The Nasopharyngeal Orifice of the Auditory Tube

The Nasopharyngeal Orifice of the Auditory Tube:

Implications for Tubal Dynamics Anatomy

STEWART R. ROOD, Ph.D. WILLIAM J. DOYLE, Ph.D. Pittsburgh, Pennsylvania 15213

This is the first part of a study designed to clarify the relationship between auditory tube dilation and observed movement of the nasopharyngeal orifice of the tube. This report seeks to delineate the anatomical parameters of the system, whereas, the second will report on findings of torus 'movement' observed during simultaneous tympan- ometric measurement of tubal function during swallowing. The disposition of the paratubal musculature, relation between the tubal cartilage and the cranial base, relations between the cartilage and the medial pyterygoid plate, relation between the two cartilaginous laminae, and the presence of a heavy coat of soft tissue over the torus were findings felt to indicate that movement of the tubal cartilage in swallowing cannot occur. Nasopharyngoscopic reports of "cartilage" movement during swallowing may be observations of soft tissue sliding over the torus and not torus movement itself.

KEY WORDS: Eustachian tube, Torus tubarius, Nasoendoscopy, Anatomy

The mechanism by which the auditory tube the results of studies involving animal models. is dilated is still a matter of some debate. The latter are perhaps the most enlightening Various muscles and muscle systems have in view of this more direct approach to settling been suggested as being responsible for the this issue. observed tubal opening during deglutition. The various studies reported show clearly These mechanisms have been based on ana- that the tensor veli palatini muscle is the sole tomic and physiologic evidence as well as on and sufficient functional dilator of the Eus- tachian tube in dogs (Rich, 1920) and in the Dr. Rood is Assistant Professor, Department of Oto- Rhesus monkey (Macaca mulatta; Cantekin laryngology, University of Pittsburgh School of Medicine, Eye and Ear Hospital, Pittsburgh Pennsylvania. Dr. et al., 1979), the two animals studied most Doyle is Assistant Professor, Department of Otolaryngol- intensively. Extrapolation of the mechanisms ogy, University of Pittsburgh School of Medicine, Chil- observed in these animal models to man has dren's Hospital, Pittsburgh, Pennsylvania. Correspond- been criticized. This has occurred in spite of ence should be addressed to Stewart R. Rood, Ph.D., the reported marked similarity in the anat- 1115 Eye and Ear Hospital, 230 Lothrop Street, Pitts- burgh, PA 15213. , . omy and function of the auditory tube and Presented in part at the Mid-winter Meeting, Associ- middle ear between the Rhesus monkey and ation for Research in Otolaryngology, St. Petersburg, man (Doyle and Rood, 1979). Direct studies Florida, January 21-23, 1980. of this system in man are not feasible, and, This study was supported in part under Grant #1PO NS16337 from NINCDS of the National Institutes of consequently, we must rely upon such evi- Health, to the Department of Otolaryngology, Children's dence as the observed dilations at the naso- Hospital of Pittsburgh. pharyngeal orifice which accompany swallow- 119 120 Cleft Palate Journal, April 1982, Vol. 19 No. 2

ing. It is, therefore, the purpose of this study Dellon, 1978). It has been presented with to outline the anatomy of the auditory tube some modifications for over a century. This is and its associated musculature and to relate supported by the observed movements of the this to possible imposed constraints and limi- tissue surrounding the nasopharyngeal orifice. tations on tubal mechanics. One of the first authors to present his observation illustrating the role of the levator Review of the Literature veli palatini muscle in tubal functions was Two basic mechanisms of auditory tube Cleland, who, in 1869 observed that the lower dilation have been proposed for man. The margin of the auditory tube was "spas- first is supported by anatomical and func- modically twitched up" during swallowing. tional studies in man and more direct evi- Simpson and Witcher (1947) and Simkins dence from animal models. This model (1943) also describe various mass tubal move- (Honjo et al., 1979) assumes that the auditory ments which involved the torus tubarius ro- tube is basically fixed to the cranial base and tating counterclockwise about an axis passing that functional dilation is accomplished by through the tubal lumen. The mechanistic contraction of the medial bundle of the tensor explanation for these movements was first veli palatini muscle (Rood and Doyle, 1978). postulated by Bryant (1907). He reported that The second model involves both the tensor the medial cartilaginous lamina is hinged su- and the levator veli palatini muscles (Seif and periorly and swings freely at its line of attach-

FIGURE 1. A photomicrograph obtained from a 1.5 mo. old otologically normal specimen (at the junction between the anterior third and middle third of the cartilaginous tube) illustrating the relationship between the tubal cartilage (A), the levator veli platini (C) and tensor veli palatini (D) muscles. An "accessory" piece of cartilage is also shown (B). The cartilage, shown here in its crooked shaped configuration, is a continuous piece of cartilage, with lateral (2) and medial (1) aspects. The description of lateral and medial laminae which are joined at the dome of the cartilage is not supported. (Original magnification-15%) Rood & Doyle, oriricE 121 ment. The primary force responsible for tubal levator veli palatini muscle and various types dilation is purportedly the posteromedial of tubal rotation have been suggested (Schu- pressure of the levator veli palatini muscle on knecht, 1974). the angular process of the medial cartilage Common to the majority of these reports is which then swings "backward, upward, and an anatomic description of the tensor veli inward, dragging with it the floor of the tube palatini (TVP) as being single bundled and and thereby forming a triangular orifice" lacking a direct tubal attachment. However, (Bryant, p.934). Bryant did not report a role past and more recent anatomic studies have for the tensor veli palatini muscle in tubal demonstrated conclusively that the TVP mus- dilation. A similar mechanism of tubal dila- cle is a composite muscle consisting of a lateral tion was postulated by Simkins (1943), though bundle (TVP proper) with bone to bone at- he ascribed to the tensor veli palatini muscle tachments (in agreement with Seif and Del- the role of tubal closure. More recently, Seif lon) and a medial bundle (the dilatator tubae and Dellon (1978) reiterated these positions muscle) which takes its origin directly from and suggested a more active function for the the posterior 1/3 of the lateral membranous tensor veli palatini muscle. They reported wall of the auditory tube and is attached on that this muscle is only capable of isometric its other end to the deep surface of the TVP. contraction. By increasing its bulk along the The vector of this muscle has been described lateral tubal margin, it may serve to passively (Doyle, 1977) for adults of various popula- assist the motion of the levator veli palatini. tions and is potentially effective in dilating More complicated hypotheses involving the the auditory tube by inferolateral displace-

FIGURE 2A. The tensor veli palatini (lateral bundle) viewed from the lateral aspect. 1-the lateral bundle of tensor veli palatini; 2-the lateral lamina of the auditory tube cartilage; 3-the lateral membranous wall of the auditory tube retracted somewhat; 4-the cranial base. 122 Cleft Palate Journal, April 1982, Vol. 19 No. 2

FIGURE 2B. The medial bundle (2) of the tensor veli palatini muscle (dilatator tubae) or seen with the lateral bundle removed. 1-the muscle as it rounds the hamulus; 2-the dilator tubae muscle; 3-the lateral cartilaginous lamina; 4-the cranial base; 5-the lateral membranous tubal wall. ment of the lateral tubal wall. Consequently, graphic and narrative documentation the more complicated mechanisms of tubal was maintained of all pertinent observa- dilation which implicitly deny this insertion tions, e.g. cartilage-cranial base relation- are at best of secondary functional impor- ship, cartilage-pyterygoid plate relation- tance. This report addresses the anatomic po- ship, and disposition of the paratubal tential for the more complex movements as- musculature. sumed under the model of tubal dilation by One side from each of six human ca- contraction of the levator veli palatini muscle. daver heads (in addition to the above) was dissected as above but studied with Materials and Methods specific attention to the soft tissue sheath Several research protocols were developed overlying the torus tubarius. Measure- in order to obtain anatomic data deemed ments were taken of the thickness of the relevant to the basic question of the reality of tubal cartilage at the lateral lanima, with tubal cartilage movement, of whatever sort, and without its soft tissue sheath. during swallowing. Five anteroinferiorly extended temporal 1. One side from each of seven adult hu- bone specimens, excised at autopsy in man cadaver heads was dissected using accordance with the procedure outlined standard dissection instruments. When by Rood and Doyle (1981), were pro- necessary, dissection was carried out us- cessed for light microscopy. The speci- ing a Zeiss binocular operating micro- mens (ages: 1.5 mo., 3 mo., 13 yrs., 21 scopic for magnification. No quantative yrs., and 27 yrs.) were decalcified in tri- measurements were obtained. Photo- chloroacetic acid, embedded in celloidin, Rood & Doyle, nasorHarynorar ortrice 123

sectioned at 25-30 um, and stained in 5) Relation of the soft tissue sheath to the hematoxylin and eosin. Tubal cross-sec- anterior termination of the tubal carti- tions and longitudinal sections were stud- lage. ied. Wide field, lowpower photomicro- graphs were obtained using a Micro- 1. ParatuBatr MuscutatTuURE Nikor 55 mm lens coupled to a Bowens Figure 1 shows the disposition of the two Illumatron. primary muscles associated with the auditory tube. These are the tensor veli palatini and Results the levator veli palatini muscles. While these The observations are presented as a series muscles have been discussed in detail else- of defined relations deemed important to an where (Rood, 1973; Rood and Doyle, 1978), evaluation of the potential for auditory tube the confusion in the more recent literature movement during swallowing. These relations (Honjo et al., 1979; Seif and Dellon, 1978) are: and the importance of these muscles to tubal 1) Disposition of the paratubal muscula- mechanics warrant a review. ture. The levator veli palatini muscle arises from 2) Relation of the tubal cartilage to the the petrosal portion of the temporal bone cranial base. immediately posterior to the osseous cartilag- 3) Relation of the tubal cartilage to the inous juncture of the auditory tube and oc- medial pterygoid plate. casionally by a few decussating fibers from its 4) Relation of the two cartilaginous lami- membranous floor. The muscle is cylinderical nac. in shape and closely follows the floor of the

FIGURE 3. The lateral bundle (tensor veli palatini-A) and the tensor tympani (B) muscles are continuous, joined by an interposed tendon. C-the tympanic membrane, as seen from the middle ear; D-the malleus. 124 Cleft Palate Journal, April 1982, Vol. 19 No. 2 tube, imposing an arch to its inferior surface. process and becomes continuous with the pal- At the anterior termination of the tube, the atal aponeurosis anteriorly. The more medial muscle passes lateral to the salpingopharyn- bundle, referred to as the dilatator tubae mus- geal fold, above the superior constrictor muscle (Rood and Doyle, 1978), takes direct origin cle, to insert in a radiating fasion into the from the lateral membranous wall of the pos- superior aspects of the velum. Contractions terior 1/3 of the cartilaginous auditory tube. result in velar elevation and a superoposterior A few slips of muscle fibers also arise from the swing of the muscle about its fixed posterior lateral tubal cartilage. Its fibers descend to origin thereby imposing a medially directed become continuous with those of the lateral force on the salpingopharyngeal fold. Conse- bundle. It is this inner bundle which is most quently, the salpingopharyngeal fold and as- often ignored by the proponents of the model sociated soft tissue will move medially result- of tubal dilation based upon levator action. ing in the observed gaping of the pharyngeal Clearly, the direct attachment of the muscle orifice of the auditory tube during swallow- to the lateral tubal wall associated with a ing. sufficient vector of action, places this muscle The tensor veli palatini muscle is divided in a unique position to open the tube by into two functional planes or bundles (Figure inferolateral displacement of the membranous 2). The more lateral bundle arises from the wall. Rotation and other complex movements scaphoid fossa and along the spine of the are not required for this action. sphenoid bone to the base of the medial pterygoid plate. Its fibers are continuous with 2. Tusar CartimacE-Crantat Base those of the tensor typani posteriorly (Figure Past reports have described the cartilagi- 3). The fibers descend inferolaterally, to nous portion of the auditory tube as being merge as a tendon which rounds the hamular suspended by a superior tubal ligament (Proc-

FIGURE 4. The cartilaginous auditory tube (1) pulled away from the cranial base (2) to illustrate the connective tissue (3) which fixes the tube to sphenoid sulcus. 4-the cranial base attachments of the levator veli palatini muscle. Rood & Doyle, nasoPHaARYNGEAL ORIFICE 125 tor, 1973; Graves and Edwards, 1944), giving 3. Tusar Cartimace-MEniar PrErvoom the impression both visually and descriptively Prate of a rather loose relation which would poten- The anterior termination of the cartilagi- tially allow for rotation. Figure 4 shows the nous portion of the auditory tube is intimately relation of the tube to the cranial base. The related to the medial pterygoid plate. On tubal cartilage was found to run within the approaching the plate, the tube crosses from margin of the petrous temporal and sphenoid the lateral to medial aspect and the lateral bones lying within a groove formed by this portion of the tubal cartilage is inset into a juncture, the sphenoid sulcus. The cartilage is depression on the posterior medial surface of tightly bound within the sulcus for its entire the pterygoid plate (Figure 5). It is tightly length. No true suspensory ligament, as a held within this depression by connective tis- characteristic of the middle ear ossicles, was sue. The relationship between the lumen and observed. Rather a dense layer of connective the pterygoid plate is shown in the accompa- tissue unites the cartilage to bone. Further, in nying CT scan (Figure 6). all specimens studied, the cartilage termi- nated posteriorly with some intrusion into the 4. RerartiON or THE CaARTILAGINOUS protympanum to which it was firmly affixed "Laminar" superiorly. These observations generally dis- The impression that one is left with in count any complex movements-either a reading many of the anatomic descriptions of "hinged mechanism" at the osseous-cartilagi- tubal morphology (Proctor, 1973; Reiner, nous junction or rotation on the "suspensory 1969) is that there exists two separate laminae ligament." of stable morphology which are joined and/

" FIGURE 5. An adult human cadavers specimen illustrating the relationship between the anterior end of the auditory tube, torus tubarius, (A) and the medial pterygoid plate (B). The depression on the medial pterygoid plate into which the cartilage is fit and held firmly by connective tissue is shown by the arrow. C-the tensor veli palatini muscle as it rounds the hamulus. 126 Cleft Palate Journal, April 1982, Vol. 19 No. 2 or hinged superiorly. Our histologic material dissection or light microscopy. Thus, no does not bear this out. Rather, the tubal breaks along the length of the cartilaginous cartilage is seen to be extremely variable in tube are available to act as a hinge point. A shape and structure, often possessing infe- possible hinge site that is often described is riorly, medially, or laterally placed indepen- the osseous-cartilaginous junction. Both light dent cartilaginous pieces, at least in the microscopy and gross dissection observations younger specimens. Seldom does there exist a demonstrated that the typically described, or superior juncture to the tubal cartilage. Most at least, implied, end-to-end joining of the often the cartilage is a continuous piece which cartilaginous and bony tubes, which may may be described as having medial and lateral have provided the hinge point, did not exist. aspects (Figure 1). Instead, the cartilage extended into the osseous tube for several millimeters, firmly 5. Sort Tissue SnratHu bound into the protympanum, negating any An anatomical parameter little discussed in possibility of movement in this area. Other the modern literature on tubal anatomy is the observations which would contraindicate heavy sheath of soft tissue that overlies the mass tubal movement were 1) the cartilagi- cartilage. It is continuous with the pharyngeal nous tube is bound to the sphenoid sulcus on soft tissue and obscures the cartilage from the cranial base by a dense layer of connective direct observation. Table I presents data on tissue and 2) the anterior end of the tubal the thickness of the anterior end of the medial aspect of the cartilage with the soft tissue sheath in place and with the soft tissue sheath removed. The thickness of the soft tissue blanket averaged 1.71 mm. Figure 7 illustrates the medial portion of the cartilage with its overlying dense soft tissue lifted superiorly. The thickness of the coat is suggested by the bulk of tissue held in the hemostat.

Discussion Several factors appear to be involved in limiting movement of the cartilaginous portion of the auditory tube. First, no hinge mechanism is evident. In order for the tube to move, it must do so by bending at some point or points. Although the cartilage is of the elastic type and may be malleable, the cartilaginous tube is quite bulky and not easily distorted. An attempt was made to bend the tube in the cadaver specimens studied. The cartilaginous tube proved not to be bendable. FIGURE 6. A CT scan illustrating the close prox- No accessory pieces of cartilage were found in imity between the tubal lumen and the medial pterygoid any adult specimen examined, either by gross plate (arrow).

TABLE 1. The Measurements Related to the Thickness of the Soft Tissue Blanket Covering the Auditory Tube Cartilage in the Seven Adult Specimens studied

Specimen Measurement - A C D E F X

Thickness of cartilage and soft tissue 4.5 6.75 6.45 5.25 5.25 5.93 (mm) Thickness of cartilage without soft tissue 1.6 5.08 6.5 3.95 245 5.04 4.16 (mm) Soft tissue Blanket (mm} 2.9 2.32 25 30 2.45 21 1.77

Rood & Doyle, nasopHaryncEar oRrIFICE 127 cartilage is fitted into a depression on the In observing the nasopharyngeal orifice of medial pterygoid plate and bound to the plate the auditory tube, it often appears as if the by connective tissue. The medial aspect of the tube is moving during swallowing. Is it really? cartilage at its most anterior end (in the na- The answer-probably not! The descriptions sopharynx) may be capable of some limited of tubal movement speak of the movement of independent radially directed movement. the cartilage. The "cartilage," however, is not This movement, however, is limited by the visible. It is covered by a heavy layer of forces available to produce motion, the bulk mucosa, as demonstrated by gross dissection of the cartilage here, and its relationship to and light microscopic study. This tubal sheath the surrounding structures. Reiner (1969), re- of tissue is continuous with the pharyngeal porting on a morphologic study of the carti- walls. Thus, any movement of the pharyngeal lage in dogs and Guild (1955), in studying walls, such as that which occurs during swal- Eustachian tube sections from human speci- lowing or speech, also results in the movement mens, identified elastic fibers coursing of the soft tissue covering the torus. This can through the dome of the tube, lying between easily be mistaken for movement of the car- the medial and lateral aspects of the cartilage. tilage, if the observer does not have an indepth This finding may provide evidence that some knowledge of tubal anatomy. That which is differential motion of the two sections may usually identified as cartilage movement dur- occur. Whether this possible motion has any ing swallowing is more likely than not, ac- relationship to tubal dilation has not as yet tually soft tissue movement over the anterior been established. end of the tubal cartilage.

FIGURE 7. The soft tissue (2) covering the auditory tube is illustrated as it is retracted away from the cartilage. 1-The soft tissue is continuous with the remainder of the soft tissue lining the pharynx; 3-levator veli palatini muscle; 4-nasopharyngeal orifice of the auditory tube. 128 Cleft Palate Journal, April 1982, Vol. 19 No. 2

Conclusions Dove, W. J., A functional anatomic description of Eus- tachian tube vector relations in four ethnic popula- The conclusions which can be drawn from tions. Unpublished Doctoral Discertation, University the first part of this long term study are as of Pittsburgh, 1977. follows: DovyLe, W. J., and Roop, S. R., Anatomy of the auditory tube and related structures in the Rhesus monkey 1. The mass movement of the tubal carti- (Macaca mulatta), Acta Anat., 105: 209-225, 1979. lage described in the literature is severely GuiLtD, S. R., Elastic tissue of the Eustachian tube, Ann. limited by the relationship between the Otol. Rhinol. Laryngol., 64: 537-545, 1955. cartilaginous tube and cranial base and Graves, G. and Epnwarps, L., The Eustachian tube, medial pterygoid plate, the absence of a review of its descriptive, micriscopic, topographic, and clinical anatomy. Arch. Otolaryngol., 63: 357-397, 1944. hinge mechanism and the bulkiness of Honjo, I., OKaAzAKI, N., and Kumazawa, T., Experimen- the cartilage itself. tal study of the Eustachian tube funcion with regard 2. The movement of the "cartilage" as seen to its related muscles. ACTA Otolaryngol. (Storkh), 87 (1- via pharyngoscopy may actually be the 2): 84-89, 1979. movement of the heavy coat of soft tis- ReinER, C., Experimental production of serous otitis me- dia in dogs. Unpublished masters thesis, Univ. of Min- sue, which overlies the torus, sliding over nesota, Mayo Clinic, 1969. the anterior end of the tubal cartilage, Proctor, B., Anatomy of the Eustachian tube. Arch. simultaneously with motion of the lat- Otolaryngol., 97: 2-8, 1973. eral pharyngeal walls, as observed dur- RicH, A. R., A physiological study of the Eustachian tube and its related muscles, Bull. Johns Hopkins Hosp., 31: ing swallowing. 206-214, 1920. This first portion of this study sought to Roon, S. R., The morphology of the m. tensor veli identify and describe the anatomical param- palatini in the five-month human fetus, Amer. J. Anat., eters of the nasopharynx-auditory tube system 138: 191-196, 1973. that may account for nasopharyngoscopic ob- Roop, S. R., and Dovir, W. T., Morphology of the tensor veli palatini, tensor tympani, and dilatator servation. The report to follow will seek to tubae muscles. Ann. Otol. Laryngol. and Rhinol., 87: 202- correlate movement of the nasopharyngeal 210, 1978. orifice of the tube with actual measurements Roop, S. R., and DovLr, W., An extreme morphologic of tubal patency. variation of the auditory tube cartilage: a case report, Cleft Palate J., 18: 293-298, 1981. References H., Pathology of the ear, Cambridge, Mas- sachusetts, Harvard University Press, 1974. Bryant, W. S., The Eustachian Tube: its anatomy and SEF, S., and DErroNn, A. L., Anatomic relationships Its movement; with a description of the cartilagies, between the human levator and tensor veli palatini muscles, fascia, and the fossa of Rosenmuller. Med. and the Eustachian tube, Cleft Palate J., 15: 329-336, Rec., 71: 931-934, 1907. 1978. CLELraAND, On the question whether the Eustachian tube Simkins, C. S., Function anatomy of the Eustachian tube, is closed or open in swallowing. J. Anat. Physiol, 3: 97- Arch. Otol., 38: 476-484, 1943. 103, 1869. Simpson, W. L., and WitcHErR, J. E., A study of the CanTtEkIN, E. I., Dover, W. J., T. J., PuiruiPps, Eustachian tubes and their orifices and lumens in D. C., and Brurstonr, C. B., Dilation of the Eusta- patients with large operative defects giving direct vis- chian tube by electrical stimulation of the mandibular ualization, Ann. Otol. Rhinol. Laryngol., 56: 355-367, nerve. Ann. Otol. Rhinol. Laryngol., 88: 40-51, 1979. 1947.