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.

Acquired Bilateral Superior Oblique Palsy: A Localising Sign in the Dorsal Midbrain

Bilateral superior oblique palsy is an uncommon ocular motility problem, the commonest cause being closed head trauma. Two cases, both adults, are presented in whom bilateral superior oblique palsy occurred as a result of neoplastic infiltration of the dorsal midbrain in the region of the anterior medullary velum. In the absence of a history of head trauma, the presence of an acquired bilateral superior oblique palsy is a definite sign of a single lesion in the region of the decussation of the trochlear nerves and appropriate imaging is indicated.

[Brown syndrome: clinical and radiological correlation]

OBJECTIVE

Brown syndrome is characterized by limitation of elevation in adduction, with complex mechanisms involving muscle, tendon, and trochlea. Here, we investigated mechanisms of Brown syndrome by magnetic resonance (MR) imaging.

METHODS

It was a retrospective case series study. Fourteen patients with unilateral Brown syndrome between 3 and 54 years of age (10 cases of congenital and 4 cases with acquired disease) were included in the study. All patients underwent complete ophthalmic and orthoptic evaluation. Imaging of the ocular motor nerves at the brainstem was performed on 3D-FIESTA sequence, the orbits were imaged with FSE T1, T2WI using surface coils.

RESULTS

Nine of 10 with congenital Brown syndrome demonstrated hypoplasia of the superior oblique (SO) of the affected side. Abnormal low signal intensity in the trochlea area was found in one patient. Three of 4 acquired patients had a history of trauma and were demonstrated fracture of the trochlea, extensive scarring, and superior orbital fracture. One acquired case was demonstrated scarring of anterior part of the SO and hypoplasia of the posterior part.

CONCLUSION

Brown syndrome consists of a series of diseases. Their clinical features are quite similar while their anatomical mechanism varies in numerous ways. Therefore, based on patient's individual pathophysiology, the management in Brown syndrome should be personalized.

Hourglass cystic schwannoma of the trochlear nerve

Cranial nerves' schwannomas most commonly arise from the vestibular nerve. Involvement of other cranial nerves, in absence of neurofibromatosis, is extremely rare. A case of a pathology proven trochlear nerve schwannoma, with internal cystic components, in a patient with isolated right superior oblique muscle palsy, is described. Only 67 cases of such entity have been previously reported in the literature.

[Intraoperative identification of oculomotor, trochlear and abducent nerves in surgery of invasive cranioorbital tumors (new technique)]

BACKGROUND

Aim of the study was to evaluate effectiveness of intraoperative identification of oculomotor nerves (OMN) in resection of skull base tumors invading superior orbital fissure and cavernous sinus.

MATERIALS AND METHODS

69 patients with cranioorbital tumors operated in Burdenko Neurosurgical Institute (Moscow, Russia) since 2000 until 2005 were included in the study. They were divided into 2 groups: 19 patients treated with intraoperative identification of OMN and 50 patients in the control group. Craniorbital meningiomas were in the majority among all cases. Intraoperative identification of OMN was performed using coaxial electrode while muscular response was registered through electrodes inserted in m. levator palpebrae superioris, m. obliquus superior and m. rectus lateralis (for III, IV and VI cranial nerves, respectively). Identification of IMN trunci was repeated throughout the whole stage of tumor resection for their preservation.

RESULTS

comparison of dynamics of oculomotor dysfunction in early postoperative period in patients of both groups demonstrated that intraoperative identification of OMN allowed to decrease the frequency of oculomotor deficit. The rates in main and control groups were: for III and IV nerves--37% and 68% (p < 0.05), for VI nerve--47% and 54% (p > 0.05), respectively.

CONCLUSION

application of intraoperative identification of OMN allows to decrease the risk of oculomotor deterioration due to III and IV nerve dysfunction by 1.8 times. Technically the method is quite simple and not time-consuming procedure.

Splitting of the extraocular horizontal rectus muscle in congenital cranial dysinnervation disorders

PURPOSE

To analyze the horizontal rectus extraocular muscles (EOMs) by orbital magnetic resonance imaging (MRI) in patients with congenital cranial dysinnervation disorders that arises from abnormal development of cranial nerve nuclei or their axonal connections.

DESIGN

Case series, retrospective analysis.

METHODS

The morphology of the horizontal rectus EOMs was analyzed in orbital MRI on 4 patients with congenital oculomotor palsy, 26 with congenital superior oblique palsy, and five with Duane syndrome. Orbital imaging was performed by 1.5 tesla (T) and 3T MRI, and quasi-coronal and sagittal images perpendicular and parallel to the long axis of the orbit were obtained at slice thicknesses of 3 and 2 mm.

RESULTS

The horizontal rectus EOMs were split in 4 of the 35 patients (11%). Splitting was observed in 2 of the five patients (40%) with Duane syndrome, one of the 26 patients (4%) with congenital superior oblique palsy, and 1 of the 4 patients (25%) with oculomotor palsy, but in none of the 6 normal subjects and 12 patients with acquired cranial nerve palsy.

CONCLUSION

Since splitting of the horizontal rectus EOMs was noted in patients with congenital dysinnervation disorders, including Duane syndrome, Sevel's theory that the horizontal rectus EOMs develop from the superior and inferior mesodermal complexes is considered to be reasonable.

Morphometry of dorsal raphe nucleus serotonergic neurons in alcoholism

BACKGROUND

Reduced serotonergic function is hypothesized in alcohol abuse and dependence. Serotonergic innervation of the cortex arises predominantly from the dorsal raphe nucleus (DRN). We sought to determine the number and morphometric characteristics of DRN serotonergic neurons postmortem in alcoholic individuals (n=9; age: 16-66 years; 8M:1F) compared with psychiatrically normal, nonalcoholic controls (n=6; age: 17-74 years; 4M:2F).

METHODS

Brainstems were collected at autopsy, fixed and cryoprotected. Alcohol dependence or abuse was determined by psychological autopsy (DSM-IV), the presence of liver fatty changes or cirrhosis and/or high blood alcohol level. Tissue was sectioned at 50 microm (-25 degrees C). A series of 1:10 sections was immunoreacted with antiserum to tryptophan hydroxylase (TPH), the rate-limiting enzyme in the biosynthesis of serotonin. The total number of TPH-immunoreactive (IR) DRN neurons was determined by stereology. Neuron morphometry indices were determined using a video-based imaging system attached to a microscope. We identified TPH-IR neurons every 1,000 microm in each brainstem and measured neuron area, total cross sectional neuron area, and the total area and density of immunolabeled processes.

RESULTS

Dorsal raphe nucleus neuron number (controls: 80,386+/-10,238; alcoholic individuals: 85,884+/-12,478) was not different between groups but TPH-IR was greater in alcoholic individuals throughout the rostrocaudal extent of the DRN. The volume of the DRN was 66+/-9 mm3 in controls and 55+/-5 mm3 in alcoholic individuals (p>0.05). The average size of DRN neurons did not differ between groups (353+/-12 microm2 for controls vs 360+/-15 microm2 for alcoholic subjects). However, the area occupied by neuron processes (area of processes/DRN area) was 2.2-fold greater in alcoholic individuals compared with controls (p<0.05).

CONCLUSIONS

The increased area occupied by neuron processes in alcoholic individuals may represent sprouting and, together with greater TPH-IR, be a compensatory response to impaired serotonergic transmission or cumulative effects of alcohol on the serotonin system.

Primary trochlear headache and other trochlear painful disorders

The trochlear region is a source of distinct pain that may give rise to specific primary pain disorders (primary trochlear headache), but also modulate other pre-existing headache disorders such as migraine. The sensory innervation of this region, by a branch of the ophthalmic division of the trigeminal nerve, may explain the modulatory influence of the nociceptive afferents of this region over migraine headache. We propose the term "trochlear migraine" to refer to the coexistence of strictly unilateral migraine and ipsilateral trochleodynia, with the improvement of migraine being dependent on the resolution of the trochleodynia. Trochleitis is an inflammatory trochleodynia, being frequently idiopathic and rarely secondary to usually immunologic and rheumatologic disorders. We postulate that nociceptive afferents from the inner part of the orbit may sustain the activation of trigeminal neurons, thus sensitizing or exacerbating migraine. Decreasing the possible wind-up induced from this nociceptive afferent stimulation may be effective in controlling headache.

Abducens length and vulnerability?

BACKGROUND

Several sources have attributed the vulnerability of the abducens nerve to its long intracranial course. However, other anatomic factors likely contribute to the apparent vulnerability of the abducens nerve to mass lesions and trauma.

METHODS

The authors performed a two-part anatomic study of the abducens nerve. In the first part of the study, they compared the length of the abducens with another cranial nerve, the trochlear, at the autopsy of 26 pediatric patients. In the second part of the study, the authors used an endoscopic exposure of these two cranial nerves in a preserved human cadaver head.

RESULTS

The abducens nerve was consistently approximately one-third the length of the trochlear nerve at all ages that they studied. The endoscopic views revealed the structural and vascular relationships of the abducens nerve in situ.

CONCLUSIONS

The authors conclude from these findings and the literature that abducens nerve vulnerability results from factors other than its intracranial length.

Cystic schwannoma of the anterior tentorial hiatus. Case report and review of the literature

Intracranial schwannomas not arising from the facial, trigeminal, or vestibular nerves in the absence of neurofibromatosis are extremely rare. We report a case of a schwannoma arising in the region of the anterior tentorial hiatus and posterior cavernous sinus. A 17-year old girl presented with headaches and intermittent diplopia. An MRI of the brain revealed a heterogeneously enhancing mass adjacent to the free edge of the tentorium, superior to the cerebellopontine angle. An orbitozygomatic pterional craniotomy was done with complete resection of the tumor. Postoperatively, the patient remained neurologically intact. The clinical presentation and treatment of schwannomas arising in this location are discussed.

Differential vulnerability of cranial motoneurons in mouse models with motor neuron degeneration

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of selective motoneuron populations, yet it remains unclear why some groups of motoneurons are more vulnerable than others. Our aim was to compare the motoneuron loss in five cranial nuclei at different stages of the disease in three mouse models of ALS: two naturally occurring murine models (progressive motor neuronopathy (pmn) and wobbler) and a transgenic mouse model with a human G93A mutation in the superoxide dismutase-1 (SOD1) gene. By quantifying these different motoneuron populations we report that the degree of degeneration in the various cranial motoneuron nuclei depends on the mouse model and the stage of the disease. The biologically most significant difference between the mutations occurs in the oculomotor/trochlear nucleus which is affected in the pmn mouse but not in the wobbler and SOD G93A mice. These results suggest that there is a selective degeneration of cranial motoneurons in these mouse models as in ALS patients.

The microsurgical anatomy of the cisternal segment of the trochlear nerve, as seen through different neurosurgical operative windows

OBJECTIVE

To describe the anatomy of the cisternal segment of the trochlear nerve as seen through different neurosurgical approaches.

METHODS

The cisternal course of ten trochlear nerves was observed in five cadaveric embalmed heads, through the view afforded by the median infratentorial-supracerebellar, the extreme-lateral infratentorial-supracerebellar, and the combined presigmoid-subtemporal transtentorial approaches. The relationships of the trochlear nerve with the surrounding neuro-vascular structures were analyzed.

RESULTS

We identified 3 segments of the cisternal trochlear nerve: quadrigeminal, ambient and tentorial. The median infratentorial-supracerebellar approach allowed exposure of the quadrigeminal segment, including the origin of the nerve. The extreme-lateral supracerebellar and the combined presigmoid-subtemporal transtentorial approaches provided visualization of the ambient and tentorial segments of the nerve. The tentorial segment runs in a dural canal contained in the free edge of the tentorium, surrounded by its own arachnoidal sleeve.

CONCLUSION

The trochlear nerve is a very delicate structure that can be easily injured during approaches to the tentorial incisura. Accurate knowledge of its anatomy as seen through different operative windows is helpful in maintaining its integrity during surgery.

Infratentorial lateral supracerebellar approach for trochlear nerve schwannoma

Schwannomas of the trochlear nerve are very rare. Only 25 cases without associated neurofibromatosis were reported in the literature, only 15 of which were surgically verified. We report an unusual case of a 31-year-old man who presented with isolated unilateral trochlear nerve palsy due to a left sided trochlear nerve schwannoma. The tumor was totally resected without additional morbidity using an infratentorial lateral supracerebellar approach.

Imaging of the upper cranial nerves I, III-VIII, and the cavernous sinuses

This article discusses the upper cranial nerves (I, III-VIII) and their anatomy as it pertains to intra-axial nuclei and tracts, cisternal portions, and extracranial portions. In addition, the most common pathologic processes affecting the upper cranial nerves are discussed and illustrated. Because the evaluation of small structures requires imaging techniques that provide high resolution and contrast, MR imaging is the examination of choice. CT still plays a limited but important role in the evaluation of intraosseous portions of some cranial nerves.

Imaging evaluation of cranial nerves 3, 4, and 6

Neuropathies of the oculomotor, trochlear, and abducens nerves may present with isolated or complex neurologic findings. An understanding of the anatomy of these cranial nerves as they traverse the brainstem, basilar cisterns, and cavernous sinus on their way to the orbit can assist in localizing the suggested site of pathology and help to focus imaging protocols. Differential diagnostic possibilities for specific anatomic locations are reviewed.

Isolated bilateral trochlear nerve palsy as the first clinical sign of a metastatic [correction of metastasic] bronchial carcinoma

PURPOSE

To report a case with isolated, nontraumatic bilateral fourth nerve palsy as the first clinical sign of a metastatic lung carcinoma.

METHODS

Case report. A 56-year-old man presented with isolated, nontraumatic bilateral fourth nerve palsy. Magnetic resonance imaging (MRI) of the brain and orbits and, subsequently, chest x-ray and a computer tomographic (CT)-scan of the thorax, the abdomen, and the pelvis were performed.

RESULTS

Magnetic resonance imaging confirmed the presence of a midline brain stem lesion in the region of decussation of the trochlear nerves. Computed tomographic scan of the chest revealed that the lesion was caused by a metastatic lung carcinoma.

CONCLUSION

The findings of isolated bilateral fourth nerve palsy in the absence of trauma should alert the clinician to the possibility of a posterior fossa lesion in the region of the trochlear nerves. Besides urgent scanning of the dorsal midbrain, investigations should be directed to search for the primary tumor.

Localization of post-traumatic trochlear nerve palsy associated with hemorrhage at the subarachnoid space by magnetic resonance imaging

PURPOSE

To report evaluation of traumatic trochlear nerve palsy using head magnetic resonance imaging.

DESIGN

Observational case reports.

METHODS

We examined two cases involving trochlear nerve palsy after closed head injury.

RESULTS

Using a fluid attenuated inversion recovery pulse sequence, MRI showed a high-intensity lesion consistent with subarachnoid hemorrhage at the trochlear nerve area in the ambient cisterns.

CONCLUSION

An impact force directed toward the tentorium can be a mechanism of injury in some post-traumatic trochlear nerve palsies. Fluid attenuated inversion recovery pulse sequence is a sensitive method for detection of abnormalities in cases associated with head injury.

Isolated superior oblique palsies with electrophysiologically documented brainstem lesions

Over a 13.5-year period, we observed 10 patients with isolated superior oblique palsies in whom electrophysiological abnormalities indicated brainstem lesions. In 7 patients unilateral masseter reflex abnormalities were seen, and were located on the side of the superior oblique palsy in 2 patients and on the opposite side in 5 patients. Two patients had slowed gain of following eye movements to the side contralateral to the superior oblique palsy. Slowed adduction saccades in the eye contralateral to the superior oblique palsy were seen in 1 patient. Clinical improvement was frequently (in 7 of 10 patients) associated with improvement or normalization of electrophysiologic findings. Magnetic resonance imaging (MRI) was normal, showing no evidence of brainstem lesions in 6 patients. Unilateral superior oblique palsy may be the only clinical sign of a brainstem lesion. Although such a cause may be underdiagnosed if based on MRI-documented lesions only, it remains a rare condition.

Neuropilin-2 is required in vivo for selective axon guidance responses to secreted semaphorins

Neuropilins are receptors for class 3 secreted semaphorins, most of which can function as potent repulsive axon guidance cues. We have generated mice with a targeted deletion in the neuropilin-2 (Npn-2) locus. Many Npn-2 mutant mice are viable into adulthood, allowing us to assess the role of Npn-2 in axon guidance events throughout neural development. Npn-2 is required for the organization and fasciculation of several cranial nerves and spinal nerves. In addition, several major fiber tracts in the brains of adult mutant mice are either severely disorganized or missing. Our results show that Npn-2 is a selective receptor for class 3 semaphorins in vivo and that Npn-1 and Npn-2 are required for development of an overlapping but distinct set of CNS and PNS projections.

Isolated trochlear nerve palsy in patients with multiple sclerosis

The authors describe five patients with trochlear nerve palsy and MS to characterize this rare association. In two patients, trochlear nerve palsy was the initial clinical manifestation of MS. In the other three patients, this sign occurred after previous neurologic events. MRI did not identify a lesion of the fourth nerve nucleus or fascicle. Ophthalmoplegia resolved within 2 months in four of the five patients. A reason this association is rare is that the fascicular course of the trochlear nerve is exposed to little myelin.

Posterior fossa epithelial cyst: case report and review of the literature

A 49-year old woman with progressive cranial nerve signs and hemiparesis was found at MR imaging and at surgery to have a cyst at the foramen magnum. Immunohistochemistry and electron microscopy showed an epithelial cyst of endodermal origin. MR findings were of an extraaxial mass, with short T1 and T2 times. Unless immunohistochemistry and electron microscopy are used in the final diagnosis of such cysts, all posterior fossa cysts lined by a single layer of epithelium should be described simply as epithelial cysts.

Magnetic resonance imaging and tendon anomaly associated with congenital superior oblique palsy

PURPOSE

To assess the relationship between tendon anomalies and the volume of the superior oblique muscle in patients with congenital unilateral superior oblique palsy.

METHODS

Thirty-three patients with unilateral congenital superior oblique palsy were enrolled. Coronal, cross-sectional magnetic resonance imaging scans of the superior oblique muscle were obtained, and the volume of the paretic superior oblique muscle belly was calculated as a percentage of the superior oblique muscle belly on the normal side. The percentage volume of the affected superior oblique muscle was compared retrospectively with the angle of the vertical deviation in the primary position, the tendon looseness determined by a traction test, and other intraoperative findings.

RESULTS

When a tendon was loose, the volume of its muscle belly was significantly smaller than the belly of muscles with a normal taut tendon (Mann-Whitney U test, P = .0005). The average vertical deviation of patients assessed to have loose tendons was 4.80 prism diopters, and the deviation in patients with normal tendons was 9.90 prism diopters. The mean vertical deviation of patients with atrophic muscle belly on magnetic resonance imaging was 18.1 prism diopters, and that with normal muscle structure was 10.1 prism diopters. The cases with loose tendon as determined by the traction test after administration of general anesthesia and the cases with atrophic muscle belly had significantly larger vertical deviation in the primary position than the cases with normal tendons and muscles. (Mann-Whitney U test, P = .01 and .0196, respectively).

CONCLUSIONS

The traction test is sensitive enough to detect anomalies of the superior oblique tendons. Anomalous superior oblique tendons are nearly always associated with attenuated superior oblique muscle and this information provides us with an explanation for the phenomenon of laxity of the superior oblique tendon.

Pituitary macroadenoma manifesting as an isolated fourth nerve palsy

PURPOSE

To describe an unusual ophthalmic manifestation of a pituitary adenoma.

METHODS

Case report.

RESULTS

A 32-year-old man had left supraorbital and frontal headaches and new-onset vertical diplopia. Examination showed a left fourth nerve palsy and increased vertical fusional amplitudes. Magnetic resonance imaging disclosed a sellar mass consistent with a pituitary macroadenoma.

CONCLUSION

A pituitary adenoma may rarely manifest with an isolated fourth nerve palsy.

Schwannoma in patients with isolated unilateral trochlear nerve palsy

PURPOSE

To describe the clinical features of patients with isolated unilateral trochlear nerve palsy secondary to imaging-defined schwannoma of the trochlear nerve.

METHODS

A chart review of all patients seen at the Neuro-Ophthalmology Unit at Emory University since 1989. Of 221 patients with trochlear nerve palsy, six had a lesion consistent with a trochlear nerve schwannoma.

RESULTS

The six patients had isolated unilateral trochlear nerve palsy. Duration of diplopia before diagnosis averaged 6 months. Magnetic resonance imaging demonstrated circumscribed, enhancing lesions along the cisternal course of the trochlear nerve, all measuring less than 5 mm in greatest dimension. Five of the patients were seen in follow-up, over periods ranging from 11 to 26 months from initial presentation (mean, 15.6 months; standard deviation, 6.0 months). All of these patients remained stable except one, who was slightly worse at 15 months by clinical measurements and magnetic resonance imaging. None of these patients have developed additional symptoms or signs of cranial nerve or central nervous system involvement.

CONCLUSIONS

The differential diagnosis of an isolated unilateral fourth cranial nerve palsy should include an intrinsic neoplasm of the trochlear nerve. Magnetic resonance imaging is useful, both for diagnosis and follow-up. These patients can remain stable and may not require neurosurgical intervention.

Fourth cranial nerve palsy in pediatric patients with pseudotumor cerebri

PURPOSE

To describe three children with acute fourth cranial nerve palsy secondary to pseudotumor cerebri.

METHODS

We reviewed the medical records of children younger than 18 years who were diagnosed with pseudotumor cerebri between 1977 and 1997. Pseudotumor cerebri was defined by normal neuro-imaging, elevated intracranial pressure measured by lumbar puncture, and normal cerebrospinal fluid composition.

RESULTS

Three children with pseudotumor cerebri presented with vertical diplopia and clinical signs of fourth cranial nerve palsy including a hypertropia of the affected eye, which increased with adduction and ipsilateral head tilt. The fourth cranial nerve palsy resolved after reduction of the intracranial pressure in all three children.

CONCLUSIONS

Fourth cranial nerve palsy may occur in children with pseudotumor cerebri and may be a nonspecific sign of elevated intracranial pressure.

Comparison of muscle volume between congenital and acquired superior oblique palsies by magnetic resonance imaging

Magnetic resonance imaging (MRI) studies of superior oblique (SO) muscles have revealed a high incidence of SO muscle atrophy/hypoplasia in congenital SO palsy patients. It has also been reported that long-standing acquired SO palsy patients show atrophic SO muscles in the affected eye. The purpose of this study was to compare the incidence of SO muscle atrophy/hypoplasia in congenital and acquired SO palsy by utilizing MRI. Coronal MRI image planes were taken from 29 cases of unilateral congenital SO palsy and 9 cases of acquired unilateral SO palsy patients. The SO muscle bellies were traced and their sizes were measured from each image plane. The total volume of the affected superior oblique muscle was compared with that of the normal fellow eye. The mean volume of the affected superior oblique muscle to that of the normal muscle was 45.3% (SD = 30.1) in the congenital group and 65.8% (SD = 22.7) in the acquired group. The volume reduction of the SO muscle in congenital SO palsy patients appears to be mainly a congenital abnormality rather than a secondary change, as seen in acquired SO palsy patients.

Trochlear nerve enhancement on three-dimensional magnetic resonance imaging in Fisher syndrome

PURPOSE

To examine the lesion associated with external ophthalmoplegia in Fisher syndrome using three-dimensional magnetic resonance imaging (3-D MRI).

METHOD

Case report. A 65-year-old woman with Fisher syndrome was investigated by gadolinium-enhanced 3-D MRI.

RESULT

The extramedullary portion of the left trochlear nerve was enhanced.

CONCLUSION

Contrast-enhanced 3-D MRI revealed that the lesion responsible for the external ophthalmoplegia in Fisher syndrome is located in the extramedullary portion of the trochlear nerve.

Oculomotor motion disorders: current imaging of cranial nerves 3, 4, and 6

The eye movements are controlled by the cranial nerves 3, 4, and 6 working in close cooperation under the supervision of the voluntary cortex. Clinically, the most common presentation of abnormal ocular motor motion is double vision. A thorough clinical examination can usually separate a local orbital cause which can produce a restriction of the muscles moving the eye from a neurogenic cause due to an abnormality of one of the three nerves or their association pathways. Recent articles in the scientific literature have described major advances in our understanding of the anatomy and vascular relationships of the three ocular motor nerves (cranial nerves 3, 4, and 6) and of the diagnosis and treatment of a variety of pathological processes that damage these nerves, including ischemia, inflammation, and compression.

Bilateral trochlear nerve palsy with arachnoid cyst of the quadrigeminal cistern

PURPOSE

To report bilateral trochlear nerve palsy and its magnetic resonance imaging characteristics in a patient with an arachnoid cyst of the quadrigeminal cistern.

METHOD

We performed magnetic resonance imaging of the brainstem of a 54-year-old man who had bilateral trochlear nerve palsy and mild truncal ataxia.

RESULTS

Magnetic resonance imaging disclosed an arachnoid cyst of the quadrigeminal cistern with enlargement of the lateral, third, and fourth ventricles. The tectum of the midbrain and the ambient and interpeduncular cisterns were markedly compressed by the arachnoid cyst.

CONCLUSION

These findings suggest that the bilateral trochlear nerve palsy in this patient was caused by the arachnoid cyst of the quadrigeminal cistern.

Third, fourth, and sixth cranial nerve palsies

Clinical manifestations of ocular motor palsies may differ according to the type and the localization of the lesions involving the third, fourth, and sixth cranial nerves. Topical diagnosis of the third, fourth, and sixth nerve palsies is therefore required before imaging studies and workup are performed. The development of modern imaging techniques has significantly improved the diagnosis of the disorders affecting the ocular motor nerves. This review covers the most important aspects, in terms of clinical signs and symptoms and differential diagnoses, of these cranial nerve palsies. The more recently published articles have added new disorders to the differential diagnosis of ocular motor palsy. Moreover, magnetic resonance imaging (MRI) has been confirmed to be the most important diagnostic tool in most cases. Finally, recently developed MRI techniques were presented and demonstrated to be more sensitive than conventional MRI in several cases.

Pathogenesis of the neurotoxicity caused by anti-GD2 antibody therapy

After treatment of melanomas with anti-GD2 monoclonal antibody (MAb) (14G2a), some patients develop sensorimotor demyelinating polyneuropathy with and without the syndrome of inappropriate antidiuretic hormone (SIADH). To clarify what causes the neurotoxicity of anti-GD2 MAb, we investigated the immunohistochemical localization of GD2 in the human nervous system. Anti-GD2 MAb (14G2a) reacted with the myelin sheaths in the peripheral nerves as well as with the pituicyte cytoplasm in the posterior lobe of the pituitary gland. We assume that the binding of anti-GD2 MAb to peripheral nerve myelin and the pituicytes in the posterior pituitary causes sensorimotor demyelinating neuropathy and SIADH.

Trochlear nerve schwannomas occurring in patients without neurofibromatosis: case report and review of the literature

OBJECTIVE AND IMPORTANCE

Despite their predilection for sensory nerves, intracranial schwannomas have been reported in a number of mixed and purely motor cranial nerves, especially in association with Type 2 neurofibromatosis. We report the rare occurrence of a trochlear nerve schwannoma in a patient without neurofibromatosis and review 17 other case reports from the literature.

CLINICAL PRESENTATION

A 35-year-old woman presented with an 8-week history of evolving left hemiparesis, bilateral bulbar paresis, and out-of-character emotional lability.

INTERVENTION

She underwent a left temporal craniotomy and a subtemporal, transtentorial approach to the tentorial hiatus, with complete excision of a cisternal trochlear nerve schwannoma.

CONCLUSION

Postoperative complications included temporary oculomotor and abducens nerve palsies and temporary right hemiparesis and mild expressive dysphasia, which were resolved at 23-month follow-up. Preoperative symptoms and signs completely resolved, but a postoperative complete trochlear nerve palsy required inferior oblique myectomy for correction of diplopia. A review of the literature showed no preoperative trochlear nerve involvement in at least 45% of cases. The tumor is isointense on T1- and T2-weighted magnetic resonance images and enhances brightly with gadolinium. The most frequently used approach for surgical excision is the subtemporal approach, and the tumor is almost always totally excised. Long-term follow-up suggests recovery of preoperative deficit, and persisting or new trochlear nerve palsy is the rule.

Cystic trochlear nerve neurinoma

A case of a cystic neurinoma of the trochlear nerve, originally interpreted as an intrinsic brainstem lesion, is presented. The history of the disease, its clinical picture and surgical treatment are described in detail.

Superficial siderosis and episodic fourth nerve paresis. Report of a case with clinical and magnetic resonance imaging findings

We describe a patient with superficial siderosis who had an episodic unilateral fourth nerve paresis. The superficial siderosis was caused by small repeated intraventricular hemorrhages from a periventricular cavernous angioma. T2-weighted magnetic resonance images demonstrated a rim of low signal intensity at the brain surface, characteristic of hemosiderin deposition. These low-signal-intensity deposits included the dorsal brain stem around the anterior medullary velum. We suggest that the hemosiderin deposits affected the proximal portion of the fourth nerve where it contains central myelin and that this in some way caused unstable conduction of nerve impulses through the nerve.

Ophthalmological and neuro-ophthalmological involvement in Churg-Strauss syndrome: a case report

BACKGROUND

It is well known that different types of eye involvement may develop during the course of systemic vasculitides.

METHODS

We report here a case of Churg-Strauss syndrome (allergic granulomatous angiitis) characterized by the presence of multiple ophthalmological and neuro-ophthalmological lesions, i.e., mononeuritis of the fourth cranial nerve, multifocal choroidal ischaemia, and bilateral ischaemic optic neuropathy.

RESULTS

Ischaemic lesions in the posterior ciliary plexus and chorio-retinal circulation, which appeared simultaneously after a phase of disease activity, were documented.

CONCLUSION

The simultaneous occurrence of multiple ocular features in a patient with Churg-Strauss syndrome suggests that regional vasculitis may be the pathological mechanism underlying the multiple ophthalmological lesions in this disorder.

Altered expression of microtubule-associated proteins in cat trochlear motoneurons after peripheral and central lesions of the trochlear nerve

Neurons lesioned in the peripheral nervous system (PNS) generally regenerate and survive, while neurons lesioned in the central nervous system (CNS) do not regenerate and often die. Investigators have traditionally compared the neuronal responses to PNS and CNS lesions in two separate populations of neurons. In this study, we compared the effects of PNS and CNS lesions on the expression of cytoskeletal proteins in a single neuronal population, the trochlear motoneurons of the cat. The trochlear nerve was lesioned either unilaterally in the PNS or bilaterally in the CNS (within the anterior medullary velum), and animals were allowed to survive 1, 2, or 4 weeks. Brain sections were reacted immunocytochemically using antibodies against microtubule -associated protein-2 (MAP-2) and a phosphorylated isoform of MAP1B, termed MAP1B-P. MAP-2 immunoreactivity (IR) was significantly decreased in the CNS-lesioned trochlear nucleus, compared to the lesioned and the unlesioned trochlear nucleus of PNS-lesioned animals. MAP1B-P IR was significantly increased in PNS- and CNS- lesioned trochlear axons, compared to axons in the unlesioned trochlear nerve of PNS-lesioned animals, and appeared in a small percentage of PNS- and CNS-lesioned cell bodies. These results support the growing body of evidence that MPA-2 can serve as a marker for cells that will eventually die following neuronal insult. The increased immunostaining of MAP1B-P in lesioned axons and its appearance in lesioned cell bodies are characteristic of the immature CNS and may reflect an initial recapitulation of early development, when the levels of this protein are high.

Cranial nerves III, IV, and VI

Movements of the eye are produced by six extraocular muscles innervated by three cranial nerves: the oculomotor (III), the trochlear (IV), and the abducens (VI). These cranial nerves are discussed together because of the interrelated nuclear origins, neural pathways, and motor functions. The normal anatomic pathway of these three nerves is presented. The clinical and pathologic manifestations of lesions producing both isolated and complex palsies of these nerves are discussed along with imaging correlation.

The ocular motor nerves

Recent articles in the scientific literature have described major advances in our understanding of the anatomy and vascular relationships of the three ocular motor nerves (cranial nerves III, IV, and VI) and of the diagnosis and treatment of a variety of pathologic processes that damage these nerves, including ischemia, inflammation, and compression.

Evidence of meningioma infiltration into cranial nerves: clinical implications for cavernous sinus meningiomas

Anatomical and biological studies of cavernous sinus meningiomas help us understand the biological heterogeneity of these tumors. The question of whether cavernous sinus meningiomas infiltrate cranial nerves is clinically important because of the effect on treatment planning. In the authors' experience of treating 36 patients with cavernous sinus meningiomas, tumor invasion into a cranial nerve was documented in two patients in whom a cranial nerve was resected during the cavernous sinus dissection. In both patients, histological examination using hematoxylin and eosin and bodian stains showed infiltration of the cranial nerves by a benign meningioma which, to the best of the authors' knowledge, is a condition previously unreported. This histological finding of meningioma invasion into a cranial nerve demonstrates the biological heterogeneity of cavernous sinus meningiomas and raises concern about the invasive character of meningioma. Because not all tumor cells can be identified radiologically or by direct visualization at surgery, occult tumor infiltration predisposes a patient to recurrence despite the best neurosurgical efforts. Evidence of cranial nerve infiltration by meningioma suggests that, in some circumstances, cavernous sinus dissection in the hope of total removal of a meningioma may be futile and, in the long term, may provide no advantage over treatment options with lower morbidity.

Trochlear nerve schwannomas: a case report and literature review

Trochlear nerve sheath tumours are extremely uncommon, only six cases diagnosed during life having been presented previously. In none of these earlier cases were magnetic resonance imaging studies obtained. We report here upon the clinical presentation, surgical management and post-operative course of a case where the diagnosis was suspected pre-operatively from MRI studies. The radiological appearances are described, together with a review of all previously published accounts of this rare tumour.

Nuclear and infranuclear disorders

Lesions of the brain stem can either affect the nuclei or the fascicles of the third, fourth or sixth cranial nerves and thus produce ocular motor disorders. Lesions of the oculomotor nuclear complex differ from lesions of the third nerve, since the motoneurones in the nucleus are specifically grouped. Similarly, a lesion of the sixth nerve nucleus results in a conjugate gaze palsy and not in an abducens palsy, because of 'interneurones' being intermingled with the abducens motoneurons. Isolated lesions of a nerve fascicle, which is the part of the cranial nerve running through the brain stem, usually cannot be distinguished clinically from lesions of the nerve outside the brain stem unless other brain stem signs are present. In the case of an isolated ocular motor nerve palsy, modern imaging techniques, particularly magnetic resonance imaging, may help to localize the lesion to the brain stem. Most often, however, brain stem lesions also involve structures surrounding the ocular motor nuclei or fascicles, sometimes leading to characteristic eponymic syndromes. In congenital eye movement disorders the pathoanatomical situation is more complex. Since the lesion takes place during intrauterine or early postnatal development, corrective misdirection of neurones occurs in addition to aplasia or hypoplasia of parts of the cranial nerves. Correspondingly, abnormal movements accompanying an attempted eye movement can be observed in some characteristic syndromes.

Stability of motor neuron number in the oculomotor and trochlear nuclei of the ageing mouse brain

The total number of neurons in the oculomotor and trochlear nuclei of the mouse brain was estimated in three sets of serial sections at 6, 25, 28 and 31 months of age. Due to the oculomotor nucleus being completely intact in only one side of the brain, in each set of sections some counts were carried out in sagittal sections from the right half of the brain and other counts were carried out in coronal sections from the left half of the brain. It proved impossible to identify the boundary between the oculomotor nucleus and trochlear nucleus in the coronal sections so that in such sections the combined total of neurons in both nuclei was estimated. The oculomotor nucleus could be clearly identified in sagittal sections and therefore the total number of oculomotor neurons was estimated in eight brains (three at 6 months, two at 25 and 28 months and one at 31 months). The trochlear nucleus was intact in all but one of the sets of sagittal sections and trochlear neuron number was estimated separately in eleven brains. The total number of neurons in both nuclei did not vary significantly with age (mean 432). The mean number of oculomotor neurons in the eight brains was 341 and the mean number of trochlear neurons was 77. There was no variation in nuclear diameter at different ages nor was there any marked loss of Nissl substance or lipofuscin accumulation in the motor neurons with age.