High-Resolution 3D Magnetic Resonance Imaging of the Sixth Cranial Nerve: Anatomic and Pathologic Considerations by Segment

High resolution 3D magnetic resonance imaging of Gruber's ligament: a pilot study

INTRODUCTION

Gruber's ligament (GL), a surgical landmark, extends from the lateral upper clivus to the petrous apex (PA), forming the superior boundary of Dorello's canal (DC). It overlies the interdural segment of the abducens nerve (CN VI). High-resolution 3D skull base MRI (SB-MRI) demonstrates anatomic details visible to the surgeon, but not well seen on traditional cross-sectional imaging. The aim of this study was to demonstrate visualization of the GL and its relationship to CN VI utilizing contrast enhanced high-resolution SB-MRI.

METHODS

Two neuroradiologists retrospectively reviewed in consensus the SB-MRIs of 27 skull base sides, among 14 patients. GL detection rate, confidence of detection, and GL length were recorded. When GL was successfully identified, the position of the interdural segment of CN VI within DC was recorded.

RESULTS

GL was readily identified in 16 skull base sides (59%), identified with some difficulty in 2 skull base sides (7%), and failed to be identified in 9 skull base sides (33%). The mean GL length was 7.1 mm (4.5-9.3 mm). Among the 18 cases where GL was successfully identified, CN VI was readily identified in all cases (100%), coursing the lateral third of DC in 72% of sides, and middle third in the remaining 28% of sides.

CONCLUSION

GL can be identified in approximately two-thirds of cases utilizing 3D high resolution SB-MRI. CN VI passes most commonly along the lateral third of DC. This is the first report demonstrating visualization of GL and its relation to CN VI, on imaging.

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.

Unilateral Abducens Nerve Palsy Following Perinatal Stroke of the Middle Cerebral Artery

The authors describe a case of unilateral abducens nerve palsy following perinatal stroke of the middle cerebral artery. A 1-year-old boy presented with left eye esotropia but no other ocular abnormalities. The patient's history, examination, and diagnostic tests were consistent with abducens nerve palsy. He underwent left medial rectus recession of 5.5 mm and left lateral rectus resection of 7 mm followed by patching. At 15 months after surgery, primary gaze by prism alternate cover testing revealed a 4 prism diopter (PD) esophoria (small angle in left gaze with essentially no action of lateral rectus) and 2 PD right hyperphoria. Ophthalmologic management of abducens nerve palsy entails addressing neurological sequelae in a timely manner, treating the esotropia and strabismic amblyopia to optimize visual system development. [J Pediatr Ophthalmol Strabismus. 2020;57:e30-e33.].

Eight Syndrome: Horizontal Gaze Palsy Plus Ipsilateral Seventh Nerve Palsy

A 62-year-old woman developed a right horizontal gaze palsy and ipsilateral facial nerve palsy due to a right pontine tegmentum infarct. This constitutes a forme fruste of the eight-and-a-half syndrome that we have termed the eight syndrome.

Imaging evaluation of trigeminal neuralgia

Trigeminal neuralgia is a debilitating pain syndrome in the sensory distribution of the trigeminal nerve. Compression of the cisternal segment of the trigeminal nerve by a vessel, usually an artery, is considered the most common cause of trigeminal neuralgia. A number of additional lesions may affect the trigeminal nerve anywhere along its course from the trigeminal nuclei to the most peripheral branches to cause facial pain. Relevant differential considerations are reviewed starting proximally at the level of the brainstem.

[Diplopia: An important symptom in internal medicine!]

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.