Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
395
Pictorial
Fast Spin-Echo Inner Ear Robert
High-Resolution
Gary J. Felsberg,
D. lien,1
and
James
MR Imaging
cannot yield excellent
prescribed
the
use of conventional
T2-weighted
by time constraints when large-matrix, with more than one excitation are used.
is a recently
developed
technique
neurosensory
thin-section techniques Fast spin-echo imaging
that can provide T2-weighted,
Fast spin-echo (FSE) imaging was performed in six normal volunand in i i consecutive patients with a variety of inner ear disorders. The FSE technique we used is a hybrid rapid-acquisition teers
et al. [1]. Received
Thin-section January
21
FSE ,
All authors:
Department
AJR 159:395-398,
August
I
1992;
technique
initially
described
by Hennig
imaging
of the
temporal
bone
accepted
of Radiology.
after revision Box 3808,
1992 0361 -803x/92/1
March Duke
592-0395
hearing
loss
main
also
advantage
had
of FSE
is shortened compared yet the signal-to-noise conventional spin-echo by the TR, the number
and Methods
(RARE)
image.
echo space,
i8-cm
of phase-encoding
Ti -weighted
images
© American
after
admin-
imaging
is that
the
Center,
Roentgen
Durham, Ray Society
NC 27710.
steps
Address
scan
time
with conventional spin-echo images, ratio is not significantly reduced. Both and FSE scary times are determined of excitations (NEX), and the number (NP).
The
scan
echo FSE sequence, however, is reduced to the value of an echo train length (ETL):
was
Medical
of
field of view,
time
reprint
requests
for
a single-
by a factor equal that is, scan time
3. 1992. University
Images
Discussion
of the inner ear.
relaxation-enhanced
localizer
istration of gadopentetate dimeglumine. Imaging parameters were 500/i 2/2 with 3-mm-thick interleaved slices and a 256 x i 92 matrix. In addition, for patients with neurosensory hearing loss, conventional T2-weighted images were obtained of the entire brain (2500/20,70/ i) with a 5-mm slice thickness and 2.5-mm gap. The normal anatomy and a variety of inner ear disorders were studied by these methods (Figs. i -5).
is limited
The
Subjects
Ti-weighted
by using FSE techniques with the following (TRITE/excitations), 1 6-msec bandwidth,
Si 2 x Si 2 matrix, and 2-mm slice thickness. Contiguous slices were obtained by interleaving separate acquisitions. Eleven to i 4 such slices were obtained. Images were acquired in both axial and coronal planes with one S-in. (1 3-cm) surface coil centered over each ear; both ears were imaged at the same time. Imaging time for this FSE technique was less than i 0 mm. Conventional spin-echo images with a quadrature head coil were also contained: axial unenhanced Ti weighted images were obtained in all patients, and patients with
thin-section (2-mm) high-resolution images with excellent contrast in a fraction of the time needed for conventional spin-echo techniques. This speed advantage allows us to obtain highresolution images in clinically acceptable time frames. Images produced by this technique are a useful addition, in conjunction with routine TI- and T2-weighted spin-echo images, in the diag-
nosis of disorders
a sagittal
echo train length of i6, 20-msec
contrast
images
from
subjects were obtained parameters: 4000/30,80/i
and spatial resolution in clinically acceptable time frames. Conventional spin-echo TI-weighted images lack tissue contrast between fluid (e.g., CSF, endolymph, penlymph), neural tissue, otic capsule septa, and surrounding temporal bone. Conventional T2-weighted imaging of the inner ear is needed to reveal the natural contrast between fluid, neural structures, and bone; unfortunately,
of the
Macfall
Advances in MR imaging continue to improve our ability to evaluate temporal bone anatomy and disease. CT remains the procedure of choice for fine-detail imaging of bone structures such as ossicular anatomy, but it is not the ideal imaging technique for soft-tissue structures (e.g., the membranous labyrinth and neural structures). Conventional spin-echo MR techniques
used to image these structures
Essay
to R. D. Tien.
TIEN
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
396
Fig. signal.
ET AL.
AJR:i59,
August
1992
1.-A, Axial T2-weighted Fine detailed anatomy
FSE MR image (4000/80) of right inner ear of a 30-year-old healthy male volunteer. Endolymph and CSF have very high of internal auditory canal and inner ear is seen. Modiolus, osseous spiral lamina, and interscalar septum of cochlea are clearly identified. Cochlear nerve (long straight arrow), vestibular nerve (short straight arrow), and facial nerve (arrowhead) are well visualized in internal auditory canal. High signal from endolymph in vestibule also is well seen (curved arrow). B, Microscopic anatomic photograph of cochlea shows anatomy similar to that imaged in A. Modiolus, osseous spiral lamina, and interscalar septum are seen. IAC = internal auditory canal. (Reprinted with permission from Schuknecht and Gulya [2].)
Fig. 2.-Intracanalicular
acoustic
schwannoma
in a 47-year-old
woman with left-sided
sensorineural
hearing
loss.
A, Axial surface-coil conventional Ti-weighted MR image (500/12) of left ear shows possible poorly defined soft-tissue signal within internal auditory canal (arrow). B, Axial FSE MR image (4000/80) shows complete replacement of normal structures in left internal auditory canal by homogeneous soft-tissue signal (arrow). C, Axial Ti-weighted MR image after contrast infusion shows enhancing mass in internal auditory canal and further suggests acoustic schwannoma (arrow). Although both FSE and enhanced Ti-weighted images showed the same information, FSE imaging may be useful in patients who refuse or are not eligible for enhanced studies.
=
NP x NEX
x TR/ETL.
Therefore,
long
TRs
(4000-5000
msec) can be used to generate heavy T2 weighting and an improved signal-to-noise ratio without significantly prolonging imaging
sequence determine
time.
In addition,
is phase encoded, spatial localization
as each
individual
echo
in this
few excitations are required to of the signal, and because the
inner ear is near the skin surface, surface-coil technology can be used to increase the signal-to-noise ratio. With this improved, diagnostically useful signal-to-noise ratio, images of
resolution (large matrix, 5i 2 x 51 2) and exquisite detail can be obtained in a clinically acceptable time period. One drawback of the FSE technique is that we cannot obtain as many slices as with the conventional spin-echo technique for the same TR. In many cases, this reduction in the number of slices is an acceptable tradeoff for the eightor i 6-fold reduction in scan time. In a limited area of interest such as the inner ear, the maximum number of slices with FSE is more than adequate. Also, when a longer TR is used, high
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
AJA:i59,
August
MR
1992
OF
Fig. 3.-Vestibular aqueduct syndrome in a 4-year-old girl with signs and symptoms of Meniere’s disease. Conventional Ti- and T2-weighted
MR images were unremarkable.
Axial FSE MR image (4000/80;
composite
of left and right ears) shows marked dilatation of left vestibular aqueduct (long arrow). Right vestibular aqueduct is of normal size (short arrow). Size difference between aqueducts was considered beyond the limit of normal variation. No other inner ear structural abnormalities were identified. On the basis of FSE images and clinical symptoms and signs, diagnosis of vestibular aqueduct syndrome was made.
the slice reduction is not as severe. A second potential drawback to the FSE technique is its sensitivity to fluid flow or pulsation, which can result in artifacts on images. This has not been a problem in our experience; because fluid moves relatively slowly through the internal acoustic canal and inner ear, flow-related artifacts on FSE images have been minimal. Last, the known diminished sensitivity to magnetic susceptibility of FSE from osseus structures or paramagnetic material is advantageous in imaging the inner ear because it is surrounded by the temporal bone.
INNER
EAR
397
This technique will not replace contrast-enhanced images for evaluation of neuritis (e.g., Bell’s palsy) or tumors [3, 4], and it is not as effective as CT in evaluating osseous structures. In cases of intracanalicular acoustic schwannoma, however, this FSE technique will enable visualization of the tumor without contrast injection (Fig. 2). This may benefit patients who are unwilling to receive contrast material or who are allergic to it, those in whom venous access is poor, or those who are in serious renal failure. The main strength of the FSE technique is that it can produce heavily T2-weighted highresolution images that delineate the fluid-filled otic capsule and internal acoustic canal. This is particularly useful when it is important to diagnose or exclude labyrinthine fistula or cochlear erosion by tumor (Figs. 4 and 5). In most patients, acquisition of a long effective TE FSE image will answer most clinical questions. However, a long effective TE may potentially, by virtue of the extremely high perilymph/endolymph/ CSF signal, mask subtle soft-tissue invasion into the cochlea or vestibule. When this is suspected, generation of a short effective TE FSE image (which produces lower intensity CSF analogous to that produced with proton-density conventional spin echo) may be of clinical use (Fig. 4). Thus, this technique can potentially aid in the diagnosis of diseases such as labyrinthine otosdlerosis or fibrous labyrinthitis. Conversely, conventional spin-echo images cannot provide the necessary contrast and spatial resolution to delineate these lesions in a reasonable scanning time. Nor does CT furnish adequate contrast resolution to identify confidently the minuscule soft tissue within the otic capsule. A further application of the FSE technique is for congenital malformations involving the membranous labyrinth. FSE can easily evaluate the size and shape of the fluid-filled otic capsule, vestibule, internal acoustic canal, and aqueducts. Our example of the vestibular aqueduct syndrome (Fig. 3) was elegantly shown by FSE and led to the clinical diagnosis;
Fig. 4.-Probable facial nerve schwannoma in a 43-year-old woman with gradual onset of mild right-sided facial weakness. A, Conventional axial Ti-weighted MR image (500/12) with surface coil shows isointense soft-tissue mass in right petrous bone (arrows). Mass cannot be separated from inner ear structures. B, Axial Ti-weighted MR image after contrast infusion shows intense enhancement of lesion (arrow). C, Axial FSE MR image (4000/30) clearly separates mass in region of geniculate ganglion (short arrow) from cochlea (long arrow) and vestibule. With
FSE image, absence of tumor invasion or erosion into cochlea or vestibule is assured. Patient refused surgery.
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
398
TIEN
A
ET AL.
AJR:159,
August
1992
B
:,.‘
.
-
T
.
‘
/
Fig. 5.-Cholesteatoma with labyrinthine fistula in a 4-year-old girl with a history of middle ear cholesteatoma and new onset of vertigo. Conventional Ti- and T2weighted MR images showed abnormal signal in middle ear, but delineation of lateral semicircular canal was not possible. A, Coronal surface-coil FSE MR image (4000/80) shows high-signal, poorly defined mass (arrowhead) in left middle ear consistent with inflammatory mass or cholesteatoma. Curved arrow = right superior semicircular canal, short straight arrow = right horizontal semicircular canal. B, Axial FSE MR image (4000/80) shows absence of bony wall of left lateral semicircular canal and communication of high signal between lesion and canal (long straight arrows, A and B), suggesting diagnosis of Iabynnthine fistula. C, Subsequent CT scan shows fistula (arrow), which was confirmed by surgery.
C on conventional spin-echo imaging this abnormality was missed because of insufficient contrast and spatial resolution. Although high-resolution CT may show the dilated aqueduct or semicircular canal fistula, the radiation exposure to the patient is unnecessary when FSE images can offer the same information without radiation. In summary, this new FSE technique can show fine contrast and spatial resolution in the inner ear in a reasonable scanning time. In most cases, CT should be performed first for middle
ear and labyrinthine mend
application
disease. of this
new
Thereafter, FSE
technique
we highly
recom-
in conjunction
with
conventional
diseases
spin-echo
images
for evaluation
of certain
of the inner ear.
REFERENCES 1 . Hennig
J, Nauerth
A, Friedburg
H. RARE
imaging:
a fast imaging
method
Med i986;3:823-833 2. Schuknecht HF, Gulya AJ. Anatomy of the temporal bone with surgical implications. Philadelphia: Lea & Febiger, 1986:131 3. Tien R, Dillon WP, Jackler RK. Contrast-enhanced MR imaging of the facial nerve in 1 1 patients with Bell’s palsy. AJNR i990;1 1 :735-741 4. Brogan M, Chakeres DW. Gd-DTPA-enhanced MR imaging of cochlear schwannoma. AJNR 1990;1 1:407-408 for clinical
MR. Magn
Reson
395
Pictorial
Fast Spin-Echo Inner Ear Robert
High-Resolution
Gary J. Felsberg,
D. lien,1
and
James
MR Imaging
cannot yield excellent
prescribed
the
use of conventional
T2-weighted
by time constraints when large-matrix, with more than one excitation are used.
is a recently
developed
technique
neurosensory
thin-section techniques Fast spin-echo imaging
that can provide T2-weighted,
Fast spin-echo (FSE) imaging was performed in six normal volunand in i i consecutive patients with a variety of inner ear disorders. The FSE technique we used is a hybrid rapid-acquisition teers
et al. [1]. Received
Thin-section January
21
FSE ,
All authors:
Department
AJR 159:395-398,
August
I
1992;
technique
initially
described
by Hennig
imaging
of the
temporal
bone
accepted
of Radiology.
after revision Box 3808,
1992 0361 -803x/92/1
March Duke
592-0395
hearing
loss
main
also
advantage
had
of FSE
is shortened compared yet the signal-to-noise conventional spin-echo by the TR, the number
and Methods
(RARE)
image.
echo space,
i8-cm
of phase-encoding
Ti -weighted
images
© American
after
admin-
imaging
is that
the
Center,
Roentgen
Durham, Ray Society
NC 27710.
steps
Address
scan
time
with conventional spin-echo images, ratio is not significantly reduced. Both and FSE scary times are determined of excitations (NEX), and the number (NP).
The
scan
echo FSE sequence, however, is reduced to the value of an echo train length (ETL):
was
Medical
of
field of view,
time
reprint
requests
for
a single-
by a factor equal that is, scan time
3. 1992. University
Images
Discussion
of the inner ear.
relaxation-enhanced
localizer
istration of gadopentetate dimeglumine. Imaging parameters were 500/i 2/2 with 3-mm-thick interleaved slices and a 256 x i 92 matrix. In addition, for patients with neurosensory hearing loss, conventional T2-weighted images were obtained of the entire brain (2500/20,70/ i) with a 5-mm slice thickness and 2.5-mm gap. The normal anatomy and a variety of inner ear disorders were studied by these methods (Figs. i -5).
is limited
The
Subjects
Ti-weighted
by using FSE techniques with the following (TRITE/excitations), 1 6-msec bandwidth,
Si 2 x Si 2 matrix, and 2-mm slice thickness. Contiguous slices were obtained by interleaving separate acquisitions. Eleven to i 4 such slices were obtained. Images were acquired in both axial and coronal planes with one S-in. (1 3-cm) surface coil centered over each ear; both ears were imaged at the same time. Imaging time for this FSE technique was less than i 0 mm. Conventional spin-echo images with a quadrature head coil were also contained: axial unenhanced Ti weighted images were obtained in all patients, and patients with
thin-section (2-mm) high-resolution images with excellent contrast in a fraction of the time needed for conventional spin-echo techniques. This speed advantage allows us to obtain highresolution images in clinically acceptable time frames. Images produced by this technique are a useful addition, in conjunction with routine TI- and T2-weighted spin-echo images, in the diag-
nosis of disorders
a sagittal
echo train length of i6, 20-msec
contrast
images
from
subjects were obtained parameters: 4000/30,80/i
and spatial resolution in clinically acceptable time frames. Conventional spin-echo TI-weighted images lack tissue contrast between fluid (e.g., CSF, endolymph, penlymph), neural tissue, otic capsule septa, and surrounding temporal bone. Conventional T2-weighted imaging of the inner ear is needed to reveal the natural contrast between fluid, neural structures, and bone; unfortunately,
of the
Macfall
Advances in MR imaging continue to improve our ability to evaluate temporal bone anatomy and disease. CT remains the procedure of choice for fine-detail imaging of bone structures such as ossicular anatomy, but it is not the ideal imaging technique for soft-tissue structures (e.g., the membranous labyrinth and neural structures). Conventional spin-echo MR techniques
used to image these structures
Essay
to R. D. Tien.
TIEN
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
396
Fig. signal.
ET AL.
AJR:i59,
August
1992
1.-A, Axial T2-weighted Fine detailed anatomy
FSE MR image (4000/80) of right inner ear of a 30-year-old healthy male volunteer. Endolymph and CSF have very high of internal auditory canal and inner ear is seen. Modiolus, osseous spiral lamina, and interscalar septum of cochlea are clearly identified. Cochlear nerve (long straight arrow), vestibular nerve (short straight arrow), and facial nerve (arrowhead) are well visualized in internal auditory canal. High signal from endolymph in vestibule also is well seen (curved arrow). B, Microscopic anatomic photograph of cochlea shows anatomy similar to that imaged in A. Modiolus, osseous spiral lamina, and interscalar septum are seen. IAC = internal auditory canal. (Reprinted with permission from Schuknecht and Gulya [2].)
Fig. 2.-Intracanalicular
acoustic
schwannoma
in a 47-year-old
woman with left-sided
sensorineural
hearing
loss.
A, Axial surface-coil conventional Ti-weighted MR image (500/12) of left ear shows possible poorly defined soft-tissue signal within internal auditory canal (arrow). B, Axial FSE MR image (4000/80) shows complete replacement of normal structures in left internal auditory canal by homogeneous soft-tissue signal (arrow). C, Axial Ti-weighted MR image after contrast infusion shows enhancing mass in internal auditory canal and further suggests acoustic schwannoma (arrow). Although both FSE and enhanced Ti-weighted images showed the same information, FSE imaging may be useful in patients who refuse or are not eligible for enhanced studies.
=
NP x NEX
x TR/ETL.
Therefore,
long
TRs
(4000-5000
msec) can be used to generate heavy T2 weighting and an improved signal-to-noise ratio without significantly prolonging imaging
sequence determine
time.
In addition,
is phase encoded, spatial localization
as each
individual
echo
in this
few excitations are required to of the signal, and because the
inner ear is near the skin surface, surface-coil technology can be used to increase the signal-to-noise ratio. With this improved, diagnostically useful signal-to-noise ratio, images of
resolution (large matrix, 5i 2 x 51 2) and exquisite detail can be obtained in a clinically acceptable time period. One drawback of the FSE technique is that we cannot obtain as many slices as with the conventional spin-echo technique for the same TR. In many cases, this reduction in the number of slices is an acceptable tradeoff for the eightor i 6-fold reduction in scan time. In a limited area of interest such as the inner ear, the maximum number of slices with FSE is more than adequate. Also, when a longer TR is used, high
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
AJA:i59,
August
MR
1992
OF
Fig. 3.-Vestibular aqueduct syndrome in a 4-year-old girl with signs and symptoms of Meniere’s disease. Conventional Ti- and T2-weighted
MR images were unremarkable.
Axial FSE MR image (4000/80;
composite
of left and right ears) shows marked dilatation of left vestibular aqueduct (long arrow). Right vestibular aqueduct is of normal size (short arrow). Size difference between aqueducts was considered beyond the limit of normal variation. No other inner ear structural abnormalities were identified. On the basis of FSE images and clinical symptoms and signs, diagnosis of vestibular aqueduct syndrome was made.
the slice reduction is not as severe. A second potential drawback to the FSE technique is its sensitivity to fluid flow or pulsation, which can result in artifacts on images. This has not been a problem in our experience; because fluid moves relatively slowly through the internal acoustic canal and inner ear, flow-related artifacts on FSE images have been minimal. Last, the known diminished sensitivity to magnetic susceptibility of FSE from osseus structures or paramagnetic material is advantageous in imaging the inner ear because it is surrounded by the temporal bone.
INNER
EAR
397
This technique will not replace contrast-enhanced images for evaluation of neuritis (e.g., Bell’s palsy) or tumors [3, 4], and it is not as effective as CT in evaluating osseous structures. In cases of intracanalicular acoustic schwannoma, however, this FSE technique will enable visualization of the tumor without contrast injection (Fig. 2). This may benefit patients who are unwilling to receive contrast material or who are allergic to it, those in whom venous access is poor, or those who are in serious renal failure. The main strength of the FSE technique is that it can produce heavily T2-weighted highresolution images that delineate the fluid-filled otic capsule and internal acoustic canal. This is particularly useful when it is important to diagnose or exclude labyrinthine fistula or cochlear erosion by tumor (Figs. 4 and 5). In most patients, acquisition of a long effective TE FSE image will answer most clinical questions. However, a long effective TE may potentially, by virtue of the extremely high perilymph/endolymph/ CSF signal, mask subtle soft-tissue invasion into the cochlea or vestibule. When this is suspected, generation of a short effective TE FSE image (which produces lower intensity CSF analogous to that produced with proton-density conventional spin echo) may be of clinical use (Fig. 4). Thus, this technique can potentially aid in the diagnosis of diseases such as labyrinthine otosdlerosis or fibrous labyrinthitis. Conversely, conventional spin-echo images cannot provide the necessary contrast and spatial resolution to delineate these lesions in a reasonable scanning time. Nor does CT furnish adequate contrast resolution to identify confidently the minuscule soft tissue within the otic capsule. A further application of the FSE technique is for congenital malformations involving the membranous labyrinth. FSE can easily evaluate the size and shape of the fluid-filled otic capsule, vestibule, internal acoustic canal, and aqueducts. Our example of the vestibular aqueduct syndrome (Fig. 3) was elegantly shown by FSE and led to the clinical diagnosis;
Fig. 4.-Probable facial nerve schwannoma in a 43-year-old woman with gradual onset of mild right-sided facial weakness. A, Conventional axial Ti-weighted MR image (500/12) with surface coil shows isointense soft-tissue mass in right petrous bone (arrows). Mass cannot be separated from inner ear structures. B, Axial Ti-weighted MR image after contrast infusion shows intense enhancement of lesion (arrow). C, Axial FSE MR image (4000/30) clearly separates mass in region of geniculate ganglion (short arrow) from cochlea (long arrow) and vestibule. With
FSE image, absence of tumor invasion or erosion into cochlea or vestibule is assured. Patient refused surgery.
Downloaded from www.ajronline.org by 60.2.165.42 on 11/05/15 from IP address 60.2.165.42. Copyright ARRS. For personal use only; all rights reserved
398
TIEN
A
ET AL.
AJR:159,
August
1992
B
:,.‘
.
-
T
.
‘
/
Fig. 5.-Cholesteatoma with labyrinthine fistula in a 4-year-old girl with a history of middle ear cholesteatoma and new onset of vertigo. Conventional Ti- and T2weighted MR images showed abnormal signal in middle ear, but delineation of lateral semicircular canal was not possible. A, Coronal surface-coil FSE MR image (4000/80) shows high-signal, poorly defined mass (arrowhead) in left middle ear consistent with inflammatory mass or cholesteatoma. Curved arrow = right superior semicircular canal, short straight arrow = right horizontal semicircular canal. B, Axial FSE MR image (4000/80) shows absence of bony wall of left lateral semicircular canal and communication of high signal between lesion and canal (long straight arrows, A and B), suggesting diagnosis of Iabynnthine fistula. C, Subsequent CT scan shows fistula (arrow), which was confirmed by surgery.
C on conventional spin-echo imaging this abnormality was missed because of insufficient contrast and spatial resolution. Although high-resolution CT may show the dilated aqueduct or semicircular canal fistula, the radiation exposure to the patient is unnecessary when FSE images can offer the same information without radiation. In summary, this new FSE technique can show fine contrast and spatial resolution in the inner ear in a reasonable scanning time. In most cases, CT should be performed first for middle
ear and labyrinthine mend
application
disease. of this
new
Thereafter, FSE
technique
we highly
recom-
in conjunction
with
conventional
diseases
spin-echo
images
for evaluation
of certain
of the inner ear.
REFERENCES 1 . Hennig
J, Nauerth
A, Friedburg
H. RARE
imaging:
a fast imaging
method
Med i986;3:823-833 2. Schuknecht HF, Gulya AJ. Anatomy of the temporal bone with surgical implications. Philadelphia: Lea & Febiger, 1986:131 3. Tien R, Dillon WP, Jackler RK. Contrast-enhanced MR imaging of the facial nerve in 1 1 patients with Bell’s palsy. AJNR i990;1 1 :735-741 4. Brogan M, Chakeres DW. Gd-DTPA-enhanced MR imaging of cochlear schwannoma. AJNR 1990;1 1:407-408 for clinical
MR. Magn
Reson
