Intradural anastomoses between the accessory nerve and the posterior roots of cervical nerves: their clinical significance

A detailed review of the spinal accessory nerve and its anatomical variations with cadaveric illustration

The spinal accessory nerve, considered part of the eleventh cranial nerve, provides motor innervation to sternocleidomastoid and trapezius. A comprehensive literature review and two cadaveric dissections were undertaken. The spinal accessory nerve originates from the spinal accessory nucleus. Its rootlets unite and ascend between the denticulate ligament and dorsal spinal rootlets. Thereafter, it can anastomose with spinal roots, such as the McKenzie branch, and/or cranial roots. The spinal accessory nerve courses intracranially via foramen magnum and exits via jugular foramen, within which it usually lies anteriorly. Extracranially, it usually crosses anterior to the internal jugular vein and lies lateral to internal jugular vein deep to posterior belly of digastric. The spinal accessory nerve innervates sternocleidomastoid, receives numerous contributions in the posterior triangle and terminates within trapezius. Its posterior triangle course approximates a perpendicular bisection of the mastoid-mandibular angle line. The spinal accessory nerve contains sensory nociceptive fibres. Its cranial nerve classification is debated due to occasional non-fusion with the cranial root. Surgeons should familiarize themselves with the variable course of the spinal accessory nerve to minimize risk of injury. Patients with spinal accessory nerve injuries might require specialist pain management.

First cephalosomatic anastomosis in a human model

Background:

Cephalosomatic anastomosis (CSA) has never been attempted before in man as the transected spinal cords of the body donor and body recipient could not be “fused” back together. Recent advances made this possible. Here, we report on the surgical steps necessary to reconnect a head to a body at the cervical level.

Methods:

Full rehearsal of a CSA on two recently deceased human cadavers was performed at Harbin Medical University, Harbin, China.

Results:

The surgery took 18 hours to complete within the time frame planned for this surgery. Several advances resulted from this rehearsal, including optimization of the surgical steps, sparing of the main nerves (phrenics, recurrent laryngeal nerves), and assessment of vertebral stabilization.

Conclusion:

Several specialties are involved in a full-scale CSA, including neck surgery, vascular surgery, orthopedic surgery, plastic surgery, gastrointestinal surgery, and neurosurgery, as well as the operating staff. This rehearsal confirmed the surgical feasibility of a human CSA and further validated the surgical plan. Education and coordination of all the operating teams and coordination of the operative staff was achieved in preparation for the live human CSA.

Disorders of the lower cranial nerves

Lesions of the lower cranial nerves (LCN) are due to numerous causes, which need to be differentiated to optimize management and outcome. This review aims at summarizing and discussing diseases affecting LCN. Review of publications dealing with disorders of the LCN in humans. Affection of multiple LCN is much more frequent than the affection of a single LCN. LCN may be affected solely or together with more proximal cranial nerves, with central nervous system disease, or with nonneurological disorders. LCN lesions have to be suspected if there are typical symptoms or signs attributable to a LCN. Causes of LCN lesions can be classified as genetic, vascular, traumatic, iatrogenic, infectious, immunologic, metabolic, nutritional, degenerative, or neoplastic. Treatment of LCN lesions depends on the underlying cause. An effective treatment is available in the majority of the cases, but a prerequisite for complete recovery is the prompt and correct diagnosis. LCN lesions need to be considered in case of disturbed speech, swallowing, coughing, deglutition, sensory functions, taste, or autonomic functions, neuralgic pain, dysphagia, head, pharyngeal, or neck pain, cardiac or gastrointestinal compromise, or weakness of the trapezius, sternocleidomastoid, or the tongue muscles. To correctly assess manifestations of LCN lesions, precise knowledge of the anatomy and physiology of the area is required.

Intradural communication between dorsal rootlets of spinal nerves: their clinical significance

BACKGROUND

Anatomical and surgical textbooks give almost no attention to the intradural communications between dorsal rootlets of adjacent spinal nerves. These communications can be of significance in various neurosurgical procedures and clinical conditions of the region.

METHODS

The spinal cord of six formaldehyde-fixed cadavers was dissected from C1-S5. The dorsal rootlets of the spinal nerves were exposed via a posterior approach and communications between adjacent spinal nerves were documented.

RESULTS

The frequency of communication between adjacent dorsal rootlets of the spinal nerves showed variations among spinal levels. Thirty-eight dorsal rootlet communications were observed in six cadavers (12 sides) and 20 (52.6%) were at cervical levels, 14 (36.8%) at thoracic levels, and four (10.5%) at lumbar levels. The majority of communications were observed on the left side (65.8%). Communications were most frequently observed at cervical (C4-C5, C5-C6) and upper thoracic (T1-T2) levels and seen least frequently at lower thoracic and lumbar levels. No communications were observed at sacral levels. Five types of communication were observed: I. oblique ascending, II. oblique descending III. short Y, IV. long Y and V shaped. None of the communication extended beyond one segment at any spinal level. The occurrence of such dorsal rootlet communications ranged from 3 to 7 for each cadaver and the mean was 4.8 ± 1.3. Histological sections from various levels of the dorsal rootlet communications showed that all consisted of myelinated fibers of varying diameters.

CONCLUSIONS

Such communications may lead to misinterpretation of the pathology on the basis of clinical signs and symptoms and also should be considered in rhizotomy.

Topographical anatomy on the communicating branch between the spinal accessory nerve and the anterior root of the first cervical nerve

The aim of this study was to clarify the morphological characteristics of the communicating branch between the spinal accessory nerve and the anterior root of the first cervical nerve (McKenzie branch), a structure severed during intradural selective rhizotomy for treatment of spasmodic torticollis. The right and left sides of 50 upper cervical segments of spinal cords were dissected and examined under a surgical microscope. Seven of the total 100 samples were found to have the McKenzie branch. Two types of McKenzie branch, which run close to the vertebral artery, were also identified, which might be helpful for improving the surgical results of intradural selective rhizotomy.