Length dimensions and morphologic variations of the external bony auditory canal A radiographic and histologic investigation ECKERDAL 0., AHLQVIST J., ALEHAGEN U. and WING K. From the Department of Oral Roentgenology, University of umea, umea, Sweden.
KEY WORDS: Radiology; tomography; care canal
Autopsy material comprising a total of 58 specimes of the temporal bone and the proximal part of the mandible was investigated tomographically and by microtome in comparative layers. Microradiographs and histologic sections were used as the main sources of information to determine the length dimensions of the different parts of the external auditory canal. The morphology and its developmental variations are compared and described. The diagnostic implications are discussed. In the authors' opinion, tomography is the method of choice to illustrate the morphologic properties of the external auditory canal. It is suggested that when the tomographic image reveals morphologic developmental or pathologic defects which give rise to problematic diagnosis, a control examination of the contralateral side should be performed.
Radiographic examination of the petrous bone and the temporomandibular joint will include the whole, or parts of the external auditory canal in the radiographic image field. The conventional technique is the main radiographic method of investigation of this region. The use of tomography, especially multidirectional, offers additional diagnostic possibilities, bringing the different anatomical layers of the structure concerned under observation. Tomography can, however, introduce diagnostic inconsistencies, as every method presents its own specific problems. The need for individual analysis is obvious and requires a thorough knowledge of the morphology and its developmental variations in order to avoid radiographic misinterpretation. Analytical diagnostic investigations of tomography in different anatomical regions can be found in the literature 4 7 9 10. The purpose of the present study was to determine the length dimensions and morDentomaxillofac. Radial. 7:43-50, 1978.
phologic variations in the different components of the adult external skeletal auditory canal to create a basis for an adequate interpretation of tomographic images of this region. Osteogenesis in the temporal bone is first apparent in the 6th - 7th fetal week 1 14. Despite this fact, the bony part of the external auditory canal, a component of the complex temporal bone, is not present in the newborn infant. The tympanic mebrane is located at the lateral inferior surface of the neurocranium, and even in the adult, an angulation of this membrane is still maintained. While still in the prenatal stage, the middle ear is separated from the temporomandibular joint by the osseous formation of the tympanic part of the temporal bone. The medial part of the joint is situated in the same sagittal layer as the tympanic cavity (Fig. 2 c). During postnatal development of the bony part of 43
a
b
c
Fig. 1: Frontal tomographs of the temporal bone showing development of the external auditory canal at; a) birth; b) 4 years; c) maturity. Arrows indicate the level of the tympanic membrane. The lateral surface is seen on the left side of the image.
a
b
c
Fig. 2: Different sagittal layers of the external auditory canal in corresponding microradiographic and tomographic images. a) lateral section at 3 mm from complete bony canal (19 mm level). Despite the lack of bone structure in the anteroinferior part of the auditory canal, the insufficient tomographic blurring gives the impression of an almost com plete closure. b) section within the complete part of the auditory canal (26 mm level). c) section showing a defect in the upper border of the canal opening into the tympanic cavity (28 mm level).
Fig. 3: Histologic section of the lateral part of the temporomandibular joint. The external auditory canal is separated from the joint cavity by soft tissue and cartilage. 44
the auditory canal, a gradual change takes place in the relationship of the tympanic cavity, the tympanic membrane and the skull surface 13 (Fig. 1). In the adult, the central part of the temporomandibular joint cavity is separated from the auditory canal by the tympanic bone (Fig. 2 b), while the lateral part of the joint cavity is separated from the auditory canal by soft tissue and cartilage (Figs 2 a and 3). MATERIAL AND METHOD The material consisted of 58 specimens taken at autopsy from 29 males and 29 females. Age and sex distribution is illustrated in Fig. 4.
n
~=d 15
0=9
10
5
20 30 40 50 60 70 80 90 100 Age Fig. 4: Age and sex distribution.
The specimens, which comprised the temporal bone and the proximal part of the mandible, were selected at random during a six year period. Cases having known abnormalities were excluded. The specimens, removed en bloc, were deep frozen, then embedded in carboxy-methyl cellulose and frozen in a mixture of hexane and dry
ice 3412. Tomography and microtomy were performed on the frozen specimen blocks; the layers in each procedure corresponded. A three-dimensional orientation system permitted correlation between the radiographic and histologic sections 4. A Philips Massiot Poly tome with hypocycloidal movement, nominal focal size 0.6 X 0.6 mm., exposure time 6 seconds at 53 kV and 25 mA, Siemens Saphir intensifying screens and Kodak RP film were used. Microradiography of the specimens followed the technique previously employed by Eckerdal 3. The enlargement factor of the tomographic images was 1.3; microradiographs were photographed and enlarged accordingly. In order to determine the length dimensions of the different parts of the skeletal auditory canal, three separate morphologic, sagittal layers were sought. 1) a layer indicating the first sign of a circular bony formation in the auditory canal, and found in the superolateral border; 2) a layer representing the complete closure of the bony auditory canal; 3) a layer in the border between the complete canal and the tympanic cavity. The sections used for histologic and microradiographic investigation were 20 m I-t thick and collected at 1 mm intervals along the auditory canal. Letters A-E denote the five different layers at which the individual specimen series were recorded, forming the basis for subsequent measurement (Figs 5 and 6). Layer A was the first sagittal layer in an uninterrupted series to show an initial sign of bone formation in the auditory canal, visualized in the superior bony wall; layer B was the last lateral section showing a defect in the bony canal in the form of an incomplete closure; layer C was the first to reveal a complete bony closure; layer D was the last medial section within the completely closed bony auditory canal; layer E was the first in an uninterrupted series of sections within the complete canal to demonstrate an opening in the upper border into the tympanic cavity. The parameters of interest were the length dimensions of the partially and completely closed auditory canal (A-C) and (C-E) respectively. 45
~E
,..... ,
Fig. 5: Sagittal sections of the external auditory canal and their division into the measured layers A-E. A - the first superolateral sign of circular bony formation in the auditory canal. S - the last lateral section showing an incomplete closure in the bony auditory canal. C - first demonstration of a complete closure in the bony auditory canal. D - last medial section within the completely closed bony auditory canal. E - first section with an opening into the tympanic cavity.
A
C
B
E D (F)
Fig. 6: Diagrammatic representation of frontal view of the auditory canal and identification of measured layers A-E. The tympanic cavity and ossicles are seen on the right. 46
Fig. 7: Diagrammatic representation of theoretic layers C a. C fl. E a and E fl. with intervals x and y into which the individual C and E layers can fall.
METHOD ERROR The method error deciding the length dimensions of the bony auditory canal depends on the final measurement of the parallel sagittal layers A, C and E, each with a variable distance to the sought for morphologic layer. In order to illustrate the method error, layers C and E are chosen as the so-called measured layers (Fig. 7). These layers inscribe a distance representing the length of the complete bony auditory canal. The individual C layers can fall at random within an interval x between the possible extreme positions of layers C II and C~; similarly, the E layers can fall within an interval y between the extreme positions of Eiland E~. The measures are at random and, under certain circumstances identical to the actual morphologic dimensions, namely, when the sought for morphologic layers and the C and E layers coincide, and when C and E measured layers within the intervals x and y fall into a comparable position in relation to the morphologic layers. This occurs only when the searched measures are in even multiples of millimetres. For a large sample the postulates can be statistically fulfilled even for uneven distances. The basic reason for this is that distribution of the method errors on both sides of the searched distances are uniform. It is then theoretically possible to find corresponding, even measurement pairs among the uniformly distributed observations of both sides. The mean value of the method error will then be ~ O. Simulating a test situation, this theory was calculated statistically. The resulting sys-
tematic mean error was 0.00051, and the variance 0.41. The latter should be compared with the mean variance of the total material, 3.46. The mean values of the length dimensions of the bony auditory canal are valid. RESULTS Table 1 illustrates the length dimensions of the external auditory canal found in adult autopsy material. Although the mean values for females were slightly lower than for males, this was statistically insignificant. Routine tomographic images in different layers are illustrated in a comparative way (Fig. 2). Developmental variations were recorded. In three cases, (5.2 %), defects in the medial complete part of the bony auditory canal were located centrally and were recorded also in two successive layers. The length dimensions of the defects should be 2-4 mm. The defects represented two types. One case demonstrated a broad tympanic bone and a well defined opening between the auditory canal and the temporomandibular joint (Fig. 8). The second type, representing two cases, showed an overall gracile tympanic bone which gradually became thinner and resulted in a defect (Fig. 9). DISCUSSION The method used in this investigation interferes with the precision in determining the length dimensions of the individual external auditory canal. In spite of this, there were several reasons for its choice. The selected method allows a concomitant anal-
Table 1: Length dimensions of different parts of the external auditory canal. A-C the lateral partially closed part. C-E the medial completely closed part. All measurements in millimetres.
total n 58
females n 29
males n 29
SO
95 Ofo confid. interv.
5,145,06 -6,50
1,99
6,086,24 -7,57
1,61
x
SO
95 Ofo confid. interv.
A-C
5,82
1,79
C-E
6,82
1,96
x
SO
95 Ofo confid. interv.
4,315,44 -5,82
1,92
4,94-5,94
6,08- 653 -7,57 '
1,80
6,06-7,00
x
47
a
c
b
e
d
g
Fig. 8: Developmental defect. Figs a, d and c, g represent mutually corresponding layers. a, d) lateral closed part of the bony auditory canal (15 mm level); the tomograph ic layer (b) clearly demonstrates the developmental defect to be seen in the microrad iographs (e, f ; 16 and 18 mm levels) ; c , g) closure of the defect just laterally of the tympanic cavity.
a
b
c
d
e
f g h Fig. 9: a-e tomographic and f -i microradiographic images demonstrating a developmental defect in the anterior wall of the auditory canal. (b, f), (c, h) and (d, i) represent mutually corresponding layers . a) lateral unclosed part of the aud itory canal (15 mm level) ; b, f) lateral part of the closed aud itory canal ; the thin unbroken bony wall is well defined in the tomographic image (17 mm level) ; c, h) layer in the central part of the developmental defect, verified in histologic section (19 mm level) ; d, i) medial closed part of the auditory canal. The thickness of the bony wall is 0.15 mm (21 mm level).
ysis of radiographic and morphologic properties within a system of complete threedimensional control. The fact that the specimens were undecalcified made it possible to perform radiographic examination of the specimens in toto as well as in sections ; in the latter case , in the form of microradlographs. 48
It may be argued that the measured layer E should have been substituted by layer F as the medial demarcation of the complete bony auditory canal (Fig . 6). However, layer F, which indicates the central cut of the tympanic membrane, is hard to define, and therefore the more easily determined layer E was chosen.
The external bony auditory canal is subject to interpretation in assoc iation with different routine radiographic examination of the temporomandibular joint and otologic examinations. Morphologic variations such as part ial or total defects in the complete bony auditory canal may, in those cases , be drawn to the attention. These defects represented 5.2 % in our material , whereas Weinmann & Sicher 13 report " almost 20 %". The bony external auditory canal shows a well delineated sagittal tomographic image . This is also true for the anterior bony wall , whether of thick or thin dimension (Fig . 2). The sharp morphologic contours depend on a favourable, almost parallel relation between the bony walls in the auditory canal and a perpendicular to the tomographic table . In routine hypocycloidal tomography, an insuffi cient blurring can give the impression of a wider sagittal extension of the bony part of the auditory canal. This phenomenon is mostly accentuated when the anterior demarcation of the tympanic bone has a wide sagittal dimension and , even more essential, a high degree of mineralization, e. g. as seen in sclerosis. The microradiographic section illustrated in Fig. 2 a is situated 3 mm laterally of the closed part of the auditorycanal.lnthe correspondingtomographic layer , blurring of the tympanic bone
is not complete despite the relative distance. The blurring capacity has been previously described graphically, with the zygomatic arch used as the test object 4 . Fractures and tumors found in this region are of special diagnostic interest. It should be mentioned that young individuals constitute an essential group amongst the cases of petro us bone fractures. Tos 11 reports an incidence of 24.7 % in age group ranging from birth to ten years. In these patients, it should be remembered that the rapid rate of growth, the developmental stage and the morphologic variations must be taken into consideration . Worthy of note is the longitudinal fracture of the petrous bone which can involve the external auditory canal and the tympanic bone 6, The partial defects reported in our investigation have length dimensions of 2-4 mm, which equals 1/3 to 1/2 of the complete auditory canal (Figs 8 and 9). This measurement is large enough to create a tomographic image showing a well delineated radiolucent defect in the bony wall. However, when evaluating suspected osteolytic tumors the appearance of morphologic variations, such as differences in sagittal dimension of the tympanic bone or defects in the formation of the bony auditory canal, can present diagnostic traps for
a
b
Fig . 10: Tomographs of patient with cancer in the anterior part of the external auditory canal on the right side. a) defect in the anterior wall of the auditory canal on the side of the manifest tumor. b) tomographs of the contralateral side reveals a similar defect in the corresponding sagittal layers of the canal.
49
the uninformed observer. In these instances a control examination of the contralateral side will help to clarify the situation in the area of prime interest. The following example describes briefly the diagnostic significance of defects observed in the auditory canal. A female patient with cancer in the anterior part of the external auditory canal was referred to the clinic. A tomographic examination revealed a bony defect adjacent to the manifest tumor in the tympanic bone (Fig. 10). However, a control examination showed a similar defect on the contralateral side. It is probable that the developmental defects are symmetrical, in which case the phenomenon on the affected side could be given an entirely different interpretation. The middle ear and the bony external auditory canal provide excellent landmarks on the radiographic image, and due to their character in the different sagittal layers serve as reliable projection controls 5. However, in longitudinal investigations started during the early developmental age, it should be remembered that the rapidity of postnatal growth will create changes in the morphology of the temporal components and great care must be taken to avoid radiographic misinterpretation. Whether dealing with the young or adult patient, it is important for the interpreter to have a thorough knowledge of the morphology and developmental features of the area under examination.
REFERENCES 1. Baume L. J.: The prenatal and postnatal development of the human temporomandibular joint. Transactions of the European Orthodontic Society, p. 1, 1962. 2. Bjork A.: Cranial base development. A followup study of the individual variation in growth occurring between the ages of 12 and 20 years and its relations to brain case and face development. Amer. J. Orthodont. 41:198, 1955. 3. Eckerdal 0.: A method for combined microradiographic and histological analysis of nondecalcified hard tissues. Acta odont. scand. 30:327, 1972. 50
4. Eckerdal 0.: Tomography of the temporomandibular joint. Correlation between tomographic image and histologic sections in a three-dimensional system. Acta radiol. Suppl. no. 329, 1973. 5. Eckerdal O. and Lundberg M.: Periodic roentgenography of the temporomandibular joint. Dentomaxillofac. Radiol. 4:4, 1975. 6. Harwood-Hash D. C.: Fractures of the petrous and tympanic parts of the temporal bone in children: A tomographic study of 35 cases. Amer. J. Roentgenol. 110:598, 1970. 7. Hemmingsson A.: Roentgenologic methods in examination of the larynx. Acta radiol. Diagnosis 12:673, 1972. 8. Hollender L. and Ridell A.: Radiography of the temporomandibular joint after oblique sliding osteotomy of the mandibular rami. Scand. J. dent. Res. 82:466, 1974. 9. Reichmann S.: Tomography of the lumbar intervertebral joint. Acta radiol. Diagnosis '12:641, '1972. 10. Reisner K.: Experimentelle Untersuchungen zur Detailerkennbarkeit im R6ntgenschichtbild des Schadels, Fortschr. Hontqenstr. 112: 332, 1970. 11. Tos M.: Clinical and therapeutic problems in trauma of the temporal bone. Lecture given at international course on tomography of the temporal bone. Copenhagen 1976. 12. Ullberg S., Hammerstrom L. and Appelqren L.-E.: Autoradiography in pharmacology. In: Int. Encyclopedia Pharmacol. Ther. Vol. I. p. 221. Ed.: Y. Cohen. Pergamon Press, Oxford and New York 1971. 13. Weinmann J. P. and Sicher H.: Bone and bones. Fundamentals of bone biology. 2nd ed. C. V. Mosby Company, St. Louis 1955. 14. Youdelis R. A.: Ossification of the human temporomandibular joint. J. dent. Res. 45:192. 1966.
Address: Dr. Olof Eckcrdal Avd. for odontologisk rontgendiagnostik Odontologiska fakulteten urnea Universitet 90187 Urnea Sweden
KEY WORDS: Radiology; tomography; care canal
Autopsy material comprising a total of 58 specimes of the temporal bone and the proximal part of the mandible was investigated tomographically and by microtome in comparative layers. Microradiographs and histologic sections were used as the main sources of information to determine the length dimensions of the different parts of the external auditory canal. The morphology and its developmental variations are compared and described. The diagnostic implications are discussed. In the authors' opinion, tomography is the method of choice to illustrate the morphologic properties of the external auditory canal. It is suggested that when the tomographic image reveals morphologic developmental or pathologic defects which give rise to problematic diagnosis, a control examination of the contralateral side should be performed.
Radiographic examination of the petrous bone and the temporomandibular joint will include the whole, or parts of the external auditory canal in the radiographic image field. The conventional technique is the main radiographic method of investigation of this region. The use of tomography, especially multidirectional, offers additional diagnostic possibilities, bringing the different anatomical layers of the structure concerned under observation. Tomography can, however, introduce diagnostic inconsistencies, as every method presents its own specific problems. The need for individual analysis is obvious and requires a thorough knowledge of the morphology and its developmental variations in order to avoid radiographic misinterpretation. Analytical diagnostic investigations of tomography in different anatomical regions can be found in the literature 4 7 9 10. The purpose of the present study was to determine the length dimensions and morDentomaxillofac. Radial. 7:43-50, 1978.
phologic variations in the different components of the adult external skeletal auditory canal to create a basis for an adequate interpretation of tomographic images of this region. Osteogenesis in the temporal bone is first apparent in the 6th - 7th fetal week 1 14. Despite this fact, the bony part of the external auditory canal, a component of the complex temporal bone, is not present in the newborn infant. The tympanic mebrane is located at the lateral inferior surface of the neurocranium, and even in the adult, an angulation of this membrane is still maintained. While still in the prenatal stage, the middle ear is separated from the temporomandibular joint by the osseous formation of the tympanic part of the temporal bone. The medial part of the joint is situated in the same sagittal layer as the tympanic cavity (Fig. 2 c). During postnatal development of the bony part of 43
a
b
c
Fig. 1: Frontal tomographs of the temporal bone showing development of the external auditory canal at; a) birth; b) 4 years; c) maturity. Arrows indicate the level of the tympanic membrane. The lateral surface is seen on the left side of the image.
a
b
c
Fig. 2: Different sagittal layers of the external auditory canal in corresponding microradiographic and tomographic images. a) lateral section at 3 mm from complete bony canal (19 mm level). Despite the lack of bone structure in the anteroinferior part of the auditory canal, the insufficient tomographic blurring gives the impression of an almost com plete closure. b) section within the complete part of the auditory canal (26 mm level). c) section showing a defect in the upper border of the canal opening into the tympanic cavity (28 mm level).
Fig. 3: Histologic section of the lateral part of the temporomandibular joint. The external auditory canal is separated from the joint cavity by soft tissue and cartilage. 44
the auditory canal, a gradual change takes place in the relationship of the tympanic cavity, the tympanic membrane and the skull surface 13 (Fig. 1). In the adult, the central part of the temporomandibular joint cavity is separated from the auditory canal by the tympanic bone (Fig. 2 b), while the lateral part of the joint cavity is separated from the auditory canal by soft tissue and cartilage (Figs 2 a and 3). MATERIAL AND METHOD The material consisted of 58 specimens taken at autopsy from 29 males and 29 females. Age and sex distribution is illustrated in Fig. 4.
n
~=d 15
0=9
10
5
20 30 40 50 60 70 80 90 100 Age Fig. 4: Age and sex distribution.
The specimens, which comprised the temporal bone and the proximal part of the mandible, were selected at random during a six year period. Cases having known abnormalities were excluded. The specimens, removed en bloc, were deep frozen, then embedded in carboxy-methyl cellulose and frozen in a mixture of hexane and dry
ice 3412. Tomography and microtomy were performed on the frozen specimen blocks; the layers in each procedure corresponded. A three-dimensional orientation system permitted correlation between the radiographic and histologic sections 4. A Philips Massiot Poly tome with hypocycloidal movement, nominal focal size 0.6 X 0.6 mm., exposure time 6 seconds at 53 kV and 25 mA, Siemens Saphir intensifying screens and Kodak RP film were used. Microradiography of the specimens followed the technique previously employed by Eckerdal 3. The enlargement factor of the tomographic images was 1.3; microradiographs were photographed and enlarged accordingly. In order to determine the length dimensions of the different parts of the skeletal auditory canal, three separate morphologic, sagittal layers were sought. 1) a layer indicating the first sign of a circular bony formation in the auditory canal, and found in the superolateral border; 2) a layer representing the complete closure of the bony auditory canal; 3) a layer in the border between the complete canal and the tympanic cavity. The sections used for histologic and microradiographic investigation were 20 m I-t thick and collected at 1 mm intervals along the auditory canal. Letters A-E denote the five different layers at which the individual specimen series were recorded, forming the basis for subsequent measurement (Figs 5 and 6). Layer A was the first sagittal layer in an uninterrupted series to show an initial sign of bone formation in the auditory canal, visualized in the superior bony wall; layer B was the last lateral section showing a defect in the bony canal in the form of an incomplete closure; layer C was the first to reveal a complete bony closure; layer D was the last medial section within the completely closed bony auditory canal; layer E was the first in an uninterrupted series of sections within the complete canal to demonstrate an opening in the upper border into the tympanic cavity. The parameters of interest were the length dimensions of the partially and completely closed auditory canal (A-C) and (C-E) respectively. 45
~E
,..... ,
Fig. 5: Sagittal sections of the external auditory canal and their division into the measured layers A-E. A - the first superolateral sign of circular bony formation in the auditory canal. S - the last lateral section showing an incomplete closure in the bony auditory canal. C - first demonstration of a complete closure in the bony auditory canal. D - last medial section within the completely closed bony auditory canal. E - first section with an opening into the tympanic cavity.
A
C
B
E D (F)
Fig. 6: Diagrammatic representation of frontal view of the auditory canal and identification of measured layers A-E. The tympanic cavity and ossicles are seen on the right. 46
Fig. 7: Diagrammatic representation of theoretic layers C a. C fl. E a and E fl. with intervals x and y into which the individual C and E layers can fall.
METHOD ERROR The method error deciding the length dimensions of the bony auditory canal depends on the final measurement of the parallel sagittal layers A, C and E, each with a variable distance to the sought for morphologic layer. In order to illustrate the method error, layers C and E are chosen as the so-called measured layers (Fig. 7). These layers inscribe a distance representing the length of the complete bony auditory canal. The individual C layers can fall at random within an interval x between the possible extreme positions of layers C II and C~; similarly, the E layers can fall within an interval y between the extreme positions of Eiland E~. The measures are at random and, under certain circumstances identical to the actual morphologic dimensions, namely, when the sought for morphologic layers and the C and E layers coincide, and when C and E measured layers within the intervals x and y fall into a comparable position in relation to the morphologic layers. This occurs only when the searched measures are in even multiples of millimetres. For a large sample the postulates can be statistically fulfilled even for uneven distances. The basic reason for this is that distribution of the method errors on both sides of the searched distances are uniform. It is then theoretically possible to find corresponding, even measurement pairs among the uniformly distributed observations of both sides. The mean value of the method error will then be ~ O. Simulating a test situation, this theory was calculated statistically. The resulting sys-
tematic mean error was 0.00051, and the variance 0.41. The latter should be compared with the mean variance of the total material, 3.46. The mean values of the length dimensions of the bony auditory canal are valid. RESULTS Table 1 illustrates the length dimensions of the external auditory canal found in adult autopsy material. Although the mean values for females were slightly lower than for males, this was statistically insignificant. Routine tomographic images in different layers are illustrated in a comparative way (Fig. 2). Developmental variations were recorded. In three cases, (5.2 %), defects in the medial complete part of the bony auditory canal were located centrally and were recorded also in two successive layers. The length dimensions of the defects should be 2-4 mm. The defects represented two types. One case demonstrated a broad tympanic bone and a well defined opening between the auditory canal and the temporomandibular joint (Fig. 8). The second type, representing two cases, showed an overall gracile tympanic bone which gradually became thinner and resulted in a defect (Fig. 9). DISCUSSION The method used in this investigation interferes with the precision in determining the length dimensions of the individual external auditory canal. In spite of this, there were several reasons for its choice. The selected method allows a concomitant anal-
Table 1: Length dimensions of different parts of the external auditory canal. A-C the lateral partially closed part. C-E the medial completely closed part. All measurements in millimetres.
total n 58
females n 29
males n 29
SO
95 Ofo confid. interv.
5,145,06 -6,50
1,99
6,086,24 -7,57
1,61
x
SO
95 Ofo confid. interv.
A-C
5,82
1,79
C-E
6,82
1,96
x
SO
95 Ofo confid. interv.
4,315,44 -5,82
1,92
4,94-5,94
6,08- 653 -7,57 '
1,80
6,06-7,00
x
47
a
c
b
e
d
g
Fig. 8: Developmental defect. Figs a, d and c, g represent mutually corresponding layers. a, d) lateral closed part of the bony auditory canal (15 mm level); the tomograph ic layer (b) clearly demonstrates the developmental defect to be seen in the microrad iographs (e, f ; 16 and 18 mm levels) ; c , g) closure of the defect just laterally of the tympanic cavity.
a
b
c
d
e
f g h Fig. 9: a-e tomographic and f -i microradiographic images demonstrating a developmental defect in the anterior wall of the auditory canal. (b, f), (c, h) and (d, i) represent mutually corresponding layers . a) lateral unclosed part of the aud itory canal (15 mm level) ; b, f) lateral part of the closed aud itory canal ; the thin unbroken bony wall is well defined in the tomographic image (17 mm level) ; c, h) layer in the central part of the developmental defect, verified in histologic section (19 mm level) ; d, i) medial closed part of the auditory canal. The thickness of the bony wall is 0.15 mm (21 mm level).
ysis of radiographic and morphologic properties within a system of complete threedimensional control. The fact that the specimens were undecalcified made it possible to perform radiographic examination of the specimens in toto as well as in sections ; in the latter case , in the form of microradlographs. 48
It may be argued that the measured layer E should have been substituted by layer F as the medial demarcation of the complete bony auditory canal (Fig . 6). However, layer F, which indicates the central cut of the tympanic membrane, is hard to define, and therefore the more easily determined layer E was chosen.
The external bony auditory canal is subject to interpretation in assoc iation with different routine radiographic examination of the temporomandibular joint and otologic examinations. Morphologic variations such as part ial or total defects in the complete bony auditory canal may, in those cases , be drawn to the attention. These defects represented 5.2 % in our material , whereas Weinmann & Sicher 13 report " almost 20 %". The bony external auditory canal shows a well delineated sagittal tomographic image . This is also true for the anterior bony wall , whether of thick or thin dimension (Fig . 2). The sharp morphologic contours depend on a favourable, almost parallel relation between the bony walls in the auditory canal and a perpendicular to the tomographic table . In routine hypocycloidal tomography, an insuffi cient blurring can give the impression of a wider sagittal extension of the bony part of the auditory canal. This phenomenon is mostly accentuated when the anterior demarcation of the tympanic bone has a wide sagittal dimension and , even more essential, a high degree of mineralization, e. g. as seen in sclerosis. The microradiographic section illustrated in Fig. 2 a is situated 3 mm laterally of the closed part of the auditorycanal.lnthe correspondingtomographic layer , blurring of the tympanic bone
is not complete despite the relative distance. The blurring capacity has been previously described graphically, with the zygomatic arch used as the test object 4 . Fractures and tumors found in this region are of special diagnostic interest. It should be mentioned that young individuals constitute an essential group amongst the cases of petro us bone fractures. Tos 11 reports an incidence of 24.7 % in age group ranging from birth to ten years. In these patients, it should be remembered that the rapid rate of growth, the developmental stage and the morphologic variations must be taken into consideration . Worthy of note is the longitudinal fracture of the petrous bone which can involve the external auditory canal and the tympanic bone 6, The partial defects reported in our investigation have length dimensions of 2-4 mm, which equals 1/3 to 1/2 of the complete auditory canal (Figs 8 and 9). This measurement is large enough to create a tomographic image showing a well delineated radiolucent defect in the bony wall. However, when evaluating suspected osteolytic tumors the appearance of morphologic variations, such as differences in sagittal dimension of the tympanic bone or defects in the formation of the bony auditory canal, can present diagnostic traps for
a
b
Fig . 10: Tomographs of patient with cancer in the anterior part of the external auditory canal on the right side. a) defect in the anterior wall of the auditory canal on the side of the manifest tumor. b) tomographs of the contralateral side reveals a similar defect in the corresponding sagittal layers of the canal.
49
the uninformed observer. In these instances a control examination of the contralateral side will help to clarify the situation in the area of prime interest. The following example describes briefly the diagnostic significance of defects observed in the auditory canal. A female patient with cancer in the anterior part of the external auditory canal was referred to the clinic. A tomographic examination revealed a bony defect adjacent to the manifest tumor in the tympanic bone (Fig. 10). However, a control examination showed a similar defect on the contralateral side. It is probable that the developmental defects are symmetrical, in which case the phenomenon on the affected side could be given an entirely different interpretation. The middle ear and the bony external auditory canal provide excellent landmarks on the radiographic image, and due to their character in the different sagittal layers serve as reliable projection controls 5. However, in longitudinal investigations started during the early developmental age, it should be remembered that the rapidity of postnatal growth will create changes in the morphology of the temporal components and great care must be taken to avoid radiographic misinterpretation. Whether dealing with the young or adult patient, it is important for the interpreter to have a thorough knowledge of the morphology and developmental features of the area under examination.
REFERENCES 1. Baume L. J.: The prenatal and postnatal development of the human temporomandibular joint. Transactions of the European Orthodontic Society, p. 1, 1962. 2. Bjork A.: Cranial base development. A followup study of the individual variation in growth occurring between the ages of 12 and 20 years and its relations to brain case and face development. Amer. J. Orthodont. 41:198, 1955. 3. Eckerdal 0.: A method for combined microradiographic and histological analysis of nondecalcified hard tissues. Acta odont. scand. 30:327, 1972. 50
4. Eckerdal 0.: Tomography of the temporomandibular joint. Correlation between tomographic image and histologic sections in a three-dimensional system. Acta radiol. Suppl. no. 329, 1973. 5. Eckerdal O. and Lundberg M.: Periodic roentgenography of the temporomandibular joint. Dentomaxillofac. Radiol. 4:4, 1975. 6. Harwood-Hash D. C.: Fractures of the petrous and tympanic parts of the temporal bone in children: A tomographic study of 35 cases. Amer. J. Roentgenol. 110:598, 1970. 7. Hemmingsson A.: Roentgenologic methods in examination of the larynx. Acta radiol. Diagnosis 12:673, 1972. 8. Hollender L. and Ridell A.: Radiography of the temporomandibular joint after oblique sliding osteotomy of the mandibular rami. Scand. J. dent. Res. 82:466, 1974. 9. Reichmann S.: Tomography of the lumbar intervertebral joint. Acta radiol. Diagnosis '12:641, '1972. 10. Reisner K.: Experimentelle Untersuchungen zur Detailerkennbarkeit im R6ntgenschichtbild des Schadels, Fortschr. Hontqenstr. 112: 332, 1970. 11. Tos M.: Clinical and therapeutic problems in trauma of the temporal bone. Lecture given at international course on tomography of the temporal bone. Copenhagen 1976. 12. Ullberg S., Hammerstrom L. and Appelqren L.-E.: Autoradiography in pharmacology. In: Int. Encyclopedia Pharmacol. Ther. Vol. I. p. 221. Ed.: Y. Cohen. Pergamon Press, Oxford and New York 1971. 13. Weinmann J. P. and Sicher H.: Bone and bones. Fundamentals of bone biology. 2nd ed. C. V. Mosby Company, St. Louis 1955. 14. Youdelis R. A.: Ossification of the human temporomandibular joint. J. dent. Res. 45:192. 1966.
Address: Dr. Olof Eckcrdal Avd. for odontologisk rontgendiagnostik Odontologiska fakulteten urnea Universitet 90187 Urnea Sweden
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