The existence of hypoglossal root ganglion cells in adult humans: potential clinical implications.

INTRODUCTION: Ganglion cells of the hypoglossal nerve (HN) have been confirmed in certain animals but have been thought not to be present in man. To investigate for the presence of these structures in adult humans and if present, to verify their functionality, the present study was performed. MATERIALS AND METHODS: We harvested adult cadaveric HN and observed for ganglion cells. Histological and immunohistochemical analyses were performed on all specimens. RESULTS: Ganglion cells were found in 33% of specimens. Using immunohistochemistry, we found that these ganglia were sympathetic in nature. Based on our findings, ganglion cells do exist in the human HN although they are located sporadically and are found inconstantly. CONCLUSIONS: Such information may be valuable in elucidating other functions of the HN and may aid in the histological diagnosis of this nerve. Additionally, pathology involving HN such as paragangliomas, are supported by our findings of the presence of autonomic ganglion cells in some HN specimens.

Histopathological basis for neurogenic thoracic outlet syndrome. Laboratory investigation.

OBJECT: To the best of the authors' knowledge, no report exists that has demonstrated the histopathological changes of neural elements within the brachial plexus as a result of cervical rib compression. METHODS: Four hundred seventy-five consecutive human cadavers were evaluated for the presence of cervical ribs. From this cohort, 2 male specimens (0.42%) were identified that harbored cervical ribs. One of the cadavers was found to have bilateral cervical ribs and the other a single right cervical rib. Following gross observations of the brachial plexus and, specifically, the lower trunk and its relationship to these anomalous ribs, the lower trunks were submitted for immunohistochemical analysis. Specimens were compared with two age-matched controls that did not have cervical ribs. RESULTS: The compressed plexus trunks were largely unremarkable proximal to the areas of compression by cervical ribs, where they demonstrated epi- and perineurial fibrosis, vascular hyalinization, mucinous degeneration, and frequent intraneural collagenous nodules. These histological findings were not seen in the nerve specimens in control cadavers. The epineurium was thickened with intersecting fibrous bands, and the perineurium appeared fibrotic. Many of the blood vessels were hyalinized. The nerve fascicles contained frequent intraneural collagenous nodules in this area, and focal mucinous degeneration was identified. CONCLUSIONS: Cervical ribs found incidentally may cause histological changes in the lower trunk of the brachial plexus. The clinician may wish to observe or perform further evaluation in such patients.

Human spinal arachnoid villi revisited: immunohistological study and review of the literature.

OBJECT: Few have described the relationship between arachnoid protrusions (villi) and adjacent spinal radicular veins, and the descriptions that do exist are conflicting. Some authors have even denied the presence of spinal arachnoid villi, suggesting that they play no role in cerebrospinal fluid (CSF) absorption. METHODS: To further elucidate these structures, laminectomies from C-2 inferiorly to S-2 were performed in 10 fresh human adult cadavers. Following removal of the laminae, the dural nerve sleeves were identified and the spinal nerves excised 1 cm lateral and medial to the intervertebral foramina. Samples were submitted for histological and immunohistological analysis. RESULTS: The authors identified arachnoid villi in all specimens. The length of these structures was approximately 50 to 170 microm. Regionally, these villi were more concentrated in the lumbar region, but they were not present at every vertebral level, with observed skip zones. Occasionally, more than one villus was identified per vertebral level. The majority of villi were intimately related to an adjacent radicular vein. There was a direct relationship between the size of the adjacent radicular vein, and the presence and number of arachnoid villi. CONCLUSIONS: Findings in the present study have demonstrated that arachnoid villi exist and are morphologically associated with radicular veins. These data support the theory that CSF absorption occurs not only intracranially but also along the spinal axis. Further animal studies are necessary to prove that CSF traverses these villi and is absorbed into the spinal venous system.

The tectorial membrane: anatomical, biomechanical, and histological analysis.

There is minimal information in the literature regarding the tectorial membrane. Further, information in the literature regarding the anatomy and function of this structure is often contradictory. We performed the current study to elucidate further this structure's detailed anatomy, function, and histology. Thirteen adult cadavers underwent dissection of their tectorial membranes and detailed observations and measurements were made of them. Ranges of motion of the craniocervical junction were performed before and after transection of this structure. Histological analysis was performed on all membranes. The tectorial membrane was found to attach much more superiorly than previously described and was found to be firmly adherent to the cranial base and body of the axis but not to the posterior aspect of the odontoid process. The mean thickness of this membrane was found to be 1 mm. Flexion of the head made the tectorial membrane fully taut at 15 degrees and extension made it fully taut at 20 degrees; however, there was a buckling effect (redundant tectorial membrane) noted at the level of the odontoid process in extension. With the alar and transverse ligaments cut and with flexion of the head, the middle portion of this membrane was stretched over the odontoid process, thus acting as a "hammock" that inhibited the odontoid process from moving posteriorly. The tectorial membrane did not limit cervical flexion per se but rather helped to insure that the odontoid process did not impinge into the cervical canal. Lateral flexion was not found to be limited by this structure. Histologically, parallel collagen fibers with spindle-shaped fibrocytes were observed within this membrane and near its attachment to the posterior axis, the collagen fibers were noted to be more homogenous with larger non-spindled fibrocytes. At the cranial attachment of the tectorial membrane, multiple calcified areas were noted that interdigitated with the underlying bone. Also near this cephalic bony attachment, there was an increase in the number of elastic fibers, which were found running parallel with the surrounding Type III collagen fibers. The tectorial membrane was found to attach much more superiorly than previously described. We would propose that the tectorial membrane provides for a second line of defense, preventing the odontoid process from compressing the spinal cord and by doing so, secondarily limits movement of the craniocervical juncture. This hypothesis is strengthened by the finding of many elastic fibers in the tectorial membrane. To our knowledge, our study is the first to perform a detailed histological analysis of the tectorial membrane. We hope that these data are useful to the clinician who investigates this ligament of the craniocervical region.

Does the ganglion of Ribes exist?

Some have included the ganglion of Ribes (Francois Ribes, 1765-1845), lying on the anterior communicating artery, as the most superior ganglion of the sympathetic nervous system. To verify the presence of this structure, the anterior communicating artery was harvested from 40 fresh adult cadavers and histological analysis and immunochemistry performed. Grossly and with magnification, no ganglion-like structures were found in or around the anterior communicating artery in any specimen. However, scattered neuronal cell bodies were found in the adventitia of the anterior communicating artery with histological immunochemical analysis. Based on the lack of vasoactive intestinal peptide staining and the positive reaction to tyrosine hydroxylase, these neurons are most likely sympathetic in nature. Based on our findings, a grossly visible ganglion of Ribes does not exist. However, neuronal cell bodies were found in the adventitia of the anterior communicating artery although the function of such cells remains speculative.