Segmental Imaging of the Trochlear Nerve: Anatomic and Pathologic Considerations.

BACKGROUND: The trochlear nerve (the fourth cranial nerve) is the only cranial nerve that arises from the dorsal aspect of the midbrain. The nerve has a lengthy course making it highly susceptible to injury. It is also the smallest cranial nerve and is often difficult to identify on neuroimaging. EVIDENCE ACQUISITION: High-resolution 3-dimensional skull base MRI allows for submillimeter isotropic acquisition and is optimal for cranial nerve evaluation. In this text, the detailed anatomy of the fourth cranial nerve applicable to imaging will be reviewed. RESULTS: Detailed anatomic knowledge of each segment of the trochlear nerve is necessary in patients with trochlear nerve palsy. A systematic approach to identification and assessment of each trochlear nerve segment is essential. Pathologic cases are provided for each segment. CONCLUSIONS: A segmental approach to high-resolution 3-dimensional MRI for the study of the trochlear nerve is suggested.

Isolated Ocular Motor Nerve Palsies.

An isolated ocular motor nerve palsy is defined as dysfunction of a single ocular motor nerve (oculomotor, trochlear, or abducens) with no associated or localizing neurologic signs or symptoms. When occurring in patients aged 50 or older, the most common cause is microvascular ischemia, but serious etiologies such as aneurysm, malignancy, and giant cell arteritis should always be considered. In this article, the authors review the clinical approach, anatomy, and differential diagnosis of each isolated ocular motor nerve palsy and discuss the clinical characteristics, pathophysiology, and treatment of microvascular ischemia.

Microsurgical Resection of a Giant Trochlear Nerve Schwannoma: 2-Dimensional Operative Video.

We present the case of a 17-year-old male, who complained of a 1-year onset of pulsatile headache, dysphagia, speech changes, and emotional lability. Neuroimaging revealed a large left-sided contrast-enhancing tumor located at the infratentorial space consistent with a large trochlear nerve schwannoma. The tumor was compressing the brainstem, obstructing the outflow of the third and lateral ventricles causing hydrocephalus, and disturbing the cortico-bulbar pathways bilaterally leading to the diagnosis of pseudobulbar palsy. After the patient consented the surgical procedure, he was operated through a subtemporal transtentorial approach placed in the lateral position. A lumbar drain was used for brain relaxation during the procedure and image guidance to define the limits of surgical exposure. A microsurgical technique was used, aiming to preserve the cranial nerves and the vascular structures running through the perimesencephalic cisterns. Gross total resection was achieved and clinical course remained uneventful aside from a transient third nerve palsy. Symptoms improved and the three-month follow-up revealed an almost complete function of the oculomotor nerve (Video 1). Trochlear nerve schwannomas are the rarest variety of the cranial nerve schwannomas. Depending on tumor size, clinical and neuroimaging signs of mass effect and brainstem compression, treatment can be observation, microsurgical resection through cranial base approaches or radiosurgery.1-5.

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

BACKGROUND AND OBJECTIVE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: Although trochlear schwannomas are rare and their treatment involves challenges, total resection with the proper approach provides the most desirable results.

Surgical Technique and Nuances of Resection of a Trochlear Schwannoma: Operative Video.

Cranial nerve schwannomas accounts for around 8% of all benign intracranial tumors, arising most commonly from the vestibular nerve, followed by the trigeminal nerve and other lower cranial nerves. However, trochlear schwannoma in a patient without neurofibromatosis-2 are extremely rare and to date, fewer than 100 cases have been reported in the literature. They are either asymptomatic or present with ophthalmologic or neurologic symptoms. Diplopia is the most common initial symptom. As the tumor grows, it can compress the surrounding brainstem and other cranial nerves, causing neurologic symptoms. Asymptomatic lesions are detected incidentally following imaging for some other reason. There are no clear guidelines for the management of these tumors. In general, small asymptomatic tumors are closely observed by serial imaging and symptomatic or larger tumors are managed by surgical excision and/or stereotactic radiosurgery.1-7 Here we present a 41-year-old female patient with incidentally detected left trochlear schwannoma during the follow-up magnetic resonance imaging (MRI) scans. She was followed up regularly with multiple repeat MRI. Recently she started complaining of occasional headaches, and MRI showed a left peimesencephalic cistern tumor causing mass effect on the ipsilateral midbrain. There was also significant brainstem edema. Hence she underwent left retromastoid suboccipital craniectomy, lateral supracerbellar approach, and complete excision of the tumor. Postoperatively the patient had an uneventful recovery without any new neurologic deficits. At 6 months' follow-up the patient is doing well.

Tinnitus in fourth nerve palsy: an indicator for an intra-axial lesion.

Accompanying neurological symptoms and signs are diagnostic hallmarks of fourth nerve palsy (4NP) from an intra-axial lesion. Due to the proximity of the trochlear nucleus and fascicles to the inferior colliculus (IC), auditory symptoms including tinnitus may occur with an intra-axial 4NP. A 53-year-old man with hypertension and diabetes developed right 4NP with a sudden worsening of tinnitus. MRI disclosed an infarction involving the trochlear fascicle and IC in the left dorsal midbrain. Tinnitus may be a symptom indicating an intra-axial lesion causing a 4NP.

Trochlear Schwannoma Arising from Transition Zone of Nerve Sheath in the Pineal Region: Case Report and Review of the Literature.

BACKGROUND: This report presents the third case of trochlear schwannoma arising from the pineal region and the first case to be resected using a paramedian infratentorial supracerebellar approach. Schwannomas of cranial nerves have traditionally been thought to arise from the transitional point where the axonal envelopment switches from glial cells to Schwann cells; however, recent temporal bone histopathologic evidence from vestibular schwannomas challenges this view. Of the 38 cases of pathology-confirmed trochlear schwannoma in the literature, there are only 2 cases arising from the pineal region, where the nerve sheath transition zone is located. Here, we discuss an unusual case of trochlear schwannoma arising from this transition zone. CASE DESCRIPTION: A 65-year-old man was admitted to our institute after a traffic accident. He complained of headache and dizziness, and a computed tomography scan revealed an isodense mass in the pineal region with obstructive hydrocephalus. Magnetic resonance imaging with contrast showed an enhancing mass in the pineal region. The tumor was subtotally resected using a paramedian infratentorial supracerebellar approach, and pathology confirmed the diagnosis of trochlear schwannoma. CONCLUSIONS: Trochlear schwannoma should be considered when a mass is identified in the pineal region. This diagnosis should still be entertained for mass lesions along the free tentorial edge because the tumor may arise distant from the glial-Schwann transition zone located by the dorsal midbrain. We propose a treatment algorithm for this rare tumor that seeks to maximize functional outcome.

Clinical course and prognosis of trochlear nerve schwannomas.

PURPOSE: To delineate the disease course and prognosis of patients with mass lesions of the fourth nerve presumed to be schwannomas. DESIGN: Nonrandomized retrospective case series. PARTICIPANTS: Thirty-seven consecutive cases of presumed trochlear nerve schwannoma from 9 tertiary university neuro-ophthalmology centers. METHODS: Cases were collected, and their clinical characteristics on presentation and follow-up are described. Inclusion criteria were brain magnetic resonance imaging (MRI) with a lesion suggestive of a schwannoma along the course of the fourth nerve. Exclusion criteria were other causes of fourth nerve palsy, such as congenital, traumatic or microvascular; normal (or lack of) initial brain MRI; lack of adequate clinical information; and disappearance of the lesion on subsequent follow-up brain MRI. MAIN OUTCOME MEASURES: Demographics of patients, presence of neurofibromatosis, symptoms on presentation, vertical deviation, lesion size (on presentation and follow-up), length of follow-up, and outcomes of treatment for lesions or diplopia. RESULTS: Seven patients were excluded and of the 30 patients included in our series, patients were predominantly male (77%) with a mean age of 51 years (range 9-102 years). In contrast with prior case reports, almost all of our cases had a fourth nerve palsy on presentation (29/30), often isolated. Mean follow-up was 3.1 years (range 0.2 months to 11.1 years). There was no significant difference between initial and follow-up lesion size (4.4 vs. 5 mm) for patients who did not receive treatment of lesions (P = 0.36). Only 3 patients underwent neurosurgical resection and an additional patient received gamma-knife radiotherapy. The majority of patients (24/30) did not pursue strabismus surgery for vertical diplopia. CONCLUSIONS: Patients with isolated fourth nerve palsy and small lesions of the fourth nerve have a good prognosis and should be followed with serial MRI scans without neurosurgical intervention unless they develop signs of brain stem compression. Most patients with diplopia and benign fourth nerve lesions typical of trochlear nerve schwannoma can adapt with either prism spectacles or no treatment at all, although strabismus surgery can be successful.

Trochlear-oculomotor synkinesis: another congenital cranial dysinnervation disorder?

This report documents an unusual phenomenon. A 6-year-old girl with trochlear-oculomotor synkinesis presented with superior oblique and palpebral levator co-contraction. The literature was reviewed and the possibility of classifying this entity as a congenital cranial dysinnervation disorder was speculated.

Cavernoma of the trochlear nerve.

Here we present the case of a 53-year old man with progressive double vision due to isolated left trochlear nerve palsy. Cranial magnetic resonance imaging (MRI) showed a small tumor within the left quadrigeminal cistern that did not increase in size after several months. Explorative neurosurgical intervention revealed a left trochlear nerve cavernoma. The lesion was microsurgically excised followed by end-to-end anastomosis of the trochlear nerve. After a one-year follow up, double vision totally disappeared and cranial MRI showed no recurrence. Cerebral cavernous malformations usually become symptomatic in seizures or focal neurological deficits after intracerebral hemorrhage. Rarely, cavernomas arise from cranial nerves. To the authors' knowledge, this is the first report on a symptomatic cavernous malformation arising from the trochlear nerve and on its successful surgical management.

Cystic trochlear nerve schwannoma. Case report.

BACKGROUND: Twenty-six cases of pathologically verified schwannomas of the trochlear nerve have been reported in the literature. Five of them had a large cystic component and a smaller solid portion. Complex skull base approaches have been usually applied for their removal. CASE DESCRIPTION: We report on a rare case of cystic trochlear schwannoma in a 52-year-old female patient. The patient presented with double vision, facial palsy, decreased hearing, hemiparesis on the right side, and severe gait instability. Magnetic resonance imaging revealed a 2.5-cm left-sided extra-axial lesion compressing the brain stem at the lower midbrain and upper pontine level. Total resection was performed via a retrosigmoid craniotomy. After the surgery, the neurological deficit diminished considerably. At 28 months follow-up, her only complaint was mild double vision when walking down the stairs and hypesthesia in the right half of her face. CONCLUSIONS: This case represents a rare pontomesencephalic lesion removed successfully via the simple retrosigmoid route.

Synchronous ipsilateral cavernous malformations of the trochlear nerve.

BACKGROUND: Cranial nerve cavernous malformations (CM) are rare benign congenital vascular anomalies, with approximately 44 preceding cases in the literature. We report the fifth case of trochlear CM, as well as the first instance of two discrete CM occurring simultaneously along the same cranial nerve. METHODS: Case report. RESULTS: A fifty-seven year-old man presented with several years of diplopia; physical examination identified a complete left trochlear nerve paralysis. MRI revealed a 1cm enhancing lesion within the left ambient cistern, and the patient underwent left pretemporal transcavernous resection. Intraoperatively, a second, discrete CM of the trochlear nerve was also discovered; wide excision of the intrinsic trochlear lesions was completed, allowing both tumors to be removed en bloc with negative margins. Pathologic analysis confirmed both to be CM of the trochlear nerve. The patient recovered with a persistent left trochlear paralysis only, and follow-up MRI was negative for residual or recurrent disease. CONCLUSION: Cranial nerve CM are rare but potentially morbid mass lesions, with the capacity to precipitate significant neuropathies. Differential diagnosis includes schwannoma and hemangioblastoma. Definitive diagnosis may not be possible preoperatively; however, resection is recommended in symptomatic patients, potentially accompanied by nerve repair.

Trochlear Schwannoma Presenting with Isolated Trigeminal Neuralgia.

BACKGROUND: Schwannomas arising from the cranial nerves controlling extraocular eye movements are very rare and usually present with some degree of diplopia. CASE PRESENTATION: We report a 50-year-old woman who presented with isolated left-sided trigeminal neuralgia of 6 months' duration. Imaging demonstrated a homogeneously enhancing mass in the left ambient cistern, and the patient was brought to the operating room for resection. A retrosigmoid approach was used, and the mass was directly visualized arising from the trochlear nerve and compressing the dorsal root entry zone of the trigeminal nerve. A gross total resection of the mass was achieved, and microvascular decompression of the trigeminal nerve was performed. The tumor was pathologically confirmed as a schwannoma. At 3-month follow-up, the patient's facial pain was resolved, and her extraocular eye movements were intact. CONCLUSIONS: A total of 32 pathology-confirmed cases of trochlear schwannoma have been previously reported in the English-language literature. Most of these tumors arose from the cisternal segment of the nerve, and most patients presented with frank trochlear nerve palsy on exam. We report the first case of trochlear schwannoma presenting with isolated trigeminal neuralgia.

Clinical features, long-term clinical outcomes, and prognostic factors of tuberculous meningitis in West China: a multivariate analysis of 154 adults.

BACKGROUND: Tuberculosis is prevalent in China, which is the second greatest contributor to the global tuberculosis burden. Tuberculosis meningitis (TBM) is the most severe disease form but few reports describe long-term clinical outcomes and prognostic factors. Thus, we studied these features in Chinese TBM patients. METHODS: A retrospective follow-up study was used to collect clinical features and outcomes of adult TB meningitis at the First Affiliated Hospital of Chongqing Medical University from June 2012 to August 2015. Univariate analysis and multivariate analysis were used to identify predictive factors associated with outcomes at discharge and follow-up. RESULTS: TBM patients (N = 154) were a median age of 41 years (range: 16-82 years). Median time to follow-up was 26.4 months (range: 9.3-46.5 months) and 31% had poor outcomes at follow-up and limb weakness (p = 0.016), lower GCS scores (p < 0.001), cranial-nerve palsy (p = 0.024), and hydrocephalus (p = 0.009) were closely associated with these poor outcomes. Furthermore, a high neutrophil to lymphocytes ratio, high D-dimer, a low albumin to globulin ratio and slow background of EEG associated with poor outcomes as well. CONCLUSIONS: Mortality and disability associated with TBM are high in China. Limb weakness, GCS scores, cranial-nerve palsy and hydrocephalus were independent predictors of poor outcomes, and AGR, NLR, D-dimer, and EEG abnormalities may be prognostic factors of TBM.

Trochlear Nerve Neurofibroma in a Clinically NF-1-Negative Patient; A Case Report and Review of Literature.

BACKGROUND: Isolated orbital neurofibroma unassociated with systemic neurofibromatosis is relatively rare and may be difficult to clinically differentiate from other orbital tumors. Sensory branches of the trigeminal nerve-namely lacrimal, nasociliary, and frontal-are the most common nerves of origin for intraorbital neurofibroma, but we discovered a neurofibroma arising out of the right trochlear nerve, in absence of clinical stigmata of neurofibromatosis type 1, which is rare. CASE DESCRIPTION: A 41-year-old adult presented with painless progressive proptosis of the right eye for 10 years without history of visual problems or diplopia. The right eye had axial proptosis with periorbital swelling. On magnetic resonance imaging (MRI), a right orbital extraconal, expansile, lobulated, cystic space-occupying lesion was seen with an enhancing component, pushing the lateral rectus with T1 isointensity and T2 hyperintensity, suggesting a preoperative working diagnosis of pseudotumor or lymphoproliferative tumor. Intraoperatively, a rudimentary slender, white, elongated structure was passing through the length of the tumor. The elongated tumor engulfing the trochlear nerve was traced up to the lateral part of the superior orbital fissure. The tumor was excised completely and was found to be a neurofibroma. CONCLUSION: Isolated trochlear nerve neurofibromas, in the absence of clinical stigmata of NF1, are rare. Multiplicity, multilobulation, ring-configured contrast enhancement, and heterogenous MRI signal intensities help in the accurate preoperative imaging diagnosis. A possible cure is thus achievable with complete excision without damaging important adjacent neurovasculo-musculotendinous structures in the orbit. To the best of our knowledge, this is the fourth reported case of isolated trochlear nerve neurofibroma.

[Painful oculomotor palsy: a diagnostic approach]. / Paralysies oculomotrices douloureuses: une approche diagnostique.

We review the question of diagnosis of painful and relatively isolated ophthalmoplegia due to diseases affecting the ocular motor nerves. For each clinical setting, we provide an overview of the main causes and a practical way to approach the diagnosis. As vascular malformations should always be kept in mind in patients with painful ophthalmoplegia, emergency neuroradiological investigations may be needed. However, the etiological scope is wide and the rationale for choosing the more appropriate examination and its optimal timing depends exclusively on the clinical evaluation. Despite advances in investigation techniques, diagnosis may remain difficult or even unresolved in a certain number of patients. We discuss successively paralysis of the third, sixth and fourth nerve, paralysis of several ocular motor nerves, recurrent ophthalmoplegia and ischaemic ocular motor palsies, which are the most frequent cause.