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.

Ocular Torsion According to Trochlear Nerve Absence in Unilateral Superior Oblique Palsy.

Purpose: To investigate the relationship between objective ocular torsion and the presence or absence of the trochlear nerve in subjects with unilateral superior oblique palsy (SOP). Methods: A total of 159 subjects with congenital and acquired unilateral SOP were reviewed. Eighty-four subjects who had a normal trochlear nerve (present group) and 75 subjects without a trochlear nerve (absent group) were included. Cyclovertical motility parameters and objective ocular torsion were compared between groups, and factors related to ocular torsion were evaluated. Results: The degree of "net" excyclotorsion in the paretic eye was larger in the absent group compared to the present group (P = 0.002). The proportion of net excyclotorsion in the paretic eye was greater in the absent group (11% vs. 37%), while net incyclotorsion was greater in the present group (41% vs. 23%) (P < 0.001). Net excyclotorsion of the paretic eye was associated with absence of the trochlear nerve (P < 0.001) and smaller size of the paretic SO (P < 0.001). Net incyclotorsion of the paretic eye was related with a normal trochlear nerve (P = 0.005), larger size of the paretic SO (P = 0.002), and greater hypertropia during ipsilateral gaze (P = 0.024). Conclusions: The status of the trochlear nerve, paretic SO size, and hypertropia during ipsilateral gaze which reflects the tensile strength of the ipsilateral superior rectus, significantly contribute to ocular torsion in unilateral SOP.

Combined Brown syndrome and superior oblique palsy without a trochlear nerve: case report.

BACKGROUND: Congenital Brown syndrome is characterized by limited elevation particularly during adduction. The pathogenesis of congenital Brown syndrome is still controversial. CASE PRESENTATION: A 6-year-old boy had been tilting his head to the left since infancy. He showed right hypertropia (RHT) of 2 prism diopters (Δ) in the primary position. He showed RHT 6Δ in right gaze, RHT 2Δ in left gaze, RHT 12Δ in right head tilt, and orthotropia in left head tilt. The right eye showed limitation of elevation and depression on adduction, and the left eye showed overdepression on adduction. MR images showed an absent right trochlear nerve with a hypoplastic ipsilateral superior oblique muscle. CONCLUSIONS: Congenital Brown syndrome may be associated with an absent trochlear nerve and hypoplastic superior oblique muscle suggesting an etiologic mechanism of congenital cranial dysinnervation disorder.

Aberrant distribution of the trochlear nerve: A cadaveric study supported by immunohistochemistry.

The trochlear nerve is generally considered to be a purely motor nerve supplying one extraocular muscle, the superior oblique. In the current study, 28 orbits were dissected and in one orbit (3.6%), the trochlear nerve divided into two main branches. The medial branch followed the classical course, entered the superior oblique muscle and was presumed to be motor in function. However, before entering the muscle, it partially fused with the frontal nerve, and gave a bundle of nerve fibres to the frontal nerve. The lateral branch gave a communication to the frontal nerve, travelled along the lacrimal nerve, received a branch from the lacrimal nerve then penetrated the lacrimal gland. The lateral branch was presumed to be sensory. Paraffin sections from the two branches were stained using immunohistochemistry. The two branches had different nerve fibre populations and showed distinct differences in neurofilament proteins (NFP) immuno-labelling. While both branches showed intense labelling for NFP-H, the lateral branch showed no staining or faint staining for NFP-M and NFP-L respectively, but the medial branch showed moderate labelling for both the NFP-M and NFP-L. Staining for substance P, a marker for nociceptive fibres, showed intense staining in a subset of fibres in the lateral branch, but no staining in the medial branch. Calcitonin gene-related peptide labelling was evident in some axons and some Schwann cells in the medial branch but widespread, weak and fine granular in the lateral branch. These findings indicate that, in some individuals (3.6%), the trochlear nerve may contain motor and sensory fibres, suggesting inter-nuclear communication within the brainstem during embryogenesis or mixing of nerve fibres in their extra-axial pathways.

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.

Imaging demonstration of trochlear nerve agenesis in superior oblique palsy emerging during the later life.

BACKGROUND: Congenital trochlear palsy may manifest with sudden vertical diplopia due to decompensation during the later life, which may bring a diagnostic challenge. CASE PRESENTATION: Two men with vertical diplopia for several years after age of 50 were referred with persisting or suddenly aggravating diplopia. Findings were consistent with unilateral superior oblique palsy (SOP) in both patients with a contraversive head tilt. Facial asymmetry was suggestive of a congenital cause in a patient. High resolution magnetic resonance image (MRI)s disclosed atrophic superior oblique and absent trochlear nerve in the side of SOP in both patients. CONCLUSION: Imaging demonstration of superior oblique atrophy and absent trochlear nerve may aid in diagnosis of congenital SOP presenting sudden vertical diplopia during the later life due to delayed decompensation.

Magnetic resonance imaging in congenital Brown syndrome.

AIMS: Our aim was to elucidate the etiology of Brown syndrome by evaluating the trochlea position, morphologic characteristics of the extraocular muscles including superior oblique muscle/tendon complex, and the presence of the cranial nerves (CN) III, IV, and VI using magnetic resonance imaging (MRI) in eight patients with unilateral congenital Brown syndrome and one patient with bilateral congenital Brown syndrome. METHODS: Nine consecutive patients diagnosed with congenital Brown syndrome had a comprehensive ocular examination and MRI for the CN III, CN VI, and the extraocular muscles. Five of the nine patients underwent additional high resolution MRI for CN IV. The distance from the annulus of Zinn to the trochlea was measured. RESULTS: Normal sized CN III, IV, and VI, as well as all extraocular muscles, could be identified bilaterally in all patients with available MRI. The distance from the annulus of Zinn to the trochlea was the same in both eyes. CONCLUSIONS: The findings for our patients, particularly in those who underwent additional high resolution MRI, did not provide evidence of a lack of CN IV as a cause of Brown syndrome.

Association of superior oblique muscle volumes with the presence or absence of the trochlear nerve on high-resolution MR imaging in congenital superior oblique palsy.

BACKGROUND AND PURPOSE: Congenital superior oblique palsy is known to relate to trochlear nerve absence and a variable degree of superior oblique muscle hypoplasia. The purpose of this study was to determine whether superior oblique muscle volume predicts trochlear nerve absence in congenital superior oblique palsy. MATERIALS AND METHODS: A retrospective study of high-resolution MR imaging to evaluate the presence of the trochlear nerve and to measure superior oblique muscle areas and volumes with the image analysis tools of a PACS was performed in 128 consecutive patients with unilateral congenital superior oblique palsy and 34 age-matched healthy controls. RESULTS: Of the 128 patients with congenital superior oblique palsy, 88 had an ipsilateral trochlear nerve absence (absent group) and 40 had both trochlear nerves (present group). In patients with congenital superior oblique palsy, the paretic side superior oblique muscle volume was significantly smaller compared with the normal side only in the absent group (P < .001). The left and right side superior oblique muscle volumes were not significantly different in controls (P = .750), and the paretic and normal side superior oblique muscle volumes were not significantly different in the present group (P = .536). The cutoff value of the paretic/normal side superior oblique muscle volume ratio for diagnosing trochlear nerve absence was ≤0.75 (sensitivity 98.9%, specificity 95.0%) in patients with congenital superior oblique palsy. CONCLUSIONS: The ratio of paretic/normal side superior oblique muscle area and volume has an excellent predictability in diagnosing trochlear nerve absence in congenital superior oblique palsy.

Variable relations of the trochlear nerve with the pontomesencephalic segment of the superior cerebellar artery.

The superior cerebellar artery (SCA) is, perhaps, the most anatomically constant cerebellar artery which, in its lateral pontomesencephalic course, is crossed above by the trochlear nerve (CNIV). The SCA may determine, as an offending vessel, CNIV compression and superior oblique myokymia and thus surgical decompression may be indicated. In this regard an accurate knowledge of the variational possibilities of the SCA-CNIV is needed. Such rare neurovascular variants are reported here. The variables are determined by the length of the SCA, and the course of the CNIV as referred to the rostral (RT) and caudal (CT) trunks of the SCA. The CNIV may be pinched between the origins of the RT and CT, may pass above the RT or the SCA main trunk, and even between the primary branches of the RT. The CNIV was found compressed between the RT and the brainstem. Perhaps the most spectacular variation was a CNIV coursing through an arterial ring formed by the RT and CT which were anastomosed distally to the CNIV. The possibilities of neurovascular relations between the CNIV and the SCA should be considered when CNIV palsy, or surgical decompression, are estimated.

Morphometry of the trochlear nerve and superior oblique muscle volume in congenital superior oblique palsy.

PURPOSE: To infer the pathogenic mechanism of congenital superior oblique palsy (SOP) by evaluating trochlear nerve diameter (CN4D) and superior oblique muscle (SO) volume in patients with congenital SOP. METHODS: The medical records of 125 patients diagnosed with unilateral congenital SOP and 34 age-matched healthy controls were reviewed retrospectively. Using thin-section high-resolution magnetic resonance imaging, we evaluated the presence of the trochlear nerve, CN4D, SO volume, and their relationship. RESULTS: Of the 125 patients with congenital SOP, 87 showed absence of the trochlear nerve (n = 87, 70%, absent group) and 38 showed bilateral presence of the trochlear nerve (n = 38, 30%, present group). The nonparetic side CN4D was smaller than controls in the absent group (P = 0.001), and larger than controls in the present group (P = 0.001). Trochlear nerve diameter positively correlated with SO volume in controls (P = 0.014, R(2) = 0.174) and in the nonparetic sides of congenital SOP (present group P = 0.023, R(2) = 0.135; absent group, P = 0.008, R(2) = 0.079). The paretic side SO volume did not show a linear correlation between CN4D and SO volume in the present group (P = 0.243). CONCLUSIONS: In congenital SOP patients without a trochlear nerve, the nonparetic side CN4D was also reduced in contrast to those with a trochlear nerve. The relatively weaker relationship of CN4D and nonparetic side SO volume in the absent group than that of the present group suggests different pathogenic mechanisms underlying these two entities of congenital SOP.

Fourth cranial nerve palsy and Brown syndrome: two interrelated congenital cranial dysinnervation disorders?

Based on neuroimaging data showing absence of the trochlear nerve, congenital superior oblique palsy is now classified as a congenital cranial dysinnervation disorder. A similar absence of the abducens nerve is accompanied by misinnervation to the lateral rectus muscle from a branch of oculomotor nerve in the Duane retraction syndrome. This similarity raises the question of whether some cases of Brown syndrome could arise from a similar synkinesis between the inferior and superior oblique muscles in the setting of congenital superior oblique palsy. This hypothesis has gained support from the confluence of evidence from a number of independent studies. Using Duane syndrome as a model, we critically review the accumulating evidence that some cases of Brown syndrome are ultimately attributable to dysgenesis of the trochlear nerve.

Possible association of congenital Brown syndrome with congenital cranial dysinnervation disorders.

BACKGROUND: Congenital cranial dysinnervation disorders (CCDDs) are known to arise from abnormal development of individual and multiple cranial nerve nuclei or abnormalities in cranial nerve axonal transport. We report our findings for several patients with Brown syndrome in association with other known abnormalities characteristic of CCDDs. METHODS: The medical records of patients presenting during a 4-year period with congenital Brown syndrome were retrospectively reviewed. Patients with Brown syndrome confirmed by forced ductions were included in the study if the Brown syndrome was associated with either an abnormal development of the superior oblique muscle or superior oblique paresis, ptosis, Duane syndrome, or other known CCDDs. RESULTS: A total of 9 patients with Brown syndrome were identified. Of these, 3 also demonstrated a contralateral superior oblique palsy; 2, a contralateral Duane syndrome; 1, an ipsilateral congenital ptosis; and 3, a moderate to severely hypoplastic ipsilateral superior oblique muscle. CONCLUSIONS: Some patients with congenital Brown syndrome are associated with and possibly in the spectrum of CCDDs. We propose that Brown syndrome may be due to abnormal development of the trochlear nerve, which results in physical changes in the superior oblique muscle-tendon-trochlea complex. This results in a tendon that is either long and lax, absent, or abnormally inserted (ie, superior oblique paresis) or a tendon that is restricted in its movements through the trochlea (Brown syndrome).

Absence of the fourth cranial nerve in congenital Brown syndrome.

PURPOSE: To elucidate the aetiology of congenital Brown syndrome. METHODS: Four consecutive patients diagnosed with unilateral congenital Brown syndrome had a comprehensive standardized ocular motility examination. Any compensatory head posture was measured. Brain magnetic resonance imaging (MRI) with regard for the IV cranial nerve (CN) was performed in all patients. Orbital MRI was performed in 2/4 patients, with images acquired in eight directions of gaze and superior oblique (SO) muscle areas compared. RESULTS: CN IV could not be identified bilaterally in two patients, but was absent only on the side of the Brown syndrome in the two other patients. On the normal side, orbital MRI revealed a smaller SO muscle area in upgaze than in downgaze, demonstrating normal actions of this muscle. On the side of the Brown syndrome, the SO area remained the same in upgaze and in downgaze and approximately symmetric to the area of SO in downgaze on the normal side. CONCLUSIONS: These cases add further anatomical support to the theory of paradoxical innervation in congenital Brown syndrome. CN IV was absent in two patients on the side of the Brown syndrome, but without muscle hypoplasia. SO muscle size did not vary in up- and downgaze, which we interpreted as a sign of constant innervation through branches of CN III.