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R. Shane Tubbs, Marios Loukas, Robert G. Louis Jr., Mohammadali M. Shoja, Leslie Acakpo-Satchivi, Jeffrey P. Blount, E. George Salter, W. Jerry Oakes and John C. Wellons III

Object

The superior and inferior sagittal sinuses have been well studied. Interestingly, other venous structures within the falx cerebri have received scant attention in the medical literature. The present study was performed to elucidate the presence and anatomy of these midline structures.

Methods

The authors examined 27 adult latex- or ink-injected cadaveric specimens to observe the morphological features of the sinuses within the falx cerebri (excluding the inferior and superior sagittal sinuses).

Results

All specimens were found to have an extensive network of small tributaries within the falx cerebri that were primarily concentrated in its posterior one third. In this posterior segment, these structures were usually more pronounced in the inferior two thirds. The portion of the falx cerebri not containing significant falcine venous sinus was termed a “safe area.” These vascular channels ranged in size from 0.5 mm to 1.1 cm (mean 0.6 mm); 100% of these vessels communicated with the inferior sagittal sinus. Classification of the structures was then performed based on communication of the falcine venous sinus with the superior sagittal sinus. Type I falcine sinuses had no communication with the superior sagittal sinus, Type II falcine sinuses had limited communication with the superior sagittal sinus, and Type III falcine sinuses had significant communication with the superior sagittal sinus. Seventeen (63%) of 27 specimens communicated with the superior sagittal sinus (Types II and III). Further subdivision revealed 10 Type I, seven Type II, and 10 Type III falcine venous plexuses.

Conclusions

There are other venous sinuses in the falx cerebri in addition to the superior and inferior sagittal sinuses. Neurosurgical procedures that necessitate incising or puncturing the falx cerebri can be done more safely via a described safe area. Given that the majority of specimens in the authors' study were found to have a plexiform venous morphology within the falx cerebri, they propose that these channels be referred to as the falcine venous plexus and not sinus. The falcine venous plexus should be taken into consideration by the neurosurgeon.

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R. Shane Tubbs, Marios Loukas, Robert G. Louis Jr., Mohammadali M. Shoja, Cameron S. Askew, April Phantana-Angkool, E. George Salter and W. Jerry Oakes

Object

The basal vein of Rosenthal (BV) courses from the premesencephalic cistern, through the ambient cistern, and terminates in the quadrigeminal cistern. The aim of this study was to describe and quantitate the surgical anatomy of this structure and specifically to provide landmarks for identifying this vessel along its course. These data may be of use, for example, to surgeons using subtemporal operative approaches through regions where this vessel is concealed.

Methods

The authors examined 15 latex-injected adult cadaveric brains (30 sides) to delineate the morphological characteristics of the BV. Dissections of the BV were then performed and measurements were made between this structure and the tentorial incisura at the anterior, middle, and posterior borders of the lateral midbrain.

All specimens were found to have a left and right BV with varying morphological characteristics. The mean distance between the BV and posterior cerebral artery at the midpoint of the lateral midbrain was 16 mm. The BV was always found superomedial to the posterior cerebral artery along the lateral aspect of the midbrain, and the BV ranged in diameter from 1 to 5 mm. The BV drained into the vein of Galen in all but two specimens. The mean distances from the tentorial edge to the BV at the anterior, middle, and posterior borders of the lateral midbrain were 11, 13, and 4 mm, respectively. No statistically significant differences were found when comparing left and right sides or male and female specimens.

Conclusions

The authors hope that these data will help the neurosurgeon operating near the BV to avoid injury to this important structure.

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R. Shane Tubbs, Marios Loukas, Mohammadali M. Shoja, E. George Salter, W. Jerry Oakes and Jeffrey P. Blount

Object

The authors describe a technique in which the cervical portion of the vagus nerve is exposed during procedures such as neuroma resection or, more commonly, during the placement of a vagus nerve stimulator.

Methods

To test their hypothesis that a posterolateral approach to the vagus nerve may be feasible and efficacious, the authors performed dissection of the left-sided vagus nerve in 13 adult cadavers. The carotid sheath was exposed via the posterior cervical triangle, and the vagus nerve was identified posterolaterally. Measurements were made of the length of available nerve, and the anatomical approach was documented. As part of a comparison study regarding the available length of nerve, the authors exposed the left vagus nerve in five additional adult cadavers via a standard anterior approach to the carotid sheath, and compared the results obtained with each technique.

A mean length of 12 cm of the vagus nerve was isolated when using the posterior approach to the carotid sheath, whereas a mean length of 11 cm of the nerve was documented when using the anterior approach. With the aforementioned posterior approach, no obvious injury occurred to the vagus nerve or other local neurovascular structures such as the spinal accessory nerve.

Conclusions

Evaluation of the findings obtained in the present cadaveric study showed that a posterior approach to the vagus nerve is feasible. The technique for posterior exposure of the carotid sheath may prove useful in surgical exposures of the vagus nerve when a standard anterior method is not possible.

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R. Shane Tubbs, Charles A. Khoury, E. George Salter, Leslie Acakpo-Satchivi, John C. Wellons III, Jeffrey P. Blount and W. Jerry Oakes

Object

New information regarding nerve branches of the brachial plexus can be useful to the surgeon performing neurotization procedures following patient injury. Nerves in the vicinity of the axillae have been commonly used for neural grafting procedures, with the exception of the lower subscapular nerve (LSN).

Methods

The authors dissected and measured the LSN in 47 upper extremities (left and right sides) obtained in 27 adult cadavers, and determined distances between the LSN and surrounding nerves to help quantify it for possible use in neurotization procedures.

The mean diameter of the LSN was 2.3 mm. The mean length of the LSN from its origin at the posterior cord until it branched to the subscapularis muscle was 3.5 cm, and the mean distance from this branch until its termination in the teres major muscle was 6 cm. Therefore, the mean length of the entire LSN from the posterior cord to the teres major was 9.5 cm.

When the LSN was mobilized to explore its possible use in neurotization, it reached the entrance site of the musculocutaneous nerve into the coracobrachialis muscle in all but three sides and was within 1.5 cm from this point in these three. In the other specimens, the mean length of the LSN distal to this site of the musculocutaneous nerve was 2 cm. The mobilized LSN reached the axillary nerve trunk as it entered the quadrangular space in all specimens. The mean length of the LSN distal to this point on the axillary nerve was 2.5 cm. Furthermore, on all but one side the LSN was found within the confines of an anatomical triangle previously described by the authors.

Conclusions

The authors hope that these data will prove useful to the surgeon for both identifying the LSN and planning for potential neurotization procedures of the brachial plexus.

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R. Shane Tubbs, James W. Custis, E. George Salter, Jeffrey P. Blount, W. Jerry Oakes and John C. Wellons III

Object

In neurotization procedures, donor nerves—either whole or in part—with relatively pure motor function can be carefully chosen to provide the optimal nearby motor input with as little donor site morbidity as possible. In this context, the ulnar nerve branches to the forearm muscles are relatively dispensable; however, quantitation of and landmarks for these branches are lacking in the literature.

Methods

The ulnar branches to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) muscles in 20 upper extremities obtained in adult cadaveric specimens were dissected and quantified.

In the forearm, a mean of four nerve branches led to the FCU and FDP muscles. A mean of 3.4 branches led to the FCU muscle; of these, one to three were medial branches and zero to two were lateral. Medial branches to the FCU muscle originated a mean of 2.7 cm inferior to the medial epicondyle. Lateral branches to the FCU muscle originated at a mean of 3.3 cm inferior to the medial epicondyle. The mean length of the medial branches was 3.2 cm, whereas the mean length of the lateral branches was 3.3 cm. All nerves had a single trunk for the FDP muscle, and in all specimens this branch was located deep to the main ulnar nerve trunk, originating from the ulnar nerve a mean of 2.7 cm inferior to the medial epicondyle. These branches had a mean length of 5.6 cm. The mean diameter of all medial and lateral branches to the FCU muscle was 1 mm, and the mean diameter of the branch to the FDP muscle was 2.1 mm. All branches to both the FCU and FDP muscles arose from the ulnar nerve, over its first approximately 5 cm from the level of the medial epicondyle. Additionally, all branches could be easily lengthened by gentle proximal dissection from the main ulnar nerve.

Conclusions

Ulnar branches to the forearm can be easily localized and used for neurotization procedures. The branch to the FDP muscle had the greatest diameter and longest length, easily reaching the median nerve and posterior interosseous nerve via a transinterosseous membrane tunneling procedure. Furthermore, this branch could be teased away from the main ulnar nerve trunk and made to reach the distal branches of the musculocutaneous nerve in the arm.

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R. Shane Tubbs, James W. Custis, E. George Salter, John C. Wellons III, Jeffrey P. Blount and W. Jerry Oakes

Object

There are scant data regarding the anterior interosseous nerve (AIN) in the neurosurgical literature. In the current study the authors attempt to provide easily identifiable superficial osseous landmarks for the identification of the AIN.

Methods

The AIN in 20 upper extremities obtained in adult cadaveric specimens was dissected and quantified. Measurements were obtained between the nerve and surrounding superficial osseous landmarks.

The AIN originated from the median nerve at mean distances of 5.4 cm distal to the medial epicondyle of the humerus and 21 cm proximal to the ulnar styloid process. The distance from the origin of the AIN to its branch leading to the flexor pollicis longus muscle and to the point it travels deep to the pronator quadratus (PQ) muscle measured a mean 4 and 14.4 cm, respectively. The mean distance from the AIN branch leading to the flexor pollicis longus muscle to the proximal PQ muscle was 12.1 cm, and the mean distance between this branch and the ulnar styloid process was 7.2 cm. The mean diameter of the AIN was 1.6 mm at the midforearm.

Conclusions

Additional landmarks for identification of the AIN can aid the neurosurgeon in more precisely isolating this nerve and avoiding complications. Furthermore, after quantitation of this nerve, the AIN branches can be easily used for neurotization of the median and ulnar nerves, and with the aid of a transinterosseous membrane tunneling technique, passed to the posterior interosseous nerve.

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R. Shane Tubbs, E. George Salter, John C. Wellons III, Jeffrey P. Blount and W. Jerry Oakes

Object

There is a paucity of information in the neurosurgical literature regarding the surgical anatomy surrounding the posterior interosseous nerve (PIN). The goal of the current study was to provide easily recognizable superficial bone landmarks for identification of the PIN.

Methods

Thirty-four cadaveric upper extremities obtained from adults were subjected to dissection of the PINs, and measurements were made between this nerve and surrounding superficial bone landmarks.

In all specimens the main radial trunk was found to branch into its superficial branch and PIN at the level of the lateral epicondyle of the humerus. Proximally, the PIN was best identified following dissection between the brachioradialis and extensor carpi radialis longus and brevis muscles. At its exit site from the supinator muscle, the PIN was best identified after retraction between the extensor carpi radialis longus and brevis and extensor digitorum communis muscles. This site was a mean distance of 6 cm distal to the lateral epicondyle of the humerus. No compression of the PIN by the tendon of origin of the extensor carpi radialis brevis muscle was seen. One specimen was found to have a proximally split PIN that provided a previously undefined articular branch to the elbow joint. The mean diameter of the PIN proximal to the supinator muscle was 4.5 mm. The leash of Henry crossed the PIN in all but one specimen and was found at a mean distance of 5 cm inferior to the lateral epicondyle. The PIN exited the distal edge of the supinator muscle at a mean distance of 12 cm distal to the lateral epicondyle of the humerus. Here the mean diameter of the PIN was 4 mm. The exit site from the distal edge of the supinator was found to be at a mean distance of 18 cm proximal to the styloid process of the ulna. This exit site for the PIN was best identified following dissection between the extensor carpi radialis longus and brevis and extensor digitorum communis muscles. The distal articular branch of the PIN was found to have a mean length of 13 cm and the proximal portion of this terminal segment was located at a mean distance of 7.5 cm proximal to the Lister tubercle.

Conclusions

The addition of more anatomical landmarks can help the neurosurgeon to be more precise in identifying the PIN and in avoiding complications during surgery in this region.

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R. Shane Tubbs, E. George Salter, James W. Custis, John C. Wellons III, Jeffrey P. Blount and W. Jerry Oakes

Object

There is insufficient information in the neurosurgical literature regarding the long thoracic nerve (LTN). Many neurosurgical procedures necessitate a thorough understanding of this nerve's anatomy, for example, brachial plexus exploration/repair, passes for ventriculoperitoneal shunt placement, pleural placement of a ventriculopleural shunt, and scalenotomy. In the present study the authors seek to elucidate further the surgical anatomy of this structure.

Methods

Eighteen cadaveric sides were dissected of the LTN, anatomical relationships were observed, and measurements were obtained between it and surrounding osseous landmarks.

The LTN had a mean length of 27 ± 4.5 cm (mean ± standard deviation) and a mean diameter of 3 ± 2.5 mm. The distance from the angle of the mandible to the most proximal portion of the LTN was a mean of 6 ± 1.1 cm. The distance from this proximal portion of the LTN to the carotid tubercle was a mean of 3.3 ± 2 cm. The LTN was located a mean 2.8 cm posterior to the clavicle. In 61% of all sides the C-7 component of the LTN joined the C-5 and C-6 components of the LTN at the level of the second rib posterior to the axillary artery. In one right-sided specimen the C-5 component directly innervated the upper two digitations of the serratus anterior muscle rather than joining the C-6 and C-7 parts of this nerve. The LTN traveled posterior to the axillary vessels and trunks of the brachial plexus in all specimens. It lay between the middle and posterior scalene muscles in 56% of sides. In 11% of sides the C-5 and C-6 components of the LTN traveled through the middle scalene muscle and then combined with the C-7 contribution. In two sides, all contributions to the LTN were situated between the middle scalene muscle and brachial plexus and thus did not travel through any muscle. The C-7 contribution to the LTN was always located anterior to the middle scalene muscle. In all specimens the LTN was found within the axillary sheath superior to the clavicle. Distally, the LTN lay a mean of 15 ± 3.4 cm lateral to the jugular notch and a mean of 22 ± 4.2 cm lateral to the xiphoid process of the sternum.

Conclusions

The neurosurgeon should have knowledge of the topography of the LTN. The results of the present study will allow the surgeon to better localize this structure superior and inferior to the clavicle and decrease morbidity following invasive procedures.

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R. Shane Tubbs, E. George Salter and W. Jerry Oakes

Object

An anomalous vertebral artery (VA) position can jeopardize an otherwise successful procedure, such as a posterior cranial fossa decompression for hindbrain herniation, and may increase the propensity for VA occlusion.

Methods

The authors describe the detailed anatomy of the entrance site of the VA in adult human crania in which there is occipitalization of the atlas. They found that if the atlantal posterior arch or hemiarch was fused to the occiput one should anticipate encountering an anomalous osseous pathway as the VA enters into the cranium, as evidenced by this finding in 80% of their specimens. An anomalous entry pathway was present in all but one left-sided specimen in which the left posterior hemiarch was not fused to the occiput and one right-sided specimen in which there was an unfused and rudimentary posterior arch of the atlas.

Conclusions

The clinician should consider the possibility that the VA takes anomalous routes into the skull in cases in which there is occipitalization of the atlas.

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R. Shane Tubbs, Kevin Ammar, Peter Liechty, John C. Wellons III, Jeffrey P. Blount, E. George Salter and W. Jerry Oakes

Object

Descriptions of the marginal venous sinus are lacking in the extant medical literature. The aim of this study was to characterize the anatomy of this intracranial venous sinus.

Methods

The authors examined the marginal sinuses in 15 adult cadavers following the injection of latex into the intracranial venous system. The maximal vertical height of the sinuses, which ranged from 7 to 15 mm (mean 10 mm), was located at the lateral aspect of the foramen magnum at or near the region at which the spinal accessory nerve crossed en route to the jugular foramen. In all specimens the sinus tapered as it traveled both anteriorly and posteriorly. Ninety-three percent of the specimens demonstrated significant drainage into the veins of the hypoglossal canal. The hypoglossal nerve rootlets pierced the sinus and its tributaries in 11 (73%) of 15 specimens. The marginal sinus communicated with the basilar venous plexus in 12 (80%) of 15 specimens and with the occipital sinus in all specimens (100%). There was venous communication with the sigmoid sinus in all specimens. The vertebral artery coursed through the marginal sinus as it pierced the posterior atlantooccipital membrane in all left sides and in 87% of the right sides.

Conclusions

These quantitative data will be useful to the neurosurgeon who operates in the region of the marginal sinus.