Comisuritis Posterior 2

Posterior Commissure of the Human Larynx Revisited

*,†John A. Tucker and *,†Sean T. Tucker *yPhiladelphia, Pennsylvania

Summary: The existence of the posterior commissure (PC) of the human larynx has been disputed (Hirano M, Sato K,

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et al. The posterior glottis. Trans Am Laryngol Assoc. 1986;107:70–75). ‘‘The term posterior commissure has no rele-vance to anatomical structure. The term commissure means a joining together. The bilateral vocal folds never join attheir posterior ends. The posterior aspect of the glottis is a wall. The posterior lateral aspect of the posterior glottis isalso the lateral wall of the posterior glottis’’ (Hirano M, Sato K, et al. The posterior glottis. Trans Am Laryngol Assoc.1986;107:70–75). This study is intended to clarify the development of anatomical and morphological aspects of the PCin conjunction with a clinical classification of the larynx in sagittal view. This study uses human embryo and fetallaryngeal sections from the Carnegie Collection of Human Embryos (the world standard) and whole organ laryngealsections from the Tucker Laryngeal Fetal Collection. Correlation of histologic and gross anatomical structure ismade with the Hirano et al atlas, the Vidic Photographic Atlas of the Human Body, and the O’Rahilly Embryonic Atlas.Embryologic data clearly describe and illustrate the posterior union of the cricoid cartilage with formation of the PC.The anatomical functional aspects of the posterior lateral cricoid lamina as the supporting buttress of the articulatingarytenoid cartilages are illustrated.Key Words: Stages–Histogenesis of cartilage–Interstitial growth–Appositional growth.

INTRODUCTION

The anterior commissure is easily recognized as the most ante-rior point of the glottic space,1,2 the most ventral attachment ofthe true vocal folds to the thyroid cartilage, which is establishedin the fourth and fifth months of development with completionof the thyroid cartilage in the fetal period.

The concept of a ‘‘posterior commissure’’ (PC) has long beena clinical impression based on the indirect and direct visual ex-amination of the human larynx. The posterior glottic space isclinically best visualized with the glottic larynx in abduction.The posterior glottic and superior subglottic space then createsan intraluminal ‘‘v,’’2 that is, the median posterior wall (PC) andthe posterior lateral buttresses of the inner surface of the cricoidcartilage. This, coupled with the abducted anterior glottic sur-face of the vocal processes and membranous vocal folds, cre-ates the diamond glottic aperture.

The PC of the human larynx is represented anatomically bythe posterior union of the developing cricoid cartilage. It ex-tends from the superior rim of the midposterior cricoid cartilagethrough the glottic level to the lower limit of the posteriorportion of the cricoid lamina (Figure 1). Most organs areformed of more than one germ layer. Interactions betweenlayers are necessary for successful morphogenesis.3

Prenatal development

In the Carnegie System of Classification, embryos are bestarranged in 23 stages in 8 weeks.4,5 Each stage is merely anarbitrarily cut section through the time axis of the life of the

ted for publication December 9, 2008.he *Department of Otorhinolaryngology—Head and Neck Surgery, University ofania School of Medicine, Philadelphia, Pennsylvania; and the yDepartment ofgology—Head and Neck Surgery, Drexel University College of Medicine,hia, Pennsylvania.

ss correspondence and reprint requests to John A. Tucker, Department ofgology—Head and Neck Surgery, Drexel University College of Medicine,oad Street, 10th Floor, Philadelphia, PA 19107. E-mail: [email protected] of Voice, Vol. 24, No. 3, pp. 252-259997/$36.00

0 The Voice Foundation.1016/j.jvoice.2008.12.006

organism. The embryonic period proper, the first eight postovu-latory weeks of development is shown in relationship to thefetal period (Graph 1). The fetus and older embryos are mea-sured by their crown-rump lengths, which correspond to thesitting height postnatally. The embryo, being approximately30 mm in length at 8 weeks, is in the end of its embryonicperiod. The fetal period originates during bone marrow produc-tion in the humerus.4,6

Cricoid development definitions

Primordium: the earliest discernible indication duringembryonic development of an organ or a part.Accretionary growth: growth that causes increase in sizeresulting from increase in the number of special cells by mi-totic division.Interstitial growth: growth occurring in the interior parts ofstructures already formed or forming—the matrix.Appositional growth: growth by addition at the periphery ofa particular structure or part—the perichondrium.Commissure: a site of union of corresponding parts, a site ofjunction, a joining together.

Histogenesis of cartilage

Embryologically, the entire connective tissue group arises frommorphologically similar mesenchymal cells. The cells secretethe specialized components of the matrix which histologicallyand biochemically characterize the tissue.

As cartilage first develops, the cells begin to separate fromone another by becoming active in secreting the fibers, muco-polysaccharides, and chondroitin sulfate, which characterizethe matrix cartilage. The accumulation of their secretion grad-ually forces them further and further apart until they come tolie isolated from one another in the matrix they have pro-duced. Such a method of increase or growth in humans isknown as interstitial growth. The formation of a matrix sorigid that interstitial growth is limited takes place first cen-trally in an area of developing cartilage. When the center be-comes too rigid for interstitial growth to continue,

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FIGURE 1. Gross illustration of the adult cricoid cartilage (Vidic

Collection).

FIGURE 2. Median section through the pharyngeal region at stage

13 (4.5 mm). The respiratory diverticulum can be seen descending

from its origin in the foregut. Its close relationship with the heart is ev-

ident. The site of the tracheoesophageal septum is clearly visible. (Re-

printed with permission from Ref. 5 (p. 520) [Carnegie Collection,

9297].)

John A. Tucker and Sean T. Tucker Posterior Commissure of the Human Larynx 253

appositional growth begins peripherally. This investing layerof mesenchyme soon becomes specialized into a connectivetissue covering called the perichondrium. It is through the ac-tivity of the chondrogentic layer that the cartilage continues togrow, peripherally by apposition. Thus, after interstitialgrowth ceases in the matrix, the perichondrium becomes theprimary growth center.

Because cartilage is devoid of blood vessels and forms large,compact masses, the nutritive fluid from the blood vessels in theperichondrium must pass through the interstitial substance toreach the cells. The interstitial substance is, thus, permeatedby the tissue fluids from the perichondrium. This appositionalability of the perichondrium to form cartilage persists, althoughlatent, in the adult organism.

Posttraumatically or surgically, new cartilage in the adultregenerates by metaplasia of the connective tissue. Further

GRAPH 1. The embryonic period proper—the first eight postovula-

tory weeks of development—is shown in relation to the fetal period.

Fetuses, and older embryos, are measured by their crown-rump length,

which corresponds to the sitting height postnatally. (Reprinted with

permission from Ref. 6 (p. 51).)

metaplasia with ossification occurs with blood vessel and vas-cular connective tissue involvement of the cartilage.7

Laryngeal development

The respiratory primordium does not appear in the developinghuman embryo before stage 11. In stage 13, a median section,

GRAPH 2. Graph showing several main features in laryngeal devel-

opment during the second half of the embryonic period proper.

(Reprinted with permission from Ref. 15.)

FIGURE 3. Stage 15: laryngeal primordium. Triangular condensa-

tion of undifferentiated mesenchyme around the respiratory canals

(Carnegie Collection, 8929).

FIGURE 5. Carnegie Collection: stage 19, 1390—early union of the

dorsal ring and formation of the posterior commissure.

Embryonic Stages Embryo Specimen Number

13 S 9297

15 T 8929

17 T 8789

19 T 1390

Journal of Voice, Vol. 24, No. 3, 2010254

approximately 3 weeks old, with 4.5-mm crown rump length,illustrates the respiratory diverticulum descending from its ori-gin in the foregut. The tracheoesophageal septum is clearlyvisible (Figure 2).

21 S 632

C 9614

23 T 9226

S 75

T D122—Silver

S 4525

Fetal

40 mm S 6658

41 mm T 6361

46 mm S 1686

54 mm T 3990

Laryngeal Development

Sequence Fetal Fetal Age

LD8 C 12 wk

LD9 S 14 wk

LD18 C 16 wk

LD2 S 18 wk

LD51 C 20 wk

LD5 T 22 wk

LD25 C 24 wk

MATERIALS AND METHODS

This research is based on the examination of 12 serial sectionspecimens from the Carnegie Collection. Sections from nineembryos, stages 13–23, and four fetal specimens, 9–12 weeks,were reviewed. In addition, 12 serial section fetal larynges fromthe Tucker Collection, 12–40 weeks, and one three-and-a-half-year postnatal specimen were also studied. A total of 25 speci-mens were evaluated.

The stains of the Carnegie Collection included hemotoxinand eosin, alum cocinal, azan and one treated with silver. TheTucker fetal collection is unique in that many of thecelloidin-blocked specimens were specifically stained insuccessive sections, not only with hemotoxin and eosin, butalso with elastic stains of Verhoff VanGeissen. The contrastingspecimens were then mounted side by side on the sameslide.

Of special importance are the stage 23 embryos of the Carne-gie Collection that were previously studied in great detail byMuller et al in 1980 through 1988.8–11 The Tucker Collectionhas also been studied by G. Tucker Jr and J. Tucker, and multi-ple publication references are noted.2,6,10,12,13

FIGURE 4. Carnegie Collection: stage 17, 8789—accretionary in-

terstitial growth.

Materials

Carnegie Collection

Tucker Collection

LD7 C 28 wk

LD48 S 30 wk

LD20 C 34 wk

LD29 C 38 wk

LD52 C 40 wk

Postnatal

LD50 C 31⁄2 y

Method of sectioning.

S¼ SagittalT¼ TransverseC¼ Coronal

Method of staining.

Tucker Fetal Alternate H & E, V.G. was used for staining.

FIGURE 6. Carnegie Collection: reconstruction of stage 20 with

dorsal union of the cricoid cartilage.

FIGURE 8. (A) Paramedian section of a stage 21 human embryo

(Carnegie Collection, 632). (B) Stage 21: lateral sagittal section of

the larynx. Both cartilaginous perichondral (appositional) growth

and interstitial cartilaginous growth are evident in the arytenoid and

cricoid cartilages of the larynx.


RESULTS

Cricoid cartilage

Cartilaginous development of the cricoid is prominent fromstages 15 through 23, weeks 4–8 (Graph 2). Stage 15 shows la-ryngeal primordium of poorly differentiated mesenchyme (Fig-ure 3). The cricoid arises from a ventral blastomere in the areaof the future arch with condensation and accretionary intersti-tial growth at stage 17 (Figure 4), with lateral progressionthrough stage 18 to dorsal union of the ring with formation ofthe PC of the cricoid at stage 19 (Figure 5). Furthermore, theepithelial lamina is mature.11 The laryngeal inlet is closed.A detailed reconstruction of stage 20 shows cricoid union inthe superior aspect of the cricoid lamina (Figures 6 and 7)and histologic union of the cricoid lamina in coronal section(stage 21). In stages 21–22, interstitial and appositional periph-eral growth is present within the cricoid and arytenoid carti-lages (Figure 8).

Stage 23 is the end of the embryonic period proper. At the endof the 8 weeks of the embryonic period, shifting of growth cen-ters and appositional perichondral activity are well established(Figure 9). At stage 23, in horizontal section and silver stain,

FIGURE 7. Carnegie Collection: stage 21, 9614—coronal section of

dorsal cricoid with union of the cricoid lamina.

portions of the thyroid and cricoid cartilage as well as the thy-roid gland are evident. On each side, the branching of the infe-rior laryngeal nerve is seen passing in the vicinity of thecricothyroid joint and ending in the thyroarytenoid muscle(Figure 10). The cricoid is the first and only laryngeal cartilageto acquire adult form during the embryonic period proper(Figure 11).4,5

Anatomical functional aspects of the cricoid

cartilage

The components of the larynx in sagittal view are summarizedin Graph 3.

FIGURE 9. Stage 23: end of the embryonic period proper. The body

of the hyoid, thyroid laminae, and cricoid cartilage are clearly visible,

as are the laryngeal cavity and the body of the laryngopharynx. The

submandibular and thyroid glands can be seen bilaterally. The thyro-

hyoid and sternothyroid muscles, and the oblique line of the thyroid

cartilage are indicated, as is the posterior cricoarytenoid muscle (trans-

verse sections of No. 9226: Carnegie Collection). (Reprinted with per-

mission from Ref. 5 (p. 520).)

FIGURE 10. Stage 23: D—122 (Carnegie Collection). Portions of

the thyroid and cricoid cartilages, as well as the thyroid gland, are ev-

ident. On each side, the anterior branch of the inferior laryngeal nerve

can be seen passing forward in the vicinity of the cricothyroid joint and

ending in the thyroarytenoid muscle.

FIGURE 11. Stage 23: photograph of embryo (Carnegie

Collection).

GRAPH 3. Sagittal view of larynx.

FIGURE 12. (A) Sagittal section of the fetus (Tucker Collection,

14 wk—LD9). (B) Adult gross specimen in sagittal section (Vidic Col-

lection). The glottis is represented at the vocal process.


Transglottic structures

The arytenoid cartilage, cricoid cartilage, and thyroid cartilageare all transglottic structures.

Supraglottis

The posterior supraglottis, the laryngeal inlet, or laryngeal ves-tibule is dominated by the interarytenoidus muscle, the superiorportion of the arytenoid cartilage and the aryepiglottic folds,and epiglottis. Physiologically, the posterior supraglottis andepiglottic complex are related to supraglottic closure with swal-lowing and squamous epithelium.

Glottis

The glottis is dominated by the anterior commissure to themembranous portion of the vocal fold, the vocal process ofthe arytenoid cartilage, the respiratory glottis, the mid-posteriorportion of the cricoid cartilage, and the wall (the PC). The PC isa fixed site as is the anterior commissure and does not vary withvocal fold mobility. In the sagittal section of the grosslydissected adult larynx, it is clear that the arytenoid portion ofthe glottis is represented by the vocal process (Figure 12).

FIGURE 13. Sagittal section: four-month-old fetus (Carnegie Col-

lection: 40 mm, 6658)—the cricoid arytenoid articulation.

FIGURE 14. Newborn larynx. (A) Horizontal section midcricoid at level of inferior rim of thyroid ala illustrating the posterior V of the crytoid.

(B) Similar section at comparable level–post intubation with pressure necrosis of the subglottic laryngeal mucosa. [Reprinted with permission from

Ref. 12 (pp. 82–85).]


Subglottis

The cricoarytenoid joint is placed laterally in the superior por-tion of the subglottis resting on the cricoid lamina lateral to theinternal ‘‘v’’ of the dorsal union,2 the PC of the cricoid (Fig-ure 13). The midsubglottis represents a thickened, posteriorlateral, supportive buttress of the cricoid arytenoid joint. Clini-cally, the internal surface buttress of the midsubglottis is themost frequent site of endolaryngeal trauma and the eventualpotential subglottic stenosis (Figure 14).

The inferior subglottis has a more rounded to oval lumenwith a flattened lamina. The cricothyroid joint is placed later-ally and externally and the arch is placed anteriorly. The infe-rior cricoid subglottis is a complete ring and, as such, is themain supporting structure for the tracheal lumen. Further,the cricoid lamina is also the origin of the supporting attach-ment of the laryngotracheal ligament and the tracheoesopha-geal septum.

DISCUSSION

The existence of the laryngeal PC was questioned first byHirano et al in 1986. The title was ‘‘The Posterior Glottis,’’ ananatomical study of excised human larynges.1

FIGURE 15. View of glottis from above during vocal fold abduc-

tion. AC, anterior commissure; TVPn, tip of vocal process in neutral

condition; TVP, tip of vocal process; PEVn, posterior end of ventricle

in neutral condition; MPW, midpoint of posterior wall. (Reprinted with

permission from Ref. 1 (p. 197).)

This was an excellent and detailed, extensive study. The firstpart was a photographic study of 20 specimens in neutral adduc-tion and abduction. The second part was a histological evalua-tion of the structures of the posterior glottis in 28 specimens,seven specimens in coronal section and three in sagittal section.The number of specimens in transverse sections was not re-corded. The authors pointed out that the anatomical definitionof the vocal folds, ‘‘the structure between the anterior commis-sure and vocal process of the arytenoid,’’ was well accepted.

The problem for the authors was to define the posterior glot-tis. Photographically, they included the arytenoid cartilage, thewall, the cricoid cartilage, as well as the posterior and superiorstructures, including the intraarytenoid muscles and other glan-dular, muscular, and mucosal elements (Figure 15).

By definition, the glottis is at the level of the vocal folds, andtherefore, is limited to that level from the anterior commissurethrough the posterior wall of the cricoid. To include the

FIGURE 16. Fetus: Hirano, Atlas—fetus weighing 3164 g found.

Transverse section, 2 mm below the glottis. Adult: Hirano, Atlas—

57-year-old female: transverse section of posterior commissure at

the midpoint of cricoid laminae. (Reprinted with permission from

Hirano M, Sato K. Histological Atlas of the Human Larynx. Singular

Publishing Group, Inc.; 1993.)

FIGURE 17. (A) Adult larynx posterior gross view. (B) Point of

union of posterior cricoid laminae, the posterior commissure, the

cricoid spine. (G. Tucker, Jr., personal communication.) (Reprinted

with permission from Vidic Atlas of Human Body. CV Mosby; 1984.)

FIGURE 18. (A) Four-month-old fetus—sagittal section, illustrating

the laryngotracheal esophageal ligament (LTEL) just inferior to the

cricoid lamina (Carnegie Collection). (B) Seven-month-old fetus—

sagittal section, X illustrating the laryngotracheal esophageal ligament.

(Reprinted with permission from Negus V. J Laryngol Otol. 1924.)


interarytenoidius muscle and supraglottis in the definition of theposterior glottis is a misnomer as the interarytenoidius muscleis anatomically a supraglottic structure. Hirano et al’s studyis, therefore, anatomically, a more inclusive and detailed eval-uation of the entire posterior laryngeal inlet, both glottic andsupraglottic.

Histologic transverse sections of the cricoid cartilage clearlyillustrate the anatomical, PC, and intraluminal ‘‘v’’ of the pos-terior cricoid, glottic, and subglottic space (Figure 16).12

FIGURE 19. (A) Transverse section of stage 23 embryo at the junction of th

cartilage lumen, laryngotracheal esophageal ligament (X) and esophagus (C

glottic larynx cricoid arch and trachea, superior to inferior, cricoid arch, trac

The median posterior wall is the point of union of the devel-oping cricoid cartilage. Development occurs at stages 19through 23, that is, 6–8 weeks of embryonic life. The PC itselfis fixed and extends to the height of the lamina of the cricoidcartilage (Figure 17).

Dysgenesis of the cricoid cartilage at stages 19–22 may createa ‘‘nonunion’’ of the cricoid lamina and a partial or complete cri-coid cleft.14,15 Extended clefts, laryngotracheal esophageal cleftresult with failure of the midline formation of the laryngotracheal

e larynx and trachea—superior to inferior-superior cricoid arch, tracheal

arnegie Collection: 9226). (B) Four year old. Endoscopic view of sub-

heal lumen, and laryngotracheal esophageal ligament (X).


esophageal ligament, which extends to the upper one-third of thetracheoesophageal septum and has its origin in the perichondriumof the cricoid lamina16 (Figures 18 and 19).

In conclusion, the posterior end of the glottis is a wall (Hir-ano),1 the cricoid cartilage; the posterior median cricoid carti-lage is also the developmental anatomical site of union of thecricoid cartilage and the PC. It is a relevant, definitive, anatom-ical site, as is the anterior commissure and does not vary withvocal fold mobility.

Acknowledgments

The authors wish to acknowledge the major contributions tohuman laryngeal development by Professors Ronan O’Rahillyand Fabiola Muller.

REFERENCES1. Hirano M, Sato K, et al. The posterior glottis. Trans Am Laryngol Assoc.

1986;107:70-75.

2. Tucker G Jr, Tucker J, et al. The anterior commissure revisited. Ann Otol

Rhinol Laryngol. 1973;82:3-11.

3. O’Rahilly R, Muller F. Human Embryology and Teratology. Wiley-Liss Inc;

1992.

4. O’Rahilly R, Tucker J. The early development of the larynx in staged

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6. Tucker J, Tucker Jr. Some aspects of fetal laryngeal development. Ann Otol

Rhinol Laryngol. 1975;84:1-6.

7. Streeter G. Development horizons in human embryology. Histogenesis of

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onic period proper: 1. The laryngeal and infrahyoid muscles and their inner-

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9. Tucker J, Vidic B, Tucker G Jr, et al. Survey of the development of laryngeal

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10. Tucker J, Tucker G Jr. The Development of the Cricoid Cartilage in

Staged Human Embryos and in Fetuses. Munich: Collegium, ORLAS;

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11. Muller E, O’Rahilly R, Tucker J. The human larynx at the end of the

embryonic period proper: 2. The laryngeal cavity and the innervation of

its lining. Ann Otol Rhinol Laryngol. 1985;94:607.

12. Tucker G, Tucker J, Vidic B. Anatomy and development of the cricoid serial

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13. Tucker J, Tucker G, Vidic B. Clinical correlation of anomalies of nor-

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14. Benjamin B. Endolaryngeal Surgery. Mosby; 1999. 339–340.

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16. Fried M. The Larynx. Little Brown Co; 1988. 18 pp.

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