Cerebellopontine Fissure Research Articles

Microsurgical treatment for superior petrosal sinus dural arteriovenous fistulas.

Superior petrosal sinus (SPS) dural arteriovenous fistulas (DAVFs) are a commonly encountered type of tentorial DAVF that occasionally requires microsurgical intervention. This study aims to analyze the tributaries of the superior petrosal vein (SPV) observed intraoperatively, their association with clinical symptoms, and venous drainage patterns.This retrospective study reviewed 34 consecutive patients with SPS DAVFs who underwent microsurgical treatment at a single institution between 2014 and 2022.The cohort had a mean age of 52.8 ± 11.8 years, with 85.3% (29/34) being male. Predominant symptoms included venous hypertensive myelopathy (VHM) (55.9%) and intraparenchymal or subarachnoid hemorrhage (23.5%). Standard retrosigmoid approach was used to ligate 94.1% (32/34) of the lesions, resulting in immediate complete fistula occlusion for all patients. Supratentorial venous drainage patterns were associated with a higher incidence of intracranial hemorrhage and venous varix (P = 0.047). Infratentorial drainage patterns were more frequently linked with VHM-related symptoms (P<0.001). Patients presenting VHM-related symptoms showed a higher prevalence of drainage through the vein of the cerebellopontine fissure (VCPF) (P = 0.01), while those with intracranial hemorrhage symptoms exhibited a higher prevalence of pontotrigeminal vein (PTV) drainage (P = 0.033) in their DAVFs.Endovascular management of SPS DAVFs carries inherent risks. Surgical treatment via standard retrosigmoid craniotomy offers favorable clinical outcomes with high rates of cure. In cases featuring infratentorial venous drainage, the predominant arterialized tributary of the SPV was the VCPF, commonly associated with VHM-related symptoms. Conversely, in cases with supratentorial venous drainage, the predominant arterialized SPV tributary was the PTV, often associated with intracranial hemorrhage symptoms.

Surgical Anatomy of the Retrosigmoid Approach With Transtentorial Extension: Protecting the 4th Cranial Nerve.

The retrosigmoid approach with transtentorial extension (RTA) allows us to address posterior cranial fossa pathologies that extend through the tentorium into the supratentorial space. Incision of the tentorium cerebelli is challenging, especially for the risk of injury of the cranial nerve (CN) IV. We describe a tentorial incision technique and relevant anatomic landmarks. The RTA was performed stepwise on 5 formalin-fixed (10 sides), latex-injected cadaver heads. The porus trigeminus's midpoint, the lateral border of the suprameatal tubercle (SMT)'s base, and cerebellopontine fissure were assessed as anatomic landmarks for the CN IV tentorial entry point, and relative measurements were collected. A clinical case was presented. The tentorial opening was described in 4 different incisions. The first is curved and starts in the posterior aspect of the tentorium. It has 2 limbs: a medial one directed toward the tentorium's free edge and a lateral one that extends toward the superior petrosal sinus (SPS). The second incision turns inferiorly, medially, and parallel to the SPS down to the SMT. At that level, the second incision turns perpendicular toward the tentorium's free edge and ends 1 cm from it. The third incision proceeds posteriorly, parallel to the free edge. At the cerebellopontine fissure, the incision can turn toward and cut the tentorium-free edge (fourth incision). On average, the CN IV tentorial entry point was 12.7 mm anterior to the SMT base's lateral border and 20.2 mm anterior to the cerebellopontine fissure. It was located approximately in the same coronal plane as the porus trigeminus's midpoint, on average 1.9 mm anterior. The SMT and the cerebellopontine fissure are consistently located posterior to the CN IV tentorial entry point. They can be used as surgical landmarks for RTA, reducing the risk of injury to the CN IV.

The Infratrigeminal Suprafloccular Approach to Intrapontine Lesions: An Anatomical Overview and Relevance for the Approach to Intrapontine Lesions.

Background and objectives Brainstem lesions have long been considered complex pathologies that may lead to permanent deficits or life-threatening complications, posing significant challenges for surgical removal. Among these lesions, intrapontine lesions are particularly challenging in the field of neurosurgery. However, with advancements in microsurgical anatomy knowledge and technology, these lesions have become more amenable to surgical treatment. In this study, the authors examine an infratrigeminal suprafloccular approach, which has been shown to be a safe surgical route, resulting in fewer postoperative complications, while evaluating the anatomical nuances of the approach and route. Methods Twenty cadaveric brainstem specimens were analyzed to assess the anatomy, focusing on the lateral aspect of the pons as a potential safe entry zone for intrapontine lesions. The authors consistently analyzed twenty brainstem specimens, carefully examining the pontine microsurgical anatomy. A triangular area of entrance was measured, with three sides or walls (X, Y, and Z) aiming to identify the safe zone that would spare the distinct pontine nuclei, ascending sensory pathways, corticospinal, corticonuclear, and corticopontine tracts of the brainstem. An illustrative case was adapted to the described safe entry zone for corroboration purposes. Results The authors measured three distinct lines on the lateral surface of the pons, named X, Y, and Z, forming a triangle in shape. Line X extended from the midpoint anteroposteriorly of the flocculus of the cerebellum to the apparent trigeminal exit in the lateral aspect of the pons. Line Y ran from the trigeminal exit in the pons to the apparent exit of the facial-vestibulocochlear complex in the far lateral aspect of the pontomedullary sulcus in the cerebellopontine fissure. Line Z represented the measurement from the vestibulocochlear complex to the midpoint anteroposteriorly of the flocculus of the cerebellum. The mean measurements were as follows: X = 14.41mm (range: 10mm to 20mm), Y = 13.1mm (range: 10mm to 21mm), and Z = 3mm (range: 2mm to 5mm). The mean surface area of the analyzed specimens within the triangle (formed by X, Y, and Z) was 20.1mm² (range: 10mm² to 40mm²). This area was identified as a safe zone for the entry of microsurgical approaches to intrapontine lesions, involving less retraction of the anterior pons and potentially sparing critical structures, such as the corticospinal tracts, pontine perforating arteries, tegmentum pontis, cranial nerve nuclei, substantia reticulata dorsally, and transverse pontine fibers. Microsurgical anatomical findings, combined with intraoperative monitoring in an illustrative case, consistently demonstrated that this entry area predicted less functional instability of the analyzed tracts and resulted in fewer postoperative complications. Conclusion Deep-seated pontine lesions present a complex range of pathologies with a high potential for devastating outcomes, particularly those involving hemorrhage. This study identifies and describes a presumed safe entry zone that allows for the creation of a surgical corridor for biopsy or microsurgical resection of these lesions, reducing morbidity in a previously considered impenetrable region.

Preoperative assessment of the individual anatomy of the superior petrosal vein complex using balanced fast field echo magnetic resonance imaging.

Here, we sought to examine the validity and reproducibility of balanced fast field echo (bFFE) for assessing superior petrosal vein (SPV) complex (SPVC) anatomy. Preoperative bFFE or equivalent scans and operative videos were studied and directly compared with regard to the individual anatomical features of SPVCs and their relation to the operative field. The anatomical details of the bFFE findings of the non-operated side (group 2) of all 50 patients were then reviewed, including the presence of petrosal-galenic anastomosis, and finally compared to the operated SPVCs (group 1). A complete correlation between bFFE and intraoperative findings was observed in 62% of cases and had a significant correlation with 3 Tesla magnet strength and higher pixel bandwidth (rbis = -0.47; p = 0.005). The sensitivity and specificity of bFFE magnetic resonance imaging were 93.7 and 95.2%, respectively, for detecting an SPV disturbing the operative field, and 97.3% and 95% for a disturbing tributary, respectively. Each group had 50 SPVCs, with a total of 70 and 64 SPVs, 10 and 11 general SPVC configurations, as well as 29 and 28 different individual anatomical variations in groups 1 and 2, respectively. Both groups had 1-3 SPVs with a similar distribution of frequencies [Chi-square (4) = 27.56; p = 0.0145 (Fisher's exact test)]. The similarity of the general configurations was not statistically significant. The same four predominant configurations constituted 80% of the SPVCs in each group. The vein of the cerebellopontine fissure was most frequently found in 86% and 88% of cases, and a petrosal-galenic anastomosis was seen in 38% and 40% of groups 1 and 2, respectively. Individual SPVC variations are extensive. Good quality bFFE or equivalents are feasible for preoperative SPVC assessments. However, methods improving vascular visualization are recommended.

Vein-related Trigeminal Neuralgia: How to Determine the Treatment Method of the Causative Vein: A Technical Note

Trigeminal neuralgia (TN) is often caused by various vein forms. Herein, we report two cases of vein-related TN. In the first case, the vein of the cerebellopontine fissure (VCPF), along with the thickened surrounding arachnoid, clung to the trigeminal nerve. As the perfusion range of this vein was expected to be wide and its injury might cause extensive venous infarction, the anchor between the trigeminal nerve and the vein was carefully dissected and the vein was successfully transposed. In the second case, the involvement of the vein of the middle cerebellar peduncle (VMCP), which penetrates the nerve bundle of the trigeminal nerve, was suspected. Because vein transposition was impossible, the vein was transected at the nerve penetration site after confirming that there was sufficient collateral venous outflow. The superior petrosal vein and its tributaries are the primary causative veins of vein-related TN, and their contact patterns are infinite. Moreover, their perfusion range and the presence or absence of collateral venous outflow vary from case to case. Therefore, it is necessary to judge the perfusion range as well as collateral venous outflow based on preoperative images and intraoperative findings and to determine the appropriate treatment method for each case.

How I do it: horizontal fissure approach to the middle cerebellar peduncle.

The horizontal fissure approach is a workhorse for brainstem lesions in the central and dorsolateral pons and middle cerebellar peduncle (MCP). The cerebellopontine fissure is a V-shaped fissure with a superior and inferior limb between the cerebellum, pons, and MCP. The horizontal or petrosal fissure is at the apex of the cerebellopontine fissure and extends laterally to divide the petrosal surface of the cerebellum into superior and inferior parts. Splitting this fissure exposes the posterolateral aspect of the MCP without excessive retraction or transgression of the cerebellum. We demonstrate and describe the horizontal fissure operative approach to the middle cerebellar peduncle for resection of a pontine cavernoma with illustrative figures and operative video. Splitting the horizontal (petrosal) fissure of the cerebellum brings the middle cerebellar peduncle into view behind the root entry zone of the trigeminal nerve, providing an expanded, safe corridor to the central and dorsolateral pons.

Characteristics and management of the offending veins in microvascular decompression surgery for trigeminal neuralgia

The optimal technique of microvascular decompression (MVD) for trigeminal neuralgia (TN) caused by venous conflict remains unclear. The objectives of this study are to characterize the offending veins identified during MVD for TN and to evaluate intraoperative technique applied for their management. From 2007 till 2019, 308 MVD surgeries were performed in 288 consecutive patients with TN, and in 58 of them, pure venous conflict was identified. In 44 patients, the offending vein was interrupted, as was done for small veins arising from the cisternal trigeminal nerve (CN V) or its root entry zone (REZ) causing their stretching (19 cases), small veins on the surface of REZ (9 cases), transverse pontine vein (TPV) compressing REZ or distal CN V (12 cases), and superior petrosal vein (SPV) using flow conversion technique (4 cases). In 14 other cases, the offending vein was relocated, as was done for the SPV or the vein of cerebellopontine fissure (8 cases), TPV (3 cases), and the vein of middle cerebellar peduncle (3 cases). Complete pain relief after surgery was noted in 49 patients (84%). No one patient experienced major neurological deterioration. Postoperative facial numbness developed in 14 patients (24%), and in 8 of them, it was permanent. In 14 patients, MRI demonstrated venous infarction of the middle cerebellar peduncle, which was associated with the presence of any (P = 0.0180) and permanent (P = 0.0002) facial numbness. Ten patients experienced pain recurrence. Thus, 39 patients (67%) sustained complete pain relief at the last follow-up (median, 48 months), which was significantly associated with the presence of any (P = 0.0228) and permanent (P = 0.0427) postoperative facial numbness. In conclusion, in cases of TN, small offending veins arising from REZ and/or distal CN V and causing their stretching may be coagulated and cut. In many cases, TPV can be also interrupted safely or considered as collateral way for blood outflow. The main complication of such procedures is facial numbness, which is associated with the venous infarction of middle cerebellar peduncle and long-term complete pain relief.

Preservation of Coexisting Normal Superior Petrosal Vein in the Microsurgical Treatment of Superior Petrosal Sinus Dural Arteriovenous Fistulas Assisted by Indocyanine Green Video Angiography

Superior petrosal sinus (SPS) dural arteriovenous fistulas (DAVFs) are a common subtype of tentorial DAVFs that often require microsurgical treatment. We have noted a rare condition involving the presence of a coexisting normal superior petrosal vein (SPV) during surgery for SPS DAVFs; this condition has not been reported in the literature. Identification and preservation of coexisting normal veins are crucial to prevent venous complications. We reviewed data of 12 patients with SPS DAVFs who underwent microsurgical treatment. Intraoperative indocyanine green video angiography was used to confirm the location of the fistula and identify the normal SPV. Postoperative radiologic examination was performed, and the clinical outcome was evaluated with the modified Rankin Scale. A coexisting normal functional SPV was found in 6 cases. Analysis of the tributaries of the SPV showed the vein of the cerebellopontine fissure was the most frequent arterialized drainage vein (66.7%), while the pontotrigeminal vein was the most frequent normal drainage vein (45.5%). The DAVFs were easily identified and disrupted using intraoperative indocyanine green video angiography. The normal SPV was also successfully preserved. All 6 patients experienced good clinical and radiologic outcomes. An SPS DAVF can coexist with a normal functional SPV, which should be preserved. Use of indocyanine green video angiography is an efficient way to identify the normal SPV.

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

BackgroundWe 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.MethodsMicrovascular 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.ResultsApplied 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 SPV in 54% of the cases and at least 1 direct tributary in 90% disturbed the operative field. The tributaries were more commonly sacrificed.ConclusionsThe 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.

Angular and metric analysis of the neural structures in the cerebellopontine angle

Introduction: The cerebellopontine angle (CPA) is a subarachnoid space in the lateral aspect of the posterior fossa. In this study, we propose a complementary analysis of the CPA from the cerebellopontine fissure.Methods: We studied 50 hemi-cerebelli in the laboratory of neuroanatomy and included a description of the CPA anatomy from the cerebellopontine fissure and its relationship with the flocculus and the 5th, 6th, 7th, and 8th cranial nerves (CN) origins.Results: The average distance from the 5th CN to the mid-line (ML) was 19.2 mm, 6th CN to ML was 4.4 mm, 7-8 complex to ML was 15.8 mm, flocculus to ML was 20.5 mm, and flocculus to 5th CN was 11.5 mm, additionally, and the diameter of the flocculus was 9.0 mm. The angle between the vertex in the flocculus and the V CN and the medullary-pontine line was 64.8 degrees.Discussion: The most common access to the CPA is through the retrosigmoid-suboccipital region and this approach can be done with the help of an endoscope. The anatomy of origins of neural structures tends to be preserved in cases of CPA lesions.Conclusion: Knowledge of the average distances between the neural structures in the cerebellar-pontine fissure and the angular relationships between these structures facilitates the use of surgical approaches such as microsurgery and endoscopy.

Suprafloccular approach via the petrosal fissure and venous corridors for microvascular decompression of the trigeminal nerve: technique notes and clinical outcomes.

OBJECTIVE Surgical exposure and decompression of the entire trigeminal nerve in a conventional lateral supracerebellar approach can be challenging because of blockages from the superior petrosal vein complex, cerebellum, and vestibulocochlear nerve. The authors demonstrate a novel suprafloccular approach via the petrosal fissure and venous corridors that can be used as a substitute for the conventional route used to treat trigeminal neuralgia and present a consecutive series of patients and their clinical outcomes. METHODS Preoperative and postoperative clinical data from 420 patients who underwent this modified approach at Hangzhou First People's Hospital between March 2012 and May 2014 were reviewed. The technique expands the working space by opening the petrosal fissure and dissecting adhesions between the vein of the cerebellopontine fissure and the simple lobule as needed. Via 3 surgical corridors, the entire trigeminal nerve is exposed and decompressed thoroughly with minimal retraction of the surrounding vital structures. RESULTS The medial one-third of the trigeminal nerve accounted for the majority (275 [65.5%] cases) of neurovascular conflict sites. The lateral corridor was used in 219 (52.1%) cases, the medial corridor was used in 175 (41.7%) cases, and the intermediate corridor was used in 26 (6.2%) cases. The entire trigeminal nerve in each patient was accessed directly and decompressed properly. At the end of the 24-month follow-up period, the rate of excellent results (Kondo score of T0 or T1) was stable at approximately 90.5%. No complications were related directly to petrosal vein or vestibulocochlear nerve injury. CONCLUSIONS Based on data from the large patient series, the authors found this suprafloccular approach via the petrosal fissure and venous corridors provides full exposure and decompression of the entire trigeminal nerve, a high cure rate, and a low neurovascular morbidity rate.

Diagnosis and management for trigeminal neuralgia caused solely by venous compression.

Trigeminal neuralgia (TN) caused solely by venous compression is uncommon. An appropriate vein management protocol for microvascular decompression (MVD) has not been established. We evaluated the management of veins for TN solely due to venous involvement. We analyzed 31 patients with TN in whom only veins were manipulated during MVD. The culprit veins smaller in diameter than the vein of the cerebellopontine fissure (VCPF) were coagulated and divided in 20 patients (divided group), while transposition was performed for larger veins in the remaining 11 patients (non-divided group). Postoperative outcomes were assessed by Barrow Neurological Institute (BNI) pain intensity score and BNI facial numbness score. Preoperative contrast-enhanced T1 spoiled gradient recalled (SPGR) imaging exhibited higher detection rates for veins (93.5%) than non-contrast fast imaging employing a steady-state acquisition image (74.2%). The transverse pontine vein (TPV) was the most frequently involved vessel. All the divided veins were small TPVs except one. The non-divided group included seven cases of large TPVs and four involving the main trunk of the superior petrosal vein or its large tributaries. The median follow-up duration was 33months. Pain relief was achieved immediately after the surgery in 28 (90.3%) and within a month in the remaining 3 (9.7%) patients. Numbness was present in seven (22.6%) patients at the final follow-up. Recurrence was observed in only two (10.0%) patients in the divided group compared with four (36.4%) patients in the non-divided group. Comparison at the final follow-up revealed that the divided group had superior outcome compared to the non-divided group. Contrast-enhanced T1 SPGR imaging is crucial to detect small veins in the preoperative diagnosis. Division of the culprit veins is recommended if the diameter is smaller than the VCPF as it provides a better outcome and lower recurrence rate than transposition.

Classification of the Superior Petrosal Veins and Sinus Based on Drainage Pattern

The increasing number of reports of complications after sacrificing the superior petrosal veins, the largest veins in the posterior fossa, has led to a need for an increased understanding of the anatomy of these veins and the superior petrosal sinus into which they empty. To examine the anatomy of the superior petrosal veins and their size, draining area, and tributaries, as well as the anatomic variations of the superior petrosal sinus. Injected cadaveric cerebellopontine angles and 3-dimensional multifusion angiography images were examined. The 4 groups of the superior petrosal veins based on their tributaries, course, and draining areas are the petrosal, posterior mesencephalic, anterior pontomesencephalic, and tentorial groups. The largest group was the petrosal group. Its largest tributary, the vein of the cerebellopontine fissure, was usually identifiable in the suprafloccular cistern located above the flocculus on the lateral surface of the middle cerebellar peduncle. The medial or lateral segment of the superior petrosal sinus was absent in 40% of cerebellopontine angles studied with venography. The superior petrosal veins and their largest tributaries, especially the vein of the cerebellopontine fissure, should be preserved if possible. Obliteration of superior petrosal sinuses in which either the lateral or medial portion is absent may result in loss of the drainage pathway of the superior petrosal veins. Preoperative assessment of the superior petrosal sinus should be considered before transpetrosal surgery in which the superior petrosal sinus may be obliterated.

Left retrosigmoid craniotomy for cavernous malformation of the middle cerebellar peduncle

We present a 25-year-old female with a history of multiple intracranial cavernous malformations complaining of vertigo. Imaging is significant for increasing size of a lesion in her left cerebellar peduncle. Given the proximity to the lateral border of the cerebellar peduncle, a retrosigmoid approach was chosen. After performing a craniotomy that exposed the transverse-sigmoid sinus junction, the dura was open and reflected. The arachnoid was sharply opened and cerebrospinal fluid was aspirated to allow the cerebellum to fall away from the petrous bone. The cerebellopontine fissure was then opened to visualize the lateral wall of the cerebellar peduncle. The cavernous malformation was entered and resected. The video can be found here: http://youtu.be/P7mpVbaCiJE .

Importancia neuroquirúrgica del complejo venoso petroso superior

To study the microsurgical anatomy of the superior petrosal venous complex (SPVC). We conducted a descriptive and prospective study. Six injected specimens were used (12 sides). The microsurgical anatomy of the SPVC was studied by means of an anterior, retrosigmoid and transpetrosal approach. Neurosurgical equipment, 0-degree rigid endoscopy and OPMI-1 surgical microscope with 6× to 20× magnification were all used in this study. The venous drainage pattern toward the superior petrosal sinus was analysed, as were the formation of tributary veins, the relationship with the trigeminal nerve and the anatomical variants of SPVC. The SPVC was present in all cases. A tributary, cerebellopontine fissure vein was identified in 100% of cases. The venous drainage pattern of the SPVC was divided into medial, intermediate and lateral with respect to the suprameatal crest. The SPVC was simple in 8 sides and duplicate in 4 sides. A triangle formed by the tentorium, the SPVC and part of the tentorial and petrosal surface of the cerebellum was also observed in the study. This triangle was called the petrosal-tentorial triangle. It is important to understand the microsurgical anatomy of the SPVC. Therefore, we propose the petrosal-tentorial triangle as a neurosurgical route for the management of pathologies from the cerebellopontine angle to the superior petroclival region.

Clinical features and surgical treatment of trigeminal neuralgia caused solely by venous compression

To summarize our experience and lessons of microvascular decompression surgery for trigeminal neuralgia caused solely by venous compression. Fifteen patients with idiopathic trigeminal neuralgia caused by venous compression only underwent microvascular decompression. The entire course of the trigeminal root was explored thoroughly; and coagulating and cutting techniques were preferred in decompressing the culprit veins. Their clinical features, outcomes and operative complications were analyzed. The compressing veins included the transverse pontine vein in five cases (33.3%), the transverse pontine vein and the vein of middle cerebellar peduncle in one (6.7%), the transverse pontine vein and the vein of cerebellopontine fissure in one (6.7%), the superior petrosal vein in three (20%), the pontotrigeminal vein in one (6.7%), the vein of the cerebellopontine fissure in two (13.3%), and the plexus venosus or venule in two (13.3%). After microvascular decompression, 11 cases (73.3%) had "excellent" or "good" pain relief. Four cases (26.7%) failed the first surgery; and two of them underwent re-operation and got "excellent" pain relief. Postoperative facial numbness appeared in four cases, due to injury to trigeminal nerve when coagulation. The transverse pontine vein is the most common offending vein. For this type of trigeminal neuralgia, coagulating and cutting techniques are preferred in decompressing the culprit veins. The entire course of the trigeminal root should be explored and decompressed. Following these principles, excellent or good pain relief could be achieved in most cases; and recurrence is rare. However, sometimes injury to the nerve is unavoidable when coagulating the culprit vein.

Transhorizontal -cerebellopontine fissure approach for microvascular decompression of trigeminal neuralgia

：Objective A new approachof transhorizontai - cerebellopontine fissure for microvascular decompression ( MVD) oftrigeminal neuralgia ( TN) was reported. Method A retrospetive analysis of the data of 17consecutive patients with TN by transhorizontai -cerebellopontine fissure approach for MVDwas performed. Results The dissection of the cerebellar horizontal - cerebellopontinefissures of the 17 cases was performed sucessfully which allowed easy identification ofthe root entry zone of trigeminal nerve and the offending vessel(s). Offending vesselswere found in all of the 17 cases. Postoperatively,15 cases were pain free immediately and2 cases were pain free after 2 and 3 days respectively. One case developed herpes labialisand one case slightly face numbness. Conclusions The transhorizontai -cerebellopontinefissure approach for MVD of TN could avoid the defects of standard suboccipitalretrosigmoidal approach, which allowes easy identification of the root entry zone oftrigeminal nerve and offending vessel(s). Minimal retraction of facial nerve andvestibulocochlear nerve could be achieved thus reduction of complication rate of heaingdisturbance and facial paralysis couild be found.

Microsurgical anatomy of the subtentorial supracerebellar and infracerebellar approach to the trigeminal and facial nerves

The microsurgical anatomy of the subtentorial supracerebellar approach to the trigeminal nerve and the infracerebellar lateral approach to the facial nerve was examined in five formalin-fixed adult cadavers. Particular attention was directed to the arrangement of the blood vessels within the posterior fossa, especially the superior petrosal vein and its tributaries, the superior cerebellar artery (SCA), the anterior inferior cerebellar artery (AICA) and the posterior inferior cerebellar artery (PICA). The subtentorial supracerebellar approach provides satisfactory exposure of both, the lateral segment of the SCA, which is the most common vessel involved in the neurovascular conflict resulting in trigeminal neuralgia and the y-inverted shaped superior petrosal vein. The latter results more often from the convergence of the pontotrigeminal vein and the vein of the cerebellopontine fissure. The relationship between the AICA, the PICA and the vertebral artery to the facial-vestibulocochlear complex was studied by an infracerebellar lateral approach. The subpial course of the facial nerve, where the vascular compression is usually found which results in hemifacial spasm, was also documented. These two approaches, as well as a historical review of the evolution of these surgical techniques, since the first description by Dandy, are discussed.

V-6-81 - Microvascular decompression for hemifacial spasm: Technique and operative results

The microsurgical anatomy of the subtentorial supracerebellar approach to the trigeminal nerve and the infracerebellar lateral approach to the facial nerve was examined in five formalin-fixed adult cadavers. Particular attention was directed to the arrangement of the blood vessels within the posterior fossa, especially the superior petrosal vein and its tributaries, the superior cerebellar artery (SCA), the anterior inferior cerebellar artery (AICA) and the posterior inferior cerebellar artery (PICA). The subtentorial supracerebellar approach provides satisfactory exposure of both, the lateral segment of the SCA, which is the most common vessel involved in the neurovascular conflict resulting in trigeminal neuralgia and the y-inverted shaped superior petrosal vein. The latter results more often from the convergence of the pontotrigeminal vein and the vein of the cerebellopontine fissure. The relationship between the AICA, the PICA and the vertebral artery to the facial-vestibulocochlear complex was studied by an infracerebellar lateral approach. The subpial course of the facial nerve, where the vascular compression is usually found which results in hemifacial spasm, was also documented. These two approaches, as well as a historical review of the evolution of these surgical techniques, since the first description by Dandy, are discussed.

Microsurgery of the fourth ventricle: Part 1. Microsurgical anatomy.

Operations on the 4th ventricle offer the potential for injury of the brain stem, cerebellum, cranial nerves, and major cerebellar arteries and veins. Twenty-five cadaver brains were examined using 3x to 25x magnification to define the relationship of these vital structures to the 4th ventricle. The 4th ventricle has a roof, a floor, and two lateral recesses. Most of the cranial nerves arise near the floor, which sits on the pons and medulla. The superior half of the roof, formed by the superior medullary velum, lingula, and cerebellar peduncles, is intimately related to the cerebellomesencephalic fissure, the superior cerebellar arteries, and the vein of the cerebellomesencephalic fissure. The inferior half of the roof, formed by the inferior medullary velum, tela choroidea, nodule, and uvula, is intimately related to the cerebellomedullary fissure, the posterior inferior cerebellar arteries, and the veins of the cerebellomedullary fissure. The lateral recesses and adjoining parts of the roof and floor are intimately related to the cerebellopontine fissures, the anterior inferior cerebellar arteries, and the veins of the cerebellopontine fissure. The cerebellar peduncles converge on and form a major part of the ventricular surface. The hili of the dentate nuclei abut on the superolateral recesses of the ventricle near the superior poles of the tonsils.