Three-dimensional computer graphics of the eustachian tube

Am J Otolaryngol 8:211-213, 1987

Three-dimensional Computer Graphics of the Eustachian Tube KAZUNORI MORhMD, YASUSHINAITO, MD, YOSHINOBU HIRONO, MD, ANDIWAOHONJO,M D Images of the eustachian tube from various directions were obtained using computer graphics. Serial cross sections of a human temporal bone specimen including the eustachian tube were digitized for reconstruction. Wire-frame models of the structures such as the eustachian tube lumen, the tubal cartilage, the tensor veil palatini muscle, and the levator veil palatini muscle were drawn. Through observation o! the eustachian tube from various directions with the tubal muscles attached or detached, the physiology of the eustachian tube system could be understood more clearly.

Much remains unknown about the functional mechanism of the eustachian tube. One of the reasons for this lack of knowledge is the difficulty in understanding the structures around the eustachian tube (such as the tubal cartilage and the tubal muscles) because they are not directly visible. Based on cross sections of a cadaver specimen, three-dimensional images of the eustachian tube system were reconstructed using a personal computer. Through the study of these images, the spatial relationships of the eustachian tube, the tubal cartilage, the tensor veli palatini muscle, and the levator veli palatini muscle could be understood more easily. This method will be of great help for the analysis of the functional mechanism of the eustachian tube system.

pen Electric). To standardize the data, small notchs were marked at both sides of each specimen slice, After correcting the coordinates properly using these standard marks, the tubal lumen, the tubal cartilage, the tensor veli palatini muscle, and the levator veli palatini muscle were approximated to polygons, respectively. These data and the Z coordinates calculated from slice width were transformed to two-dimensional projections. Thus, a wire-frame model of the eustachian tube system was obtained. The hidden structures were shaded using the Z-buffer method (drawing from distant to near). The program language used was FORTRAN, and the program consisted of about 1,500 lines. It took about 5 minutes to draw the whole image from one direction.

MATERIALS AND METHODS

RESULTS

A human left temporal bone specimen with a normal eustachian tube was used for the study. Twenty-eight vertical cross sections of the eustachian tube of 1.2-mm slice width were obtained from the specimen. After the digitization of photographs of these slices by a graphic digitizer (NEC MPC-8501, Nippon Electric, Tokyo, Japan), XYcoordinate data for reconstruction were entered into a personal computer (NEC PC-9801VM, Nip-

Figure 1 shows a lateral view of a left eustachian tube system from the anterosuperior direction, and Figure 2 shows a lateral view from the posterosuperior direction. Figure 3 shows a medial view from the posterosuperior direction. Figure 4 is an image with the tubal cartilage removed from Figure 3. Figure 5 shows a lateral view with the tensor yell palatini muscle removed. The tubal cartilage was constricted slightly at the junction of the medial one third with the lateral two thirds, and the junction of the lateral one third with the medial two thirds was thick, especially in the inferomedial direction. The most posterior part of the tubal cartilage situated superior to the tubal lumen, and it was fixed to the temporal bone. Figure 6 is a lateral view of the eustachian tube

Received March 3, 1987, from the Department of Otolaryngology, KyotoUniversity, Kyoto,Japan. Acceptedfor publication March 23, 1987. Address correspondence and reprint requests to Dr. Mori: Department of Otolaryngology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606, Japan. 0196-0709/87 $0.00 + .25 211

THREE-DIMENSIONAL COMPUTER GRAPHICS OF THE EUSTACHIAN TUBE

~

.

~

"

" "

tympanic orifice

~:::."-'~..~/~r -::,;~\z~ 2,

- t ~, , , , . '! ':.... ',,' ;4~ ~'r .' , ~'.~

)

( " " "~.

levator

. " t: , ,

'~ ".i'!!~ '- ' ~ ~ \

,;,...~ /

cartilage

' ""4 ) ~"l ,~'-~t';ili I..~';.~ ,'-tt-'i--LJ'l/"~"~

( "," ...-"iv~",,J,.,,,, ~, .'~.,~.,.~ . f..., - \ //....", ~,' ;~ ~,{,~7

cartileoeX

~'-,~!;t~ ~'~',~, "~;i',, ~,~.' ':~i~,"~ ,,,."

~

tensor evfltor

tinier

'~:"% '. 3

',flit '~'~

~'-~:~"

\..i~il

tensor

tensor

,.1._~

~'f-"~ -~.~ "i

pharyngeal orifice

,,~."~"-':?~,~,, .cartilage 9~:~'::~,~.~'/" ~~__:~;,,.. ,.,,'-~"' . ,..~ :,' !,~.-.L-~, ',',.i .,~':.. ' j..~

9 *':"" "

"" '."

~'"

I'

~---~.;--.';.-..~,,~ ,..I':.":.

~

" '

-r:_?" .: ..'-. "'

, ~ "

"

~:/W,,,

:," :.,5'

-7:"',.

- 9 '~;

9

I.ator tympanic ~1:t: ~ orifice ~;i!~J~

tympanic orifice

tul~

} ~ tympanic

orifice

tube

Figure 1 (top left). Lateral view of a left eustachian tube system from anterosuperior direction. Figure 2 (top right). Lateral view from posterosuperior direction. Figure 3 (bottom left). Medial view from posterosuperlor direction. Figure 4 (bottom right). Medial view from posterosuperior direction with the tubal cartilage removed.

and the tubal cartilage. The transverse sections of the tubal cartilage were hook shaped at its anterior one-third point, but they became C shaped at its posterior one-third point where the tubal cartilage surrounded the tubal lumen. Here the levator veli palatini muscle was separated from the tubal lumen by the tubal cartilage. There was no evidence that the levator veli palatini muscle arose from the tubal cartilage. Figure 7 shows a tubal lumen alone, and it was S shaped. The osseous part of the tubal lumen was almost horizontal, but its membraneous part was inclined anteroi~eriorly. DISCUSSION

American Journal of Otolaryngology 212

Many attempts--such as roentogengrams using a contrast medium, wax models of the eustachian tube of cadavers, and observation using fiberendoscopy--have been made to understand the three-dimensional structure of the eustachian tube system. These attempts have failed to show the spatial relationship of the tubal lumen, the tubal

cartilage, and the muscles around it. The development of computer technology has made it possible to reconstruct graphically the three-dimensional structure of the eustachian tube system. Recently, some papers have reported three-dimensional computer graphics of the eustachian tube system, 1 but these graphics are not yet satisfactory enough to observe the detailed anatomy of the eustachian tube system. When reconstructing the structure from serial cross sections using computer graphics, it is important to hold standard points and to consider the continuity of each slice. The wire-frame model is suitable for computer graphics because it takes a short time to calculate, and the programming is not difficult. Our technique made it possible to obtain a clear reconstructed model with relatively small effort. Computer graphics is advantageous in analyzing the anatomy of the eustachian tube system because it is possible to draw any respective structures seen from any direction, Proctor 2 reported that the tensor yell palatini muscle consists of both a superficial layer and deep layer

MORI ET AL.

cartilage _ ~ ! "

E

tympanic orifice

;':/ .,,~_~::"-:L: L4.;!~:,-:.,~ f..:-'. ...~--~ . ~ ;:.~:F,

.~2~

.,..l"~.." ~,.'~ . ' . . : . ,.. . :.... ... . -: ~,~'~;~'/gS.::.:J'

"'

tubal lumen

.',"~:;::~,::V,~."!~/

~t~.~i.~,.~.,

~ ;

levator

tyml:lanic ostium

tympanic orifice

Figure 5 (top left). muscle removed.

Lateral view with the tensor veli palatlni

Figure 6 (top right). Lateral view of the eustachian tube and the tubal cartilage.

Figure 7 (bottom). Lateral view of the tubal lumen alone, and that the f o r m e r arises f r o m the skull base and the latter f r o m the t u b a l cartilage. Figure 8 is a lateral v i e w of the e u s t a c h i a n t u b e system with its superficial layer r e m o v e d . It shows that the deep layer of the tensor yell palatini muscle arises f r o m b e t w e e n the j u n c t i o n of the m e d i a l one half w i t h the lateral one half a n d the junction of the tympanic orifice

I

I
lateral one fourth with the medial three fourths of the tubal cartilage as m e n t i o n e d by McMyn. 3 Here the tubal cartilage thickens inferomedially as c o m p a r e d with the anterior one-third point, where the tubal cartilage constricts slightly as mentioned by Aschan, 4 and here the tubal cartilage is C shaped, so the lavator veli palatini muscle is separated from the tubal l u m e n by the cartilage. These anatomic findings suggest that the tubal l u m e n opens at this part by the tensor veli palatini muscle alone, as pointed out by Honjo et al., s and Cantekin et a12

.;" .......~~S"~J',), v"(,.3t" .......

.,., .,.

-:' ~-"~:;~ ~,,:~'A..t: ~'~':~

I"-:, ,.. ,,,: ";A.~;..~;~:.....~ "./[:~' 9,: ,,~. ;~,.,;,~:~:

';'

pharyngeal orifice

.~:~.~, ,~,

,;::,r i ' P"~4~'/.~"~.:;,:')~:J '~ "1 - - ,..... ~, , t" .',,' '~...r ~'-~,.~r " -,-~ :~ -:,..,':I:

tensor, deep layer

References I. Siegel MI, et ah Computer reconstruction of eustachian tube anatomy. Ann Otol Rhinol Laryngo11983;92(suppl 107):10 2. Proctor B: Anatomy of the eustachian tuba. Arch Otolaryngol 1973;97:2-8 3. McMyn JK: The anatomy of the salpingopharyngeus muscle, J Laryngol Oral 1940:55:172-186 4. Aschan G: The eustachian tuba. Acta Otolaryngol (Stockh) 1954;44:295-311

levator

Figure 8. Lateral view with the superficial layer of the tensor veli palatini muscle removed.

5. Honjo I, et ah Experimental study of the eustachian tube function with regard to its related muscles. Acta Otalaryngol (Stockh) 1979;87:84-89 6. Cantekin EI, et ah Dilation of the eustachian tube by electrical stimulation of file mandibular nerve. Ann Otol Rhinol Laryngol 1979;88:40-51

Volume 8 Number 4 July 1987 213