Giant Arachnoid Granulations: Diagnostic Workup and Characterization in Three Symptomatic Adults.

Giant arachnoid granulations (GAGs) are poorly investigated. Here, we document clinical findings associated with five new GAGs and illustrate the anatomical composition of these structures as well as diagnostic considerations in three symptomatic adults. The GAGs ranged from 1.1 to 3.6 cm (mean, 2.2 cm) in maximum dimension and manifested in middle-aged individuals who presented with long-standing brain mass and/or chronic headache. On imaging examinations, the tissues appeared as irregular parasagittal and/or perisinus structures that demonstrated heterogeneous internal elements. The GAGs abutted dura, extended through calvarial marrow spaces, and impinged on dural venous sinuses, causing their stenosis. The histologic workup of two GAG specimens resected from separate individuals revealed central collagen with pronounced internal vascular proliferation. One specimen additionally exhibited reactive changes within the lesion, including venous thrombosis, hemorrhage, and conspicuous inflammation. The salient immune component consisted of a foam cell-rich infiltrate that obstructed subcapsular and internal sinusoidal GAG spaces. Within this specimen, meningothelial hyperplasia was also appreciated. Notably, proliferated lymphatic vascular elements were additionally observed within the structure, extending into deep central collagen regions and engulfing many extravasated erythrocytes in the subcapsular space. In both surgically treated patients, symptoms resolved completely following resection. This report is the first to definitively depict reactive vascular and immunological changes within GAGs that were clinically associated with headache. The frequency of reactive changes within these meningeal structures is unclear in the literature, as GAGs are rarely sampled and investigated. Further systematic analyses are warranted to elucidate the causes and consequences of GAG genesis and their roles in physiology and disease states.

Arachnoid Granulation Causing Unilateral Pulsatile Tinnitus Treated With Dural Venous Sinus Stenting.

BACKGROUND: Large arachnoid granulations that protrude into dural venous sinuses and partially obstruct outflow are an underappreciated etiology of pulsatile tinnitus (PT). Endovascular dural venous sinus stenting is thought to diminish turbulent venous outflow and may relieve obstruction caused by arachnoid granulations. METHODS: Four patients at two institutions were evaluated for unilateral PT. Magnetic resonance imaging and digital subtraction angiography revealed moderate-to-severe stenoses from large arachnoid granulations within the implicated transverse sinus. All patients underwent venous manometry and endovascular sinus stenting. RESULTS: All patients experienced immediate and complete remission of their PT. Stenoses were relieved by a mean of 93% by Warfarin-Aspirin Symptomatic Intracranial Disease criteria. There were no procedural or periprocedural complications. All patients continued to report complete symptom resolution at a mean of 8-month follow-up. CONCLUSIONS: PT from arachnoid granulations are an underappreciated pathomechanism. Endovascular dural venous sinus stenting is an effective intervention for treating unilateral PT secondary to large arachnoid granulation.

Dural Venous Sinus Arachnoid Granulations in Patients with Pulsatile Tinnitus.

OBJECTIVE: To determine the relationship, if any, between dural venous sinus arachnoid granulations (AGs) and pulsatile tinnitus. STUDY DESIGN: Retrospective case-control study. METHODS: Between October 1999 and March 2020, magnetic resonance imaging of patients with tinnitus (pulsatile [PT] and nonpulsatile [NPT]) were assessed for the presence of dural venous sinuses AG. During the same interval, patients with AGs found incidentally on all magnetic resonance imagings ordered without an indication of tinnitus were reviewed. Demographic variables recorded included patient age, sex, race, body mass index, and a history of idiopathic intracranial hypertension (IIH) or obstructive sleep apnea. Location of AGs, when present, were recorded. RESULTS: A total of 651 (PT 250, NPT 401) were found to have AGs. AGs had a higher prevalence in PT patients (10.4% [n = 26]) versus NPT patients (0.3% [n = 1]; odds ratio, 31.0; confidence interval 4.1-234; p < 0.001). Of the 77,607 patients who had an indication for imaging other than tinnitus, 230 patients (0.30%) were found to have incidental AGs, suggesting that the NPT cohort was an adequate control. Patients with PT were more likely to have a higher body mass index, be female, be non-White, and have an existing diagnosis of IIH. For all patients with AGs, AGs were more likely to be found in the lateral sinuses (i.e., sigmoid, transverse) in the PT group (odds ratio, 8.1; confidence interval, 1.1-61.1; p = 0.0218). CONCLUSIONS: This study evaluates the association between AG and PT, finding higher rates of AG in patients with PT than in NPT. However, despite the increased prevalence of AG in patients with IIH, these data combined with existing literature would suggest that AGs are not necessarily the missing link to explain PT pathophysiology in IIH.

A rare MRI finding of NF-1: perineural arachnoidal gliomatosis.

Optic pathway gliomas are the most common central nervous system neoplasms in patients with neurofibromatosis type 1. Perineural arachnoidal gliomatosis is a rare and distinctive growth pattern of optic nerve glioma, in which the tumor infiltrates through the pia mater and pre-dominantly involves the subarachnoid space around the optic nerve. Here, we report an 8-year-old girl with perineural arachnoidal gliomatosis associated with neurofibromatosis type 1.

Brain herniation (encephalocele) into arachnoid granulations: prevalence and association with pulsatile tinnitus and idiopathic intracranial hypertension.

PURPOSE: Brain herniation into arachnoid granulations (BHAG) of the dural venous sinuses is a recently described finding of uncertain etiology. The purpose of this study was to investigate the prevalence of BHAG in a cohort of patients with pulsatile tinnitus (PT) and to clarify the physiologic and clinical implications of these lesions. METHODS: The imaging and charts of consecutive PT patients were retrospectively reviewed. All patients were examined with MRI including pre- and post-contrast T1- and T2-weighted sequences. Images were reviewed separately by three blinded neuroradiologists to identify the presence of BHAG. Their location, signal intensity, size, presence of arachnoid granulation, and associated dural venous sinus stenosis were documented. Clinical records were further reviewed for idiopathic intracranial hypertension, history of prior lumbar puncture, and opening pressure. RESULTS: Two hundred sixty-two consecutive PT patients over a 4-year period met inclusion criteria. PT patients with BHAG were significantly more likely to have idiopathic intracranial hypertension than PT patients without BHAG (OR 4.2, CI 1.5-12, p = 0.006). Sixteen out of 262 (6%) patients were found to have 18 BHAG. Eleven out of 16 (69%) patients had unilateral temporal or occipital lobe herniations located in the transverse sinus or the transverse-sigmoid junction. Three out of 16 (19%) patients had unilateral cerebellar herniations and 2/16 (13%) patients had bilateral BHAG. CONCLUSION: In patients with PT, BHAG is a prevalent MRI finding that is strongly associated with the clinical diagnosis of IIH. The pathogenesis of BHAG remains uncertain, but recognition should prompt comprehensive evaluation for IIH.

A case report of prostate cancer with leptomeningeal metastasis.

BACKGROUND: Prostate cancer is the most prevalent cancer in men. However, leptomeningeal involvement by prostate carcinoma is a rare event. CASE: Here, we report a 69-year-old patient with castration-resistant metastatic prostate cancer who presented with headache and ataxia. Brain MRI revealed a huge invasive interaxial mass at right occipital lobe with diffuse thickening and enhancement of meninges, the arachnoid, and the pia mater, and he was diagnosed with leptomeningeal carcinomatosis. The patient received whole brain radiotherapy. CONCLUSION: Despite the fact that brain and leptomeningeal metastases are not very common in patients with prostate cancer, signs and symptoms of nervous system disorders should be assessed carefully, and consideration of such unusual metastases must be considered.

Preserved arachnoid membrane acts as a predictor of postoperative visual improvement in clinoidal meningioma.

OBJECTIVES: Improvement of patient visual outcome is very important in the treatment of clinoidal meningioma (CLM). The purpose of this study is to determine the association between arachnoid preservation and visual outcome. PATIENTS: Fifteen patients with CLMs that caused visual impairment underwent surgery in our hospital. The patients included 4 men and 11 women, and the mean age was 53.3 years. METHODS: The clinical findings of these patients were retrospectively reviewed. We divided the patients into two groups based on the presence or absence of the arachnoid membrane. Group 1 comprised cases in which arachnoid preservation was intraoperatively confirmed. Group 2 comprised cases in which the arachnoid membrane was not preserved. The Landolt C chart was used to evaluate visual acuity, and dynamic visual field tests using Goldmann perimetry were used to evaluate the visual field. Results were compared before and after surgery. RESULTS: The visual acuity of the ipsilateral eye was significantly improved in Group 1 (p = 0.038). There were no other significant differences between the two groups in terms of tumor volume, patient age, and symptom duration. CONCLUSIONS: Patients in which arachnoid preservation could be intraoperatively confirmed had good improvement in visual acuity. Further research with an increased number of cases is needed to confirm these findings.

Changes of arachnoid granulations after subarachnoid hemorrhage in cynomolgus monkeys.

This research explores ultrastructural changes of arachnoid granulations associated with hydrocephalus after subarachnoid hemorrhage in cynomolgus monkeys. It provides a theoretical basis for further study of the etiology and prevention of hydrocephalus. Female cynomolgus monkeys about one-year-old were selected. The position range of arachnoid granulations in superior sagittal sinus and transverse sinus was determined in a randomly selected control monkey. The morphology of normal arachnoid granulations in cynomolgus monkeys was observed under a transmission electron microscope. A primate model of subarachnoid hemorrhage was established by injecting autologous blood into cisterna magna. Vomiting, movement disorder, and reduced level of consciousness were gradually observed in monkeys. Computed tomography and magnetic resonance imaging scan results confirmed subarachnoid hemorrhage and hydrocephalus, and the morphology of arachnoid granulations in hydrocephalus was observed under a transmission electron microscope. Extensive fibrosis of arachnoid granulations was observed under a transmission electron microscope in cynomolgus monkeys with hydrocephalus after subarachnoid hemorrhage.

MicroRNA Dysregulation in Canine Meningioma: RT-qPCR Analysis of Formalin-Fixed Paraffin-Embedded Samples.

MicroRNAs (miRNAs) are small non-coding RNAs that play key roles in tumorigenesis as modulators of cell signaling pathways. miRNA expression has been found to be dysregulated in several human and canine tumors, but data are not yet available on canine meningioma. In this study, we analyzed the expression of 12 miRNAs (i.e. miR-335, miR-200a, miR-98, miR-96, miR-190a, miR-29c, miR-219-5p, miR-155, miR-146a, miR-145, miR-136, miR-451) by RT-qPCR in a series of 41 formalin-fixed, paraffin-embedded canine meningiomas, and normal arachnoid samples. We identified 8 dysregulated miRNAs that might be involved in canine meningioma pathogenesis. Five miRNAs (i.e. miR-96, miR-145, miR-335, miR-200a, miR-29c), were downregulated in tumor samples and 3 (i.e. miR-136, miR-155, miR-146a) were upregulated. Moreover, miR-200a was overexpressed in grade III compared to grade I and grade II meningiomas, suggesting that it might have a dual role in tumor initiation and progression. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses suggest that dysregulated miRNAs might influence cellular processes and pathways mainly involved in tumor cell migration, extracellular matrix interactions, cell proliferation, and inflammatory responses. The characterization of miRNA functions in canine meningiomas is needed to assess their potential clinical utility, also in view of the relevance of the dog as a potential spontaneous animal model of human disease.

Aging-associated inflammation and fibrosis in arachnoid membrane.

BACKGROUND: The physiological and pathological significance of the arachnoid membrane (AM) is still unknown. In this study, we investigated various characteristics of the AM, focusing on the influence of inflammation and fibrosis. METHODS: Small pieces of AM sample were obtained during neurosurgical procedures from 74 cases. The clinical and pathological characteristics of the hyperplastic AM group (≥ 50 µm) and the non-hyperplastic AM group (< 50 µm) were compared. Then, potential correlations between AM thickness and clinical characteristics were analyzed. Moreover, VEGFα, TGFß, and TGFα levels were quantitated by real time PCR. Then, the potential correlations between AM thickness and these inflammatory or anti-inflammatory markers, and the influence of the original disease were calculated. RESULTS: The median age of the patients in hyperplastic AM group was significantly older than that of the non-hyperplastic AM group. Moreover, the number of fibroblasts, CD68+ cells, CD86+ cells, and CD206+ cells in the hyperplastic AM group was significantly higher than that in the non-hyperplastic AM group. The AM thickness was significantly correlated to age and number of fibroblasts, CD68+ cells, CD86+ cells, and CD206+ cells. The thickness of the AM was significantly correlated to the messenger RNA expression levels of VEGFα (ρ = 0.337), and the VEGFα expression levels were significantly correlated with TGFß and TNFα. CONCLUSIONS: The AM hyperplasia was influenced by aging and could be a result of inflammation and fibrosis through cytokine secretion from the inflammatory cells and fibroblasts in the AM.

Arachnoiditis Ossificans of the Lumbar Spine: A Rare Cause of Progressive Cauda Equina Syndrome.

Arachnoiditis ossificans of the spine is a rare entity defined as an ossification of the leptomeninges resulting in neurologic decline. We describe the case of a 42-year-old woman, without any obvious predisposing factor, who presented with a progressive cauda equina syndrome. The imaging findings on magnetic resonance imaging were confusing by showing an atypical intraspinal lesion extending from L1 to S1. The computed tomography scan was more specific by showing suggestive images of a huge arachnoiditis ossificans of the lumbar spine. The patient underwent a large lumbar laminectomy with an incomplete resection of the ossified arachnoid. The histologic study confirmed the bony nature of the lesion. This illustrative case highlights the importance of helical computed tomography scan with multiplanar reconstruction for the diagnosis of arachnoiditis ossificans.

Histological and intraoperative evaluations of the arachnoid in patients with Chiari I malformation.

BACKGROUND: Arachnoid dissection for decompression of Chiari I malformation is controversial. Whether arachnoid changes have an impact on the clinical course is not established. This paper documents the histological spectrum of arachnoid changes and evaluates correlations with preoperative, intraoperative, and postoperative data. METHOD: Arachnoid samples of 162 consecutive foramen magnum decompressions from 2006 to 2016 were studied. Arachnoid thickness and degrees of fibrosis and cellularity were determined with the examiner blinded for clinical data. Based on 145 first time decompressions, a histological classification for arachnoid features was developed. RESULTS: The arachnoid was thicker in secondary compared with primary decompressions (176.1 ± 158.2 µm vs. 35.9 ± 43.5 µm; p = 0.0026) and in adults compared to children (37.3 ± 45.3 µm vs. 21.8 ± 7.7 µm; p = 0.0007). In primary decompressions, arachnoid thickness, degrees of fibrosis, and cellularity followed a normal distribution with all features shifted significantly to higher grades in secondary decompressions. The histological classification correlated with the preoperative severity of gait ataxia, motor weakness, and sensory deficits, whereas it had no predictive power for postoperative short- or long-term results. By comparison, the intraoperative evaluation of arachnoid changes accounting for relationships between arachnoid and surrounding tissues showed higher correlations with preoperative symptoms and had significant predictive power for postoperative short- and long-term results. CONCLUSIONS: Histological changes of the arachnoid correlate with preoperative symptoms. Relationships between arachnoid and surrounding tissues show even higher correlations with predictive power for short- and long-term outcomes. These findings suggest a pathophysiological role for the arachnoid in Chiari I malformation.

Multi-modality imaging evaluation of the dorsal arachnoid web.

PURPOSE: Dorsal arachnoid web (DAW) is a rare intradural abnormality which is associated with progressive myelopathy. Our objective was to review multi-modality imaging techniques demonstrating the scalpel sign appearance in evaluation of DAW. METHODS: We retrospectively reviewed various imaging modalities of patients found to have DAW at our institution during January 2015 to February 2020. Five patients underwent surgical decompression with pathological correlation. The remaining patients were presumptively diagnosed based on the characteristic finding of scalpel sign. Clinical data were evaluated and correlated to imaging findings. All imaging modalities demonstrated the characteristic scalpel sign. RESULTS: Sixteen patients (10 females, and six males) with multi-imaging modalities were evaluated. Their mean age was 52 year (range 23-74 years). Fifteen patients underwent conventional spine MRI. Further high-resolution MR imaging techniques, e.g. 3D T2 myelographic sequence, were utilized with two patients. MRI spine CSF flow study was performed to evaluate the flow dynamic across the arachnoid web in one patient. Eight patients were evaluated with CT myelogram. Syrinx formation was discovered in seven (44%) patients; five (71%) of them underwent surgical resection and decompression. Two patients underwent successful catheter-directed fenestration of the web with clinical improvement. We found a statically significant positive correlation between the degree of cord displacement and compression with syrinx formation (r = 0.55 and 0.65 with p-value of 0.03 and 0.009, respectively). CONCLUSION: DAW has characteristic scalpel sign independent of imaging modality. Multi-modality imaging evaluation of DAW is helpful for evaluation and surgical planning.

Intradural Pathology Causing Cerebrospinal Fluid Obstruction in Syringomyelia and Effectiveness of Foramen Magnum and Foramen of Magendie Dredging Treatment.

OBJECTIVE: This article discusses the procedure of foramina magnum and Magendie dredging, summarizing the pathologic changes in the intradural region of the craniocervical junction in patients with syringomyelia and the pathophysiologic mechanism of cerebrospinal fluid (CSF) circulation obstruction. METHODS: Clinical data from 50 adult patients with syringomyelia treated at Xuanwu Hospital from July 2018 to January 2019 were collected and retrospectively analyzed. All operations were performed with foramina magnum and Magendie dredging, and all intradural factors that may have induced the obstruction of CSF circulation were recorded. RESULTS: Intradural pathology was found in all patients. The pathologic changes that may have caused obstruction of the CSF circulation include tonsil occupying the foramen magnum and overlying foramen of Magendie in 88% (44/50), intertonsillar arachnoid adhesions in 36% (18/50), tonsil to medulla arachnoid adhesions in 18% (9/50), medialized tonsils in 70% (35/50), vermian branch of posterior inferior cerebellar artery in 22% (11/50), arachnoid veil in 16% (8/50), cisterna magna cyst in 4% (2/50), and tonsil to dura mater arachnoid adhesions in 8% (4/50). Mean duration of follow-up was 13.3 months. The long-term effective rate was 96.0%. Postoperative magnetic resonance imaging revealed that the size of the syringomyelia was reduced or completely resolved in 88% of patients. The mean preoperative Japanese Orthopaedic Association score was 12.9 ± 3.1, which improved to 14.7 ± 3.2 (P < 0.05) at last clinical follow-up. CONCLUSIONS: Intradural pathology that causes CSF circulation obstruction exists in many forms. Relieving the obstruction of the foramen magnum and foramen of Magendie is key to surgical treatment.

Surgical Release of a Dorsal Thoracic Arachnoid Web.

Dorsal arachnoid web (DAW) is a rare clinical entity with unknown etiology, and it can mimic other conditions on imaging.1,2 We present a surgical video of a patient with DAW that was misdiagnosed as ventral cord herniation. A 35-year-old woman presented with upper back pain and progressive bilateral lower extremity weakness and numbness for a few months. Magnetic resonance imaging (MRI) of the thoracic spine (T) showed ventral cord displacement with a syrinx that extended from T2-4. The computed tomography myelogram showed no contrast anterior to the spinal cord. The patient underwent T3-5 laminectomy. Intraoperatively, we found a thoracic DAW and cord displacement with no herniation (Video 1). We performed adhesiolysis to restore the cerebrospinal fluid circulation. On 4-month follow-up, the patient examination had demonstrated progressive improvement of her previous symptoms (weakness, numbness, and urinary retention), and the repeat MRI scan showed a significant reduction in the size of the syrinx. DAW can mimic other pathologies on preoperative imaging, such as ventral cord herniation and arachnoid cyst. The presence of "scalpel sign" and a syrinx on MRI with no arachnoid cyst on myelography support the diagnosis of DAW.

Unexpected and Sudden Death Due to Undiagnosed Moraxella catarrhalis Meningoencephalitis in a 40-day-old Infant: Case Report and Literature Review.

Acute bacterial meningitis in infants and newborns represents a medical emergency and a significant cause of mortality and morbidity worldwide. Moraxella catarrhalis has been considered a microorganism with low pathogenic potential, and only in exceptional cases has it been found to cause meningitis in infants and immunocompetent people. We will now document an unusual case of an unexpected and sudden death of a 40-day-old infant due to acute meningitis from M. catarrhalis, apparently asymptomatic and subsequently diagnosed by an autopsy. According to our knowledge this is the first case of unexpected infant death due to undiagnosed M. catarrhalis meningitis.The suggested case, as well as for the rarity of such a fatal event, should be considered a caution to pediatrics and neonatologists for M. catarrhalis can cause paucisymptomatic meningoencephalitis in infants which can be potentially fatal.From a forensic point of view, an autopsy accompanied by a multidisciplinary assessment is always necessary in cases of unexpected infant deaths to identify the causes.

Reinvestigation of the origins of pineal meningiomas based on its related veins and arachnoid membranes.

BACKGROUND: A series of patients harboring pineal region meningiomas were respectively analyzed to explore the origin of these tumors and the true meaning of the term "velum interpositum (VI) meningiomas". METHODS: 21 patients with pineal meningiomas underwent operation in Nanfang Hospital of Southern Medical University from January 2005 to December 2016 were retrospectively included to analyze the clinical features, imaging findings and surgical video data of these patients. According to the method of literature, the data of this group were also divided into falcotentorial (FT) meningiomas and VI meningiomas, and the differences between the two types of tumors were compared. RESULTS: Among the 21 cases of tumor, there were 12 cases of FT meningiomas, including 4 cases originating from cerebral falx, 4 cases from tentorium of cerebellum and 4 cases from straight sinus; there were 9 cases of VI meningiomas, 7 of which originated from the arachnoid sleeve of the Galen vein, 1 from the posterior part of the internal cerebral vein and 1 from the posterior surface of the pineal gland. Postoperative pathological examination showed meningiomas in all the 21 patients, including 16 cases of total resection and 5 cases of subtotal resection. Postoperatively limitation of binocular vertical motion was found in 3 cases, homotropic hemianopia in 7 cases, hemiplegia in 1 case and death in 1 case. CONCLUSIONS: This study suggests that pineal meningiomas are more suitable to be described by FT meningioma and meningiomas of the arachnoid of the pineal region by analyzing the origin of tumors. The term "VI meningiomas" can only reflect a part of meningiomas of the arachnoid of the pineal region. Before the removal of pineal meningiomas, more attention should be paid to the effects of the two types of tumors on the Galen vein and the straight sinus, and the establishment of venous collateral circulation.

Case Report: A Case of Severe Cryptococcal Immune Reconstitution Inflammatory Syndrome Presenting with Brain and Intradural Abscesses in an HIV Patient.

Clinical worsening or new manifestation of cryptococcal disease following initiation of anti-retroviral therapy (ART) in an HIV patient is a hallmark of cryptococcal immune reconstitution inflammatory syndrome (C-IRIS). However, it can be difficult to distinguish IRIS from worsening or new infection. Here, we present a case of severe C-IRIS involving multiple cerebellar, spinal, and intradural abscesses and spinal arachnoiditis 7 months after ART initiation in an AIDS patient with uncertain prior ART compliance. He had multiple prior episodes of cryptococcal meningitis with complications necessitating ventriculoperitoneal shunt placement and was on suppressive fluconazole when he developed worsening brain manifestations. He received empiric anti-cryptococcal re-induction without improvement. All cerebrospinal fluid cultures remained sterile, with negative Cryptococcus PCR testing, and his condition continued to worsen prior to corticosteroid initiation. Ultimately, C-IRIS was diagnosed by brain biopsy. This case demonstrates an extreme in severity of C-IRIS and in the timeline of presentation after ART initiation.

Arachnoid bands and venous compression as rare causes of hemifacial spasm: analysis of etiology in 353 patients.

BACKGROUND: Hemifacial spasm is usually caused by arterial compression at the root exit zone of the facial nerve. However, other etiologies have been reported. The aim of this study was to analyze the frequency of other causes of hemifacial spasm. METHODS: Our prospectively maintained hemifacial spasm database containing all patients who underwent microvascular decompression (MVD) for hemifacial spasm from 2002 to 2018 was reviewed. All offending structures were identified and recorded by the surgeon at the time of surgery. Additionally, the operative videos were analyzed retrospectively. RESULTS: MVD was performed in 353 patients. Arterial compression was the main cause of hemifacial spasm in 341 (96.9%) patients. Combined venous-arterial compression was seen in 7 (2.0%) patients. In one patient, the compression was from a large vein. In two patients, no compression was found. One patient who suffered from Bell's palsy many years previously had severe synkinesis and the other had facial tics. In two patients, the spasm was caused due to strangulation of the facial nerve by arachnoid bands. Long-term follow-up of more than 18 months was available in 249 patients with total resolution or near total resolution of spasms in 89.96% of patients. CONCLUSIONS: In most patients with hemifacial spasm, arterial vessels are involved in compressing the facial nerve. Purely venous compression is rarely encountered. We report for the very first time arachnoid bands strangulating the nerve as a cause for hemifacial spasm without involvement of any vessel.