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Ansa Cervicalis Nerve: Review of the Topographic Anatomy and Morphology

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Ansa Cervicalis Nerve: Review of the Topographic Anatomy and Morphology The Laryngoscope Lippincott-Raven Publishers, Philadelphia 0 1997 The American Laryn ological, Rhinological and Otological gociety, Inc. Ansa Cervicalis Nerve: Review of the Topographic Anatomy and Morphology ~ ~~ Dinesh K. Chhetri, MD; Gerald S. Berke, MD In recent years, there has been a proliferation its proximity to the larynx and because it is quite ac- of techniques utilizing the ansa cervicalis nerve to tive during phonation. Ansa is a Latin term mean- reinnervate the paralyzed larynx. The anatomic ing “handle of a cup” or “haft.”6 The ansa cervicalis course and morphology of the ansa cervicalis are nerve is formed by the junction of two main nerve complicated by the variable course and location along the great vessels of the neck, as well as the roots derived entirely from ventral cervical rami. A significant differences observed in the arrange- loop (summit) is formed at the point of their anasto- ment of its contributing roots and regional branch- mosis. For decades the superior root was called the ing patterns. Herein, we review the surgical descendens hypoglossi because it branches off from anatomic course of ansa cervicalis and its innerva- the hypoglossal nerve. In the past the ansa cervi- tion of the muscles of the neck, and develop specific calis was called the ansa hypoglossi.The branches of recommendations with respect to the use of this the ansa cervicalis innervate the infrahyoid (strap) nerve in laryngeal reinnervation. muscles of the neck. Laryngoscope, 107:1366-1372,1997 Recently, there has been an interesting debate as to which branch of the ansa cervicalis used for la- INTRODUCTION ryngeal reinnervation would result in the best vocal In the past few decades, laryngology has wit- quality, Frazier and Mosser7 were the first to report nessed a dramatic proliferation of surgical proce- the anastomosis of the ansa cervicalis nerve to the dures designed for the treatment of dysphonia sec- recurrent laryngeal nerve in humans. They utilized ondary to unilateral paralysis of the vocal cord. They the superior root of the ansa cervicalis and achieved include medialization procedures such as Teflon an “improved”surgical outcome in five of 10 patients. (DuPont, Wilmington, DE) injection,l thyroplasty,2 Crumley et a1.8 have recommended the ansa cervi- and arytenoid adduction,3 and reinnervation proce- calis branch to the sternothyroid. They reason that dures such as nerve-muscle pedicle implantation4 the branch to the sternothyroid is located very near and nerve-nerve anastomosis using ansa cervicalis the recurrent laryngeal nerve, and although the pat- nerve transfer to the recurrent laryngeal nerve.5 tern of sternothyroid activation is predominantly in- Reinnervation procedures are purported to work by spiratory, it discharges throughout the respiratory preventing vocal cord atrophy and maintaining cycle and would provide a certain degree of continu- symmetric vocal cord mass and tension.5 ous tone to the vocalis muscle after reinnervation. It is also thought that the subsequent paralysis of the The ansa cervicalis nerve has become a prime sternothyroid muscle relaxes tension on the thyroid choice for use in laryngeal reinnervation because of cartilage and further medializes the paralyzed cord. Some investigators, however, have argued against the use of the sternothyroid branch because the pat- Presented at the Meeting of the Western Section of the American Laryngological, Rhinological and Otological Society, Inc., January 12,1997, tern of activation from this nerve may result in cord Tucson, Arizona. adduction during inspiration rather than phona- From the Division of Head and Neck Surgery, UCLA School of Med- tion.9 The thyrohyoid is the most active strap mus- icine, Los Angeles, California. cle during phonation, with peak activity during ex- This research was supported by the VA Merit Review Funds. piration. Crumley,8Jo however, has advised against Send Correspondence to Gerald S. Berke, MD, Division of Head and Neck Surgery, 62-132 CHS, UCLA School of Medicine, Los Angeles, CA using the nerve branch to this muscle because it 90024, U.S.A. would require a cable graft to reach the recurrent la- Laryngoscope 107: October 1997 Chhetri and Berke: Ansa Cervicalis Nerve 1366 ryngeal nerve stump and the resulting paralysis of the carotid artery. It then passes laterally and downward thyrohyoid would eliminate the adductor properties of to lie against the posterior surface of the vagus nerve, this muscle on the vocal fold. where it exchanges branches of communication with The ansa cervicalis nerve formation is relatively this nerve and with the sympathetic trunks. It contin- complex, as its course and location along the great ves- ues downward between the jugular vein and the in- sels of the neck vary. Yet there is a remarkable paucity ternal carotid artery. Close to its exit from the skull it of information on this nerve in the current otolaryn- is usually joined by branches of communication from gology literature. Therefore we have undertaken a lit- the first cervical nerve; it is these fibers which leave erature review on the anatomic course, morphologic the hypoglossal nerve as the superior root of the ansa variation, and regional branching patterns of this cervicalis, the nerve to the thyrohyoid, and the nerve nerve. We report our findings below and provide some to the geniohyoid. The fibers within the hypoglossal recommendations on the use of this nerve in laryngeal nerve itself supply only muscles of the tongue.11 reinnervation. At the level of the origin of the occipital artery from the external carotid arteq, the hypoglossal nerve METHODS forms an arc away from its vertical course to become The MEDLINE database was searched from 1966 to horizontal (Fig. 1).It passes forward, across the lateral 1996 for all publications with the keywords “ansa cervicalis.” surfaces of both the internal and the external carotid All relevant articles from search results were reviewed. In arteries, medial to the posterior belly of the digastric, addition, many major anatomical textbooks published in the and gives off the superior root of the ansa cervicalis.12 20th century were consulted for classical descriptions of the In a series of 20 adult dissections reported by Kuniak ansa cervicalis nerve. Any references in the textbooks were and Klacansky,l2 the average width of the hypoglossal further pursued. This information formed the core for the fol- nerve was 2.2 mm before the superior root of the ansa lowing review. cervicalis branched off and 2.05 mm afterward. RESULTS Nerve to the Thyrohyoid Hypogtossal Nerve The nerve to the thyrohyoid muscle branches The hypoglossal nerve emerges from the skull from the hypoglossal before the latter nerve dips be- base through the hypoglossal canal medial to the in- neath the stylohyoid muscle in close proximity to the te;mal jugular vein and posteromedial to the internal posterior border of the hyoglossus muscle (Fig. 1).Af- Fig. 1. Regional anatomy of the ansa cervicalis nerve. The nerve and its branches are illustrated in their most frequent morphologic and topographic form. The nerve to the thyrohyoid branches from the hypoglossal nerve and runs obliquely across the hyoid bone to innervate the thyrohyoid. The nerve to the superior belly of the omohyoid branches from the superior root and enters the muscle at a level between the thyroid notch and a horizontal plane 2 cm inferior to the notch. The nerves to the sternohyoid and sternothyroid share a common trunk, which branches from the loop. The nerve to the inferior belly of the omohyoid also branches from the loop. The loop is most frequently located just deep to the site where the superior belly (or tendon) of the omohyoid muscle crosses the internal jugular vein. Laryngoscope 107: October 1997 Chhetri and Berke: Ansa Cervicalis Nerve 1367 ter arising from the hypoglossal nerve, it runs The descent of the superior root of the ansa cer- obliquely across the greater cornu of the hyoid bone vicalis can be followed down the neck along its inti- to innervate the thyrohyoid muscle. Its fibers are de- mate relationship to the great vessels. Caliot and rived from the communication of the hypoglossal Dumontl5 observed its vertical descent on the exter- nerve with the first cervical nerve.13 The hypoglossal nal carotid in 60% of the cases, and on the internal nerve continues forward under cover of the sub- carotid in 40%. Further down and closer toward its mandibular gland, passing above the hyoid bone on anastomosis with the inferior root, the superior root its way to innervate the tongue.llJ3J4 In its course, is found in direct relation to the internal jugular the hypoglossal nerve passes within 4 to 5 mm of the vein and is most frequently observed passing later- intermediate tendon of the digastric muscle.15 ally to the anterolateral side of the internal jugular vein.12 As the nerve descends, it gets progressively Superior Root narrower. Kuniak and Klacanskylz measured the average diameter of the superior root at the point of Origin and course. The superior root of the separation from the hypoglossal nerve at 1.03 mm. ansa cervicalis is classically described as a long At the point of anastomosis to form the loop, the slender branch that emerges from the superior por- nerve width had decreased to 0.79 mm. Total length tion of the arc of the hypoglossal nerve as that nerve of the superior root on average was 7.1 cm. makes the turn around the occipital artery to as- sume a horizontal course toward the tongue.11J4J6J7 Innervation to the superior belly of the At its origin, the superior root is medial to the pos- omohyoid. Classically, the branch to the superior terior belly of the digastric muscle and lateral to the belly of the omohyoid was almost invariably re- internal and external carotid arteries.12 It descends ported to originate directly from the superior root of obliquely downward and slightly medially on the in- the ansa cervicalis (Fig.
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