Imaging the ocular motor nerves

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.

Diabetic Oculomotor Nerve Palsy Displaying Enhancement of the Oculomotor Nerve in the Orbit and Cavernous Sinus on MRI

INTRODUCTION

Imaging data were scarce on diabetic oculomotor nerve palsy (ONP). Our study explored the MRI features and their clinical implications for diabetic ONP.

METHODS

Fifty-nine patients with a clinical diagnosis of diabetic ONP were recruited from our department between January 2015 and December 2019. Orbital MRI was retrospectively analyzed, and follow-up scans were obtained for 5 patients. Based on the ocular motor nerve palsy scale, the difference in the scores on the first and last hospital days was defined as the improvement score and was used to assess the treatment effects in all.

RESULTS

Thirty-eight (64.41%) patients presented thickening and enhancement of the cavernous segment and inferior division of the intraorbital segment of the ipsilateral oculomotor nerve, with the cisternal segment spared in all. After complete resolution of symptoms, follow-up MRI in 5 patients revealed that the enhancement was less obvious compared with the previous images. 6 patients in the enhancement group and 4 patients in the nonenhancement group were treated with 80 mg of methylprednisolone. Significant differences were not detected in the median improvement scores between patients with and those without corticosteroid use (p = 0.240).

CONCLUSION

Thickening and enhancement of the unilateral oculomotor nerve were common imaging findings in diabetic ONP, and they persisted after complete resolution of symptoms in some patients. The cavernous segment and the inferior division of the intraorbital segment were simultaneously involved, and the cisternal segment was often spared. Refraining from corticosteroids was recommended even with nerve enhancement.

Trochlear cistern of the cavernous sinus: an anatomical study using magnetic resonance imaging

PURPOSE

The present study aimed to explore the trochlear cistern (TC) of the cavernous sinus using magnetic resonance imaging (MRI).

METHODS

Following conventional MRI examination, a total of 73 patients underwent the constructive interference steady-state (CISS) sequence in thin-sliced coronal sections. Moreover, three injected cadaver heads were dissected.

RESULTS

In the cadaver specimens, the extent of the TC was difficult to identify on any dissected side. On the CISS images, the TC was identified in 98.6% on the right side and 94.5% on the left, while transmitting the trochlear nerve (TN) was identified in 83.6% on the right and 79.5% on the left. Most TNs were delineated as a single trunk, while duplication of the nerve was found in 3% of cases. The TC, commonly located inferior or inferolateral aspect of the oculomotor trigone. The size and extent of TC were highly variable. The TN location in the TC was also variable and was identified throughout the upper, middle, and lower parts of the TC. Moreover, relationships between the TC and Meckel's cave were highly variable.

CONCLUSIONS

TC shows morphological variability. The coronal CISS sequence is useful for exploring TC and TN in clinical practices.

Anatomical location of the abducens nerves (VI) in the ventral approach of clival tumors

The aim of this work was to determine reliable anatomical landmarks for locating and preserving the abducens nerves (6th cranial nerves) during trans-facial or trans-nasal endoscopic approaches of skull base tumors involving the clivus and the petrous apex. In order to describe this specific anatomy, we carefully dissected 10 cadaveric heads under optic magnification. Several measurements were taken between the two petro-sphénoidal foramina, from the bottom of the sella and the dorsum sellae. The close relationship between the nerves and the internal carotid artery were taken into account. We defined a trapezoid area that allowed drilling the clivus safely, preserving the 6th cranial nerve while being attentive to the internal carotid artery. The caudal part of this trapezium is, on average, 20 mm long at mi-distance between the two petro-sphenoidal foramina. The cranial part is at the sella level, a line between both paraclival internal carotid arteries. Oblique lateral edges between the cranial and caudal parts completed the trapezium.

Cranial Nerve Imaging and Pathology

This review provides a symptom-driven approach to neuroimaging of disease processes affecting the cranial nerves. In addition to describing characteristic imaging appearances of a disease, the authors emphasize exceptions to the rules and neuroimaging pearls. The focus is on adult neurology although some important pediatric conditions are included. On reviewing this material, the reader should be able to (1) differentiate intra- and extra-axial causes of cranial nerve dysfunction and (2) appropriately use neuroimaging to investigate abnormalities of cranial nerve function.

Guidelines for radiographic imaging of cranial neuropathies

Disruption of the complex pathways of the 12 cranial nerves can occur at any site along their course, and many, varied pathologic processes may initially manifest as dysfunction and neuropathy. Radiographic imaging (computed topography or magnetic resonance imaging) is frequently used to evaluate cranial neuropathies; however, indications for imaging and imaging method of choice vary considerably between the cranial nerves. The purpose of this review is to provide an analysis of the diagnostic yield and the most clinically appropriate means to evaluate cranial neuropathies using radiographic imaging. Using the PubMed MEDLINE NCBI database, a total of 49,079 articles' results were retrieved on September 20, 2014. Scholarly articles that discuss the etiology, incidence, and use of imaging in the context of evaluation and diagnostic yield of the 12 cranial nerves were evaluated for the purposes of this review. We combined primary research, guidelines, and best practice recommendations to create a practical framework for the radiographic evaluation of cranial neuropathies.

Clinically Directed Neuroimaging of Ophthalmoplegia

PURPOSE

Ophthalmoplegia (OP) can have numerous etiologies and different clinical presentations. Most causes of OP can be narrowed down to specific anatomical locations based on clinical information. The aim of this study was to outline the different categories of diseases encountered in patients with OP, based on the location along the ocular motor pathways, and the most appropriate imaging modality for the given scenarios.

METHODS

Representative neuroimaging examples of pathological processes causing OP are displayed, sequenced by anatomical location and disease category. Correlations between the clinical presentation and site of pathology with imaging protocol recommendations are also presented.

RESULTS

Diseases affecting ocular movement can be divided into categories including: injuries or diseases of the cerebral hemispheres, midbrain, pons, and cerebellum, ocular motor nerve palsies, intrinsic extraocular muscle diseases and orbital diseases secondarily affecting the extraocular muscles. The cranial nerves responsible for ocular movements can be affected intrinsically or extrinsically along their nuclei, their course in the brainstem, in the cisterns, skull base, cavernous sinuses and orbits. The extraocular muscles can be affected primarily or secondarily by adjacent pathological processes in the orbit. Clinical information can help narrow down the differential diagnoses in terms of anatomical site of involvement and prompt the most appropriate neuroimaging techniques.

CONCLUSION

By understanding the pathophysiology of OP the neuroradiologist can discuss clinical cases with the referring clinician and determine a timely, accurate method of imaging to achieve the most precise differential diagnosis.

Clinical and radiological findings suggesting disorders other than tolosa-hunt syndrome among ophthalmoplegic patients: a retrospective analysis

OBJECTIVE

To investigate clinical and radiological features of Tolosa-Hunt syndrome (THS) and examine their diagnostic value, and to propose clinical and radiological features that indicate other symptomatic painful ophthalmoplegias (SPOs) in order to distinguish them from THS.

BACKGROUND

Clinical presentations of THS are nonspecific and may overlap with many etiologies. Therefore, excluding other SPOs is essential for correct diagnosis. At the present time, the predictive value of the current International Classification of Headache Disorders (ICHD) criteria is not well established, and specific imaging markers that can discriminate SPOs from THS are lacking.

METHODS

Patients referred with painful ophthalmoplegia over 12 years were recruited retrospectively and allocated into THS or SPO groups. Typical symptoms (episodic unilateral orbital pain preceding or developing with diplopia) and imaging of THS (inflammatory lesions in the cavernous sinus/orbit by magnetic resonance imaging) were proposed based on ICHD-3 beta criteria and previous literature. Atypical clinical and radiological features suggesting alternative diagnoses were also proposed to predict SPO. Initial presentations and imaging findings were registered and correlated with diagnostic outcomes. The predictive value of clinical and imaging findings was then evaluated.

RESULTS

Of the 61 referred cases, 25 were classified as THS and 36 as SPO. Of the SPO cases, 52.8% manifested typical THS symptoms at onset. Patients with SPOs were prone to have atypical symptoms (47.2%) and radiographical findings (82.1%) in comparison to those with THS (4.0% and 4.2%, respectively; both P < .001). Both typical symptoms and imaging findings predicted a diagnosis of THS with high sensitivity (95.8% and 100%, respectively) but low specificity (47.2% and 28.6%, respectively). High sensitivity (82.1%) and specificity (95.8%) were achieved using atypical imaging features to predict SPO.

CONCLUSION

A diagnosis of THS based strictly on clinical presentations or imaging results is not completely reliable. Identification of atypical imaging features may have a useful role in discriminating SPOs and thus avoid erroneous diagnoses of THS. Future studies with larger sample sizes are warranted to evaluate their validity in general population.

The human trochlear and abducens nerves at different ages - a morphometric study

The trochlear and abducens nerves (TN and AN) control the movement of the superior oblique and lateral rectus muscles of the eyeball, respectively. Despite their immense clinical and radiological importance no morphometric data was available from a wide spectrum of age groups for comparison with either pathological or other conditions involving these nerves. In the present study, morphometry of the TN and AN was performed on twenty post-mortem samples ranging from 12-90 years of age. The nerve samples were processed for resin embedding and toluidine blue stained thin (1µm) sections were used for estimating the total number of myelinated axons by fractionator and the cross sectional area of the nerve and the axons by point counting methods. We observed that the TN was covered by a well-defined epineurium and had ill-defined fascicles, whereas the AN had multiple fascicles with scanty epineurium. Both nerves contained myelinated and unmyelinated fibers of various sizes intermingled with each other. Out of the four age groups (12-20y, 21-40y, 41-60y and >61y) the younger groups revealed isolated bundles of small thinly myelinated axons. The total number of myelinated fibers in the TN and AN at various ages ranged from 1100-3000 and 1600-7000, respectively. There was no significant change in the cross-sectional area of the nerves or the axonal area of the myelinated nerves across the age groups. However, myelin thickness increased significantly in the AN with aging (one way ANOVA). The present study provides baseline morphometric data on the human TN and AN at various ages.

Validation of ICHD-3 beta diagnostic criteria for 13.7 Tolosa-Hunt syndrome: Analysis of 77 cases of painful ophthalmoplegia

BACKGROUND

Three editions of International Classification of Headache Disorders (ICHD) diagnostic criteria for Tolosa-Hunt syndrome (THS) have been published in 1988, 2004 and 2013, in ICHD-3 beta, there have been considerable changes [corrected]. The validity of these new diagnostic criteria remains to be established.

METHODS

We retrospectively identified 77 patients with non-traumatic painful ophthalmoplegia (PO) admitted between 2003 and 2013. We reviewed patients' age at onset and gender, time courses between onset of pain and development of cranial nerve palsy, the cranial nerves involved, imaging findings, therapeutic efficacy of steroid treatment and recurrence of attacks.

RESULTS

THS was the most frequent type of PO (46/77). In THS patients, the third cranial nerve was most commonly involved (76.3%). The median time interval between pain and cranial nerve palsy was two days, although in five patients (10.9%) the interval ranged from 16 to 30 days. Definitely abnormal MRI findings were found in 24 patients (52.2%).

CONCLUSIONS

It is essential to rule out other causes of PO in diagnosing THS, with MRI playing a crucial role in differential diagnosis. It may be helpful to understand and master the entity of THS for researchers and clinicians to adjust the gradation and ranking of the diagnostic criteria.

Radiology update in neuro-ophthalmology

PURPOSE OF REVIEW

Radiologic imaging is indispensible for the diagnosis and management of many neuro-ophthalmologic conditions. Advances in the radioimaging of neuro-ophthalmologic disorders may evolve from the clinical or the radiological side, meaning there is a constant stream of new information for the clinician.

RECENT FINDINGS

Functional MRI, diffusion tensor MRI, magnetization transfer imaging, and magnetic resonance spectroscopy are examples of nonstandard radiographic techniques, which have expanded the knowledge of neuro-ophthalmologic conditions. Studies using conventional MRI have also led to advances in understanding optic neuropathies, the ocular motor system, pseudotumor cerebri, posterior reversible encephalopathy syndrome and migraine.

SUMMARY

This article discusses recent radiologic advances relevant to neuro-ophthalmology.

Magnetic Resonance Imaging of the Oculomotor Nerve

Oculomotor/cranial nerve III palsy is caused by numerous etiologies involving the brainstem, subarachnoid space, cavernous sinus or superior orbital fissure or orbit. Magnetic resonance imaging (MRI) is the most suitable neuro-imaging technique in patients with this presentation to rule out a mass, aneurysm or ischemic vasculopathy. A pictorial review of various pathologies affecting the oculomotor nerve is presented along with their MRI morphology.