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.

Central Trochlear Palsy: Report of Two Patients With Ipsilesional Palsy and Review of the Literature.

BACKGROUND: The trochlear (fourth) nerve is the only cranial nerve that decussates before emerging from the posterior aspect of the brainstem. Lesions involving the trochlear nucleus or fascicles mostly give rise to contralesional superior oblique palsy (SOP). METHODS: We report 2 patients with SOP on the side of intraaxial lesions with a literature review on central trochlear palsy. RESULTS: The lesions are more commonly located posterior to the cerebral aqueduct in patients with ipsilesional SOP than in those with contralesional SOP. CONCLUSIONS: Intraaxial lesions may cause ipsilesional or contralesional SOP depending on the lesion location along the course of trochlear fascicle in the brainstem.

Infratrochlear neuralgia.

INTRODUCTION: The infratrochlear nerve supplies the medial aspect of the upper eyelid, the superolateral aspect of the nose and the lacrimal caruncle. This nerve may contribute to the pain stemming from the trochlea, but infratrochlear neuralgia has not been identified as a specific cause of pain. METHODS: Over a 10-year period we have been recruiting patients with pain in the internal angle of the orbit that did not show features of trochlear pain. RESULTS: Seven patients (six female, one male; mean age, 46.1 ± 18.9) presented with pain in the territory of the infratrochlear nerve. The pain appeared in the internal angle of the orbit and upper eyelid (n = 3), the superolateral aspect of the nose (n = 3), or the lacrimal caruncle (n = 1). All patients had a paroxysmal pain, with the attacks lasting five to 30 seconds. Pain attacks were mostly spontaneous, but two patients had triggers. Between attacks, all patients had local allodynia. Pain did not increase with vertical eye movements. Six patients were treated with gabapentin with complete response, and one patient experienced long-lasting relief with an anesthetic blockade of the infratrochlear nerve. CONCLUSION: Infratrochlear neuralgia should be considered as a possible cause of pain in the internal angle of the orbit.

[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.

Microvascular decompression for superior oblique myokymia: case report.

BACKGROUND: Superior oblique myokymia (SOM) is a rare disorder in which the patient suffers episodic uniocular torsional eye movement associated with diplopia and oscillopsia . Although the pathophysiology has been narrowed down to erratic discharge of the trochlear nerve, yet the exact etiology remains unclear; a handful of cases have been described in association with an identifiable space occupying lesions or dural AV fistulae. Neurovascular compression theory has been postulated in the early 1980s and to our knowledge, very few reports exist in the literature accrediting this hypothesis in the pathogenesis of superior oblique myokymia. CASE REPORT: We report a case of successful resolution of severe medication refractory SOM following microvascular decompression of the trochlear nerve. The clinical response has been sustained for a follow-up period of 18 months to date. CONCLUSION: Microvascular decompression may be considered as a definitive and least destructive surgical option for the treatment of medication refractory superior oblique myokymia.

Sihler staining study of anastomosis between the facial and trigeminal nerves in the ocular area and its clinical implications.

INTRODUCTION: The trigeminal nerve (CN V) supplies mostly sensory innervation to the face, and the facial nerve (CN VII) conveys primarily motor fibers. The aim of this study was to elucidate their distributions and anastomoses. METHODS: Fourteen specimens of hemisectioned faces were gathered from human cadavers and stained with Sihler staining. RESULTS: The temporal (Tbr), zygomatic (Zbr), and buccal (Bbr) branches of CN VII formed trigeminofacial anastomoses in the ocular area. Communications were observed between the supraorbital nerve and the Tbr (85.7%), the infraorbital nerve and the Bbr (100%) and Zbr (28.6%), and the zygomaticofacial nerve and the Zbr (41.7%). Anastomoses were formed between the supratrochlear nerve and the Tbr (57.1%) and Bbr (50%), and the infratrochlear nerve and the Bbr (85.7%). CONCLUSIONS: Motor and sensory axons to the face contribute to trigeminofacial anastomoses, which may play key roles in subtle movements of muscles of facial expression.

Effect of inferior oblique myectomy on ocular torsion according to the absence of the trochlear nerve in unilateral congenital superior oblique palsy.

OBJECTIVES: To evaluate the effect of inferior oblique (IO) myectomy on ocular torsion according to the absence of the trochlear nerve in unilateral congenital superior oblique palsy (UCSOP). METHODS: We retrospectively reviewed the clinical data of patients who had been diagnosed with UCSOP and underwent ipsilateral IO myectomy (n = 43). Patients were classified into the present and absent groups according to the absence of the trochlear nerve and superior oblique hypoplasia on magnetic resonance imaging (MRI). For quantitative analysis of ocular torsion, disc-fovea angles (DFA) were collected in both eyes using fundus photographs taken within three months before surgery and one month after surgery. RESULTS: DFA of the paretic eye did not differ according to the absence of the trochlear nerve (9.4±5.6° in the present group vs. 11.0±5.4° in the absent group, p = 0.508). However, the present group had a larger DFA in the non-paretic eye than the absent group (14.1±6.7° in the present group vs. 8.0±5.0° in the absent group, p = 0.003). The change of ocular torsion after IO myectomy in the paretic eye was -5.3±3.7° in the present group and -4.8±3.5° in the absent group, respectively (p = 0.801). In the non-paretic eye, the change in DFA was -1.5±3.0° in the present group, which was larger than that in the absent group (0.7±2.6°, p = 0.047). In the multivariate analysis, the change in DFA was correlated with only the preoperative DFA (standardized ß = -0.617, p<0.001 in the paretic eye, and standardized ß = -0.517, p<0.001 in the non-paretic eye). CONCLUSIONS: In the paretic eye, there was no significant difference in the change of ocular torsion between both groups, whereas in the non-paretic eye, the present group had a larger change in DFA after IO myectomy than the absent group. However, in the multivariable analysis, the change in ocular torsion was significantly correlated with preoperative excyclotorsion but not with the presence of the trochlear nerve itself.

Congenital superior oblique palsy and trochlear nerve absence: a clinical and radiological study.

OBJECTIVE: To evaluate patients with congenital superior oblique palsy (SOP) by classifying them according to their magnetic resonance imaging (MRI) findings and cross-comparing the clinical characteristics of each group. DESIGN: Retrospective, observational study. PARTICIPANTS: Ninety-seven consecutive patients diagnosed with congenital SOP. METHODS: Medical records of patients who demonstrated typical signs of congenital SOP were reviewed. The presence or absence of the trochlear nerve was visualized with thin-section high-resolution MRI of the cranial nerves. MAIN OUTCOME MEASURES: Presence of the trochlear nerve and superior oblique (SO) muscle hypoplasia on MRI, age at the onset of symptoms or signs, ocular motility examination results, objective ocular torsion, and surgical outcomes. RESULTS: Of the 97 patients with congenital SOP, 73% of patients were identified with an ipsilateral absent trochlear nerve and variable degree of SO muscle hypoplasia (absent group), whereas the remaining 27% had a normal trochlear nerve and normal symmetric SO muscle (present group). Patients with an absent trochlear nerve showed more frequent head tilt (P = 0.030) that was manifest at an earlier onset before 1 year of age (P<0.001). Patients with a normal trochlear nerve had a more prominent overelevation in adduction (P = 0.008) and more frequently were associated with dissociated vertical deviation (DVD; P = 0.025). CONCLUSIONS: Congenital SOP patients without a trochlear nerve had a hypoplastic SO muscle and frequently manifested head tilt at an earlier age, whereas patients with a normal trochlear nerve showed prominent overelevation in adduction and frequent DVD. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Unilateral Isolated Trochlear Nerve Palsy due to Ipsilateral Midbrain Infarction.

Ischemic stroke is a very rare etiology in cases of isolated trochlear nerve palsy, and no reports of ipsilateral trochlear nerve palsy caused by unilateral stroke have so far been published. However, we now report a case of isolated trochlear nerve palsy due to ipsilateral dorsal small midbrain infarction in a 70-year-old woman who presented with acute onset of diplopia. There were no other clinical manifestations, but brain magnetic resonance imaging revealed a small ischemic lesion in the right dorsal midbrain, showing that isolated trochlear nerve palsy can be caused by stroke.

Absence of the trochlear nerve in patients with superior oblique hypoplasia.

OBJECTIVE: Congenital cranial dysinnervation disorders (CCDDs) are developmental abnormalities involving the hypoplasia or aplasia of the cranial nerves with muscle dysinnervation. This study aimed to determine if congenital superior oblique palsy with superior oblique hypoplasia also can be classified as a CCDD. DESIGN: Observational case series. PARTICIPANTS: Ten patients with superior oblique hypoplasia. METHODS: Ophthalmologic examination and thin-section magnetic resonance imaging (MRI) at the brainstem level as well as across the orbit were performed in 10 patients with superior oblique hypoplasia. To confirm the accuracy of the procedure, the results obtained were compared with those of a control group comprising 12 children by using the same technique. MAIN OUTCOME MEASURES: Examination of ductions and versions, 3-step test, angle of deviation, and presence of the trochlear nerve and superior oblique hypoplasia on MRI. RESULTS: Trochlear nerve was absent on the affected side in 10 patients with confirmed hypoplastic superior oblique muscles. The trochlear nerves as well as normal-sized superior oblique muscles were observed in 24 (100%) of 24 eyes screened as controls. CONCLUSIONS: Congenital superior oblique palsy with superior oblique hypoplasia also can be classified as a CCDD by the MRI documentation of congenital aplasia of the trochlear nerve. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

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.

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.

[Diplopia: An important symptom in internal medicine!] / Diplopie : un symptôme important en médecine interne !

Diplopia is defined as "double vision" when looking at a single object. Monocular diplopia is related to an ocular disorder and must be differentiated from binocular diplopia which is secondary to ocular misalignment. The examination of the patient with binocular diplopia is often challenging for non-specialists. However, a careful and systematic clinical examination followed by targeted ancillary testing allows the clinician to localize the lesion along the oculomotor pathways. The lesion may involve the brainstem, the ocular motor nerves III, IV or VI, the neuromuscular junction, the extraocular ocular muscles, or the orbit. Causes of binocular diplopia are numerous and often include disorders typically managed by internal medicine such as inflammatory, infectious, neoplastic, endocrine, and metabolic disorders. In addition to treating the underlying disease, it is important not to leave diplopia uncorrected. Temporary occlusion of one eye by applying tape on one lens or patching one eye relieves the diplopia until more specific treatments are offered should the diplopia not fully resolve.

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.