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R. Shane Tubbs, Andrés A. Maldonado, Yolanda Stoves, Fabian N. Fries, Rong Li, Marios Loukas, Rod J. Oskouian and Robert J. Spinner

OBJECTIVE

The accessory nerve is frequently repaired or used for nerve transfer. The length of accessory nerve available is often insufficient or marginal (under tension) for allowing direct coaptation during nerve repair or nerve transfer (neurotization), necessitating an interpositional graft. An attractive maneuver would facilitate lengthening of the accessory nerve for direct coaptation. The aim of the present study was to identify an anatomical method for such lengthening.

METHODS

In 20 adult cadavers, the C-2 or C-3 connections to the accessory nerve were identified medial to the sternocleidomastoid (SCM) muscle and the anatomy of the accessory nerve/cervical nerve fibers within the SCM was documented. The cervical nerve connections were cut. Lengths of the accessory nerve were measured. Samples of the cut C-2 and C-3 nerves were examined using immunohistochemistry.

RESULTS

The anatomy and adjacent neural connections within the SCM are complicated. However, after the accessory nerve was “detethered” from within the SCM and following transection, the additional length of the accessory nerve increased from a mean of 6 cm to a mean of 10.5 cm (increase of 4.5 cm) after cutting the C-2 connections, and from a mean of 6 cm to a mean length of 9 cm (increase of 3.5 cm) after cutting the C-3 connections. The additional length of accessory nerve even allowed direct repair of an infraclavicular target (i.e., the proximal musculocutaneous nerve). The cervical nerve connections were shown not to contain motor fibers.

CONCLUSIONS

An additional length of the accessory nerve made available in the posterior cervical triangle can facilitate direct repair or neurotization procedures, thus eliminating the need for an interpositional nerve graft, decreasing the time/distance for regeneration and potentially improving clinical outcomes.

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R. Shane Tubbs, Isaiah Tubbs, Marios Loukas and Aaron A. Cohen-Gadol

OBJECT

Additional distal sites for placement of CSF diversionary shunts may be necessary in some patients. The present study aimed to investigate the marrow space of the ilium as a potential receptacle for CSF in patients with hydrocephalus.

METHODS

Cannulation of the marrow space of the ilium was performed in 5 fresh human cadavers less than 4 hours from time of death. Tap water was infused via a metal trocar for approximately 60 minutes.

RESULTS

A total of 30 L of water was easily injected into all cadaveric specimens without overflow from the infusion site or noticeable edema of the body. Upon inspection of the thoracic and abdominal cavities, no fluid accumulation was identified, ensuring that all infused fluid had gone into the vascular system.

CONCLUSIONS

Based on this cadaveric study, the ilium appears to be an ideal location for placement of the distal end of a CSF diversionary shunt when other anatomical receptacles are not an option. In vivo human studies are now required to verify these findings.

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R. Shane Tubbs, Anand N. Bosmia, Marios Loukas, Eyas M. Hattab and Aaron A. Cohen-Gadol

Object

Although it is often visualized surgically, details regarding the inferior medullary velum are lacking in the literature. The present study is intended to better elucidate this neuroanatomical structure using microsurgical and immunohistochemical analyses.

Methods

To study the inferior medullary velum, the authors performed microdissection in 15 adult cadavers. Following gross study, specimens were examined histologically.

Results

The inferior medullary velum extended from the flocculus to the middle cerebellar peduncle and stretched between the inferior cerebellar peduncle and the nodule and pyramid. The average thickness of the velum was found to be 0.5 mm (range 0.35–0.8 mm) and the average length was found to be 6 mm (range 5.5–7.2 mm). Arterial branches were identified in all specimens that arose from medullary branches of the posterior inferior cerebellar artery and supplied the inferior medullary velum. Histologically and from internal to external, a choroid plexus epithelium as a single cell layer was adjacent to a cuboidal layer of ependymal cells with no visible cilia. The next layer contained scattered glia in single cells or small clusters. The most external layer was composed of flat spindle cells resembling fibroblasts. No neurons of any type were identified. Only rare axons traversed the thin hypocellular zone that disappeared toward the midline.

Conclusions

Based on this cadaveric study, the authors conclude that division of the inferior medullary velum should be relatively harmless as no neuronal cells were identified in this structure, which appears to be a vestigial bridge of tissue between the left and right sides of the cerebellum.

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R. Shane Tubbs, Mitchel Muhleman, Samuel G. McClugage, Marios Loukas, Joseph H. Miller, Joshua J. Chern, Curtis J. Rozzelle, W. Jerry Oakes and Aaron A. Cohen-Gadol

Cysts of the choroidal fissure are often incidentally identified. Symptoms from such cysts appear to be exceedingly rare. Herein, the authors report a case series of symptomatic enlargement of choroidal fissure cysts that were surgically treated. Although cysts of the choroidal fissure do not normally become symptomatic, the neurosurgeon should be aware of such a complication. Based on the authors' experience, surgical fenestration of such cysts has good long-term results.

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R. Shane Tubbs, Olivia J. Rompala, Ketan Verma, Martin M. Mortazavi, Brion Benninger, Marios Loukas and M. Rene Chambers

Object

Although the uncovertebral region is neurosurgically relevant, relatively little is reported in the literature, specifically the neurosurgical literature, regarding its anatomy. Therefore, the present study aimed at further elucidation of this region's morphological features.

Methods

Morphometry was performed on the uncinate processes of 40 adult human skeletons. Additionally, range of motion testing was performed, with special attention given to the uncinate processes. Finally, these excrescences were classified based on their encroachment on the adjacent intervertebral foramen.

Results

The height of these processes was on average 4.8 mm, and there was an inverse relationship between height of the uncinate process and the size of the intervertebral foramen. Degeneration of the vertebral body (VB) did not correlate with whether the uncinate process effaced the intervertebral foramen. The taller uncinate processes tended to be located below C-3 vertebral levels, and their average anteroposterior length was 8 mm. The average thickness was found to be 4.9 mm for the base and 1.8 mm for the apex. There were no significant differences found between vertebral level and thickness of the uncinate process. Arthritic changes of the cervical VBs did not necessarily deform the uncinate processes. With axial rotation, the intervertebral discs were noted to be driven into the ipsilateral uncinate process. With lateral flexion, the ipsilateral uncinate processes aided the ipsilateral facet joints in maintaining the integrity of the ipsilateral intervertebral foramen.

Conclusions

A good appreciation for the anatomy of the uncinate processes is important to the neurosurgeon who operates on the spine. It is hoped that the data presented herein will decrease complications during surgical approaches to the cervical spine.

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R. Shane Tubbs, Eyas M. Hattab, Marios Loukas, Joshua J. Chern, Melissa Wellons, John C. Wellons III, Bermans J. Iskandar and Aaron A. Cohen-Gadol

Object

Endocrine dysfunction following endoscopic third ventriculostomy (ETV) is rare, but it has been reported. In the present study the authors sought to determine the histological nature of the floor of the third ventricle in hydrocephalic brains to better elucidate this potential association.

Methods

Five adult cadaveric brains with hydrocephalus were examined. Specifically, the floors of the third ventricle of these specimens were studied histologically. Age-matched controls without hydrocephalus were used for comparison.

Results

Although it was thinned in the hydrocephalic brains, the floor of the third ventricle had no significant difference between the numbers of neuronal cell bodies versus nonhydrocephalic brains.

Conclusions

Although uncommon following ETV, endocrine dysfunction has been reported. Based on the present study, this is most likely to be due to the injury of normal neuronal cell bodies found in this location, even in very thinned-out tissue.

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R. Shane Tubbs, Martin M. Mortazavi, Marios Loukas, Anthony V. D'Antoni, Mohammadali M. Shoja and Aaron A. Cohen-Gadol

Object

The nerves of the posterior neck are often encountered by the neurosurgeon and are sometimes the focus of denervation procedures for muscular, joint, or nervous pathologies. One collection of fibers in this region that has not been previously investigated is the Cruveilhier plexus, interneural connections between the dorsal rami of the upper cervical nerves.

Methods

Fifteen adult cadavers (30 sides) were subjected to dissection of the upper cervical and occipital regions with special attention given to identifying potential connections between adjacent extradural dorsal rami of the cervical nerves. When connections were identified, measurements were made and random samples were immunohistochemically stained.

Results

At least one communicating branch was identified on 86.7% of sides. Sampled nervous loops were composed primarily of sensory fibers, but occasional motor fibers were identified. For C-1, a communicating loop joined the medial branches of C-2 on 65.4% of sides. On 29.4% of sides, this loop pierced the obliquus capitis inferior muscle before joining C-2. On 54% of sides, a communicating loop joined the medial branches of the dorsal rami of C-2 and C-3; and on 15.4% of sides, a communicating loop joined the medial branches of the dorsal rami of C-3 and C-4. No specimen had communicating branches between the dorsal rami of cervical nerves C-5 to C-8. Articular branches arose from the deep surface of the interneural connections as they crossed the adjacent facet joint on 34.6% of sides. Loops giving rise to fibers that terminated into surrounding musculature were seen on 35% of sides.

Conclusions

Physical examinations that reveal unexpected results, such as altered sensory dermatome findings, may be attributed to the Cruveilhier plexus. Based on findings in the present study, surgical procedures, such as those aimed at completely denervating the upper posterior cervical musculature, facets, or nerves supplying the skin of the occiput, must also transect the Cruveilhier plexus.

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Marios Loukas, Brian J. Shayota, Kim Oelhafen, Joseph H. Miller, Joshua J. Chern, R. Shane Tubbs and W. Jerry Oakes

A single pathophysiological mechanism of Chiari Type I malformations (CM-I) has been a topic of debate. To help better understand CM-I, the authors review disorders known to be associated with CM-I. The primary methodology found among most of them is deformation of the posterior cranial fossa, usually with subsequent decrease in volume. Other mechanisms exist as well, which can be categorized as either congenital or acquired. In understanding the relationship of such disorders with CM-I, we may gain further insight into the process by which cerebellar tonsillar herniation occurs. Some of these pathologies appear to be true associations, but many appear to be spurious.

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R. Shane Tubbs, Martin M. Mortazavi, Marios Loukas, Anthony V. D'Antoni, Mohammadali M. Shoja, Joshua J. Chern and Aaron A. Cohen-Gadol

Object

Occipital neuralgia can be a debilitating disease and may occur following operative procedures near the occipital and nuchal regions. One nerve of this region, the third occipital nerve (TON), has received only scant attention, and its potential contribution to occipital neuralgia has not been appreciated. Therefore, in the present study the authors aimed to detail the anatomy of this nerve and its relationships to midline surgical approaches of the occiput and posterior neck.

Methods

Fifteen adult cadavers (30 sides) underwent dissection of the upper cervical and occipital regions. Special attention was given to identifying the course of the TON and its relationship to the soft tissues and other nerves of this region. Once identified superficially, the TON was followed deeply through the nuchal musculature to its origin in the dorsal ramus of C-3. Measurements were made of the length and diameter of the TON. Additionally, the distance from the external occipital protuberance was measured in each specimen. Following dissection of the TON, self-retaining retractors were placed in the midline and opened in standard fashion while observing for excess tension on the TON.

Results

Articular branches were noted arising from the deep surface of the nerve in 63.3% of sides. The authors found that the TON was, on average, 3 mm lateral to the external occipital protuberance, and small branches were found to cross the midline and communicate with the contralateral TON inferior to the external occipital protuberance in 66.7% of sides. The TON trunk became subcutaneous at a mean of 5 cm inferior to the external occipital protuberance. In all specimens, the cutaneous main trunk of the TON was intimately related to the nuchal ligament. Insertion of self-retaining retractors in the midline placed significant tension on the TON in all specimens, both superficially and more deeply at its adjacent facet joint.

Conclusions

Although damage to the TON may often be unavoidable in midline approaches to the craniocervical region, appreciation of its presence and knowledge of its position and relationships may be useful to the neurosurgeon who operates in this region and may assist in decreasing postoperative morbidity.