Clinical and Educational Aspects of Neuroimaging in Microsurgery of the Posterior Fossa: A Comprehensive Review.

The clinical and educational value of modern high-resolution magnetic resonance imaging (MRI) and image processing in neurovascular diseases of the posterior fossa with regard to preoperative planning and intraoperative comparison with the actual anatomical situation was consecutively evaluated. Patients with trigeminal neuralgia (TN), hemifacial spasm (HFS), glossopharyngeal neuralgia (GN) and arterial hypertension (HTN) were analyzed. The high-resolution MRI data was segmented and visualized three-dimensionally using computer graphics methods. New anatomical insights were gained, such as the classification of neurovascular compression (NVC) in HFS and GN. It was also possible to visualize the pathognomonic cerebrospinal fluid signal in patients with TN for the first time. Using the new imaging methods, pregnant hypertensive patients were examined and the existence of NVC was confirmed for the first time, and the findings were compared to other studies dealing with NVC syndromes. This review gives an overview on the established methods of neuroimaging and image processing of neurovascular structures in the posterior fossa with the focus on clinical and educational aspects.

Neurooncological Rehabilitation in Diffuse Gliomas.

BACKGROUND: With the further advancement of surgical technology and modern tumor-targeted treatment strategies, longer survival rates can be achieved in diffuse gliomas. Pre- and post-therapeutic physical and cognitive deficits are frequently associated with gliomas. The clinical impact of physical therapy and rehabilitation on neurooncological disorders has not been analyzed consecutively. This study investigates the clinical effect of rehabilitation in patients with diffuse gliomas. METHODS: Patients with surgically and radio-/oncologically treated diffuse gliomas were recruited into this study. They were admitted to an inpatient program for three weeks. The patients underwent physical and occupational therapy, exercise programs, and psychooncological support. The outcome measures included motor strength, mobility, neuropsychological deficits, and tumor localization-dependent symptoms for the statistical determination and comparison of the respective Eastern Cooperative Oncology Group (ECOG) scores on admission and discharge by a two-tailed t-test. RESULTS: A total of 25 patients (f/m: 11/14) with diffuse gliomas were recruited into the program. Four patients (16%) had CNS WHO grade 2, seven patients (28%) had grade 3, and 14 patients (56%) had grade 4 tumors. Major improvement in motor, cognitive, and functions of the daily activities was achieved in the examined population. Major improvement in motor, cognitive, and neurological functions of the daily activities screened in the admission of all patients was achieved. The comparison of the ECOG scores determined on admission and on discharge showed a statistical significance derived from the undertaken t-test with a p-value <0.05. CONCLUSION: We herein show that a clearly defined inpatient rehabilitation protocol significantly enables the improvement of the quality of life of patients with diffuse gliomas. The effectiveness of the exercise program and psychooncological assistance was confirmed by the course of patient-reported functions. Based on the limited number of our patient collective, multicenter studies with broader patient sizes should be performed to confirm our significant results.

The Mini-Spheno-Supraorbital Craniotomy for Treatment of Ruptured Anterior Circulation Aneurysms.

Objective:Yasargil introduced the pterional approach mainly for clipping of anterior circulation (AC) aneurysms. We implemented the mini-spheno-supraorbital (MSS) craniotomy, changing the shape and reducing the size of the classical pterional craniotomy. The literature on clipping ruptured AC aneurysms through reduced-in-size craniotomies is sparse. This study aims to describe the technique and present our experience in clipping ruptured AC aneurysms through the MSS approach. Materials and methods: The MSS craniotomy was used in 114 cases of clipping ruptured AC aneurysms. A single burr hole was placed at the "keyhole" and an ellipsoid bone flap in the spheno-supraorbital region was raised. The tabula interna was thinned circumferentially, the roof of the orbit was flattened. Among aneurysm clipping, the lamina terminalis and the subarachnoid basal cisterns were opened. The imaging modality, the severity of the subarachnoid hemorrhage (SAH) according to Hunt & Hess (H&H), the size of the bone flap, the surgery duration and the aneurysm obliteration rate seen at the postoperative DSA were examined. Results:Out of all patients in the study, 71% had exclusively CT-angiogram as initial imaging and suffered low-grade (H&H I°) SAH (71%). The mean size of the bone flap was 1.6 x 4.5 cm (1.3 x 4.3 - 2 x 8.5 cm). The approach allowed adequate 360°-dissection, sufficient proximal and distal control, brain relaxation though laminoterminotomy and opening of the basal cisterns. The mean duration from skin incision to clip application was 130 minutes (64-236 mins). Total obliteration rate was 97.3%. Conclusion:The MSS craniotomy is feasible in terms of safety and speed for clipping of ruptured AC aneurysms especially in lower-grade SAH.

Tissue Healing in Hemicraniectomy.

Introduction Decompressive hemicraniectomy (DHC) is a last-resort treatment for refractory intracranial hypertension. Perioperative morbidity is associated with high risks of wound healing disturbances (WHD). Recently, a retromastoidal frontoparietooccipital (RMF) incision type was performed to avoid healing disturbance due to enhanced tissue flap perfusion compared to the classical reverse "question mark" ("Dandy flap") incision. The goal of this study was to analyze the details of tissue healing problems in DHC.  Materials and methods A total of 60 patients who underwent DHC were retrospectively analyzed. In 30 patients the "Dandy flap" incision (group A) and in 30 patients the RMF incision (group B) was made. Since no evidence-based data for the incision type that favors better wound healing exists, the form of incision was left at the surgeon´s discretion. Documentation of the patients was screened for the incidence of WHD: wound necrosis, dehiscence, and cerebrospinal fluid (CSF) leakage. Patient age, the time interval from surgery until the appearance of WHD, the length of surgeries in minutes, and the indications of the DHC were analyzed. A Chi-square test of independence was performed to examine the relationship between the incision type and the appearance of WHD with the statistical significance level set at p<0.05. The mean age of the patients, the mean time interval from surgery until the occurrence of WHD, and the mean length of the surgery between the two groups were compared using an independent sample t-test with the statistical significance level set at p<0.05. Results The most common indication for DHC in both groups was malignant MCA infarction (n=20, 66.6% for group A and n=16, 53.3% for group B). CSF leakage was 20% of the most frequent WHD in each group. Wound necrosis was observed only in group A. Although group B showed 13.3% fewer WHD than group A, this difference was not statistically significant. There was no statistically significant difference in the time range between surgery and the occurrence of WHD between the two groups. The length of surgery in group B was significantly shorter than in group A (120.2 mins vs. 103.7 mins). Conclusion A noticeable trend for reduced WHD was observed in the patient group using the RMF incision type although the difference was not statistically significant. We praise that the RMF incision allows an optimized skin-flap vascularization and, thereby, facilitates better wound healing. We were able to show a statistically shorter length of surgery with the RMF incision in contrast to the classic "Dandy flap" incision. Larger multicenter studies should be implemented to analyze and address the major advantages and pitfalls of the routinely applied incision techniques.

The evaluation of the usefulness of CO2 laser in microsurgical resection of brain tumors.

Background: Since its introduction to surgery, the CO2 laser has been used in the treatment of various neurosurgical pathologies as it combines cutting, vaporizing, and coagulating properties in one tool and has a safe penetration depth. In this case series of 29 patients, we present the evaluation of the usefulness of the closed system type - sealed tube surgical CO2 laser in the surgical removal of brain tumors. Methods: The Sharplan 40C model SurgiTouch, sealed tube type CO2 laser, was used in the resection of 29 brain tumors; 13 meningiomas, six metastases, nine gliomas, and one acoustic neuroma. The same senior surgeon (BT) assessed and classified the benefit provided by the CO2 laser in the resection of the neoplasms to considerable (Group 1), moderate (Group 2), and poor (Group 3). Results: Group 1 included 14 patients with 13 meningiomas and one acoustic neuroma, Group 2 included six patients, all of whom had metastases, and Group 3 included nine patients of which six had glioblastoma and three astrocytoma. No complications or technical problems occurred due to the use of the CO2 laser. Conclusion: The CO2 laser is a valuable complementary tool in brain tumor surgery displaying high efficacy and practicality in the resection of neoplasms which are fibrous and have hard consistency. It has high acquisition and maintenance cost and cannot replace the bipolar diathermy. The newest generation of flexible CO2 laser fiber provides more ergonomy and promises new perspectives of its neurosurgical use in the modern era.

Differentiation of arterial and venous neurovascular conflicts estimates the clinical outcome after microvascular decompression in trigeminal neuralgia.

BACKGROUND: Balanced Steady State Free Precession (b-SSFP) sequences and the newly developed Fast-Spin-Echo (FSE)-sequences enable an optimized visualization of neurovascular compression (NVC) in patients with trigeminal neuralgia (TN). Arterial conflicts are mostly associated with a favorable outcome of microvascular decompression (MVD) compared to venous conflicts. An additional Time-of-Flight (TOF) angiography provides the differentiation between offending arteries and veins and a precise counselling of the patient concerning postoperative pain relief. The goal of this study was to analyze the reliability and impact of the combination of highly-resoluted MRI techniques on the correct prediction of the vessel type and the estimation of postoperative outcome of microvascular decompression (MVD). METHODS: In total, 48 patients (m/f: 32/16) underwent MVD for TN. All the preoperative imaging data (T2: b-SFFP and FSE, MRA: TOF) were compared to the intraoperative microsurgical findings during MVD. b-SFFP was available in 14 patients, FSE in 34 patients and an additional TOF sequence was available in 38 patients (9 times in combination with b-SSFP, 29 times in combination with FSE). The patients were categorized into four subgroups: 1) NVC negative, 2) venous NVC, 3) arterial NVC, 4) combined arterial and venous NVC. The preoperative MRI findings were compared to the intraoperative morphological findings. Postoperative pain relief was quantified by the Barrow Neurological Institute pain score. RESULTS: Twenty-five purely arterial NVC, 9 purely venous NVC and 5 combined arterial and venous NVC were detected by MRI. In 9 cases NVC was absent on MRI. Overall, the MRI findings correctly predicted the intraoperative findings in 91.7% of the 48 patients. The percentage of correct prediction increased from 80 to 94.7%, when TOF angiography was adjoined. CONCLUSION: The visualization of the trigeminal nerve using sequences such as b-SSFP or FSE in combination with TOF angiography enables an optimized delineation of arterial and venous neurovascular conflicts and may allow a more reliable differentiation between veins and arteries, resulting in superior prediction of postoperative pain relief compared to T2 imaging data alone.

Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase 2 Expression in Brain Arteriovenous Malformations and its Association with Brain Arteriovenous Malformation Size.

BACKGROUND AND OBJECTIVE: Brain arteriovenous malformations (bAVM) are severe conditions that can cause severe neurologic deficits and mortality. The underlying cellular and molecular mechanisms associated with bAVM growth and rupture remain unclear. The objective of this study was to explore the potential role of PLOD2 (procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2) in the pathophysiology of bAVM. METHODS: Expression and localization of PLOD2 were analyzed on tissue microarrays from patients with bAVM (n = 60) by immunohistochemistry. Correlations between PLOD2 levels and clinical parameters were examined with a Pearson test or Spearman rank correlation coefficient. Comparison between different clinical parameters was performed using a t test or nonparametric Mann-Whitney U test. A Fisher exact test was used for categorical data. RESULTS: PLOD2 was mainly expressed within the tunica media of the blood vessels. High levels of PLOD2 expression correlated with bAVM size (linear regression, P = 0.0083, R2=0.158). Small bAVM showed a higher frequency of hemorrhage compared with large ones (P = 0.001). Although PLOD2 was not directly associated with bAVM hemorrhage, high PLOD2-expressing bAVM had a lower frequency of hemorrhage compared with low or medium PLOD2-expressing bAVM (25% vs. 63% and 75%, respectively). CONCLUSIONS: This study reports for the first time the expression of PLOD2 in bAVM and suggests a potential role of PLOD2 in bAVM pathophysiology. These findings contribute to an better understanding of the microenvironment of bAVM and may foster the development of improved therapeutic strategies for this disease.

Fleece-Bound Tissue Sealing in Microvascular Decompression.

AIM: Cerebrospinal fluid (CSF) leakage is a feared complication after microvascular decompression (MVD). In this study, we present our experience of fleece-bound tissue sealing in MVD with an aim to minimize the rate of postoperative CSF leakage. MATERIAL AND METHODS: We treated 50 patients (female/male: 26/24) with neurovascular compression (NVC) syndromes (trigeminal neuralgia, hemifacial spasm and glossopharyngeal neuralgia) by MVD from 2003 to 2006. All patients underwent retromastoid craniectomy and duraplasty by fleece-bound tissue sealing using the so-called "sandwich technique" by a three-layer reconstruction and cranioplasty. RESULTS: In 49 (98%) of 50 patients, we did not observe postoperative CSF leakage. One patient (2%) suffered postoperative CSF leakage and required surgical revision. CONCLUSION: Fleece-bound tissue sealing by a three-layer reconstruction is effective and safe in the prevention of cerebrospinal fluid leakage in microvascular decompression.

New Clinical and Morphologic Aspects in Trigeminal Neuralgia.

OBJECTIVE: High-resolution magnetic resonance imaging can be used to delineate the morphology of neurovascular compression (NVC) in detail. This study focuses on essential morphologic parameters in relation to the clinical appearance of patients with trigeminal neuralgia (TN). METHODS: A total of 180 patients with TN underwent magnetic resonance-constructive interference in steady state/time of flight. Parameters of the affected nerves (length) and causative vessels were examined: (1) the relationship between the NVC site (caudal/cranial/laterocaudal/mediocranial) and affected area (V1, V2, V3); (2) nerve deformity; (3) vascular loop; (4) existence of a "cerebrospinal fluid (CSF) sign" by a separation of trigeminal fascicles by a vessel; and (5) localization of the causative vessel. RESULTS: A total of 10 patients with V1 affection showed 6 caudal, 0 cranial and laterocaudal, and 4 mediocranial NVC; 26 patients with V2 affection showed 17 caudal, 0 cranial, 1 laterocaudal, and 8 mediocranial NVC; 29 patients with V3 affection showed 23 caudal, 1 cranial, 3 laterocaudal, and 2 mediocranial NVC; 25 patients with V1 and V2 affection showed 17 caudal, 1 cranial, 0 laterocaudal, and 7 mediocranial NVC; 36 patients with V2 and V3 affection showed 30 caudal, 3 cranial, 1 laterocaudal, and 2 mediocranial NVC; and 6 patients with V1, V2, and V3 affection showed 4 caudal, 1 cranial, 0 laterocaudal, and 1 mediocranial NVC. A total of 63 patients (35%) showed nerval deformity by distorsion of the trigeminal fascicles from compressing vessel; 37 of 39 patients (95%) with right-sided deformity showed right-sided TN; and 21 of 22 patients (95%) with left-sided TN showed left-sided nerve deformation. Two patients with bilateral nerve deformity showed bilateral TN. Rostral superior cerebellar artery (SCA) loop compression was seen in 24 patients (17%), caudal SCA loop compression was seen in 10 patients (7%), and double SCA loop compression was seen in 33 patients (23%). Sandwich compression was seen in 18 (12%), and a CSF sign was seen in 24 patients. All 24 patients (100%) with a CSF sign had V1 affection. CONCLUSIONS: The CSF sign is pathognomonic for V1 affection. Vascular loops from cranial on the nerve were the most frequent types of compression in all areas of pain, followed by mediocranial loops. This evaluation is reproducible and contributes to the role of magnetic resonance imaging and a classification of findings in the preoperative evaluation of NVC.

Hearing preservation in acoustic neuroma resection: Analysis of petrous bone measurement and intraoperative application.

BACKGROUND: There is an increased risk for labyrinthine injury for the resection of acoustic neuromas (AN) on the suboccipital, retrosigmoid approach. Prognostic factors should be analyzed for the postoperative hearing function. METHODS: We examined 51 patients with ANs using preoperative intact hearing function. Audiological data were obtained by pure tone audiogram (PTA) and speech audiogram. The preoperative and postoperative anatomical localization of the labyrinth was measured with specific distances regarding the tumor and corresponding anatomy of the posterior fossa by high-resolution magnetic resonance imaging (MRI). RESULTS: Postoperative MRI controls confirmed no injuries to the labyrinth (0%). The postoperative hearing results showed 100% hearing preservation for T1-tumors (<1 ml/<1.1 cm), 50% for T2-tumors (1-4 ml/1.1-1.8 cm), 40% for T3-tumors (4-8 ml/1.8-2.3 cm) and 18% for T4-tumors (>8 ml/>2.3 cm). Postoperative deafness was seen in all cases with ventral tumor extension higher than 5.5 mm. Postoperative loss of hearing was seen in all cases with hearing preservation with 6-8% of speech discrimination and an increase in the hearing threshold of 12 dB in the PTA compared to the preoperative hearing status. CONCLUSION: Petrous bone measurement by high-resolution MRI data enables safe surgical exposure of the internal acoustic canal with avoidance of injury to the labyrinth and a better postoperative prognosis, especially for intrameatal ANs and for the resection of intrameatal portions of larger neuromas. The prognostic factors enable the patients and the surgeon a better estimation of postoperative results regarding deafness and postoperative hypacusis and support a consolidated treatment planning.

Classification of neurovascular compression in glossopharyngeal neuralgia: Three-dimensional visualization of the glossopharyngeal nerve.

BACKGROUND: We introduce a method of noninvasive topographical analysis of the neurovascular relationships of the glossopharyngeal nerve (CN IX) by three-dimensional (3D) visualization. Patients with glossopharyngeal neuralgia (GN) resulting from neurovascular compression (NVC) were studied. METHODS: 15 patients with GN were prospectively examined with 3D visualization using high-resolution magnetic resonance imaging with constructive interference in steady state (MR-CISS). The datasets were segmented and visualized with the real, individual neurovascular relationships by direct volume rendering. Segmentation and 3D visualization of the CN IX and corresponding blood vessels were performed. The 3D visualizations were interactively compared with the intraoperative setup during microvascular decompression (MVD) in order to verify the results by the observed surgical-anatomical findings. RESULTS: 15 patients (female/male: 5/10) were examined. All of them underwent MVD (100%). Microvascular details were documented. The posterior inferior cerebellar artery (PICA) was the most common causative vessel in 12 of 15 patients (80%), the vertebral artery (VA) alone in one case (6.7%), and the combination of compression by the VA and PICA in 3 patients (13.3%). We identified three distinct types of NVC within the root entry zone of CN IX. CONCLUSION: 3D visualization by direct volume rendering of MR-CISS data offers the opportunity of noninvasive exploration and anatomical categorization of the CN IX. It proves to be advantageous in supporting to establish the diagnosis and microneurosurgical interventions by representing original, individual patient data in a 3D fashion. It provides an excellent global individual view over the entire neurovascular relationships of the brainstem and corresponding nerves in each case.

Preoperative MRI in neurovascular compression syndromes and its role for microsurgical considerations.

BACKGROUND: Neurovascular compression (NVC) in the posterior fossa is characterized by complex, three-dimensional (3D) neurovascular relationships at the root entry zones (REZ) and other parts of cranial nerves, resulting in syndromes such as trigeminal neuralgia (TN), hemifacial spasm, vertigo and glossopharyngeal neuralgia. Microvascular decompression (MVD) requires microsurgical experience and 3D orientation within the cisternal spaces to achieve adequate clinical results. The vascular structures in anatomical relation to the trigeminal nerve root at the lateral pontine aspect of the brainstem should be examined and maximally decompressed to minimize the risk of recurrent TN. Indication was traditionally based on clinical decisions, only. New MR techniques have become available, and their chances and potential impact should be evaluated in this study. METHODS: In our study we examined 7 consecutive patients with TN and one patient with vertigo analyzing the details of NVC with high resolution magnetic resonance (MR) imaging in correlation to the intraoperative findings. All 8 patients underwent 1.5 T MRI with T2 fast spin echo. The MRI data were retrospectively analyzed and compared to the intraoperative findings with the focus on the length of the corresponding cranial nerve and topography of the NVC site, the distance of the location of the NVC from the surface of the brainstem. RESULTS: The superior cerebellar artery (SCA) was the most common causative vessel in 5 of 8 cases (62.5%), the anterior inferior cerebellar artery (AICA) in 2 of 8 cases (25%) and veins in 1 of 8 cases (12.5%). The cisternal length of the examined trigeminal nerve on the high resolution MR images at the affected side ranged from 8.1mm to 10.8mm and on the unaffected contralateral sides from 9.4mm to 11.4mm. The vestibular nerve in one vertigo patient had an equal cisternal length of 18.0mm on either side, whereas the distance of the neurovascular conflict site was 8.0mm from the surface of the flocculus. The distance of the neurovascular conflict location site to the brainstem ranged from 1.4mm to 8.5mm on the reviewed MR image slices. One patient with vertigo showed an AICA loop in the MR images, which was confirmed intraoperatively. All causative vessels on the trigeminal nerve performed loops from cranially to caudally. All 7 patients (100%) with TN and one vertigo patient were symptom-free since discharge. CONCLUSION: We show that high resolution MR images provide reliable and detailed information on corresponding intraoperative anatomy. Especially in unusual cases, the application of such MR techniques and preoperative evaluation may contribute to indication, planning, and also for teaching purposes.

Intraoperative three-dimensional visualization in microvascular decompression.

OBJECT: The authors systematically analyzed 3D visualization of neurovascular compression (NVC) syndromes in the operating room (OR) during microvascular decompression (MVD). METHODS: A total of 50 patients (26 women and 24 men) with trigeminal neuralgia (TN), hemifacial spasm (HFS), and glossopharyngeal neuralgia (GN) were examined and underwent MVD. Preoperative imaging of the neurovascular structures was performed using constructive interference in the steady state magnetic resonance (CISS MR) imaging, which consisted of 2D image slices. The 3D visualization of the neurovascular anatomy is generated after segmentaion of the CISS MR imaging in combination with direct volume rendering (DVR). The 3D representations were stored on a personal computer (PC) that was mounted on a mobile unit and transferred to the OR. During surgery, 3D visualization was applied by the surgeon with remotely controlled plasma-sterilized devices such as a wireless mouse and keyboard. The position of the 3D visualized neurovascular structures at the PC monitor was determined according to the intraoperative findings observed through the operating microscope. RESULTS: The system was stable during all neurosurgical procedures, and there were no operative or technical complications. Interactive adjustment of the 3D visualization guided by the view through the microscope permitted observation of the neurovascular relationships at the brainstem. Vessels covered by the cranial nerves could be noninvasively viewed by intraoperative 3D visualization. Postoperatively, the patients with TN and GN experienced pain relief, and the patients with HFS attained resolution of their facial tics. Vascular compression of nerves was explored in all 50 patients during MVD. Intraoperative 3D visualization delineated the compressing vessels and respective cranial nerves in 49 (98%) of 50 patients. CONCLUSIONS: Interactive 3D visualization by DVR of high-resolution MR imaging data offered the opportunity for noninvasive virtual exploration of the neurovascular structures during surgery. An extended global survey of the neurovascular relationships was provided during MVD in each case. The presented method proved to be extremely advantageous for optimizing microneurosurgical procedures, supporting superior safety and improving the operative results when compared with the conventional strategy. This modality proved to be a very valuable teaching instrument and ensured the improvement of neurosurgical quality.

Classification of neurovascular compression in typical hemifacial spasm: three-dimensional visualization of the facial and the vestibulocochlear nerves.

OBJECT: In this paper, the authors introduce a method of noninvasive anatomical analysis of the facial nerve-vestibulocochlear nerve complex and the depiction of the variable vascular relationships by using 3D volume visualization. With this technique, a detailed spatial representation of the facial and vestibulocochlear nerves was obtained. Patients with hemifacial spasm (HFS) resulting from neurovascular compression (NVC) were examined. METHODS: A total of 25 patients (13 males and 12 females) with HFS underwent 3D visualization using magnetic resonance (MR) imaging with 3D constructive interference in a steady state (CISS). Each data set was segmented and visualized with respect to the individual neurovascular relationships by direct volume rendering. Segmentation and visualization of the facial and vestibulocochlear nerves were performed with reference to their root exit zone (REZ), as well as proximal and distal segments including corresponding blood vessels. The 3D visualizations were interactively compared with the intraoperative situation during microvascular decompression (MVD) to verify the results with the observed microneurosurgical anatomy. RESULTS: Of the 25 patients, 20 underwent MVD (80%). Microvascular details were recorded on the affected and unaffected sides. On the affected sides, the anterior inferior cerebellar artery (AICA) was the most common causative vessel. The posterior inferior cerebellar artery, vertebral artery, internal auditory artery, and veins at the REZ of the facial nerve (the seventh cranial nerve) were also found to cause vascular contacts to the REZ of the facial nerve. In addition to this, the authors identified three distinct types of NVC within the REZ of the facial nerve at the affected sides. The authors analyzed the varying courses of the vessels on the unaffected sides. There were no bilateral clinical symptoms of HFS and no bilateral vascular compression of the REZ of the facial nerve. The authors discovered that the AICA is the most common vessel that interferes with the proximal and distal portions of the facial nerve without any contact between vessels and the REZ of the facial nerve on the unaffected sides. CONCLUSIONS: Three-dimensional visualization by direct volume rendering of 3D CISS MR imaging data offers the opportunity of noninvasive exploration and anatomical categorization of the facial nerve-vestibulocochlear nerve complex. Furthermore, it proves to be advantageous in establishing the diagnosis and guiding neurosurgical procedures by representing original MR imaging patient data in a 3D fashion. This modality provides an excellent overview of the entire neurovascular relationship of the cerebellopontine angle in each case.