A note on the anastomoses between the hypoglossal nerve and the cervical plexus

Sternothyroid receives a supplementary innervation separate to the ansa cervicalis: a case report of a variation

We report on an additional innervation to the sternothyroid that, to our knowledge, has not been previously described. During a cadaveric neck dissection, we found an aberrant nerve to the sternothyroid in addition to the normal innervation. The classical innervation to the sternothyroid is through the ansa cervicalis (C1-C3), and the sternothyroid muscle is important for depression of the thyroid cartilage that is involved with swallowing and speech. The cervical plexus is difficult and time consuming to elucidate in fixed cadavers, which limits knowledge of variations from this source. Branches of the plexus are delicate and can be damaged during operations on the neck. Awareness of variations in innervation during operation reduces the chance of damage to nerves and prevents functional changes postoperatively.

An Anatomic Variant of the Ansa Cervicalis Precluding Its Use as a Donor Nerve

BACKGROUND

The ansa cervicalis is useful for cranial nerve repair, and may be harvested without apparent morbidity. Herein we report an unusual and surgically relevant anatomic variant of the ansa cervicalis.

METHODS

An adult male with left parotid adenoid cystic carcinoma underwent parotidectomy with upper-division facial nerve resection and planned interposition repair using the ansa cervicalis. The ipsilateral hypoglossal nerve was identified, together with a descending branch producing strap muscle contraction when stimulated. This presumed descendens hypoglossi was unusually large in caliber; further dissection revealed continuity with the vagus nerve.

RESULTS

Ansa cervicalis harvest was aborted when its separation from vagus nerve epineurium was not possible. The sural nerve was alternatively harvested. The patient awoke with left vocal fold palsy, which completely resolved within 3 months.

CONCLUSION

Anatomic variants of the ansa cervicalis exist that may preclude graft harvest and place the vagus nerve at risk of inadvertent injury.

Ansa cervicalis: a comprehensive review of its anatomy, variations, pathology, and surgical applications

The ansa cervicalis is a neural loop in the neck formed by connecting the superior root from the cervical spinal nerves (C1-2) and the inferior root descending from C2-C3. It has various anatomical variations and can be an important acknowledgment in specific operations of the neck region. This is a review the anatomy, variations, pathology and clinical applications of the ansa cervicalis.

An Unusual Superior Root of the Ansa Cervicalis

The ansa cervicalis is located around the carotid sheath and forms a neural loop, which consists of superior and inferior roots. It innervates the infrahyoid muscles. Anatomical variations of the superior root of the ansa cervicalis are uncommon. Herein, we present an extremely rare case of the superior root of the ansa cervicalis arising both from the hypoglossal and vagus nerves.

Report of a non-looped variant of ansa cervicalis with omohyoid innervation from accessory nerve branch and omohyoid attachment to mastoid process

INTRODUCTION

A variant of the innervation of the infrahyoid neck musculature is reported in which the typical looped ansa cervicalis structure is absent. In this variant, the infrahyoid muscles (sternohyoid, sternothyroid omohyoid and thyrohyoid) were innervated by a presumptive superior root of "ansa cervicalis" traveling with vagus nerve (CN X) and not branching from hypoglossal nerve (CN XII). The omohyoid muscle, typically innervated by the inferior root of ansa cervicalis, is instead innervated by nerve fibers branching from the accessory nerve (CN XI). This formation created a non-looping variant of ansa cervicalis. Furthermore, the omohyoid muscle did not attach to the hyoid bone but instead attached to the mastoid process of the temporal bone by merging its fibers superiorly and posteriorly with the clavicular portion of the sternocleidomastoid muscle, creating a "sternocleidoomomastoid" muscle innervated by a branch of accessory nerve.

MATERIALS AND METHODS

This variation was found in one black male cadaver from a cohort of 25 male and female cadavers.

RESULTS

Only one variation of ansa cervicalis was observed.

CONCLUSIONS

As neck dissections and surgical procedures of this region are performed for a variety of conditions-including coronary artery bypass grafting and metastatic neck disease-variations of this type are of broad clinical surgical importance.

Unilateral anatomical variation of the ansa cervicalis

The ansa cervicalis is a loop of nerves that is usually formed by the union of ventral rami of spinal nerves C1, C2, and C3. It is located in the carotid triangle of the neck, lying superficial to the carotid sheath. During routine dissection, unilateral variation of the ansa cervicalis was observed. The superior root, arising from hypoglossal nerve, was initially bifurcated and later united to form a single superior root. IN addition, the inferior root consisted of fibres arising from the spinal accessory nerve, C1, C2 and C3 spinal nerves that joined separately. Fibres from the spinal accessory and C1 joined to form a single root. Thus, a 'triple form' of ansa cervicalis was observed. An interconnection was observed between the C2 and C3 fibres. Knowledge of such anatomical variations is important for surgery, clinical intervention or trauma involving the carotid triangle or the structures within or deep to this region.

A comprehensive review with potential significance during skull base and neck operations, Part II: glossopharyngeal, vagus, accessory, and hypoglossal nerves and cervical spinal nerves 1-4

Knowledge of the possible neural interconnections found between the lower cranial and upper cervical nerves may prove useful to surgeons who operate on the skull base and upper neck regions in order to avoid inadvertent traction or transection. We review the literature regarding the anatomy, function, and clinical implications of the complex neural networks formed by interconnections between the lower cranial and upper cervical nerves. A review of germane anatomic and clinical literature was performed. The review is organized into two parts. Part I discusses the anastomoses between the trigeminal, facial, and vestibulocochlear nerves or their branches and other nerve trunks or branches in the vicinity. Part II deals with the anastomoses between the glossopharyngeal, vagus, accessory and hypoglossal nerves and their branches or between these nerves and the first four cervical spinal nerves; the contribution of the autonomic nervous system to these neural plexuses is also briefly reviewed. Part II is presented in this article. Extensive and variable neural anastomoses exist between the lower cranial nerves and between the upper cervical nerves in such a way that these nerves with their extra-axial communications can be collectively considered a plexus.

Relationship between the ansa cervicalis and the omohyoid muscle: clinical consequences in parathyroid surgery

PURPOSE

To determine the position of the lower loop of the ansa cervicalis (AC) compared to the inferior edge of the omohyoid muscle to guide minimally invasive surgery for the lateral oblique approach of parathyroid glands.

METHODS

Authors performed 36 anatomical dissections in the laboratory of anatomy (Laboratoire d'Anatomie Des Alpes Françaises) of the Grenoble medical school in 2012 on human cadavers. They independently measured the distance between the caudal extremity of the AC and the lower edge of the superior belly of the omohyoid muscle. Then, they controlled this measure on pictures.

RESULTS

The study shows a majority of long AC (under the omohyoid muscle) in 66.7 % of cases. In addition, the AC was located on an average value of 0.1 cm below the lower edge of the omohyoid muscle (median -0.5 cm). Thus, two-thirds of AC are between 0 and -2 cm under the omohyoid muscle. Furthermore, the AC is generally non-symmetrical: there is a mean difference of 1.3 cm between the left and right AC. In this series, there are as many long AC on the right side as on the left side.

CONCLUSIONS

These results are in contradiction with literature data. To preserve the ansa cervicalis and its phonatory functions, it is necessary for the surgeon to perform a systematic per operative identification of the AC because the position of the AC is mainly under the omohyoid muscle and because of an asymmetry. Per operative neurostimulation and/or magnified lenses might be helpful during the surgical approach.

Anatomy of the ansa cervicalis: nerve fiber analysis

Ansa cervicalis complex, which innervates the infrahyoid muscles, is formed by the union of two roots derived from the anterior primary rami of the first three or four cervical spinal nerves. According to its relationship with the internal jugular vein, there are three ansa types: medial, lateral, or mixed. Nerve fiber microscopy was carried out in 18 ansa cervicalis complexes after staining with Sudan Black, in order to study composition and structural arrangement in detail. Fibers from both first and second cervical nerves (C1, C2) joined the hypoglossal nerve and later left it partially in the superior root of the ansa, which also contained ascending fibers derived from the inferior root components; usually the second and third cervical nerves. Those ascending fibers, together with the C1 and C2 fibers remaining in the hypoglossal nerve, innervate thyrohyoid and geniohyoid muscles. Cervical nerve fibers could be observed within the hypoglossal nerve even after the ramification of those branches. Further, cervical nerve fibers were continuously issued to the peripheral layers of the hypoglossal nerve where the fibers of the two nerves intermingled, forming a complex structure. The general arrangement of the ansa did not change according to its type or segmental composition. Although the hypoglossal nerve does not make any significant contribution to the formation of the ansa, the close relationship between the two nerves observed in the present study calls for the use of a more descriptive term such as ansa hypoglosso-cervicalis. The pattern of innervation of the infrahyoid muscles is also discussed.

Ansa cervicalis as a variant of spinal accessory nerve plexus: a case report

The ansa cervicalis is a neural loop in the neck formed by the union of two main nerve roots, namely superior and inferior roots, derived from ventral rami of the cervical nerves. With the expanding use of the ansa cervicalis for reinnervation procedures and the fact that it is located in the vicinity of major nerves and vessels of the neck, knowledge of the topography and morphology of this loop is quite necessary in the modern era. Any variation in the course, contributing roots or branching pattern of the ansa cervicalis, potentially alters and perhaps complicates the course of the procedures involving this nerve such as neurorrhaphy, skull base surgery, neck dissection, and anterior cervical spinal approach. Here, we present an unusual case of an ansa cervicalis encountered upon routine dissection of an adult male cadaver. In this case, the inferior root of the ansa cervicalis was formed by the joining of two rootlets, one originating from spinal accessory nerve and the other from a branch of the cervical plexus to the sternocleidomastoid muscle. The fibers traversing the branch of spinal accessory nerve were derived from the first segments of the cervical spinal cord. This case demonstrates a variant of the spinal accessory nerve plexus that contributed to the formation of the ansa cervicalis. Review of the literature was performed to reveal the possible clinical aspects of this anatomical variation.

Bilateral absence of ansa cervicalis replaced by vagocervical plexus: case report and literature review

The bilateral absence of the ansa cervicalis was discovered during dissection of the neck in an elderly male cadaver. On both sides it was replaced by a vagocervical plexus formed by the vagus nerve and C1 and C2 ventral rami from the cervical plexus. A descending branch from this vagocervical plexus supplied the strap muscles of the neck. From a review of the literature the incidence of bilateral absence of the ansa cervicalis and its replacement by a vagocervical plexus appears to be extremely rare. Morphological variability, embryological basis, and clinical relevance of this uncommon anatomical variant are discussed.

Contributions of the hypoglossal nerve to the innervations of the recti capiti lateralis and anterior

We dissected five Japanese cadavers (three males, two females) to investigate the innervations of the anterior vertebral muscles. According to our observations, it could be considered that the hypoglossal nerve would participates in the innervations of the recti capiti lateralis and anterior. In addition, we observed the small muscle bundle spanning between the recti capiti lateralis and anterior, which was not reported in previous studies as far as we know. This bundle received a branch of the hypoglossal nerve or the first cervical nerve. Based on the morphology and the innervation pattern, this bundle was considered to have close relationships with the recti capiti lateralis and anterior, especially with the former muscle.

Bilateral oblique approach to parathyroid glands

OBJECTIVE

To propose a simple and minimally invasive approach for parathyroid surgery.

SUMMARY BACKGROUND DATA

Minimally invasive approaches to the parathyroid glands may involve preoperative morphologic explorations, perioperative biologic controls, or videocervicoscopy, a new method.

METHODS

The authors describe 597 patients who underwent parathyroidectomy through an original bilateral oblique approach between 1976 and 1997. None underwent morphologic exploration or biologic perioperative monitoring. In primary hyperparathyroidism, the four glands are controlled and it is possible to check their abnormalities of location or number. In secondary hyperparathyroidism and multiple endocrine neoplasia (MEN), a total or subtotal parathyroidectomy is performed.

RESULTS

The results and vocal morbidity are the same as that from authors using transverse cervicotomy, but this approach is more comfortable for the patient and allows total exploration of the location through short incisions without bleeding, visceral contusions, or muscle lesion.

CONCLUSIONS

This cervicotomy is easy and secure even if the surgeon is not trained in this approach because it uses and respects the anatomy of the cervical fasciae. It can be used without preoperative localization, intraoperative monitoring, or specialized material. But this approach could be also proposed for unilateral exploration guided by these methods and for surgical treatment of recurrent hyperparathyroidism after a transverse cervicotomy.

Ansa cervicalis nerve: review of the topographic anatomy and morphology

In recent years, there has been a proliferation of techniques utilizing the ansa cervicalis nerve to reinnervate the paralyzed larynx. The anatomic course and morphology of the ansa cervicalis are complicated by the variable course and location along the great vessels of the neck, as well as the significant differences observed in the arrangement of its contributing roots and regional branching patterns. Herein, we review the surgical anatomic course of ansa cervicalis and its innervation of the muscles of the neck, and develop specific recommendations with respect to the use of this nerve in laryngeal reinnervation.

Vagocervical complex replacing an absent ansa cervicalis

Absence of the ansa cervicalis was noticed in only one out of 200 cadavers, and that only on the right side, where it was replaced by the vagocervical complex. This complex was formed by the vagus nerve with the C1 and C2 components from the cervical plexus, giving off a descending branch to supply the infrahyoid muscles of the neck.

Anatomical basis of the anterior cervical spine approach: topographic study of the nerve structure

The results of the surgical anterior approach to the cervical spine are marked in a number of cases by dysphagia and dysphonia, especially when the approach is extensive or performed at the upper cervical spine. 35 cadaver dissections were performed to define the topography of the nerve structures during operative exposure at various vertebral levels: superior and recurrent laryngeal nerves, hypoglossal nerve and its superior root of the ansa cervicalis. The authors suggest some technical improvements, for each stage of surgical dissection.

Physiologic variations of the internal jugular vein surface, role of the omohyoid muscle, a preliminary echographic study

The action of the omohyoid muscle on the hemodynamics of the internal jugular vein is controversial. For some authors, contraction of this muscle, by tightening the cervical fascia, promotes jugular venous return. For others, contraction of this muscle compresses the jugular vein in its cervical path. With this latter point in mind, the hemodynamics of the internal jugular vein have been studied in its cervical path by echography in 10 healthy volunteers. One hundred twenty measurements of the venous surface were made at rest, with the mouth open and during deep inspiration. In the last 2 situations, evidence of a significant increase in the venous surface was found above the omohyoid muscle. These data confirm the role of compression of the vein by the omohyoid muscle, leading to modifications in intracerebral venous hemodynamics, which can be affected in yawning.