Original Article
AN ATOM ICAL VARIATION S IN THE AN SA CERVICALIS AN D
INNERVATION OF INFRAHYOID M USCLES
Lydia S. Quadros* , Nandini Bhat, Arathy Babu, Antony Sylvan D’souza.
ABSTRACT
Address for Correspondence: Lydia S. Quadros, Depart ment of Anat omy, Kast urba M edical College, M anipal Universit y, M adhavnagar, M anipal, Karnataka, India – 576104.
Telephone – 0820 2922327. E-M ail: lidibudy@gmail.com
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Depart ment of Anat omy, Kast urba M edical College, M anipal Universit y, M adhavnagar, M anipal, Karnataka, India
Background: – Infrahyoid m uscles are supplied by t he ansa cer vicalis. The present st udy aim ed t o st udy t he var iat ions in t he ansa cervicalis and t he innervat ion of infrahyoid m uscles. M et hods: The st udy w as conduct ed on 40 cadaveric hem i-necks. Results: Out of t he 40 hem i-necks, high level of ansa cervicalis w as obser ved in 2 hem i-necks, int erm ediat e level of ansa w as observed in 35 hem i-necks and low level of ansa w as obser ved in 3 hem i-necks. Addit ionally, dual ansa w it h absence of inferior root w as seen in 4 hem i-necks, dual ansa w it h absence of inferior root and int er-com m unicat ion bet w een C2 and C3 w as seen in 2 hem i-necks, com m on t r unk supplying all inf rahyoid m uscles including superior belly of om ohyoid w as seen in 2 hem i-necks, nerve t o infe-rior belly of om ohyoid from infeinfe-rior root w as seen on 1 side. In one specim en unilat erally, super ior belly of om ohyoid w as inner vat ed by a branch f rom hypoglossal ner ve, t w o superior root s ar ising from hypoglossal ner ve and t he inferior root form ed only by C3 w as seen in t he sam e specim en. Discussion: The know ledge of t he possible variat ions of ansa in relat ion t o t he great vessels of t he neck prevent s t he inadvert ent injury t o t hose vessels. Any injury can result t o phonat ion disabi lit y in professional voice users. In case of infrahyoid m uscles palsy, pat ient s have no serious voice problem s in t heir norm al speech but t he pitch of t heir voice and also prosody in t heir singing are lost dram at ically. Conclusion: These variat ions are of clinical im portance for t he reconst r uct ive surgeries w hich involve t he infrahyoid m uscles.
KEY W ORDS:ANSA CERVICALIS; DUAL ANSA; INFRAHYOID M USCLES; RECONSTRUCTIVE SURGERIES.
BACKGROUND
Int J Anat Res 2013, Vol 1(2):69-74. ISSN 2321- 4287
Received: 29 July 2013
Peer Review : 29 July 2013 Published (O):23 Aug 2013 Accepted: 20 Aug 2013 Published (P):30 Sep 2013
Internat ional Journal of Anat omy and Research ISSN 2321-4287
w w w.ijmhr.org/ ijar.ht m
Infrahyoid m uscles nam ely, t he st ernohyoid, sternot hyroid, t hyrohyoid and omohyoid usually depress t he hyoid bone during deglut it ion and during phonat ion [1]. These st rap muscles are usually found in pairs. They are innervated by t he branches arising from t he ansa cervicalis. Alt hough variat ions in t heir absence, presence of accessory bellies, presence of addit ional tendons, duplicat ion of m uscles are report ed, st udies regarding t heir innervat ion are limited.
Variat ions in the format ion of ansa cervicalis has been w ell documented in t he lit erat ure. Ansa cervicalis is a loop of nerves found in t he neck.
70 Three branches arise from t he loop of ansa
cervicalis t o supply t he rem aining infrahyoid muscles [1].
Therefore, in t his st udy, w e aimed t o find out t he variat ions in t he format ion of ansa cervicalis and also t he innervat ion of all t he infrahyoid muscles.
M ATERIALS AND M ETHODS
RESULTS
Necks of 20 formalin-fixed cadavers of bot h sexes (18 males and 2 females) of age approximately 30-50 years w ere dissected bilaterally during t he rout ine dissect ion for undergraduate st udent s follow ing t he Cunningham’s manual of pract ical anat omy volum e 3. The ansa cervicalis w as painted and phot ographed. Gross variat ions in t he infrahyoid muscles w ere also observed.
Based on t he level of t he loop w it h respect t o t he om ohyo id m uscle, an sa cer v icalis w as divided int o 3 categories. The loop at t he level of t he hyoid bone was classified as high level ansa (Fig. 1).
It was seen in 2/40 (5%) hemi-necks unilaterally. The loop in bet w een t he hyoid bone and t he omohyoid muscle was classified as intermediate ansa (Fig. 2). It was seen in 35/40 (87.5%) hemi-necks unilaterally. The loop below t he omohy-oid muscle was classified as low level ansa. It was seen in 3/40 (7.5%) hemi-necks unilaterally (Fig. 3).
Figure 1: Right hem i- neck show ing high level ansa.
C2 – 2n d ce r v i cal n er v e, C3 – 3r d ce r v i cal n er ve ,
DH – Descendens hypoglossi, HN – Hypoglossal ner ve, * - com m on t r unk w hich supplies all t he inf rahyoid m uscles including t he superior belly of om ohyoid, SOH – Superior belly of om ohyoid.
Figure 2: Left hem i-neck show ing int erm ediat e ansa.
C2 – 2nd cervical nerve, C3 – 3rd cervical ner ve,
DH – Descendens hypoglossi, HN – Hypoglossal ner ve, SOH –Superior belly of om ohyoid.
Figure 3: Left hem i- neck show ing low level ansa.
DC – Descendens cervicalis, DH –Descendens hypoglo-ssi, HN – Hypoglossal ner ve, SOH – Super ior belly of om ohyoid.
Figure 4: Left hem i- neck show ing dual ansa form at ion
w it h absent infer ior root . C2 – 2nd cervical ner ve,
C3 – 3rd cervical nerve, DH – Descendens hypoglossi,
Figure 5: Left hem i- neck show ing dual ansa w it h ab-sent inferior root and int er-com m unicat ion bet w een C2 and C3. C2 – 2nd cervical nerve, C3 – 3rd cervical ner ve,
DH – Descendens hypoglossi, HN – Hypoglossal ner ve, w hit e arrow - com m on t runk from t he loop, * - int er-comm unicat ion bet w een C2 and C3, SOH – Superior belly of om ohyoid.
Figure 6: Lef t sid e of t he neck sh ow in g ansa w i t h DH – 2 descendens hypoglossi, SOH – Super ior belly of om ohyoid, * - ner ve supply by a branch of hypoglossal ner ve, C3 – form ing descendens cervicalis.
Based on its formation, ansa cervicalis w as classified as follow s –
a. Normal ansa (w it h superior root formed by C1 fibers and inferior root formed by C2 and C3 fibers) – seen in 32 hemi-necks (80%).
b. Dual ansa w it h absent inferior root (C2 and C3 joining t he superior root separately) – seen in 4 hemi-necks (10%) (Fig. 4).
c. Dual ansa w it h absent inferior root and inter-communicat ion bet ween C2 and C3 fibers – seen
Figure 7: Right hem i-neck show ing dual ansa w it h
absent inferior root and t he nerve supply of all infrahyoid m u scl es b y a co m m o n t r u n k f r o m t h e l o o p . C2 – 2n d cer vi cal n e r ve, C3 – 3r d cer vi cal n er v e,
DH – Descendens hypoglossi, HN – Hypoglossal ner ve, SOH – Superior belly of om ohyoid, * - Com m on t r unk w hich supplies all infrahyoid m uscles including super ior belly of om ohyoid.
d. Inferior root formed by C3 fibers only – seen in in 1 hemi-neck (2.5%) (Fig. 6).
Unusual ansa w it h t w o superior root s (one root from C1 fibers, t he ot her a branch of hypoglossal nerve) – seen in 1 hemi-neck (2.5%) (Fig. 6).
Innervation of Infrahyoid muscles –
a. Superior belly of omohyoid muscle: Supplied by t he superior root (C1 fibers) in 36 hemi-necks (90%); by a com mon t runk from t he ansa in 3hemi-necks (7.5%) (Figures 1 and 7) and from hypoglossal nerve in 1hemi-neck (2.5%) (Figure 6).
b. Inferior belly of omohyoid muscle: Supplied by a common t runk from t he ansa in 39 hemi-necks (97.5%) (Figures 1 and 7), by inferior root in 1 hemi-neck (2.5%).
c. Sternohyoid muscle: Supplied by a common t runk from t he ansa in 40 hemi-necks (100%) (Figures 1 and 7).
d. Sternothyroid muscle: Supplied by a common t runk from t he ansa in 40 hemi-necks (100%) (Figures 1 and 7).
72 hemi-necks w it h superior root below t he muscle
and 4/76 (5.26%) hemi-necks show ed superior
root at t he level of t he posterior belly of digastric muscle [5]. Caliot and Dumont [9] in a series of
80 dissect ions show ed t hat t he superior root
above posterior belly of digast ric muscle in 60/
80 (75%) of cases and at t he level of t he muscle in 20/80 (25%) cases. In t he present st udy, t he
superior root was seen above t he posterior belly
of digast ric muscle.
Vent ral rami of C2 and C3 bot h formed inferior
root in 28/108 cases (26%), from vent ral ramus of C3 in 63/108 cases (63/108) and from vent ral
rami of C2 in 17/108 cases (16%) [4]. Loukas et
al.[3] in his st udy on 100 cadavers show ed t hat
inferior root was derived from t he vent ral rami of C2 and C3 in 38% cases, C2, C3 and C4 in 40%
cases and from C3 in 40% cases and from C2 in
12% cases. In a st udy on 25 fresh post-mortem
cadavers conducted by Hegazy [10] show ed t hat t he inferior root was formed by C2 and C3 in 42/
50 cases (84%), by C2 in 8/50 cases (16%).
According t o Caliot and Dumont [9], C3 most
often cont ributed t o t he inferior root . How ever, in t he present st udy, C2 and C3 w ere t he main
cont ribut ors of inferior root .
Double loops w it h t he presence of bot h t he
descendens hypoglossi and descendens vagi
w ere already described [11, 12]. In bot h t hese
cases, t he upper loop is formed by t he fusion of descendens hypoglossi and descendens vagi and
t he low er loop is formed by descendens vagi and
descendens cervicalis. The present st udy does
not report any such finding.
Double loop (dual ansa cervicalis) w it h C2 and C3 joining t he superior root separat ely w as
reported in 2/80 fet uses (3%) [4]. The presence
of a unilateral dual ansa was reported in a single
case [13]. In t he present st udy, dual ansa was observed unilaterally in 4/40 (10%) hemi-necks.
Yamada [14] described t he posit ion of ansa as medial (w hen t he ansa lies medial t o IJV) and lateral (w hen t he ansa lies lateral t o IJV). M edial and lateral series of ansa – 34/40 (85%)
hemi-necks show ed medial ansa (Figures 1, 4, 5 and 7) and 6/40 (15%) hemi-necks show ed lateral ansa (Figures 2, 3 and 6).
DISCUSSION
Variat ions in t he ansa cervicalis have been w ell
documented in t he literat ure. Chhetri and Berke
classif ied t he posit ion of t he l oop of ansa
cervicalis as short and long ansa [2]. According t o a st udy conducted by Loukas et al. on 100
adult formalin-fixed cadavers, 70% cases showed
long ansa (above the omohyoid muscle) and 30%
cases show ed short ansa (below t he omohyoid muscle) [3]. According t o a st udy conducted by
Pillay et al. [4] 63/80 fetuses (79%) depicted short
ansa and 17/80 fet uses (61%) depicted long ansa.
M wachaka et al. [5] in t heir study on 38 (76 hemi-necks) form alin-fixed cadavers show ed short
ansa in 46/76 (64.6%) hemi-necks, 7/76 (9.21%)
hemi-necks show ed long ansa and 16/76 (24.6%)
h em i -n eck s sh o w ed an sa at t h e lev el o f omohyoid m uscle. In t he present st udy, high
ansa (at t he level of hyoid bone) was seen in 2/
40 (5%) hem i-necks; int er m ediat e ansa (in
betw een hyoid bone and omohyoid muscle) was seen in 35/40 (87.5%) hemi-necks and low ansa
(below om ohyoid m uscle) w as seen in 3/40
(7.5%). Therefore, t he present st udy show ed
greater percentage of short ansa.
The origin of t he superior root in t his st udy was only from t he C1 fibers passing t hrough t he
hy po gl ossal n er v e. Sev eral au t h or s hav e
reported t he vago cervical complex, w here t he
superior root alt hough derived from t he C1 f i ber s, descen ds t hr ough t he vagus ner ve
(descendens vagi) [6,7,8]. In a st udy conducted
on 80 fet uses, t he vago cervical complex formed
by t he cont ribut ion from hypoglossal nerve, vagus and C2 and C3 nerves was observed in 2/
80 fet uses (3%) [4]. The present st udy does not
report any such finding.
M w achaka et al. show ed 42/76 (56%) hem
i-necks w it h superior root above t he posterior
Addit ionally Bannehaka [15] added a mixed type w hen t he t w o separate inferior root s lies lateral and m edial t o IJV t o join t he superior root . Superior root descended infront of com m on carotid artery and internal jugular vein in 69/108 cases (64 %) and posterior t o IJV in 39/108 cases (36 %)[4]. M wachaka et al. [5] show ed lateral series in 53/76 (81.5%) hemi-necks and medial ser ies in 12/76 (18.5%) hem i-necks. In t he present st udy, 20/40 (50%) hemi-necks show ed m edial ser ies and 20/40 (50%) hem i-necks show ed lateral series.
1/80 fet uses (1%) show ed dual superior root s. Inferior root formed by C3 only [4]. A similar case was seen unilaterally in t he present st udy.
Superior root of AC gave branch t o Superior belly of omohyoid in 48/50 cases (96%).Inferior root gave a branch t o Inferior belly of omohyoid in 2/ 50 cases (4%). The rest of t he m uscles had normal innervat ion.
No st udies in t he literat ure have show n inter-com m unicat ing nerves bet w een C2 and C3. Therefore, t his is a significant finding in t his st udy.
Among t he seven morphologic forms of t he ansa cervicalis described by Caliot and Dumont [9], w e have found t hree forms. Type A – double classic form, in w hich t he C1 forms t he superior root and C2 and C3 joins t o form the inferior root . This was seen in 32 hemi-necks (80%). Type C – Double form w it h t w o separate root s, w hich is t he dual ansa described in t his st udy. It was seen in 4 hemi-necks (10%). Type E – Double short form, w hich is high ansa described in t his st udy. It was seen in 2 hemi-necks (5%).
Embryological significance – The hypoglossal nerve af t er get t ing incorporat ed w it hin t he cranium, est ablishes comm unicat ion w it h t he upper cervical nerves and t hus furnishes t he nerve supply t o t he infrahyoid muscles [16, 17]. The hypoglossocervical plexus innervat es t he infrahyoid muscles since the muscles of t he neck (scal ene, pr ev er t ebr al , geni o hyo i d an d infrahyoid) are derived from t he different iat ion of t he branchial arch mesenchyme and cervical somites [17, 18].
Surgical im por t ance – Dam age t o t he ansa cervicalis can lead to change in voice qualit y after somet ime, even t hough t he exact reason is not
CONCLUSION
know n for t his phenomenon. It may be because of t he loss of support provided by t he st rap m uscles t o t he lar yngeal car t i l ages dur ing movement s of vocal folds [19].
The know ledge of t he possible variat ions of ansa in relat ion t o t he great vessels of t he neck prevent s t he inadvertent injury t o those vessels. Any injury can result t o phonat ion disabilit y in professional voice users. In case of infrahyoid muscles palsy, pat ient s have no serious voice problems in t heir normal speech but t he pitch of t heir voice and also prosody in t heir singing are lost dramat ically [20]. In cases of unilateral vocal cord paralysis, anast omoses bet w een t he ansa cervicalis and the recurrent laryngeal nerve have resulted in excellent t o normal funct ion in t he vocal cord affect ed [ 21-23] . During t he su rgi cal exp o sur e of t hyr o i d gl an d , t h e st er nohyoid and st er not hyroid m uscles are f r equent l y cu t , of t en dam aging t he ner ve branches of t he ansa cervicalis [2].
Th e pr ecise k no w l edge of t he an at om ical relat ions and variat ions of ansa cervicalis is of great clinical importance for t he head and neck su rgeo ns t o accurat ely kno w t h e po ssi b le variat ions w hile perform ing surgery t hereby reducing t he risks of damaging t he nerves and vasculat ure w hile performing neural blocks in regional anest hesia and nerve graft s.
REFERENCES
Competing interests
The aut h o rs d ecl are t hat t h ey h av e n o compet ing interest s.
Acknow ledgements
The aut hors w ish t o t hank all t he teaching and non-teaching staff for t heir support .
1. Borley NR: Ansa cervicalis. In: Standring S, Collins P, Crossmen AR, Gat zoulis M A, Healy JC, et al. edit ors. Gray’s anat omy: t he anat omical basis of clinical pract ice. 40t h ed. Edinburgh:
Elsevier Churchill Livingst one; p. 981. 2008
3. Loukas M , Thorsell A, Tubbs RS, et al. The ansa cervicalis revisit ed. Folia M orphol 2007, 66(2):120-125.
4. Pillay P, Partab L, Lazarus, Sat yapal KS. The ansa cervicalis in fet uses. Int . J. M orphol 2012, 30(4):1321-1326.
5. M w achaka PM , Ranket i SS, Elbusaidy H, Ogeng’o J. Variat ions in t he anat omy of ansa cervicalis. Folia M orphol 2010, 69(3):160-163.
6. D’souza AS, Ray Bisw abina. St udy of t he format ion and dist ribut ion of t he ansa cervicalis and it s clinical significance. Eur J Anat 2010, 14(3):143-148.
7. Abu-Hijleh M F. Bilat eral absence of ansa cervicalis replaced by vagocervical plexus: a case report and literat ure review. Ann Anat . 2005, 187:121-125.
8. Rat h G, Anand C. Vagocer vical com plex replacing an absent ancs cervicalis. Surg Radiol Anat 1994, 16:441-443.
9. Caliot P, Dumont D, Bousquet V, M idy D. A n o t e o n t h e an at o m oses b et w een t h e hypoglossal nerve and t he cervical plexus. Surg Radiol Anat 1968, 8:75-79.
10. Hegazy AM S. Anatomical study of t he human ansa cervicalis nerve and it s variat ions. Int . J. Anat . Physiol.2013, 2(3):14-19.
11. Rao TR, Shett y P, Rao SR. A rare case of f or m at i o n o f do u b le ansa cer v ical is. Neuroanat omy 2007, 6:26-27.
12. Jyot hi SR, Dayakshini KR. Variat ion in t he for m at ion of ansa cer vicali s on r ight side. Anat omica Karnataka 2013, 7(1):81-83.
13. Babu PB. Var iant infer ior root of ansa cervicalis. Int J M orphol 2011, 29(1):240-243.
14. Yam ad a M , M an n en H. An at o m y f o r dissect ors. Tokyo, Nankodo 1985:188.
15. Banneheka S. M orphological st udy of t he ansa cervicalis and t he phrenic nerve. Anat Sci Int 2008, 83(1):31-44.
16. Kent GC. Com parat ive anat om y of t he vertebrates. 4t h ed. M osby Co., Saint Louis 1978:
352.
17. Kitamura S. Nishiguchi T, Okubo J, Cen K, Sakai A. An HRP st udy of t he m ot orneurons supplying t he rat hypobranchial muscles: central localization, peripheral axo course and soma size. Anat Rec 1986, 216:73-81.
18. Kikuchi T. A cont ribution t o the morphology of t he ansa cervicalis and t he phrenic nerve. Acta Anat Nippon 1970, 45:242-281.
19. Vollala VR, Bhat SM , Nayak S, et al. A rare origin of upper root of ansa cervicalis from vagus nerve: a case report . Neuroanat omy 2005, 4:8-9.
20. M ahmood A, M orteza K. A rare anat omical variant of ansa cervcialis: case report . M JIRI 2011, 24(4):238-240.
21. Brondbo K, Jacobsen E, Gjellan M , Refsum H. Recurrent laryngeal nerve – ansa cervcialis nerve anast omoses: A t reat ment alternat ive in u ni l at eral r ecu r ren t ner ve par al y si s. Act a Ot olaryngol 1992, 112:353-357.
22. Crum ley RL. Updat e; Ansa cervicalis t o recur rent lar yngeal ner ve anast om oses for unilat eral laryngeal paralysis. Lar yngoscope 1991, 101:384-388.
23. Gr een DC, Ber ke GS, Gr av es M C. A funct ional evaluat ion of ansa cervicalis nerve t ransfer for unilateral vocal cord paralysis: Fut ure d i rect io n s f o r l ar yn geal r ein n er vat io n . Ot olaryngol – Head Neck Surg 1991, 104:453-456.
How to cite this article
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Lydia S. Quadros, Nandini Bhat , Arat hy Babu, Ant ony Sylvan D’souza. Anat omical variat ions in t he Ansa cer vicalis and inner vat ion of infrahyoid muscles. Int J Anat Res, 2013;02:69-74.
