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Roentgen anatomy of the temporal bone using the polytome
Roentgen
Anatomy of the Temporal Using the Polytome
Bone
By S. BR~~NNQR, M.D. HE MASSIOT-PHILIP’S POLYTOME with its hypocycloidal movement has provided an opportunity for the radiologist to better visualize the small structures in the temporal bone.lm4z6 Various positions have been used, but in our experience the anteroposterior and lateral projections are best in providing the clearest picture of the anatomic details.
T
ANTEROPOSTEFUOR PROJECTION With the patient supine and the median plane of the head vertical to the table, a line from the lateral angle of the eye to the tragus should also be vertical to the table. The area to be visualized extends approximately 20 mm. posteriorly from the root of the tragus. The AP tomogram of the normal temporal bone shown in Figure 1 is an anterior cut taken on a level with the tragus. The external auditory canal, tympanic cavity, epitympanic recess or attic, cochlea, and the carotid canal are well outlined. The superomedial lip of the external .auditory canal extends to the lateral wall of the attic and forms the so-called “spur.” The spur ends medially in the attic as a prominent broad-based wedge. The medial part of the external auditory canal is delimited by the tympanic membrane, which normally appears as a faintly streaked contour. In older people the tympanic membrane may be calcified and then is plainly seen on tomograms. It continues superiorly in the handle of the malleus. The head of the malleus rises in the middle of the attic as a club-shaped shadow. The spiral-shaped cochlea is shown medially and therefore this cut is called the cochlear plane. The lateral part of the cochlea represents the promontory. At the upper part of the promontory, just above the cochlea,
plane, AP tomogram and diagram of a cut through the anterior cavity on the left showing: (1) external auditory canal, (3) facial canal, (4) cochlea, (9) malleus and tympanic membrane. Fig. I.-(=ochlear
part of the tympanic
S. BR~NNER, M.D.: Department
118
of Radiology,
Gentofte
Hospital,
Copenhagen,
Denmark.
SEMINARS IN ROENTGENOLOGY, VOL. 4, No. 2 (APRIL),
1969
ANATOMY
OF TEMPORAL,
Fig. 2.-Vestibular
the tympanic cavity (5) oval (vestibular) laterally, (7) lateral turn of cochlea, (11)
BONE
USING
POLYTOME
plane. AP tomogram and diagram made more posteriorly in than Fig. 1 showing: (1) external auditory canal, (2) vestibule, window, (6) internal auditory canal with crista falciformis semicircular canal, (8) vertical semicircular canal, (10) basal antrutn.
two holes are outlined. The medial one is produced by the petrous segment of the facial canal; it is larger because it contains the geniculate ganglion. The lateral hole, which often appears more like a groove than a hole, is produced by the most proximal portion of the tympanic segment of the facial canal. Superiorly the roof is made up of the tegmen tympani. Since this is only faintly visible or entirely absent on the tomogram, lack of visualization should not be considered a pathologic sign. The wstibular plane is 2 mm. posterior to the eochlear plane and shows the vestibule and the semicircular canals most distinctly (Fig. 2). The ossicles in this plane are formed by the long process and the body of the incus shaped as a short club. But often it is difficult to separate the malleus from the incus in this view. The ampullar limbs of the lateral and superior semicircular canals are visible. The oval or vestibular window can be seen on the lateral wall of the vestibule, It is bounded inferiorly by the subiculum, which in turn forms the upper limit of the round window. Superior to the oval window is the second bend of the facial canal. Normally the footplate of the stapes does not cast a linear density in this projection because it is oblique to the plane of the film. Medial to the vestibulme one sees the internal auditory canal with its lateral wall (lamina cribrosa) divided by the horizontal crest (crista falciformis). The mastoid antrum is demonstrated superolateral to the semicircular canals. LATERAL PROJECTION The patient is prone with the side of his head resting on the table. The ear to be examined is up and both external auditory meatus are in a line perpendicular to the table. The structures to be examined extend from 2 to 4 cm. from the outer surface of the external auditory canal. Figure 3 shows the external auditory canal, attic or epitympanic recess, and ossicles, the bodies of which are in the attic. The malleus is the most anterior one and
S. BRtiNNEFt
Fig. S.-Lateral tomogram and diagram of a cut through the external part of the tympanic cavity showing: (M) malleus, (I) incus, (3) facial canal, (8) part of the lateral semicirccllar canal, (T) temporomandibular joint.
its handle projects into the tympanic cavity. The body of the incus is immediately posterior to the head of the malleus. The long process of the incus parallels the handle of the malleus. It is extremely important to realize that these two processes are parallel to each other; if not, the ossicles are abnormal or displaced. Potter5 has called the normal picture of the ossicles in this projection the “molar tooth sign.” Crus breve incudis is diEcult to show and is often covered by the posterosuperior wall of the external auditory canal. Posteriorly, the vertical radiolucency of the third portion of the facial nerve canal is recognizable. Anterosuperior to the facial canal the lateral semicircular canal is visualized in the sclerotic area just posterior to the epitympanic recess. Anteriorly, the condyle of the mandible is well demonstrated.
ANATOMY
OF TEMPORAL
BONE
USING
121
POLYTOME
REFERENCES 1. Briinner, S., Petersen, @., and Stocksted, P.: Laminagraphy of the temporal bone. Amer. J. Roentgen. 86:281, 1961. 2. Briinner, 8, Petersen, 0., and Stocksted, P.: Tomography of the auditory ossicles. Acta Radiol. 56:20, 1961. 3. Frey, K. W.: Schichtaufnahmen des Felsenbeines mit polyzyklischer Verwischung. Fortschr. Roentgenstr. 85:433, 1956. 4. Langfeldt, B.: Tomography of the
DABBLER’S
middle ear in columella operations: Stapedectomy and autotransplantation of the ossicles. Acta Radiol. 53:129, 1960. 5. Potter, C. D.: The lateral projection in tomography of the petrous pyramid. Amer. J. Roentgen. 104:194, 1968. 6. Valvassori, G. E.: Laminagraphy of the ear: Normal roentgenographic anatomy. Amer. J. Roentgen. 89:1155, 1963.
DANGLING
DETECTOR
Strong, tall, and heavily moustachioed Henry Hulst (1859-1949) of Grand Rapids, Michigan, was one of several American medical electrologists who joined the roentgen pioneers. His (innocent ?) approach to ionizing radiation in the parlor can be gleaned from a brief statement, published in the Anrer. Quart. RoentgenoL in 1911. “A way of detecting the rays is as follows: Electrify a strand of silk and it will stand out straight. Take that strand of silk into the dark room and it will not fall down. Use it around the X-ray box, and it will fall down. I hung it up in the parlor and it would take half an hour before it fell down. I ran the machine and it came down in five minutes. Whether such rays do any harm or not, I do not know.“-E. R. N. Grigg, M.D.
Anatomy of the Temporal Using the Polytome
Bone
By S. BR~~NNQR, M.D. HE MASSIOT-PHILIP’S POLYTOME with its hypocycloidal movement has provided an opportunity for the radiologist to better visualize the small structures in the temporal bone.lm4z6 Various positions have been used, but in our experience the anteroposterior and lateral projections are best in providing the clearest picture of the anatomic details.
T
ANTEROPOSTEFUOR PROJECTION With the patient supine and the median plane of the head vertical to the table, a line from the lateral angle of the eye to the tragus should also be vertical to the table. The area to be visualized extends approximately 20 mm. posteriorly from the root of the tragus. The AP tomogram of the normal temporal bone shown in Figure 1 is an anterior cut taken on a level with the tragus. The external auditory canal, tympanic cavity, epitympanic recess or attic, cochlea, and the carotid canal are well outlined. The superomedial lip of the external .auditory canal extends to the lateral wall of the attic and forms the so-called “spur.” The spur ends medially in the attic as a prominent broad-based wedge. The medial part of the external auditory canal is delimited by the tympanic membrane, which normally appears as a faintly streaked contour. In older people the tympanic membrane may be calcified and then is plainly seen on tomograms. It continues superiorly in the handle of the malleus. The head of the malleus rises in the middle of the attic as a club-shaped shadow. The spiral-shaped cochlea is shown medially and therefore this cut is called the cochlear plane. The lateral part of the cochlea represents the promontory. At the upper part of the promontory, just above the cochlea,
plane, AP tomogram and diagram of a cut through the anterior cavity on the left showing: (1) external auditory canal, (3) facial canal, (4) cochlea, (9) malleus and tympanic membrane. Fig. I.-(=ochlear
part of the tympanic
S. BR~NNER, M.D.: Department
118
of Radiology,
Gentofte
Hospital,
Copenhagen,
Denmark.
SEMINARS IN ROENTGENOLOGY, VOL. 4, No. 2 (APRIL),
1969
ANATOMY
OF TEMPORAL,
Fig. 2.-Vestibular
the tympanic cavity (5) oval (vestibular) laterally, (7) lateral turn of cochlea, (11)
BONE
USING
POLYTOME
plane. AP tomogram and diagram made more posteriorly in than Fig. 1 showing: (1) external auditory canal, (2) vestibule, window, (6) internal auditory canal with crista falciformis semicircular canal, (8) vertical semicircular canal, (10) basal antrutn.
two holes are outlined. The medial one is produced by the petrous segment of the facial canal; it is larger because it contains the geniculate ganglion. The lateral hole, which often appears more like a groove than a hole, is produced by the most proximal portion of the tympanic segment of the facial canal. Superiorly the roof is made up of the tegmen tympani. Since this is only faintly visible or entirely absent on the tomogram, lack of visualization should not be considered a pathologic sign. The wstibular plane is 2 mm. posterior to the eochlear plane and shows the vestibule and the semicircular canals most distinctly (Fig. 2). The ossicles in this plane are formed by the long process and the body of the incus shaped as a short club. But often it is difficult to separate the malleus from the incus in this view. The ampullar limbs of the lateral and superior semicircular canals are visible. The oval or vestibular window can be seen on the lateral wall of the vestibule, It is bounded inferiorly by the subiculum, which in turn forms the upper limit of the round window. Superior to the oval window is the second bend of the facial canal. Normally the footplate of the stapes does not cast a linear density in this projection because it is oblique to the plane of the film. Medial to the vestibulme one sees the internal auditory canal with its lateral wall (lamina cribrosa) divided by the horizontal crest (crista falciformis). The mastoid antrum is demonstrated superolateral to the semicircular canals. LATERAL PROJECTION The patient is prone with the side of his head resting on the table. The ear to be examined is up and both external auditory meatus are in a line perpendicular to the table. The structures to be examined extend from 2 to 4 cm. from the outer surface of the external auditory canal. Figure 3 shows the external auditory canal, attic or epitympanic recess, and ossicles, the bodies of which are in the attic. The malleus is the most anterior one and
S. BRtiNNEFt
Fig. S.-Lateral tomogram and diagram of a cut through the external part of the tympanic cavity showing: (M) malleus, (I) incus, (3) facial canal, (8) part of the lateral semicirccllar canal, (T) temporomandibular joint.
its handle projects into the tympanic cavity. The body of the incus is immediately posterior to the head of the malleus. The long process of the incus parallels the handle of the malleus. It is extremely important to realize that these two processes are parallel to each other; if not, the ossicles are abnormal or displaced. Potter5 has called the normal picture of the ossicles in this projection the “molar tooth sign.” Crus breve incudis is diEcult to show and is often covered by the posterosuperior wall of the external auditory canal. Posteriorly, the vertical radiolucency of the third portion of the facial nerve canal is recognizable. Anterosuperior to the facial canal the lateral semicircular canal is visualized in the sclerotic area just posterior to the epitympanic recess. Anteriorly, the condyle of the mandible is well demonstrated.
ANATOMY
OF TEMPORAL
BONE
USING
121
POLYTOME
REFERENCES 1. Briinner, S., Petersen, @., and Stocksted, P.: Laminagraphy of the temporal bone. Amer. J. Roentgen. 86:281, 1961. 2. Briinner, 8, Petersen, 0., and Stocksted, P.: Tomography of the auditory ossicles. Acta Radiol. 56:20, 1961. 3. Frey, K. W.: Schichtaufnahmen des Felsenbeines mit polyzyklischer Verwischung. Fortschr. Roentgenstr. 85:433, 1956. 4. Langfeldt, B.: Tomography of the
DABBLER’S
middle ear in columella operations: Stapedectomy and autotransplantation of the ossicles. Acta Radiol. 53:129, 1960. 5. Potter, C. D.: The lateral projection in tomography of the petrous pyramid. Amer. J. Roentgen. 104:194, 1968. 6. Valvassori, G. E.: Laminagraphy of the ear: Normal roentgenographic anatomy. Amer. J. Roentgen. 89:1155, 1963.
DANGLING
DETECTOR
Strong, tall, and heavily moustachioed Henry Hulst (1859-1949) of Grand Rapids, Michigan, was one of several American medical electrologists who joined the roentgen pioneers. His (innocent ?) approach to ionizing radiation in the parlor can be gleaned from a brief statement, published in the Anrer. Quart. RoentgenoL in 1911. “A way of detecting the rays is as follows: Electrify a strand of silk and it will stand out straight. Take that strand of silk into the dark room and it will not fall down. Use it around the X-ray box, and it will fall down. I hung it up in the parlor and it would take half an hour before it fell down. I ran the machine and it came down in five minutes. Whether such rays do any harm or not, I do not know.“-E. R. N. Grigg, M.D.