Home » Biology Articles » Anatomy & Physiology » Anatomy, Human » Anatomy of the Spinal Accessory Nerve Plexus: Relevance to Head and Neck Cancer and Atherosclerosis » Gross Anatomy and Dissection Microscopy Intracranially and Extracranially of the Spinal Accessory Nerve Plexus and Its Blood Supply With Some Practical and Theoretic Observations
Gross Anatomy and Dissection Microscopy Intracranially and Extracranially of the Spinal Accessory Nerve Plexus and Its Blood Supply With Some Practical and Theoretic Observations
- Anatomy of the Spinal Accessory Nerve Plexus: Relevance to Head and Neck Cancer and Atherosclerosis
Two central nervous system origins are customarily ascribed to each cranial nerve: 1.) Superficial origins are from the surface of the central nervous system, while 2.) Deep origins are from cell bodies and nuclei within the central nervous system (30). The general location and approximate number of rootlets of origin for cranial nerves have been well described in standard anatomy texts (31). Contrariwise, descriptions of the interconnections of these rootlets are not readily found. Bischoff published such a study in 1865 (32). Fragmentary descriptions of individual nerve connections often have been found only scattered throughout the literature. For example, Hovelaque (33) quotes earlier authors Hirshfield and Sappy in their descriptions of variations in interconnections of the ansa of von Haller, also called the nerve of Jacobson, lying between the hypoglossal and facial nerves. As another example of a variable interconnection observed in our laboratory, in one subject, the rootlets of the glossopharyngeal were connected to the vestibulocochlear as well as the facial nerve. The latter interconnection was other than the inconstant but well-known branch of the facial nerve to the tympanic cavity just described, i.e., the nerve of Jacobson or the Ansa of von Haller (33, 34). In this regard, it would be useful to know the topographical anatomy of the cranial nerves as discussed in 1980 by Lang (35) and Sunderland (36). Many descriptions of cranial nerve rootlet interconnections are found only in comparative anatomic studies (37, 38). Variable connections intracranially between cranial nerve rootlets involving the spinal accessory nerve plexus and extracranially between the nerves themselves may give very different composition to nerves in the same location in different patients. Thus, very different impairments may occur when nerves in the same location are cut in these different patients. These variations in connections also explain in part why the spinal accessory nerve itself need not be cut for severe head, neck, and shoulder impairment to occur when there is loss of other cervical nerves in the plexus (1, 39).Cranial nerves, unlike peripheral nerves, lack an epineurium, do not stretch, and have less collagen, and so are more subject to injury than peripheral nerves (36, 40). Because of the unpredictability of what may be serious impairment from cutting a rootlet or one of its branches to any of these important nerves, much clinical and anatomic study has gone into efforts to protect them during operations, as for example, coating them with fibrin (40). Also, to avoid iatrogenic injury, before operating or radiation therapy, it becomes important to know whether dural, perineural areas, or venous sinuses close to these nerves are invaded by skull-based tumors. Assistance is given by magnetic resonance imaging (MRI) alone or together with pial enhancement, preoperatively (41). The radiation vulnerability intracranially of all four of the lower cranial nerves is illustrated by what was believed to be radiation induced bulbar palsy 14 years after a 41-year-old man had irradiation arrest of a nasopharyngeal carcinoma. The mechanism was theorized to be either from radiation-induced nerve damage or to vascular endothelial damage with resulting ischemia, fibrosis, and neural tissue compromise (42). Partly for the above reasons, our laboratory has recently restudied not only the numbers of rootlets of the lower four cranial nerves, but also their interconnections that are very probably important clinically. In addition, because of possible nerve ischemic dysfunction from atherosclerosis or radiation or operative loss, we have also restudied the blood supply to the lower four cranial nerves (39).
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