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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.

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

Object. The spinal accessory nerve (SAN) within the posterior cervical triangle (PCT) is the most commonly iatrogenically injured nerve in the body. Nevertheless, there is a paucity of published information regarding superficial landmarks for the SAN in this region. Additional identifiable landmarks of this nerve may assist the surgeon in identifying it for repair, use of it in peripheral nerve neurotization, or avoiding it as in proximal brachial plexus repair. The present study was undertaken to provide reliable superficial landmarks for the identification of the SAN within the PCT.

Methods. The PCT was dissected in 30 cadaveric sides. Measurements were made between the SAN and surrounding landmarks. The mean distances between the entry site of the SAN into the trapezius and a midpoint of the clavicle, mastoid process, acromion process, and lateral aspect of the sternocleidomastoid (SCM) muscle were 6, 7, 5.5, and 3.5 cm, respectively. The mean distances between the angle of the mandible and the mastoid process and the exit point of the SAN from the posterior border of the SCM muscle were 6 and 5 cm, respectively. The mean width and length of the SAN were 3 and 3.5 cm, respectively.

Conclusions. It is the authors' hope that these data will aid those who may need to locate or avoid the SAN while undertaking surgery in the PCT and thus decrease morbidity that may follow manipulation of this region.

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R. Shane Tubbs and W. Jerry Oakes

✓The authors present the case of a child diagnosed as having Beckwith—Wiedemann syndrome and Chiari I malformation. Hemihypertrophy is associated with Beckwith—Wiedemann syndrome and has been described in conjunction with Chiari I malformation. The authors hypothesize that the hemihypertrophy that may involve the skull base and Chiari I malformation found in their patient are not spurious findings but are pathologically related, perhaps by slight dysmorphologies of the posterior cranial fossa.

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R. Shane Tubbs, Randall Lee Murphy, David R. Kelly, Robert Lott, E. George Salter and W. Jerry Oakes

Object

The filum terminale externum (FTE) is the extradural component of the filum terminale internum and little attention has been dedicated to this structure in the literature. The authors theorized that the rare intrasacral ependymomas may originate from ependymal cell collections within the FTE.

Methods

To address this hypothesis, the FTE was dissected and analyzed histologically in 15 adult cadavers. None of the specimens was found to harbor ependymal or other glial cell collections.

Conclusions

The authors found previously undescribed smooth-muscle cells within the FTE. Furthermore, histological analysis identified adipose, nerve, bone, and cartilage cells.

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R. Shane Tubbs and W. Jerry Oakes

✓The authors present a case of an adolescent with achondroplasia and symptoms of neurogenic claudication who, interestingly, also presented with intermittent priapism. Both the neurogenic claudication and priapism were relieved following a thoracolumbar laminectomy. To our knowledge, this is the first report of a dwarf with thoracolumbar spinal canal stenosis presenting with priapism.

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Jeffrey P. Blount, R. Shane Tubbs, Mamehri Okor, Elizabeth C. Tyler-Kabara, John C. Wellons III, Paul A. Grabb and W. Jerry Oakes

Object

The authors describe the technique of transecting the spinal cord in children born with myelomeningocele who have undergone multiple detherings and are functionally paraplegic.

Methods

The authors' technique involves identifying the neural placode and sectioning the normal spinal cord just superior to this site. No postoperative complications have been identified in 14 patients undergoing this procedure over an 11-year period. No patient at last follow up was found to have symptoms referable to a tethered spinal cord. The advantage of this procedure is to excise the normally pia-coated cord, which is unlikely to retether compared with the neural placode, which is often covered with scar tissue and does not have a well-formed pial surface—hence, predisposing it to frequent dorsal adhesions.

Conclusions

The authors believe that this technique is of benefit in a small, carefully selected group of myelodys-plastic patients with repetitive tethering of the spinal cord.

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W. Jerry Oakes