differences of a few major technical aspects that are perhaps typical to certain surgical environments and cultures. These microsurgical nuances and styles are useful pearls that can be mastered with training by any novice neurosurgeon.

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The anatomy of the parapharyngeal segment of the internal carotid artery for endoscopic endonasal approach

Neurosurgical Review
https://doi.org/10.1007/s10143-019-01176-3

Injury to the internal carotid artery (ICA) is a life-threatening complication of endoscopic endonasal approaches. The objective of this study is to illustrate the detail anatomy of the parapharyngeal segment of the ICA (PPICA) to safe endoscopic endonasal surgery.

The anatomical dissection was performed in 10 cadaveric specimens and several crucial anatomical landmarks were identified and measured. In addition, 50 dry skulls were studied to further assess the relationship between the pharyngeal tubercle and carotid foramen. From the endoscopic endonasal perspective, in the median plane, the pharyngeal tubercle and the carotid foramen on both sides were located on a line.

The average distance between the pharyngeal tubercle and anterior border of the external orifice of the carotid canal was measured as 25.2 ± 3.2 mm. In the paramedian plane, the PPICA was located between the levator veli palatini muscle (LVPM) and the stylopharyngeal muscle (SPM) in upper parapharyngeal space in all specimens, and the distance from the posterior border of the LVPM to the anterior border of the SPM was recorded as 15.1 ± 2.8 mm at the level of the carotid foramen. The distance from the attachment of the LVPM to the anterior border of the external orifice of the carotid canal was about 5.1 ± 0.2 mm. The fully developed stylopharyngeal fascia (SPhF) was observed in 10 cases, and the PPICA was always anteriorly enclosed by and adhered to the SPhF.

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Nervus intermedius and the surgical management of geniculate neuralgia

J Neurosurg 131:343–351, 2019

Geniculate neuralgia (GN) is an uncommon craniofacial pain syndrome attributable to nervus intermedius (NI) dysfunction. Diagnosis and treatment can be challenging, due to the complex nature of ear sensory innervation, resulting in clinical overlap with trigeminal neuralgia (TN) and glossopharyngeal neuralgia (GPN).

METHODS A retrospective review of a prospective neurosurgical database at our institution was performed, 2000–2017, with a corresponding systematic literature review. Pain outcomes were dichotomized as unfavorable for unchanged/worsened symptoms versus favorable if improved/resolved. Eight formalin-fixed brains were examined to describe NI at the brainstem.

RESULTS Eleven patients were surgically treated for GN—9 primary, 2 reoperations. The median age was 48, 7 pa- tients were female, and the median follow-up was 11 months (range 3–143). Seven had ≥ 2 probable cranial neuralgias. NI was sectioned in 9 and treated via microvascular decompression (MVD) in 2. Five patients underwent simultaneous treatment for TN (4 MVD; 1 rhizotomy) and 5 for GPN (3 MVD; 2 rhizotomy). Eleven reported symptomatic improvement (100%); 8 initially reported complete resolution (73%). Pain outcomes at last contact were favorable in 8 (73%)—all among the 9 primary operations (89% vs 0%, p = 0.054). Six prior series reported outcomes in 111 patients.

CONCLUSIONS GN is rare, and diagnosis is confounded by symptomatic overlap with TN/GPN. Directed treatment of all possible neuralgias improved pain control in almost all primary operations. Repeat surgery seems a risk factor for an unfavorable outcome. NI is adherent to superomedial VIII at the brainstem; the intermediate/cisternal portion is optimal for visualization and sectioning.

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The approach angle to the interoptic triangle limits surgical workspace when targeting the contralateral internal carotid artery

Acta Neurochirurgica (2019) 161:1535–1543

The interoptic triangle (IOT) offers a key access to the contralateral carotid artery’s ophthalmic segment (oICA) and its perforating branches (PB), the ophthalmic artery (OA), and the superior hypophyseal artery (SHA). It has been previously reported that the assessment of IOT’s size is relevant when attempting approaches to the contralateral oICA. However, previous studies have overseen that, since the oICA is a paramedian structure and a lateralized contralateral approach trajectory is then required, the real access to the oICA is further limited by the approach angle adopted by the surgeon with respect to the IOT’s plane. For this reason, we determined the surgical accessibility to the contralateral oICA and its branches though the IOT by characterizing the morphometry of this triangle relative to the optimal contralateral approach angle.

Methods We defined the “relative interoptic triangle” (rIOT) as the two-dimensional projection of the IOT to the surgeon’s view, when the microscope has been positioned with a certain angle with respect to the midline to allow the maximal contralateral oICA visualization. We correlated the surface of the rIOT to the visualization of oICA, OA, SHA, and PBs on 8 cadavers and 10 clinical datasets, using for the last a 3D-virtual reality system.

Results A larger rIOT correlated positively with the exposure of the contralateral oICA (R = 0.967, p < 0.001), OA (R = 0.92, p < 0.001), SHA (R = 0.917, p < 0.001), and the number of perforant vessels of the oICA visible (R = 0.862, p < 0.001). The exposed length of oICA, OA, SHA, and number PB observed increased as rIOT’s surface enlarged. The correlation patterns observed by virtual 3D-planning matched the anatomical findings closely.

Conclusions The exposure of contralateral oICA, OA, SHA, and PB directly correlates to rIOT’s surface. Therefore, preoperative assessment of rIOT’s surface is helpful when considering contralateral approaches to the oICA. A virtual 3D planning tool greatly facilitates this assessment.

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Probabilistic Tractography to Predict the Position of Cranial Nerves Displaced by Skull Base Tumors: Value for Surgical Strategy Through a Case Series of 62 Patients

Neurosurgery, Volume 85, Issue 1, July 2019, Pages E125–E136

Predicting the displacement of cranial nerves by tumors could make surgery safer and the outcome better. Recent advances in imaging and processing have overcome some of the limits associated with cranial nerve tractography, such as spatial resolution and fiber crossing. Among others, probabilistic algorithms yield to a more accurate depiction of cranial nerve trajectories.

OBJECTIVE: To report how cranial nerve probabilistic tractography can help the surgical strategy in a series of various skull base tumors.

METHODS: After distortion correction and region of interest seeding, a probabilistic tractography algorithm used the constrained spherical deconvolution model and attempted the reconstruction of cranial nerve trajectories in both healthy and displaced conditions.

RESULTS: Sixty-two patients were included and presented: vestibular schwannomas (n = 33); cerebellopontine angle meningiomas (n = 15); arachnoid or epidermoid cysts (n = 6); cavernous sinus and lower nerves schwannomas (n = 4); and other tumors (n = 4). For each patient, at least one ‘displaced’ cranial nerve was not clearly identified on classical anatomical MRI images. All 372 cranial nerves were successfully tracked on each healthy side; among the 175 cranial nerves considered ‘displaced’by tumors, 152 (87%) were success- fully tracked. Among the 127 displaced nerves of operated patients (n = 51), their position was confirmed intraoperatively for 118 (93%) of them. Conditions that led to tractography failure were detailed. On the basis of tractography, the surgical strategy was adjusted for 44 patients (71%).

CONCLUSION: This study reports a cranial nerve probabilistic tractography pipeline that can: predict the position of most cranial nerves displaced by skull base tumors, help the surgical strategy, and thus be a pertinent tool for future routine clinical application.

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The medial wall of the cavernous sinus. Part 1: Surgical anatomy, ligaments, and surgical technique for its mobilization and/or resection

J Neurosurg 131:122–130, 2019

The medial wall of the cavernous sinus (CS) is often invaded by pituitary adenomas. Surgical mobilization and/or removal of the medial wall remains a challenge.

METHODS Endoscopic endonasal dissection was performed in 20 human cadaver heads. The configuration of the medial wall, its relationship to the internal carotid artery (ICA), and the ligamentous connections in between them were investigated in 40 CSs.

RESULTS The medial wall of the CS was confirmed to be an intact single layer of dura that is distinct from the capsule of the pituitary gland and the periosteal layer that forms the anterior wall of the CS. In 32.5% of hemispheres, the medial wall was indented by and/or well adhered to the cavernous ICA. The authors identified multiple ligamentous fibers that anchored the medial wall to other walls of the CS and/or to specific ICA segments. These parasellar ligaments were clas- sified into 4 groups: 1) caroticoclinoid ligament, spanning from the medial wall and the middle clinoid toward the clinoid ICA segment and anterior clinoid process; 2) superior parasellar ligament, connecting the medial wall to the horizontal cavernous ICA and/or lateral wall of the CS; 3) inferior parasellar ligament, bridging the medial wall to the anterior wall of the CS or anterior surface of the short vertical segment of the cavernous ICA; and 4) posterior parasellar ligament, which anchors the medial wall to the short vertical segment of the cavernous ICA and/or the posterior carotid sulcus. The caroticoclinoid ligament and inferior parasellar ligament were present in most CSs (97.7% and 95%, respectively), while the superior and posterior parasellar ligaments were identified in approximately half of the CSs (57.5% and 45%, respec- tively). The caroticoclinoid ligament was the strongest and largest ligament, and it was typically assembled as a group of ligaments with a fan-like arrangement. The inferior parasellar ligament was the first to be encountered after opening the anterior wall of the CS during an interdural transcavernous approach.

CONCLUSIONS The authors introduce a classification of the parasellar ligaments and their role in anchoring the medial wall of the CS. These ligaments should be identified and transected to safely mobilize the medial wall away from the cavernous ICA during a transcavernous approach and for safe and complete resection of adenomas that selectively invade the medial wall.

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Amygdala and Hypothalamus: Historical Overview With Focus on Aggression

Neurosurgery, 85, 1: 11–30, 2019

Aggressiveness has a high prevalence in psychiatric patients and is a major health problem. Two brain areas involved in the neural network of aggressive behavior are the amygdala and the hypothalamus.

While pharmacological treatments are effective in most patients, some do not properly respond to conventional therapies and are considered medically refractory. In this population, surgical procedures (ie, stereotactic lesions and deep brain stimulation) have been performed in an attempt to improve symptomatology and quality of life.

Clinical results obtained after surgery are difficult to interpret, and the mechanisms responsible for postoperative reductions in aggressive behavior are unknown.

We review the rationale and neurobiological characteristics that may help to explain why functional neurosurgery has been proposed to control aggressive behavior.

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Somatotopy and Organization of Spinothalamic Tracts in the Human Cervical Spinal Cord

Neurosurgery, Volume 84, Issue 6, June 2019, Pages E311–E317

Understanding spinothalamic tract anatomy may improve lesioning and outcomes in patients undergoing percutaneous cordotomy.

OBJECTIVE: To investigate somatotopy and anatomical organization of spinothalamic tracts in the human cervical spinal cord.

METHODS: Patients with intractable cancer pain undergoing cordotomy underwent preoperative and postoperative quantitative sensory testing for sharp pain and heat pain on day 1 and 7 after cordotomy. Intraoperative sensory stimulation was performed with computed tomography (CT) imaging to confirm the location of the radiofrequency electrode during cordotomy. Postoperative magnetic resonance (MR) imaging was performed to define the location of the lesion.

RESULTS: Twelve patientswere studied, and intraoperative sensory stimulation combined with CT imaging revealed a somatotopy where fibers from the legs were posterolateral to fibers from the hand. Sharpness detection thresholds were significantly elevated in the area of maximum pain on postoperative day 1 (P = .01). Heat pain thresholds for all areas were not elevated significantly on postoperative day 1, or postoperative day 7. MR imaging confirmed that the cordotomy lesion was in the anterolateral quadrant, and in this location the lesion had a sustained effect on sharp pain but a transient impact on heat pain.

CONCLUSION: In the high cervical spinal cord, spinothalamic fibers mediating sharp pain for the arms are located ventromedial to fibers for the legs, and these fibers are spatially distinct from fibers that mediate heat pain.

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Vidian Neurectomy for Management of Chronic Cluster Headache

Neurosurgery (84),1059–1064, 2019

Management of chronic cluster headache (CCH) remains a challenging endeavor, and the optimal surgical approach for medically refractory CCH remains controversial.

OBJECTIVE: To conduct a preliminary evaluation of the efficacy and safety of vidian neurectomy (VN) in patients with medically refractory CCH.

METHODS: Between March 2013 and December 2015, 9 CCH patients, all of whom had failed to respond to conservative therapy, underwent VN with a precise nerve cut and maximal preservation of the sphenopalatine ganglion. Data included demographic variables, cluster headache onset and duration, mean attack frequency, mean attack intensity, and pain disability index measures pre- and through 12-mo postsurgery.

RESULTS: Seven of the 9 cases (77.8%) showed immediate improvement. Improvement was delayed by 1 mo in 1 patient, after which the surgical effects of pain relief were maintained throughout the follow-up period. One patient (11.1%) did not improve after surgery. One year after VN, patients’ mean attack frequency, mean attack intensity, and pain disability index decreased by 54.5%, 52.9%, and 56.4%, respectively. No patient experienced treatment-related side effects or complications.

CONCLUSION: VN is an effective treatment method for CCH patients. Precise Vidian nerve identification and maximal preservation of the sphenopalatine ganglion may achieve good surgical outcomes and dramatically improve quality of life among patients, without significant adverse events.

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An anatomical study of the foramen of Monro: implications in management of pineal tumors presenting with hydrocephalus

Acta Neurochirurgica (2019) 161:975–983

For pineal tumors presenting with hydrocephalus, simultaneous endoscopic third ventriculostomy (ETV) and tumor biopsy is commonly used as the initial step in management. To analyze the restriction which the foramen of Monro poses to this procedure, one must start with a detailed description of the microsurgical anatomy of the foramen in living subjects. However, the orientation and shape of the foramen of Monro make this description difficult with conventional imaging techniques.

Method Virtual reality technology was applied on MRIs on living subject without hydrocephalus, as well as patients with hydrocephalus, to generate precise anatomical models with sub-millimeter accuracy. The morphometry of the foramen of Monro was studied in each group. In addition, displacement of the margins of the foramen was studied in detail for simultaneous ETVand pineal tumor biopsy through a single burr hole.

Results In 30 normal subjects, the foramen of Monro had oval-shaped openings averaging 5.23 mm2. The foramen was larger in people above age 55 (p = 0.007) and on the left side compared to the right (p = 0.002). For patients with clinical presentation of hydrocephalus, the average opening was 32.6 mm2. Simulated single burr hole simultaneous ETVand pineal tumor biopsy was performed in 10 specimens. Average displacement of the posterior and anterior margins of the foramen was 5.71 mm and 5.76 mm, respectively. However, maximum displacement reached 9.3 mm posteriorly and 10 mm anteriorly.

Conclusions The foramen of Monro is an oval-shaped cylinder that changes in size and orientation in the hydrocephalic patient. If universally applied to all patients regardless of foramen and tumor size, ETV/biopsy can displace structures around the Foramen of Monro up to 1 cm, which can potentially lead to neurological damage. Careful pre-operative assessment is critical to determine if a single burr hole approach is safe. Keywords Foramen ofMonro . Hydrocephalus . Pineal . Fornix . Endoscopic third ventriculostomy

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

J Neurosurg 130:1435–1445, 2019

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.

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

J Neurosurg 130:1426–1434, 2019

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 s1 segment and proximal s2 segment of the superior cerebellar artery (SCA) and P2A 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, s1- and s2-SCA, and P2A-PCA. This window may be efficiently used to address various pathologies in the region and is considerably expandable by TcA and/or UnR.

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Caroticoclinoid Bar: A Systematic Review and Meta-Analysis of Its Prevalence and Potential Implications in Cerebrovascular and Skull Base Surgery

World Neurosurg. (2019) 124:267-276

The presence of a caroticoclinoid bar (CCB) has been implicated in both transcranial and endonasal surgery. Its morphology reflects differences in the microsurgical anatomy of the parasellar area and its manipulation during anterior or middle clinoidectomy can result in internal carotid artery injury. Although adjustment of the surgical technique according to the CCB anatomic variants is required for safe surgical access to the paraclinoid region, a review indicated the lack of a systematic assortment of reported data regarding the prevalence of the CCB. Thus, our objective was to systematically review and document the prevalence of the CCB and its anatomic variations.

METHODS: Three databases were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement through August 2018 to identify relevant studies.

RESULTS: A total of 27 reports (7521 subjects or specimens, 14,449 sides) were included in the present meta-analysis. The overall pooled prevalence of the CCB was 32.6% (95% confidence interval [CI], 26.6%e38.8%) when measured in the subjects or specimens and 23.6% (95% CI, 19.7%e27.6%) when measured in each side. The overall prevalence of the CCB reported from imaging studies was 23.1% (95% CI, 8.9%e41.4%) for the subjects/specimens and 18.7% (95% CI, 12.6%e25.7%) for each side. The presence of the CCB was slightly more prevalent (P [ 0.050) on the right side.

CONCLUSIONS: Our results showed a considerable prevalence of the CCB, with lower prevalence rates found among imaging studies. Although meticulous preoperative investigation is mandatory, surgeons treating patients with parasellar pathologic entities should always be vigilant regarding the CCB.

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