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CURRENTOPINION Superior laryngeal nerve injury: effects, clinicalanagement options

K. Chhetri

ervation to the cricothyroid muscle. However, thef the nerve that supplies it are not fully understood.seitch

toh. Cnif, thpi

ciates

effects of SLNp will improve diagnosis and treatment.

Keyworcricothyr

INTRODUCTION

The superior laryngealalthough physiologicone of the least underegion. Most of the rethe field of neurolarrecurrent laryngealbecause RLN injury iswell as easier to ident

The prevalence ofunknown as many cathe external branch ofreported to be as highlated injury to the extedetect because of subtle symptoms and variability inthe clinical signs and symptoms. Inmon trunk of the SLN can also oduringto the pharynx, as a result of direvagus nlack ofcontrib

David Geffen School of Medicine at University of California Los Angeles,Los Angeles, California, USA

: morestes@mednet.ucla.edu

1068-95

REVIEWsensation from the supraglottic larynx andutes to dysphagia.

Curr Opin Otolaryngol Head Neck Surg 2014, 22:439443

DOI:10.1097/MOO.0000000000000097

08 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins www.co-otolaryngology.comrerve. Injury to the internal branch results inCHSe-mailight Lippincott Williamteral approachesct injury to the

of Medicine at University of California Los Angeles, 10833 LeConte Ave.,62-132, Los Angeles, CA 90095, USA. Tel: +1 310 825 5179;skull base surgery or with laLaboratory, Department of Head and Neck Surgery, David Geffen Schooljury to the com-ccur, primarily

Correspondence to Michael I. Orestes, MD, Laryngeal Physiologydsoid muscle, superior laryngeal nerve, voice disorder

nerve (SLN) and its functions,ally important, may still berstood in the head and necksearch and clinical interest inyngology is focused on thenerve (RLN). This is likelyclinically more important asify and treat.SLN injury and dysfunction isses go undiagnosed. Injury tothe SLN in thyroidectomies isas 58% [1,2]. However, iso-

rnal branch can be difficult to

Anatomy

The SLN branches from the vagus nerve near theinferior half of the nodose ganglion, about 36mmbelow the jugular foramen and 40mm above thecarotid bifurcation [2,3]. It then travels 1.5 cm cau-dally in which it divides into the internal and exter-nal branches [1]. The internal branch, which piercesthe thyrohyoid membrane, provides sensory inner-vation to the supraglottic larynx, whereas the exter-nal branch, carrying motor innervation, travels toand innervates the cricothyroid muscle. There is

Laryngeal Physiology Laboratory, Department of Head and Neck Surgery,muscles poses difficulties in treating patients with this condition. A more thorough understanding of thefindings, prognosis, and m

Michael I. Orestes and Dinesh

Purpose of reviewThe superior laryngeal nerve (SLN) provides motor innfunctions of this muscle and the anatomic variations oSLN paresis and paralysis (SLNp) is difficult to diagnoand its effects on the voice likely go beyond simple p

Recent findingsAlthough SLNp has traditionally been thought to leadreveal multiple roles for this nerve in voice and speecfundamental frequency of voice. SLNp can lead to sigvibratory phase asymmetry, and acoustic aperiodicityaddition, cricothyroid muscles may also play a role insounds during speech.

SummarySubtle signs, symptoms, and diagnostic findings assocharacterize clinically. Lack of treatment methodologis & Wilkins. Unauthorizebecause of a lack of consistent laryngeal findings,elevation control.

voice pitch limitation, recent research findingsricothyroid muscles are the primary controls oficant contraction of pitch range, vocal foldus leading to an overall poor vocal quality. Intch lowering and shifting from voiced to unvoiced

ed with SLNp make this disorder difficult toto restore the dynamic action of the cricothyroidd reproduction of this article is prohibited.

Copyrigh

some vspecificvesselsadditiotor masuperfimuscledescribare repbranchmusclenerve [was premay aswhethethyroar

Thecricothrecta athe infepars reroid tutuberclthe anttilage. Awhichthe thythat thits attastrap marily mjointsmotionaxis ofin theof thecricoid

cricothyroid space, posterior and inferior motionof the arytenoids, and lengthening and thinningof the vocal folds. When the cricothyroid joint is

raconcriubletery

EC

lilyse [tstyeasy eetthlit ocyfuhaowstamgrteeoleasovcrasnc

KEY POINTS

SLN paralysis has a complex effect on voice, whichacco

Vibrafindipara

LEMGalthoof ou

Voicinitia

Comtypeprom

Laryngology and bronchoesophagology

440ariation within the course of the nerve,ally with relation to the superior thyroidas originally described by Cernea [2]. Inn, its relationship with the superior constric-y be highly variable, as it can run entirelycial to the muscle, completely within theor partially within the muscle as first

ed by Friedman et al. [4]. In addition, thereorts of a connection from the external SLNto the midportion of the thyroarytenoid

, described as the human communication2,5]. According to Wu et al. [5], this nervesent in less than half of the specimens andsist in adduction of the vocal fold. However,r the SLN provides motor innervation to theytenoid remains to be investigated.major muscle supplied by the SLN, the

yroid muscle, consists of two parts: the parsnd the pars oblique. Both parts originate atrior margin of the thyroid cartilage with thecta originating from the midline to the thy-

contmotithewithpar oin thunilaall la

EFF

VeryparavoicaffecabilidecrstudRoycricowitheffecquenablealsothe lwithfunddurinimpobetwphondecrandas inincreto i

unts for more than just increases in pitch.

tory phase asymmetry is likely the most commonng on laryngoscopy but is not specific to SLNlysis.

is currently the gold standard in diagnosis,ugh this has not been well studied in termstcomes.

e therapy is the most commonly prescribedl treatment.

bined medialization laryngoplasty and modified4 thyroplasty appears to be one of the mostising surgical treatment options.t Lippincott Williams & Wilkins. Unauthorized

bercle and the pars oblique from the thyroide to the inferior cornu. These then insert onerior and lateral portions of the cricoid car-third muscle belly has also been described,

originates from the inner perichondrium ofroid cartilage [3,6]. It is generally acceptede thyroid cartilage remains fixed because ofchments to the hyoid and sternum via theuscles, thus cricothyroid contraction prim-oves the cricoid cartilage. Paired cricothyroidand ligaments allow two main types of: first, rotation around the common frontalboth; and second, sliding horizontal motionsagittal direction [6]. Symmetric contractioncricothyroid muscles raises the anteriorcartilage, resulting in narrowing of the

vation.fundam[10

&&

]. Tngeal r

Roylateralition aphase asymmetry, length asymmetry, or vocal foldheightof the pof pativer. Thwith hthe pos50% ofsniff m

www.co-otolaryngology.comreproduction of this article is prohibited.

mismatch. Instead, they reported deviationetiole toward the side of theweakness in 60%ents, particularly with glissando up maneu-ey also reported improved glottic closureigh-pitched voice tasks and axial rotation ofterior commissure toward the normal side inpatients with rapidly alternating eee andaneuver. Chhetri et al. [12

&

] showed, in a

Volume 22 Number 6 December 2014ted to its limits of motion, the slidingis not possible because of distension of

cothyroid ligaments [6]. It is believed thatnilateral contraction, particularly with theique, this sliding motion may occur resultingrotation of the larynx sometimes seen withral paralysis, although this may not occur innges [3].

TS

ttle has been written about SLN paresis andis (SLNp) regarding specific effects on the3]. It is commonly felt that SLNp primarilyprofessional voice users as it hampers theirto produce higher vocal registers andes vocal projection [2,3]. In an excellentvaluating phonatory effects of SLN paralysis,al. [7] performed selective blockade of theyroid muscle and external branch of the SLNdocaine in 10 patients. The most commonn the voice was reduced fundamental fre-range and reduction in the highest obtain-

ndamental frequency. Interestingly, patientsd contraction of fundamental frequency ater range as well. This would be compatibleudies showing role of cricothyroid muscles inental frequency lowering and devoicingspeech [8

&

,9]. Voicing and devoicing areant phenomena in which sounds are shiftedn voiced and unvoiced, depending on theogic environment. Roy et al. [7] also noted ae in mean airflow with normal phonationerall increase in subglottic pressures as welleased phonatory instability characterized byed jitter. These changes arepossibly secondaryreased compensatory thyroarytenoid acti-Thyroarytenoid activation can also increaseental frequency in certain circumstanceshis would also explain overall increased lary-esistance and increased subglottic pressure.et al. [11] also evaluated the effects of uni-

external branch SLN block on laryngeal pos-nd vibration. They did not find vibratory

Copyr ize

canine model, that simulated unilateral SLNpresulted in a significant vibratory phase asymmetry,with the side with the intact SLN opening earlier.Althouthere athe coSLNp [stratedhumantromyoasymmphase abe seensuch as

CudiagnoIn ourin variain the cwhichtransvepresentaxis, mexpecteis likelylates with more severe voice changes [3,6]. Thesecondmusclenoidmusclefold tisvibratiochange

DIAGN

LEMGnosis odenervreliableresearcnosis ostudiesJanssonpostopmajorithad a rever, thoperatitime operformfindinglimitatfindingdepending an

technical issues may remain such as sampling ofadjacent nontarget muscle, such as the strapmuscles [18]. Others have reported the possibility

mcleer

ingalnterydthet, t

G

e as ratascted to behave in a manner similar to RLNlysnos dou

outcommme oniylyarbsethlsomaSLNu

AT

ideiountiicalasty, modified type 4 thyroplasty, variationsricg nusy,dooi

apyugriam

SLN injury Orestes and Chhetri

1068-950ight Lippincott Williams & Wilkins. Unauthor

is the compensatory action of the intrinsics of the larynx, particularly the thyroaryte-and possibly the lateral cricoarytenoids, which affects the overall balance of vocalsue stiffness and thus laryngeal posture andn. In addition, this compensation maysignificantly over time.

OSTIC TEST

has been used as the gold standard in diag-f SLNp because of its ability to detect signs ofation [3]. Although LEMG may be morethan laryngoscopy, there is very little

h specifically addressing its role in the diag-r treatment of SLN injury. There have been nocomparing LEMG finding and vocal quality.et al. [1] showed, using preoperative and

erative EMG after thyroidectomy, that they of patients with EMG-diagnosed SLNpeduced pitch and poorer quality voice. How-ey also noted that several patients with pre-ve SLNp had no vocal abnormalities at thef testing. Dursun et al. [17] recommendeding LEMG combined with physical exams to confirm the diagnosis. There are severalions of LEMG. First, interpretation of LEMGs is subjective and accuracy of findings isent on the experience of the person perform-d interpreting the test. Second, some

recovoicare ulikelsimpthe pof ocricocan aandtheisthm

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8 2014 Wolters Kluwer Health | Lippincott Williams & Wilkinsgh not seen in the study by Roy et al. [11],re several case reports/case series that supportncept of phase asymmetry resulting from1315]. Phase asymmetry has been demon-in physical models, canine models, ands diagnosed with SLNp using laryngeal elec-graphy (LEMG). We believe that a phaseetry is present with SLNp. Unfortunately,symmetry is not specific for SLNp and canwith other causes of tension asymmetryRLN paresis and paralysis [16].

rrent literature provides no consensus forsis of SLNp based on laryngoscopy alone.opinion, there are two main factors resultingbility of examination. The first is variabilityricothyroid joint horizontal sliding motion,may add to vocal fold stiffness changes in therse plane [12

&

]. If no horizontal sliding wasand the joint only moved along the frontalinimal changes to the voice would bed with unilateral cricothyroid paralysis. Itthat the degree of sliding permitted corre-

of samusreinnleadmaypatiesurgceivewhemen

PRO

ThernosiIdiopbeenexpeparadiagery itaned reproduction of this article is prohibited.

othyroid approximation, and reinnervationerve muscle pedicle technique [3,2022].

e of difficulty in accurately diagnosing SLNdiscussion of treatment options is limited total evidence.ce therapy is the most commonly prescribedfor long-standing isolated SLN paralysis,h it seems that the improvement in voiceble. Therapy is targeted at building cricothy-uscle strength using activities such as

www.co-otolaryngology.com 441is [12&

]. Because of the difficulty in reliablysing SLN injury, determining a rate of recov-ifficult. For SLNp after thyroidectomy, spon-s recovery is variable [2]. Many report thees as poor or worse than RLN injury andend early voice therapy to prevent poorutcomes. However, these recommendationsformly based on anecdotal observations. It isthat these cases with poor outcomes arecases severe enough to be diagnosed withalysis in the first place, leading to a high levelrvational bias [13]. It is our opinion thatyroid dysfunction following thyroid surgeryresult from direct injury to the cricothyroidy occur more commonly from that injury to. This may occur during dissection of thes, pyramidal lobe, or delphian node [3].

MENT

variety of treatment options have beensly reported, ranging from steroids for acuteal viral injury, voice therapy, and a variety ofl procedures including medialization lary-pling error examining partially denervatedor longstanding paralysis with variability invation. Repeated EMG needle insertionsto muscle hemorrhage or transient damageso lead to false positive results [18]. Finally,s with voice problems, especially following, are hesitant to undergo procedures per-to be invasive, especially if it is unclearr it would change the recommended treat-hus limiting the usefulness of LEMG [19].

NOSIS

re no studies specifically addressing the prog-elating to a SLN injury, regardless of cause.hic SLNp, which appears to be fairly rare, hassumed to be due to viral neuropathy and is

Copyrigh d

glissando maneuvers [17]. The variability in theeffectiveness of voice therapy likely stems from boththe difficulty in diagnosing SLN paralysis via clinicalmeansent patuating

Altseveralment fusedapprox10 patiin the qterm foshoweddecrease in range over time, likely due to decreasedtensionMaragothyropwere replasty wnotedZhangadditiothe comuscleallowsures, lerange.formed

Anin a smmuscleprocedcricothinto pateral siresultsis a lotjust buresearcto restmuscle

CONC

The maadequageneralmanyresearcconditiand hocontribneedednation

patients with poor voice quality and reduced vocalrange. Once there is improved diagnostic accuracy,further work can be performed on treatment of this

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Laryngology and bronchoesophagology

442t Lippincott Williams & Wilkins. Unauthorize

on the suture over time. Nasseri ands [20] performed both type 1 and type 4lasty in nine patients. Again, good resultsported. The addition of the type 1 thyro-as added, because of the decreased power

with SLN paralysis. The study by Yin and[10

&&

] would support this concept. Then of medialization likely further enhancesmpensatory activity of the thyroarytenoid, increases stiffness of the vocal fold, andfor more efficient increase in subglottic press-ading to improvement in vocal quality andHowever, more research needs to be per-to prove that these surgeries are effective.

other surgical procedure has been describedall series of patients using a muscle nerve pedicle using a nerve cable graft. In thisure, a nerve cable is attached to the normalyroid muscle on one side; it is then graftedralyzed cricothyroid muscle on the contrala-de [22]. Although the authors describe goodwith this technique, it would seem that thereof room for failure when using a cable graftried into muscle bellies. However, furtherh into reinnervation techniques is warrantedore the dynamic role of the cricothyroidduring phonation.

LUSION

jor factor impeding progress in determiningte treatment for SLN paralysis has been thelack of diagnostic criteria, likely leading toundiagnosed or misdiagnosed cases. Newh into voice changes associated with thison will likely improve diagnostic accuracypefully remove the idea that the SLN onlyutes to pitch elevation. Further research isto determine improved diagnosis on exami-and to improve the index of suspicion in

REFREAPapersbeen h& of&& of

1. Jales52

2. BathsustS1

3. SuC

4. Frpr12

5. Wexco

6. Arsc

7. Rosu11

8.&

Clargl

This arspeech9. Lo

co10.&&

Yiac20

This armusclethat thelevatio11. Ro

lar11

12.&

ClarSL

This arcricoth13. Zh

lef20

14. Mvidne

15. Tssu20

www.co-otolaryngology.comand variable effects of SLN paralysis on differ-ients. There are no studies adequately eval-the effects of voice therapy on SLN paralysis.hough not commonly performed, there aresmall case series describing surgical treat-or SLN injury. One study by Shaw et al. [21]carefully applied unilateral cricothyroidimation (type 4 thyroplasty) in a series ofents with reportedly excellent improvementuality of the voice and vocal range. A long-llow-up for a similar procedure, however,persistent quality improvement but a

com

Ack

None

Con

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wledgements

cts of interest

s expressed in this article are those of the authornot reflect the official policy or position of theent of the Army, Department of Defense, or thetates Government. There are no other conflicts of.

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SLN injury Orestes and Chhetri

1068-950ight Lippincott Williams & Wilkins. Unauthor8 2014 Wolters Kluwer Health | Lippincott Williams & Wilkinsd reproduction of this article is prohibited.www.co-otolaryngology.com 443