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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.

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.

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.

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.

Object: Reports describing surgical landmarks with which to identify the branches of the lumbar plexus found on the posterior abdominal wall are lacking in the English-language literature., Methods: The authors examined 22 sides from six female and five male cadavers. Measurements were made between the branches of the lumbar plexus and various bone landmarks such as the midline vertebral bodies, supracristal plane--a horizontal line connecting the superior-most aspect of the left and right iliac crests approximating the LA-5 vertebrae--and anterior superior iliac spine (ASIS). The mean distances from the midline and as they emerged through or lateral to the psoas major muscle to the subcostal, iliohypogastric, ilioinguinal, lateral femoral cutaneous, genitofemoral, and femoral nerves, were 5.5, 6, 6.5, 6, 4.5, and 4.5 cm, respectively. At a vertical line through the midpoint between the ASIS and the midline, the subcostal, iliohypogastric, and ilioinguinal nerves were superior to the supracristal plane at mean distances of 8, 4, and 5 cm, respectively. Inferior to the supracristal plane and in a vertical line through a midpoint between the ASIS and the midline, the lateral femoral and femoral nerves were found to have mean distances of 5 and 5.5 cm, respectively. The obturator nerve had a mean distance of 3 cm lateral to the midline. Additionally, the lateral femoral cutaneous nerve had a mean distance of 1.5 cm inferomedial to the ASIS., Conclusions: A good working knowledge of the locations and anatomy of the nerves of the lumbar plexus on the posterior abdominal wall is necessary for the surgeon who operates in this region. The measurements provided herein will aid the surgeon who wishes to expose or avoid these nerves, thus precluding injury.