CHAPTER III. ANATOMY AND MORPHOLOGY
ANATOMY OF THE NORMAL AND CLEFT PALATE EUSTACHIAN TUBE DAVID
R.
DICKSON, PH.D.
PITTSBURGH, PENNSYLVANIA
SUMMARY - This report presents preliminary findings from a study of cleft palate and noncleft palate human fetuses to determine whether differences in Eustachian tube and cranial base structures could be found which might explain the universal appearance of otitis media in infants with cleft palate. Differences were found which are consistent with the previous hypothesis of reduced elasticity in the Eustachian tube. Principal findings included medial to lateral compression of the tube and reduced tubal width.
The Eustachian tube is normally closed. The muscular force for opening the Eustachian tube is provided by the tensor veli palatini muscle. First I will review the anatomy of the tensor veli palatini muscle and its relationship to the Eustachian tube and to the tensor tympani muscle. 1 I will then present preliminary findings from our current study of the anatomy of the Eustachian tube and related craniofacial structures in normal and cleft palate human fetuses. The purpose of this study is to determine possible anatomical deviations which may be related to the high incidence of Eustachian tube malfunction in children with cleft palate.t" The major attachment of the tensor veli palatini muscle is to the lateral membranous wall of the Eustachian tube. While some authors have described this muscle as attaching to the cartilage of the tube, in our studies we have found only occasional fibers of tensor ending on the cartilage. Superiorly, the tensor ends in two tendons: a lateral or anterior tendon which goes to the angular spine of the sphenoid bone; and a medial or posterior tendon which is the medial
tendon of the tensor tympani muscle. Thus the tensor tympani muscle and at least a part of the tensor veli palatini muscle form a digastric muscle. The question then arises as to whether the two muscles act together in middle-ear clearance, with tensor tympani increasing middle ear pressure by its action on the tympanic membrane to trigger Eustachian tube dilation by the action of tensor palatini. Or, perhaps, there is some type of stretch-reflex linkage between the two muscles. At least we can say that the two muscles are closely linked anatomically and possibly closely linked functionally. At the inferior end of the tensor palatini muscle the anatomy is more complex, or at least less well understood. The fibers descend lateral to the hamulus and end in a tendon which loops around the hamulus and enters the anterior velum. As it does so, it forms a bursa at the hamulus. However, between that portion of the tendon at the bursa and that portion of the tendon superolateral to the bursa are short muscle fibers (Fig. 1). While these fibers have been noted in all of the fetuses which we have examined,
"The cleft palate study is under the direction of Dr. Wilma Maue Dickson, Department of Anatomy, University of Pittsburgh, in cooperation with the Cleft Palate Center and with Dr. Stewart Rood of Mercy Hospital, Pittsburgh. From the Cleft Palate Center, University of Pittsburgh, Pittsburgh, Pennsylvania. The research was supported, in part, by U.S. Public Health Service Grant Number DE-01697, National Institute of Dental Research.
25
26
DAVID ROSS DICKSON
Fig. 1. Sagittal section of a human fetus illustrating the intratendon muscle fibers ( arrow) of the tensor veli palatini muscle (T). Other landmarks are the Eustachian tube lumen (L), and membranous wall (M); the hamulus (H) and the levator palatine muscle (P).
they need further description. In addition, fibers of other muscles, possibly buccinator and superior constrictor, attach to the ligament as it passes around the hamulus (Fig. 2). After passing around the hamulus, the tendon attaches to the length of the posterior border of the hard palate. Muscle fibers from su-
perior constrictor, or possibly from palatopharyngeus, insert into the tendon within the velum (Fig. 3). It is apparent that the anatomical relationships in the area of the hamulus and velum are in need of clarification. Whether there is action of the tensor veli palatini tendon around the hamulus, an activity sug-
Fig. 2. Coronal section of a human fetus illustrating muscle fiber (arrow) ,possibly from the buccinator, attaching to the tensor tendon near the hamulus (H). Other landmarks are the velum (V) and tongue (G).
27
ANATOMY OF EUSTACHIAN TUBE
-., .
•
Fig. 3. Transverse section of a human fetus through the level of the velum (V) and hamulus (H) illustrating apparent superior constrictor muscle attachments to the tensor tendon within the velum (arrows).
gested by the presence of the bursa, is still open to question. The functional significance of the various muscle bundles inserting into the tendon is also unknown. In terms of innervation, while the small amount of research which has been reported suggests trigeminal innervation of both tensor palatini and tensor tympani, further study is necessary here also. It is well known that the presence of middle ear effusions in infants with cleft palate is universal. This is believed to be caused by a failure of the Eustachian tube to open, which in turn has been at-
tributed to a lack of stiffness in the tubal walls," The morphology of the tensor palatini muscle has been found to be normal in human cleft-palate fetuses." Therefore, our current investigation was undertaken to determine differences between cleft palate and noncleft palate human fetuses which might be relevant to tubal function. This includes examination of the cranial base, pterygoid plates, epipharynx, and palate, as well as of the tubal lumen, cartilage and associated muscles. I want to stress that the findings from
Fig. 4. Coronal section of normal human fetal head through the plane of the medial (M) and lateral (L) pterygoid plates.
28
DAVID ROSS DICKSON
Fig. 5. Coronal section of cleft lip and palate of a human fetal head through the plane of the medial (M) and lateral (L) pterygoid plates.
the research which I will present today are preliminary findings based on the first few pairs of cleft and noncleft fetuses selected for this study. All of the specimens on which these preliminary data are based are complete unilateral clefts of the lip and palate. The first set of measurements in which significant differences were found are internal width measurements, including the width of the nasopharynx and the distances be-
tween the lateral pterygoid plates, medial pterygoid plates, Eustachian tube lumina, Eustachian tube cartilages, and hamuli. All of these measurements were greater in the cleft than in the noncleft. Since all were expressed as a proportion of external head width, this means that the tissues between the lateral wall of the nasopharynx and the side of the head are compressed in the cleft fetuses. Secondly, the lumina of the cleft and non-
Fig. 6. Coronal section of normal human fetal head through the Eustachian tube lumen (L). Other landmarks are the tensor (T) and levator (P) palatini muscles.
ANATOMY OF EUSTACHIAN TUBE
29
Fig. 7. Coronal section of cleft lip and palate human fetal head through the Eustachian tube lumen (L). Other landmarks are the tensor (T) and levator (P) palatini muscles.
cleft heads were found to be. different. In the cleft palate fetuses the width of the lumen was reduced and the walls were found to be highly convoluted. Other differences which have been observed in some cleft heads but which do not seem to be typical of the group include increased width of the sphenoid body, an increased angle between the pterygoid plates and the midsagittal plane, and bilateral dissymmetry of the
greater and lesser wings of the sphenoid. Thus it seems apparent that cleft palate may involve deformities of the entire cranial base structure. We must proceed further, however, to determine the likelihood that any or all of the differences observed could affect tubal function. In addition, developmental studies must be carried out to determine the nature of changes in these relationships during late fetal and early postnatal life.
REFERENCES 1. Rich AR: A physiological study of the Eustachian tube and its related muscles. Johns Hopkins Med J 352:206-214, 1920 2. Paradise JL, Bluestone CD, Felder H: The universality of otitis media in 50 infants
with cleft palate. Pediatrics 44:35-42, 1969 3 D' k DR G t JCB S' h H t of: Sta:~s s~f rese~rchr~: cleft pal;~e e:nat~;y and physiology, Part I, Cleft Palate J 11:471492, 1974
REPRINTS - David R. Dickson, Ph.D., Mailman Center for Child Development, University of Miami, Box 520006, Biscayne Annex, Miami, FL 33152.
ANATOMY OF THE NORMAL AND CLEFT PALATE EUSTACHIAN TUBE DAVID
R.
DICKSON, PH.D.
PITTSBURGH, PENNSYLVANIA
SUMMARY - This report presents preliminary findings from a study of cleft palate and noncleft palate human fetuses to determine whether differences in Eustachian tube and cranial base structures could be found which might explain the universal appearance of otitis media in infants with cleft palate. Differences were found which are consistent with the previous hypothesis of reduced elasticity in the Eustachian tube. Principal findings included medial to lateral compression of the tube and reduced tubal width.
The Eustachian tube is normally closed. The muscular force for opening the Eustachian tube is provided by the tensor veli palatini muscle. First I will review the anatomy of the tensor veli palatini muscle and its relationship to the Eustachian tube and to the tensor tympani muscle. 1 I will then present preliminary findings from our current study of the anatomy of the Eustachian tube and related craniofacial structures in normal and cleft palate human fetuses. The purpose of this study is to determine possible anatomical deviations which may be related to the high incidence of Eustachian tube malfunction in children with cleft palate.t" The major attachment of the tensor veli palatini muscle is to the lateral membranous wall of the Eustachian tube. While some authors have described this muscle as attaching to the cartilage of the tube, in our studies we have found only occasional fibers of tensor ending on the cartilage. Superiorly, the tensor ends in two tendons: a lateral or anterior tendon which goes to the angular spine of the sphenoid bone; and a medial or posterior tendon which is the medial
tendon of the tensor tympani muscle. Thus the tensor tympani muscle and at least a part of the tensor veli palatini muscle form a digastric muscle. The question then arises as to whether the two muscles act together in middle-ear clearance, with tensor tympani increasing middle ear pressure by its action on the tympanic membrane to trigger Eustachian tube dilation by the action of tensor palatini. Or, perhaps, there is some type of stretch-reflex linkage between the two muscles. At least we can say that the two muscles are closely linked anatomically and possibly closely linked functionally. At the inferior end of the tensor palatini muscle the anatomy is more complex, or at least less well understood. The fibers descend lateral to the hamulus and end in a tendon which loops around the hamulus and enters the anterior velum. As it does so, it forms a bursa at the hamulus. However, between that portion of the tendon at the bursa and that portion of the tendon superolateral to the bursa are short muscle fibers (Fig. 1). While these fibers have been noted in all of the fetuses which we have examined,
"The cleft palate study is under the direction of Dr. Wilma Maue Dickson, Department of Anatomy, University of Pittsburgh, in cooperation with the Cleft Palate Center and with Dr. Stewart Rood of Mercy Hospital, Pittsburgh. From the Cleft Palate Center, University of Pittsburgh, Pittsburgh, Pennsylvania. The research was supported, in part, by U.S. Public Health Service Grant Number DE-01697, National Institute of Dental Research.
25
26
DAVID ROSS DICKSON
Fig. 1. Sagittal section of a human fetus illustrating the intratendon muscle fibers ( arrow) of the tensor veli palatini muscle (T). Other landmarks are the Eustachian tube lumen (L), and membranous wall (M); the hamulus (H) and the levator palatine muscle (P).
they need further description. In addition, fibers of other muscles, possibly buccinator and superior constrictor, attach to the ligament as it passes around the hamulus (Fig. 2). After passing around the hamulus, the tendon attaches to the length of the posterior border of the hard palate. Muscle fibers from su-
perior constrictor, or possibly from palatopharyngeus, insert into the tendon within the velum (Fig. 3). It is apparent that the anatomical relationships in the area of the hamulus and velum are in need of clarification. Whether there is action of the tensor veli palatini tendon around the hamulus, an activity sug-
Fig. 2. Coronal section of a human fetus illustrating muscle fiber (arrow) ,possibly from the buccinator, attaching to the tensor tendon near the hamulus (H). Other landmarks are the velum (V) and tongue (G).
27
ANATOMY OF EUSTACHIAN TUBE
-., .
•
Fig. 3. Transverse section of a human fetus through the level of the velum (V) and hamulus (H) illustrating apparent superior constrictor muscle attachments to the tensor tendon within the velum (arrows).
gested by the presence of the bursa, is still open to question. The functional significance of the various muscle bundles inserting into the tendon is also unknown. In terms of innervation, while the small amount of research which has been reported suggests trigeminal innervation of both tensor palatini and tensor tympani, further study is necessary here also. It is well known that the presence of middle ear effusions in infants with cleft palate is universal. This is believed to be caused by a failure of the Eustachian tube to open, which in turn has been at-
tributed to a lack of stiffness in the tubal walls," The morphology of the tensor palatini muscle has been found to be normal in human cleft-palate fetuses." Therefore, our current investigation was undertaken to determine differences between cleft palate and noncleft palate human fetuses which might be relevant to tubal function. This includes examination of the cranial base, pterygoid plates, epipharynx, and palate, as well as of the tubal lumen, cartilage and associated muscles. I want to stress that the findings from
Fig. 4. Coronal section of normal human fetal head through the plane of the medial (M) and lateral (L) pterygoid plates.
28
DAVID ROSS DICKSON
Fig. 5. Coronal section of cleft lip and palate of a human fetal head through the plane of the medial (M) and lateral (L) pterygoid plates.
the research which I will present today are preliminary findings based on the first few pairs of cleft and noncleft fetuses selected for this study. All of the specimens on which these preliminary data are based are complete unilateral clefts of the lip and palate. The first set of measurements in which significant differences were found are internal width measurements, including the width of the nasopharynx and the distances be-
tween the lateral pterygoid plates, medial pterygoid plates, Eustachian tube lumina, Eustachian tube cartilages, and hamuli. All of these measurements were greater in the cleft than in the noncleft. Since all were expressed as a proportion of external head width, this means that the tissues between the lateral wall of the nasopharynx and the side of the head are compressed in the cleft fetuses. Secondly, the lumina of the cleft and non-
Fig. 6. Coronal section of normal human fetal head through the Eustachian tube lumen (L). Other landmarks are the tensor (T) and levator (P) palatini muscles.
ANATOMY OF EUSTACHIAN TUBE
29
Fig. 7. Coronal section of cleft lip and palate human fetal head through the Eustachian tube lumen (L). Other landmarks are the tensor (T) and levator (P) palatini muscles.
cleft heads were found to be. different. In the cleft palate fetuses the width of the lumen was reduced and the walls were found to be highly convoluted. Other differences which have been observed in some cleft heads but which do not seem to be typical of the group include increased width of the sphenoid body, an increased angle between the pterygoid plates and the midsagittal plane, and bilateral dissymmetry of the
greater and lesser wings of the sphenoid. Thus it seems apparent that cleft palate may involve deformities of the entire cranial base structure. We must proceed further, however, to determine the likelihood that any or all of the differences observed could affect tubal function. In addition, developmental studies must be carried out to determine the nature of changes in these relationships during late fetal and early postnatal life.
REFERENCES 1. Rich AR: A physiological study of the Eustachian tube and its related muscles. Johns Hopkins Med J 352:206-214, 1920 2. Paradise JL, Bluestone CD, Felder H: The universality of otitis media in 50 infants
with cleft palate. Pediatrics 44:35-42, 1969 3 D' k DR G t JCB S' h H t of: Sta:~s s~f rese~rchr~: cleft pal;~e e:nat~;y and physiology, Part I, Cleft Palate J 11:471492, 1974
REPRINTS - David R. Dickson, Ph.D., Mailman Center for Child Development, University of Miami, Box 520006, Biscayne Annex, Miami, FL 33152.
