Age changes in the human oculomotor nerve - a stereological study

Bilateral Simultaneous Optic Neuritis Following Envenomations by Indian Cobra and Common Krait

In India, most snakebite envenomation (SBE) incidents are caused by the "Big Four" snakes which include Russell's viper, common krait, Indian cobra, and saw-scaled viper. Their common envenomation effects include neurotoxicity, myotoxicity, and coagulopathy. However, they also induce rare complications such as priapism, pseudoaneurysm, and sialolithiasis. Ocular manifestations such as optic neuritis develop rarely following envenomations by non-spitting snakes and they may cause temporary vision changes and blindness if untreated. While optic neuritis following Indian cobra envenomation has been reported previously, this was not encountered in victims of common kraits. Hence, for the first time, we report optic neuritis developed in a victim following envenomation by a common krait and compare its clinical features and diagnostic and therapeutic methods used with another case of optic neuritis in a victim of an Indian cobra bite. Both patients received antivenom treatment and made an initial recovery; however, optic neuritis developed several days later. The condition was diagnosed using ophthalmic examination together with computed tomography and/or magnetic resonance imaging methods. Due to very similar clinical features, both patients received intravenous corticosteroids which restored their vision and successfully treated optic neuritis. This case report suggests that the optic neuritis developed in a common krait envenomation is comparable to the one developed following a cobra bite, and therefore, the same diagnostic and therapeutic approaches can be used. This study also raises awareness of this rare complication and provides guidance for the diagnosis and treatment of SBE-induced optic neuritis.

Oculomotor nerve root split: incidental finding on MRI-case report and literature review

BACKGROUND

The oculomotor nerve (OMN) innervates the pupil, ciliary body, upper eyelid, and extraocular muscles through two divisions: a superior division that innervates the levator palpebrae superioris (LPS) and superior rectus (SR), and an inferior division that supplies the medial rectus (MR), inferior rectus (IR), inferior oblique (IO), and parasympathetic fibers to the pupil and ciliary body. We present a case of complete splitting of the cisternal segment of bilateral OMNs that was discovered incidentally on magnetic resonance imaging (MRI) in a patient who had no ocular complaints.

CASE REPORT

A 69-year-old patient was found to have bilateral splitting of the cisternal segments of OMNs during an MRI for trigeminal neuralgia workup. Both nerves sprang from the midbrain as distinct roots. They were symmetric on the right and minimally asymmetric on the left. On both sides, the medial root was slightly inferiorly situated. The patient had no visual problems and continued to function normally. A review of the literature for similar cases identified no such variants; however, it did identify eight examples of OMN fenestrations produced by aneurysms (AN), six of which had no OMN palsy symptoms.

CONCLUSION

An anatomic variant of split bilateral OMN cisternal segments is described. The superior and inferior divisions may have different brainstem origins. Although this variant is an anatomic curiosity, it may have clinical significance and explain the various presentation of compressive OMN palsies.

Unruptured internal carotid-posterior communicating artery aneurysm splitting the oculomotor nerve: A case report and literature review

Background:

Although it is well known that internal carotid-posterior communicating artery (ICA-PcomA) aneurysms compress the oculomotor nerve and cause nerve palsy, cases of ICA-PcomA aneurysms splitting the oculomotor nerve are extremely rare.

Case Description:

We present the rare case of an asymptomatic, growing, left-sided ICA-PcomA aneurysm that was confirmed to split the oculomotor nerve. We report the clinical course and discuss the underlying mechanism. The oculomotor nerve, which is an aggregate of multiple fibers, exhibits age-related loss of compactness in the arrangement of its nerve fibers.

Conclusion:

We speculate that injury to the nerve fibers by aneurysmal compression was avoided because of the rare phenomenon of splitting of the oculomotor nerve.

Published Human Cadaveric Measurements Are Strongly Biased Toward the Elderly Population

Understanding of anatomy is based on the study of anatomical variations. Morphometric variations can have important implications in surgical practice. The sizes of some anatomical structures are affected by age; however, cadavers used in anatomical research are usually of advanced age. The main aim of this study is to quantify the mean age of samples in cadaveric studies reporting morphometric values. PubMed was searched for the last 3 years to locate cadaveric studies reporting size values, excluding histological, forensic, and osteological collections. Out of the 390 potentially relevant papers, 109 (28%) studies did not report the ages of their samples. In total, 177 studies were included for analysis comprising 4,807 subjects. The most studied structures were those of the musculoskeletal system. The mean age of the pooled sample was 71.1 ± 11.0 years. The lowest reported age was 16 while the highest was 104 years. Univariate and multivariate analyses showed no correlation with any of the following variables: country of study, anatomical region, anatomical structure, or journal type. The mean age of cadavers used to measure the sizes of human anatomical structures falls largely within the senior age category. The reported values in an aging population will not necessarily mirror other populations such as the pediatric. The outcomes of surgeries that depend to some extent on tight morphometric values such as flap surgeries, microsurgery, tendon transfer, or mini-invasive procedures could differ when they are performed on other age categories. More anatomical research is needed for better reporting of age-related morphometric changes. Clin. Anat., 33:804-808, 2020. © 2019 Wiley Periodicals, Inc.

A comparative study of oculomotor, trochlear and abducens nerves in Arabian foals

We investigated the microscopic structure of transverse sections of the oculomotor, trochlear and abducens nerves of Arabian foals using stereological methods. Bilateral nerve pairs from 2-month-old female Arabian foals were analyzed. The tissues were embedded in plastic blocks, then 1 µm thick sections were cut and stained with osmium tetroxide and methylene blue-azure II. Stereology was performed using light microscopy. Morphometry showed that the right and left pairs of nerves were similar. The transverse sectional areas of the oculomotor, trochlear and abducens nerves were 1.93 ± 0.19 mm², 0.32 ± 0.06 mm² and 0.70 ± 0.08 mm², respectively. The oculomotor nerve exhibited a significantly greater number of myelinated axons (16755 ± 1279) and trochlear (2656 ± 494) and the abducens nerves (4468 ± 447). The ratio of the axon diameter to myelinated nerve fiber diameter was 0.58, 0.55 and 0.55 for the oculomotor, trochlear and abducens nerves, respectively. Of the three nerves studied, the abducens nerve exhibited the greatest nerve fiber area, myelin area, nerve and axon diameters, and myelin thickness. The ratio of small myelinated nerve fibers was greatest in the oculomotor nerve.

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.

Developmental changes in the connective tissues of the porcine recurrent laryngeal nerve

The recurrent laryngeal nerve (RLN) branches from the vagus cranial nerve to innervate structures important for voicing and swallowing. Damage to this nerve, commonly associated with surgery or idiopathic etiologies that largely occur with aging, results in impaired voicing and swallowing (Myssiorek, 2004). Sunderland proposed a model of peripheral nerve damage whereby a nerve's ability to resist damage from stretch and compression is determined by the quantity and composition of its epineurial connective tissues (Sunderland, 1951). Thus, it would be expected that epineurium differs depending upon the forces imposed on a nerve within its anatomical setting. The purpose of this study was to investigate RLN epineurium quantity and composition with development. A porcine model (piglet vs. juvenile) was used because of the similarity between porcine and human laryngeal innervation, anatomy and function. The entire RLN was excised bilaterally, and stereological methods were used to quantify the composition of epineurial connective tissues. Compared with the piglet, the juvenile pig RLN was double the diameter. While the piglet had no differences in the percentage of epineurial collagen and adipose between proximal and distal segments of both sides of the RLN, the juvenile pig had a greater percentage of collagen in the proximal segment of both sides of the RLN and a greater percentage of adipose in the distal segment of the left RLN compared with the proximal segment. In addition, unlike the piglet, the juvenile pig had a greater number of fascicles in the proximal than distal segment of the RLN, regardless of nerve side. These findings are consistent with predicted patterns associated with the different anatomical settings of the left and right RLN, show that the RLN changes with age, and support Sunderland's model.