Imaging evaluation of cranial nerves 3, 4, and 6

The Oculomotor Cistern and Its Role in the Management of Pituitary Lesions: An Anatomical, Radiographic, and Clinical Scoping Review

BACKGROUND

The oculomotor cistern (OMC) is a cerebrospinal fluid space bound by meningeal layers that surrounds the oculomotor nerve as it crosses the oculomotor triangle to reach the lateral wall of the cavernous sinus at the level of the anterior clinoid process. Although several anatomical and radiological studies are available, its anatomy and relationship with pituitary adenomas (PAs) are still matter of discussion.

OBJECTIVE

The aim of the study is to provide an updated and focused overview of the OMC, highlighting the different perspectives and descriptions from anatomical, radiological, and clinical points of view.

METHODS

A scoping review was conducted up to 29th October 2022, according to PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) criteria. PubMed, Web of Science, Scopus databases, and correlated citations were investigated.

RESULTS

Of the 562 records identified, 22 were included in the present analysis. There were 13, 5, and 4 anatomo-surgical, radiological, and clinical studies, respectively. Though there is general consensus on its definition, data are variable on different features of OMC. Defects or absence of dural layers adjacent to the oculomotor nerve were described in only 4 papers. The transition from meningeal to neural layers is still unclear. PAs with OMC involvement are poorly studied and have unique clinical characteristics. To date, 21 patients have been described; the reported prevalence of OMC involvement by PAs ranges from 4.1% to 14.6%.

CONCLUSIONS

Clarifying the OMC features with further systematic studies may not only broaden theoretical knowledge but also have implications on endoscopic transnasal pituitary surgery.

Improved Lesion Conspicuity with Contrast-Enhanced 3D T1 TSE Black-Blood Imaging in Cranial Neuritis: A Comparative Study of Contrast-Enhanced 3D T1 TSE, 3D T1 Fast-Spoiled Gradient Echo, and 3D T2 FLAIR

BACKGROUND AND PURPOSE

Contrast-enhanced 3D-turbo spin-echo (TSE) black-blood sequence has gained attention, as it suppresses signals from vessels and provides an increased contrast-noise ratio. The purpose was to investigate which among the contrast-enhanced 3D T1 TSE, 3D T1 fast-spoiled gradient echo (FSPGR), and 3D T2 FLAIR sequences can better detect cranial nerve contrast enhancement.

MATERIALS AND METHODS

Patients with cranial neuritis based on clinical findings (n = 20) and control participants (n = 20) were retrospectively included in this study. All patients underwent 3T MR imaging with contrast-enhanced 3D T1 TSE, 3D T1 FSPGR, and 3D T2 FLAIR. Experienced and inexperienced reviewers independently evaluated the 3 sequences to compare their diagnostic performance and time required to reach the diagnosis. Additionally, tube phantoms containing varying concentrations of gadobutrol solution were scanned using the 3 sequences.

RESULTS

For the inexperienced reader, the 3D T1 TSE sequence showed significantly higher sensitivity (80% versus 50%, P = .049; 80% versus 55%; P = .040), specificity (100% versus 65%, P = .004; 100% versus 60%; P = .001), and accuracy (90% versus 57.5%, P = .001; 90% versus 57.5%, P = .001) than the 3D T1 FSPGR and 3D T2 FLAIR sequences in patients with cranial neuritis. For the experienced reader, the 3D T1-based sequences showed significantly higher sensitivity than the 3D T2 FLAIR sequence (85% versus 30%, P < .001; 3D T1 TSE versus 3D T2 FLAIR, 85% versus 30%, P < .001; 3D T1 FSPGR versus 3D T2 FLAIR). For both readers, the 3D T1 TSE sequence showed the highest area under the curve (inexperienced reader; 0.91, experienced reader; 0.87), and time to diagnosis was significantly shorter with 3D T1 TSE than with 3D T1 FSPGR.

CONCLUSIONS

The 3D T1 TSE sequence may be clinically useful in evaluating abnormal cranial nerve enhancement, especially for inexperienced readers.

Diagnostic imaging in neuro-ophthalmology

Neuro-ophthalmology is a field combining neurology and ophthalmology that studies diseases that affect the visual system and the mechanisms that control eye movement and pupil function. Imaging tests make it possible to thoroughly assess the relevant anatomy and disease of the structures that make up the visual pathway, the nerves that control eye and pupil movement, and the orbital structures themselves. This article is divided into three sections (review of the anatomy, appropriate imaging techniques, and evaluation of disease according to clinical symptoms), with the aim of providing useful tools that will enable radiologists to choose the best imaging technique for the differential diagnosis of patients' problems to reach the correct diagnosis of their disease.

Delayed Trochlear Nerve Palsy Following Traumatic Subarachnoid Hemorrhage: Usefulness of High-Resolution Three Dimensional Magnetic Resonance Imaging and Unusual Course of the Nerve

Cranial nerve palsies are relatively common after trauma, but trochlear nerve palsy is relatively uncommon. Although traumatic trochlear nerve palsy is easy to diagnose clinically because of extraocular movement disturbances, radiologic evaluations of this condition are difficult to perform because of the nerve's small size. Here, we report the case of a patient with delayed traumatic trochlear nerve palsy associated with a traumatic subarachnoid hemorrhage (SAH) and the related radiological findings, as obtained with high-resolution three-dimensional (3D) magnetic resonance imaging (MRI). A 63-year-old woman was brought to the emergency room after a minor head trauma. Neurologic examinations did not reveal any focal neurologic deficits. Brain computed tomography showed a traumatic SAH at the left ambient cistern. The patient complained of vertical diplopia at 3 days post-trauma. Ophthalmologic evaluations revealed trochlear nerve palsy on the left side. High-resolution 3D MRI, performed 20 days post-trauma, revealed continuity of the trochlear nerve and its abutted course by the posterior cerebral artery branch at the brain stem. Chemical irritation due to the SAH and the abutting nerve course were considered causative factors. The trochlear nerve palsy completely resolved during follow-up. This case shows the usefulness of high-resolution 3D MRI for evaluating trochlear nerve palsy.

In Vivo Visualization of Cranial Nerve Pathways in Humans Using Diffusion-Based Tractography

OBJECTIVE

Diffusion-based tractography has emerged as a powerful technique for 3-dimensional tract reconstruction and imaging of white matter fibers; however, tractography of the cranial nerves has not been well studied. In particular, the feasibility of tractography of the individual cranial nerves has not been previously assessed.

METHODS

3-Tesla magnetic resonance imaging scans, including anatomic magnetic resonance images and diffusion tensor images, were used for this study. Tractography of the cranial nerves was performed using 3D Slicer software. The reconstructed 3-dimensional tracts were overlaid onto anatomic images for determination of location and course of intracranial fibers.

RESULTS

Detailed tractography of the cranial nerves was obtained, although not all cranial nerves were imaged with similar anatomic fidelity. Some tracts were imaged in great detail (cranial nerves II, III, and V). Tractography of the optic apparatus allowed tracing from the optic nerve to the occipital lobe, including Meyer's loop. Trigeminal tractography allowed visualization of the gasserian ganglion as well as postganglionic fibers. Tractography of cranial nerve III shows the course of the fibers through the midbrain. Lower cranial nerves (cranial nerves IX, XI, and XII) could not be imaged well.

CONCLUSION

Tractography of the cranial nerves is feasible, although technical improvements are necessary to improve the tract reconstruction of the lower cranial nerves. Detailed assessment of anatomy and the ability of overlaying the tracts onto anatomic magnetic resonance imaging scans is essential, particularly in the posterior fossa, to ensure that the tracts have been reconstructed with anatomic fidelity.

The oculomotor cistern: anatomy and high-resolution imaging

BACKGROUND AND PURPOSE

The oculomotor cistern (OMC) is a small CSF-filled dural cuff that invaginates into the cavernous sinus, surrounding the third cranial nerve (CNIII). It is used by neurosurgeons to mobilize CNIII during cavernous sinus surgery. In this article, we present the OMC imaging spectrum as delineated on 1.5T and 3T MR images and demonstrate its involvement in cavernous sinus pathology.

MATERIALS AND METHODS

We examined 78 high-resolution screening MR images of the internal auditory canals (IAC) obtained for sensorineural hearing loss. Cistern length and diameter were measured. Fifty randomly selected whole-brain MR images were evaluated to determine how often the OMC can be visualized on routine scans. Three volunteers underwent dedicated noncontrast high-resolution MR imaging for optimal OMC visualization.

RESULTS

One or both OMCs were visualized on 75% of IAC screening studies. The right cistern length averaged 4.2 +/- 3.2 mm; the opening diameter (the porus) averaged 2.2 +/- 0.8 mm. The maximal length observed was 13.1 mm. The left cistern length averaged 3.0 +/- 1.7 mm; the porus diameter averaged 2.1 +/-1.0 mm, with a maximal length of 5.9 mm. The OMC was visualized on 64% of routine axial T2-weighted brain scans.

CONCLUSION

The OMC is an important neuroradiologic and surgical landmark, which can be routinely identified on dedicated thin-section high-resolution MR images. It can also be identified on nearly two thirds of standard whole-brain MR images.

Pupil sparing incomplete third nerve palsy secondary to a cavernous sinus meningioma: challenges in management

BACKGROUND

The diagnosis of incomplete third nerve palsy can be clinically challenging because the aetiologies, as well as presentations, can be variable and subtle. The optometric clinician should be familiar with the association of third nerve palsy with compressive lesions, including the clinical presentations and management of these patients.

CASE REPORT

We present a 68-year-old hypertensive male complaining of intermittent diplopia for the previous six months. Neurological examination revealed a mild deficit in adduction, reduced range of vertical motility and questionable ptosis, all limited to the OD. No pupillary involvement was noted. MRI revealed a cavernous sinus meningioma. The patient elected against surgery, choosing MRI every six months.

CONCLUSION

Due to the subtle clinical presentation of incomplete pupil sparing third nerve palsy, this ophthalmoplegia may be easily overlooked. The associated aetiologies of palsy of cranial nerve three (CN3) carry increased risk of morbidity and mortality. Management should include evaluation for mass lesions and/or vascular aetiologies, regardless of pupillary involvement.

The aetiology and management of long-lasting sixth nerve palsy in ophthalmoplegic migraine

The features and management of two adult patients with ophthalmoplegic migraine and longlasting sixth nerve palsies are described. Both had had previous shorter episodes of diplopia following migraine-like headaches. One recovered following an injection of botulinum toxin to the medial rectus of her affected eye 11 months after the onset of diplopia. The other patient had previously had surgery for a consecutive divergent squint and required further squint surgery to realign his eyes 1 year after the onset of his sixth nerve palsy. Both botulinum toxin and squint surgery may be useful in the management of longstanding sixth nerve palsy in patients with ophthalmoplegic migraine. The aetiology of ophthalmoplegic migraine is discussed.