Trochlear Nerve Research Articles

Cavernous sinus syndrome: a case report

Background: Cavernous sinus syndrome (CSS) is a rare, but potentially life- and sight-threatening condition. We report a case of multiple cranial neuropathies with CSS.Case presentation: A 70-year-old woman presented with unilateral complete ptosis, ophthalmoplegia, and diplopia. Examination showed left-sided multiple cranial nerve palsies, with the involvement of cranial nerve III (oculomotor nerve), IV (trochlear nerve), V1 and V2 (ophthalmic and maxillary branches of trigeminal nerve), and VI (abducens nerve). A clinical diagnosis of CSS was made. Neuroimaging revealed a left-sided cavernous sinus mass for further investigation.Conclusion: In this case report, we highlight the clinical and radiological features of CSS to raise clinical suspicion for similar diagnosis in the future.

Function of oculumotor, trochlear and abducens nerves in patients with cerebral aneurysms undergoing endovascular treatment

Background. Functional impairment of nerves, which move an eyelid, is a serious problem in patients with aneurysms, especially concerning enlarging number of endovascular procedures on cerebral aneurysms.Aim. To evaluate frequency of malfunction of oculomotor, trochlear, abducens nerves in patients with cerebral aneurysms.Methods. From 2019 to 2021 189 patients with 202 aneurysms underwent endovascular treatment. Location of the aneurysms: cavernous, clinoid and communicating segments of the internal carotid arteries, superior cerebellar arteries, P1 and P2 segments of the posterior cerebral arteries. Patients did not have dislocation syndrome as a result of a stroke. There were 37 male patients and 152 female patients. The age of patients ranged from 17 to 78 years, the mean age was 52±12 years. Distribution of aneurysm location: 42 (21%) – cavernous segment of the internal cerebral artery, 25 (12%) – clinoid segment, 110 (55%) – communicating segment, 18 (9%) – superior cerebellar arteries, 7 (3%) – P1 and P2 segments of the posterior cerebral arteries. Morphologically 11 (5%) of the aneurysms were fusiform, 191 (95%) of the aneurysms were saccular. 43 aneurysms (21%) were embolized with coils, 49 (24%) were treated using assisted coiling (balloon- and/or stent-assistance), 83 (42%) of the aneurysms were treated with flow-diverters. 27 (13%) patients underwent several endovascular procedures, including a combination of aforementioned techniques. Function of oculomotor, trochlear and abducens nerves was evaluated at the admission, during the hospitalization and at the discharge. Follow-up was achieved in 102 (54%) patients with 115 aneurysms, the mean follow-up period in June 2022 is 13 months. Checking cerebral angiography was performed 8months after the operation on the average.Results. In 89 (77%) patients checking cerebral angiography showed complete obliteration of the aneurysms, in 26 (23%) filling part of the aneurysm was found out to be smaller. 11 patients had preoperative oculomotor nerve paresis, after the procedure 1 patient had no oculomotor nerve impairment and made a complete recovery, 2 patients had partial improvement, 7 patients had no changes, in 1 patient paresis worsened. In our group we did not observe any case of trochlear nerve palsy either prior or after the operation during follow-up. 6 patients had preoperative abducens nerve paresis, after the treatment 1 patients had a complete recovery of abducens nerve function, 3 patients had partial improvement, 2 patients had no changes.Conclusion. In patients with cerebral aneurysms without cerebral dislocation as result of a stroke function of trochlear nerve did not suffer either prior or after endovascular treatment. Endovascular treatment in this category of patients may positively affect the oculomotor and abducens nerve impairment, but in rare cases it can lead to deterioration of neurological deficit.

Development of acquired non-accommodative esotropia in a patient without a trochlear nerve.

Development of acquired non-accommodative esotropia in a patient without a trochlear nerve.

Letter to the Editor Regarding “Surgical Treatment of Trochlear Nerve Schwannomas: Case Series and Systematic Review”

Letter to the Editor Regarding “Surgical Treatment of Trochlear Nerve Schwannomas: Case Series and Systematic Review”

Ocular Motor Nerve Palsy After Traumatic Brain Injury: A Claims Database Study.

Traumatic brain injury (TBI) is one of the common causes of ocular motor nerve (oculomotor nerve [CN3], trochlear nerve [CN4], and abducens nerve [CN6]) palsies, but there has been no large study of ocular motor nerve palsy caused by TBI. This study aimed to investigate the characteristics of and differences in ocular motor nerve palsy after TBI, according to patient age and severity of TBI. This was a population-based retrospective cohort study that included patients who had ocular motor nerve palsy after TBI with ≥6 months of continuous enrollment using claims data from the IBM MarketScan Research Databases (2007-2016). We assessed sex, age at the first diagnosis of TBI, the severity of TBI, and the rates of strabismus procedures according to the age and severity of TBI. The rates of muscle transposition surgery and chemodenervation in CN3, CN4, and CN6 palsy were investigated. A total of 2,606,600 patients with TBI met the inclusion criteria. Among them, 1,851 patients (0.071%) had ocular motor nerve palsy after TBI. The median age of the patients was 39 (Q1-Q3: 19-54) years, and 42.4% of the patients were female. The median continuous enrollment period after the first diagnosis of TBI was 22 (Q1-Q3: 12-38) months. Of the 1,350,843 children with TBI, 454 (0.026%) had ocular motor nerve palsy. Of the 1,255,757 adults with TBI, 1,397 (0.111%) had ocular motor nerve palsy. Among these 1,851 patients, CN4 palsy (697, 37.7%) occurred most frequently, and strabismus procedures were performed in 237 patients (12.8%). CN6 palsy developed most frequently in children. More children (16.5%) underwent strabismus surgeries than adults (11.6%) ( P = 0.006). The proportion of CN4 palsy (52.3%) was higher while the proportion of CN3 palsy (15.5%) was lower in patients with mild TBI than in patients with moderate-to-severe TBI ( P < 0.001). CN4 palsy developed most frequently among patients of all ages, and only approximately 13% of the patients underwent strabismus procedures for ocular motor nerve palsy after TBI. The rate of development of ocular motor nerve palsy was approximately 4.3 times lower in children than adults, and children most frequently had CN6 palsy after TBI.

Intracranial Breakthrough Through Cavernous Sinus Compartments: Anatomic Study and Implications for Pituitary Adenoma Surgery.

Pituitary adenomas (PAs) with cavernous sinus (CS) invasion can extend into the intradural space by breaking through the CS walls. To elaborate on the potential breakthrough route through CS compartments for invasive PAs and describe relevant surgical anatomy and technical nuances, with an aim to improve resection rates. Twelve colored silicon-injected human head specimens were used for endonasal and transcranial dissection of the CS walls; ligaments, dural folds, and cranial nerves on each compartment were inspected. Two illustrative cases of invasive PA are also presented. The potential breakthrough routes through the CS compartments had unique anatomic features. The superior compartment breakthrough was delimited by the anterior petroclinoidal ligament laterally, posterior petroclinoidal ligament posteriorly, and interclinoidal ligament medially; tumor extended into the parapeduncular space with an intimate spatial relationship with the oculomotor nerve and posterior communicating artery. The lateral compartment breakthrough was limited by the anterior petroclinoidal ligament superiorly and ophthalmic nerve inferiorly; tumor extended into the middle fossa, displacing the trochlear nerve and inferolateral trunk to reach the medial temporal lobe. The posterior compartment breakthrough delineated by the Gruber ligament, petrosal process of the sphenoid bone, and petrous apex inferiorly, posterior petroclinoidal ligament superiorly, and dorsum sellae medially; tumor displaced or encased the abducens nerve and inferior hypophyseal artery and compressed the cerebral peduncle. The superior lateral and posterior components of the CS are potential routes for invasion by PAs. Better identification of CS breakthrough patterns is crucial for achieving higher gross total resection and remission rates.

Masquerading Superior Oblique Palsy

We evaluated patients with hypertropia compatible with a diagnosis of superior oblique (SO) palsy to ascertain whether the 3-step test (3ST) can distinguish SO atrophy characteristic of trochlear nerve pathology from masquerading conditions. Prospective cross-sectional study. In an academic practice, we performed quasi-coronal plane, surface coil magnetic resonance imaging in 83 patients clinically diagnosed with SO palsy. We evaluated alignment, SO cross-sectional area, SO contractility, and rectus muscle pulley positions. A total of 57 patients with mean age 39 years (SD = 21 years) had unilateral SO palsy manifested by SO atrophy (22 congenital and 35 acquired). There was normal SO size in 26 patients with an average age of 39 years (SD =16 years) considered masquerades (8 congenital and 18 acquired). Maximum palsied SO cross-section averaged 9.5 ± 3.8 mm2, less than 18.4 ± 3.9 mm2 contralaterally (P < 10-24). In masquerades, maximum hypertropic SO cross-section was 20.7 ± 3.1 mm2, which was not different from the hypotropic SO or the contralesional muscle in SO palsy. Head tilt testing in masquerades was indistinguishable from SO palsy. In SO palsy, central hypertropia averaged 13.2 ± 9.4Δ, increasing to 21.1 ± 14.0Δ in ipsilateral tilt, and decreasing to 4.3 ± 5.3Δ in contralateral tilt. In masquerades, central hypertropia averaged 13.1 ± 8.7Δ, and was 17.7 ± 11.1Δ in ipsilateral and decreasing to 4.9 ± 5.1Δ in contralateral tilt. Upright hypertropia was larger at 17.7 ± 9.9Δ in congenital than 12.0 ± 8.4Δ in acquired SO palsy (P = 0025) but was indistinguishable from congenital masquerades. Contractile change in SO cross-section was bilaterally similar in masquerades. Relevant coordinates of rectus pulleys were similar bilaterally in masquerades. The 3ST pattern characteristic of unilateral SO palsy may be mimicked in all respects by masquerades.

Trigeminal neuralgia as a complication after anterior temporal lobectomy: A case report

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy. Anterior temporal lobectomy (ATL) leading to high rate of seizure freedom is a safe and well-established procedure in TLEs. Cranial nerve deficits, especially for oculomotor, trochlear and facial nerve were reported as a complication after ATL. Nonetheless, trigeminal neuralgia due to ATL is a very rare complication documented in the literature. The surgeons performing ATL procedures must be aware of the risk of trigeminal nerve injury, avoid excessive electrocautery use in the medial part of middle fossa and provide clean surgery in there to prevent this rare complication.

Diplopia following microvascular decompression surgeries: illustrative cases

BACKGROUNDMicrovascular decompression is an effective treatment strategy for trigeminal neuralgia. However, there may be inadvertent complications involving adjacent cranial nerves during or months after the operation. This case lesson highlights the potential manifestations, both optical and nonneurologic (monocular) and binocular diplopia, after microvascular decompression in two patients. Neurosurgeons should recognize monocular versus binocular causes of diplopia after neurosurgical microvascular decompression.OBSERVATIONSThe authors reported on two patients who presented with diplopia after microvascular decompression for trigeminal neuralgia. The first patient had binocular diplopia with a paradoxical head tilt potentially due to a contiguous trochlear nerve palsy. The second patient had monocular diplopia due to dry eye syndrome from trigeminal nerve dysfunction. However, within 2 years after their operations, both patients had resolution of their diplopia without additional surgical intervention.LESSONSBoth monocular and binocular diplopia can be presenting symptoms of cranial neuropathies after microvascular decompression for trigeminal neuralgia. Most cases of postoperative diplopia (both monocular and binocular) resolve spontaneously over time without additional neurosurgical treatment.

The Trochlear Nerve: Anatomy and Pathology

The trochlear is a thin nerve that provides motor innervation to the superior oblique muscle and, usually, is not identified in conventional magnetic resonance imaging (MRI). It can be affected by congenital disorders, trauma, inflammatory and neoplastic conditions. This article aims to review the trochlear nerve's normal anatomy, functions, and imaging technique.

Endoscopic Far-Lateral Supracerebellar Infratentorial Approach for Petroclival Region Meningioma: Surgical Technique and Clinical Experience.

The management of petroclival region meningioma remains the ultimate achievement in neurosurgery, because of the formidable technical challenges involved. To describe the technique and feasibility of the purely endoscopic far-lateral supracerebellar infratentorial approach (EF-SCITA) for the treatment of petroclival region meningiomas. We reviewed the clinical data of 10 consecutive cases of petroclival region meningiomas treated with the EF-SCITA from August 2018 to August 2020. The clinical outcomes were analyzed. The patient was placed in the lateral position, and then, a "C" shaped incision and craniotomy with exposed sigmoid and transverse sinuses were performed. With the endoscopic holder, endoscopic procedures were performed using standard 2-hand microsurgical techniques. Whether the tentorium or Meckel cave was handled depended on the tumor extension. The mean diameter was 45 × 25 mm. Dizziness and headache were the main symptoms. All 10 patients achieved gross total or subtotal resection (Petroclival Meningioma Grade I-III) with good neurological outcomes. The EF-SCITA provides satisfactory, direct exposure to the petroclival region. Cranial nerve deficits are the main postoperative complications. Two patients had a trochlear nerve injury, 3 patients had transient facial paralysis, and 2 patients had oculomotor paralysis (1 total and 1 incomplete), but both of them recovered during the follow-up period. One patient experienced an ipsilateral superior cerebellar artery infarction, and another patient had transient hemiparesis. The EF-SCITA is effective for most petroclival region meningiomas, except for the cavernous sinus type. This approach simplifies craniotomy procedures, omits burdensome petrosectomy, and avoids crossing posterior neurovascular structures.

Hypopituitarism and cranial nerve involvement mimicking Tolosa-Hunt syndrome as the initially presenting feature of diffuse large B-cell lymphoma: a case report

BackgroundEarly diagnosis of lymphoma involving the central nervous system is sometimes difficult but emergent to avoid the delay of therapeutic initiation. Pituitary insufficiencies are usually associated with lymphoma in the pituitary gland. There have been no cases of lymphoma originating from extra pituitary gland with hypopituitarism that simultaneously presenting unilateral upper cranial nerve palsies and ophthalmalgia. These symptoms are mostly caused by neoplastic involvement of the skull base or benign diseases such as Tolosa-Hunt syndrome (THS). We report a case of lymphoma with unique clinical courses initially presenting hypopituitarism and symptoms mimicking THS with a mass in sphenoidal and cavernous sinuses accompanying sphenoidal bone erosion.Case presentation.A 71-year-old woman visited our hospital with left ophthalmalgia, ptosis, and diplopia. Neurological findings revealed left oculomotor, trochlear and abducent nerve palsies. Endocrine tests indicated partial hypopituitarism. Initial CT and MRI revealed that a mass in sphenoidal and cavernous sinuses had invaded the sella with osteolysis of the sphenoid bone. At around four weeks, almost all the symptoms of cranial nerve palsies were relieved. Seven weeks later, she had a high fever and cervical lymph node (CLN) swellings. CLN biopsy revealed CD20-positive B-cells. She was diagnosed with diffuse large B-cell lymphoma (DLBCL). 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) revealed elevated uptake at the erosion lesion of the sphenoidal bone, but not the pituitary gland. After chemotherapy, all the symptoms related to systemic lymphoma were relieved, but partial hypopituitarism remained. The mass in sphenoidal and cavernous sinuses and elevated uptake by PET/CT were dissolved.ConclusionThis case of DLBCL had a unique clinical course; initial presentation of hypopituitarism and symptoms mimicking THS. There was also rare demonstration of mass lesions related to DLBCL in the sphenoidal and cavernous sinuses compressing the pituitary gland through an eroded area of the sphenoidal bone. It should be clinically cautioned that DLBCL can be associated with erosion of the sphenoidal bone and cause both hypopituitarism and THS-mimicking symptoms.

Surgical Treatment of Trochlear Nerve Schwannomas: Case Series and Systematic Review

Cranial nerve schwannomas almost always arise from sensory or mixed nerves. Motor cranial nerves, such as the trochlear nerve, are rarely associated with schwannomas. No consensus has yet been made for surgical intervention because of the low number of reported cases of trochlear nerve schwannomas. This study comprises a systematic review of the literature and our experience for surgically treated trochlear nerve schwannomas. Three databases (Web of Science, PubMed, and Cochrane Library) were searched without date restrictions. Studies were included if they were published in the English literature and presented patients of any age who underwent surgical treatment for trochlear schwannoma. Data extracted from the included studies were combined with our experience. Forty-one studies, presenting 43 patients, met the inclusion criteria. The total number of patients was 45 after our experience was added. The most common symptoms were diplopia (62.2%), headache (46.7%), and motor weakness (37.8%). Mean age during the diagnosis was 45.1 years. Although the subtemporal transtentorial approach (n= 14) is the most preferred method, its application has decreased in recent years. In the last decade, the lateral suboccipital approach (n= 11) has gained popularity. Residual postoperative trochlear nerve deficit was detected in 81% of patients. The probability of neurologic deficit was not statistically associated with tumor volume (P= 0.914), location (P= 0.669), or resection rate (P= 0.554). Although trochlear schwannomas are rare and their treatment involves challenges, total resection with the proper approach provides the most desirable results.

The Final Cut: Evolution of Cavernous Sinus Decompression Beyond the Dolenc Cut.

Meningiomas involving the cavernous sinus (CS) represent a formidable challenge to neurosurgeons. Because of high morbidity, aggressive tumor resection within the CS has been largely replaced by extracavernous tumor resection and decompression of the CS. The widely used Dolenc method involves blind dural transection over the oculomotor nerve, potentially placing the crossing trochlear nerve at risk. To provide a safer way for the decompression of the CS and at the same time, circumferential resection of the temporal lobe dura. Cadaveric dissection of 8 cadaveric heads (16 sides) was performed. Frontotemporal craniotomy with zygomatic osteotomy was performed. Extradural and intradural dissection of the lateral wall of the CS and free edge of tentorium was performed. Photographic documentation, artistic illustrations, and illustrative video cases are provided. Three tether points were released: anterior-the meningo-orbital band, lateral-dura over the V2 and V3, and medial-superficial layer of the free edge of tentorium. Transection of the superficial layer of the free edge of the tentorium along its edge, in conjunction with a lateral cut over the temporal convexity, constitutes the final cut, allowing a resection of the lateral CS wall and the circumferential resection of temporal lobe dura. Using the "final cut" technique allows for a circumferential resection of the temporal lobe dura and lateral CS wall while avoiding blind cuts that could put cranial nerves at risk. All dural transections are performed in anatomically separated layers under constant visualization.

Trochlear Nerve Palsy Caused by a Superior Cerebellar Artery Aneurysm

Purpose: We report a case of trochlear nerve palsy caused by a superior cerebellar artery (SCA) aneurysm.Case summary: A 34-year-old woman visited our clinic complaining of distance diplopia and a temporal headache 7 days in duration. She had no previous relevant medical or trauma history. Her visual acuity; intraocular pressure; and pupil, anterior segment, and fundus evaluations were unremarkable. Extraocular muscle examination (EOM) revealed six prism diopters (PD) of right hypertropia in the primary gaze; this worsened when the head was tilted to the right. Brain magnetic resonance imaging revealed a round solid nodule between the temporal lobe and pons; we thus suspected a petrous ridge meningioma. She was referred to our neurosurgery department for meningioma treatment. However, 1 hour later, she visited our emergency room with severe headache and nausea. Brain computed tomography angiography revealed a subarachnoid hemorrhage and a ruptured SCA aneurysm. Emergency coil embolization was successfully performed. Four weeks after surgery, the right hypertropia was slightly decreased. Four months later, the diplopia had disappeared and EOM revealed orthotropia.Conclusions: SCA aneurysms are rare and can be misdiagnosed even after radiological examination. Our case emphasizes that an SCA aneurysm should be considered during the differential diagnosis of patients with diplopia and headache.

Root exit zone of the trochlear nerve on the dorsal brainstem: an MRI study

To date, no study has explored the root exit zone of the trochlear nerve (TroN) on the dorsal brainstem; therefore, we aimed to characterize the location using magnetic resonance imaging (MRI). A total of 85 patients underwent thin-slice axial T2-weighted MRI. TroN was identified in 91% of 85 patients, 60 (71%) on the right side, and 67 (79%) on the left. The distances between the apex of the inferior colliculus and the original site of TroN on the dorsal brainstem were variable, with mean values of 2.4 ± 1.8mm (range 0-8mm) on the right and 2.2 ± 1.7mm (range 0-5mm) on the left. Most of the root exit zones were distributed within 0-5mm below the apex of the inferior colliculus. In addition, the distances between the midline and the root exit zones of the TroN were variable, with mean values of 4.4 ± 1.4mm (range 1.9-7.5mm) on the right and 4.6 ± 1.6mm (range 1.1-7.8mm) on the left. Most of the root exit zones were located within 1-7mm range lateral to the midline. The root exit zone of the TroN may be mostly located in a small square area measuring 8mm × 8mm, lying at and below the apex of the inferior colliculus. The TroN may arise from any site in the square area, and significant attention is necessary when performing surgical maneuvers in and around it.

Cranial nerve involvement in mucormycosis in post-COVID patients: a case series

BackgroundOne of the largest outbreaks of rhinosinocerebral mucormycosis (RSCM) occurred in India close to the second wave of the SARS-CoV-2 infection. RSCM is a rare infection caused by several fungal species occurring in immunocompromised subjects. Mucor shows a high propensity to invade the central nervous system. There have been limited studies, mostly isolated case reports, on the neurological manifestations of RSCM. The outbreak of mucormycosis infection was thus the most opportune to study the neurological manifestations and cranial nerve involvement in mucormycosis in greater depths.Aim of the studyThe purpose of the study was to investigate and review the involvement of cranial nerves in a series of cases of rhinosinocerebral mucormycosis associated with the novel coronavirus disease caused by SARS-CoV-2.ResultsIt was a retrospective cross-sectional study of seven patients who were undergoing treatment of RSCM with a recent history of coronavirus disease caused by SARS-CoV-2 infection within the last 3 months. Patients with cranial nerve involvement were identified by magnetic resonance imaging (MRI) at a single institution. Demographic details of the patients, clinical presentation, imaging, microbiological and pathological findings were recorded. All subjects had two or more cranial nerves affected by fungal infection. The most commonly involved cranial nerve was found to be the optic nerve followed by the trigeminal nerve and its branches. We document three cases with extensive involvement of the inferior alveolar branch of the mandibular division of the trigeminal nerve (V3), a previously unreported finding. In one case, in addition to the second and fifth cranial nerves, the third, fourth, sixth, seventh, eighth, and twelfth cranial nerves were involved without any sensory or motor long tract involvement, suggestive of Garcin syndrome secondary to intracranial abscesses and skull base osteomyelitis due to invasive fungal infection. This case is of rare occurrence in the literature, and our study provides one such example.ConclusionCranial nerve involvement in patients of mucormycosis tends to have a poor prognosis, both cosmetic and functional. Radical surgeries and aggressive medical management is needed in such cases to improve the outcome.

Strabismus outcomes after surgery: the nationwide SOS France study.

To describe the types of strabismus operated on, the surgical procedures performed, and the 2-year reoperation rate in France. Entire population 5-year cross-sectional analysis of a national medico-administrative database in France between January 2013 and December 2017 included all patients who underwent a first strabismus surgery, with a 2-year follow-up. Patient identification was based on the diagnostic codes of the 10th International Classification of Diseases and surgical procedures on the codes of the Common Classification of Medical Acts. A subgroup analysis comparing non-paralytic and paralytic strabismus was performed. Among the 56,654 patients included (women: 50.8%), 26,892 (47.5%) patients were under 10years old. Overall, 52,711 (93%) were diagnosed with non-paralytic strabismus and 3,943 (7%) with paralytic strabismus. Among the non-paralytics, the most frequent diagnosis was esotropia (21,282, 37.6%), followed by exotropia (14,392, 25.4%) and vertical strabismus (2,017, 3.6%). Among the paralytics, fourth cranial nerve palsy (1,499, 2.6%) was more frequent than sixth cranial nerve palsy (691, 1.2%) and third cranial nerve palsy (431, 0.8%). The 2-year reoperation rate was 7.7% (4,362 patients), the lowest for non-paralytic (7.4%) and the highest for paralytic (11.4%). This first French population-based study about strabismus will contribute to the evaluation of practices at a national level and permit comparisons between countries. Although the 2-year reoperation rate was found to be 1 out of 13 patients, it should be interpreted with caution. Long-term follow-up is still warranted due to considerable variability of the type and severity of strabismus as well as surgical practices.

An endoscope-assisted craniometric cadaveric study for the brain stem and the cisternal segment of the trochlear nerve.

This study analyzed the relationship of trochlear nerve with neurovascular structures using craniometric measurements. The study was aimed to understand the course of trochlear nerve and minimize the risk of injury during surgical procedures. Twenty trochlear nerves of 10 fresh cadavers were studied bilaterally using endoscopic assistance through the view afforded by the lateral infratentorial-supracerebellar, and the combined presigmoid-subtemporal transtentorial approaches. Trochlear nerves were exposed bilaterally taking seven parameters into consideration: the distance between the cisternal segment of trochlear nerve and vascular structures (superior cerebellar artery/SCA; posterior cerebral artery/PCA), the origin of the trochlear nerve in the brain stem, the angle in the level of tentorial junction, length, diameter, and length of nerve in the cisternal segment. We identified the brain stem and cisternal segments of the trochlear nerve. The lateral infratentorial supracerebellar approach allowed the exposure of the cisternal segments (crural and ambient cisterns), including the origin of the nerve in the brain stem. The combined presigmoid-subtemporal transtentorial approaches provided visualization of the cisternal segment of the nerve and the free edge of the tentorium. In this study, the mean length and width of the trochlear nerve in the cisternal segment were 30.3 and 0.74 mm, respectively. Length of the trochlear nerve from its origin to its dural entrance was 37.2 mm, tentorial dural entrance angle of the trochlear nerve and exit angle of the trochlear nerve from the brain stem were 127.0 degrees and 54 degrees, PCA to trochlear nerve in mid ambient cistern and SCA to trochlear nerve in mid ambient cistern were 7.3 mm and 6.8mm. Trochlear nerve is vulnerable to injury during the surgical procedures. Therefore, it is necessary to have a sufficient knowledge of the anatomy of cisternal segment and its relationship with adjacent neurovascular structures. The anatomical and craniometric data can be helpful in middle and posterior fossa surgery in minimizing the potential injury of the trochlear nerve.

A Trochlear Nerve Schwannoma with Spindle Cells detected by Cerebrospinal Fluid Cytology following Severe Hydrocephalus : A Case Report and Literature Review

急速に進行する視力障害で発症した37歳男性. CTおよびMRIにて重度の水頭症と脳底槽左側に境界明瞭な腫瘍性病変を認めた. 入院後, 緊急脳室ドレナージを行い, 後日, 脳室-腹腔シャント留置術と開頭腫瘍摘出術を施行した. 腫瘍は左滑車神経より発生しており, 病理組織診断より神経鞘腫と診断された. 術前の髄液検査ではタンパク濃度の上昇を認め, さらに髄液細胞診にて腫瘍の一部と考えられるspindle cellが多数検出された. 神経鞘腫に水頭症が併発する原因として, これらが関与していた可能性がある.