AJR 2004; 182:379-384
© American Roentgen Ray Society
High-Resolution Virtual MR Endoscopy of the Cerebellopontine Angle
Vicky Nowé1,
Johan L. P. Michiels2,
Rodrigo Salgado1,
Dirk De Ridder3,
Paul H. Van de Heyning4,
Arthur M. De Schepper1 and
Paul M. Parizel1
1 Department of Radiology, Universitair Ziekenhuis Antwerpen (University of
Antwerp), Wilrijkstraat 10, Edegem B-2650, Belgium.
2 Siemens Medical Solutions, Charleroisesteenweg 116, Brussels 1060,
Belgium.
3 Department of Neurosurgery, Universitair Ziekenhuis Antwerpen, Edegem B-2650,
Belgium.
4 Department of Otorhinolaryngology, Universitair Ziekenhuis Antwerpen, Edegem
B-2650, Belgium.
Received January 27, 2003;
accepted after revision May 28, 2003.
Address correspondence to P. M. Parizel
(parizelp{at}uia.ua.ac.be).
Introduction
The development of new techniques and indications for surgery of the
cerebellopontine angle (CPA) cistern requires a precise understanding of the
complex anatomy of this region. The CPA cistern is located at the junction of
the pons, medulla oblongata, and cerebellum; it contains cranial nerves, blood
vessels, the cerebellar flocculus, the choroid plexus extending through the
foramen of Luschka, and the jugular tubercle of the occipital bone.
Three-dimensional imaging techniques such as virtual endoscopy are useful in
understanding these complex anatomic relationships
[1], in deciding on the
indication for surgery (e.g., in patients with microvascular compression
syndrome), and in creating preoperative simulations
[2]. Virtual CT endoscopy has
been shown to be of value in the diagnosis of and surgical planning for
lesions involving the temporal bone and internal auditory canal
[1] but cannot provide reliable
information on the CPA because of the poor contrast resolution between the
cranial nerves and cerebrospinal fluid.
Heavily T2-weighted high-resolution MRI is a more useful method with which
to visualize the cranial nerves in the CPA because it provides excellent
contrast resolution between the cerebrospinal fluid and all other structures
[3]. The image data set can be
used to generate virtual MRI endoscopy of this anatomic region
[2,
4–6].
Increased spatial resolution of the T2-weighted data set improves the quality
and accuracy of virtual endoscopy. The purpose of our pictorial essay is to
illustrate the normal anatomy of the CPA on virtual MR endoscopy and to
provide examples of preoperative clinical use, such as in tumor resection or
microvascular decompression.
Principles and Methods
Image Acquisition Technique
Virtual endoscopy through the CPA can be performed using high-resolution
heavily T2-weighted MRIs (source images) suitable for 3D reconstructions. The
pulse sequence and parameter settings used to obtain the source images are
chosen to provide the best contrast between the high-intensity cerebrospinal
fluid and all other structures outlined as low-intensity areas, such as the
cranial nerves, blood vessels, brain stem, cerebellum, and surrounding bones.
Source images can be obtained with either a 3D Fourier transform gradient-echo
sequence, such as constructive interference in the steady state; a true fast
imaging with steady-state precession (true FISP) sequence; or a 3D fast
spin-echo sequence with forced improvement of the longitudinal recovery using
a driven equilibrium pulse at the end of the echo train, such as the 3D driven
equilibrium Fourier transform fast spin-echo technique
[7]. All virtual MR endoscopy
images in this article were obtained with transverse true FISP or constructive
interference in the steady-state sequences, with a slice thickness of 0.6 mm,
a field of view of 100 mm, and a matrix of 256 x 256. Use of these
parameters results in nearly isotropic voxels of 0.6 x 0.4 x 0.4
mm3. We used a 1.5-T system (Sonata, Siemens), with either a
standard circularly polarized head coil or an eight-channel phased array head
coil.
Virtual Endoscopy Postprocessing Technique
The source image data set was transferred to a dedicated workstation
(Leonardo, Siemens). Images are reformatted to generate a 3D internal surface
image of the CPA. For postprocessing, we used an interactive fly-through
software program (Leonardo, Siemens) that enables the user to navigate a
virtual camera within the cerebrospinal fluid space, thereby creating the
illusion of performing actual endoscopy. Movements such as zooming in or out
and roaming or rotating around a fixed viewing point alter the perspective and
allow the user to visualize the region of interest from different angles and
distances. Image thresholds are adapted to each case to achieve optimal
clarity while avoiding artifacts. All voxels with a signal intensity above the
upper threshold level are considered to be cerebrospinal fluid.
Movement inside the CPA allows us to study the anatomic relationships
between nerves and blood vessels. Spatial relationships may be distorted by
the so-called "fish-eye" artifact inherent to the virtual
endoscopy reconstruction technique. Surface rendering is performed using a
"wet look" algorithm. Sequential serial images saved on the hard
drive can be used to create a fly-through video of the path taken by the
camera. Total time required for postprocessing the images of each patient
averaged 10 min.
Normal Anatomy
Virtual MRI endoscopy provides accurate views of the cranial nerves and
vessels within the CPA. The trigeminal, facial, and vestibulocochlear nerves
are easily identified because of their comparatively large calibers, whereas
the smaller abducent, glossopharyngeal, and vagus nerves are more difficult to
visualize. The trigeminal nerve is easily recognizable as a thick, robust
nerve bundle in the upper part of the prepontine cistern. The facial and
vestibulocochlear nerves are seen as two distinct structures, running from the
brainstem to the internal auditory canal. In the CPA, the thinner facial nerve
lies anterior to the main trunk of the thicker vestibulocochlear nerve. In the
internal auditory canal, the vestibulocochlear nerve splits into three
separate branches: the cochlear and the superior and inferior vestibular
nerves. Within the internal auditory canal, the arrangement of the facial,
cochlear, and superior and inferior vestibular nerves is cranial to caudal and
anterior to posterior. Arterial branches of the vertebrobasilar system,
including the anterior and posterior inferior cerebellar arteries, are
identifiable, as are the venous structures within the CPA (petrous vein and
smaller veins).
Most of these structures are best seen with a viewing perspective traveling
from anterior to posterior and medial to lateral (Fig.
1A,
1B,
1C,
1D). When viewing these
structures as seen by the surgeon using a retrosigmoidal approach (Fig.
2A,
2B,
2C,
2D)— from posterior to
anterior and lateral to medial—the flocculus can get in the way,
obscuring the CPA. The best results are obtained in patients with a wide CPA
(e.g., due to severe atrophy or to a tumor pushing away the cerebellum). In
patients with a narrow CPA, adequate viewing angles are more difficult to
obtain on virtual MR endoscopy.
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Fig. 1A. —Normal anatomy of left cerebellopontine angle (CPA) in
58-year-old woman as seen on source MRI (A) and on virtual MR endoscopy
images (B–D). Projection was anterior to posterior and medial to
lateral. On virtual MR endoscopy images, pons (P) is on left, and trigeminal
nerve (V) is easily recognized as thick straight structure in upper part of
CPA. Facial nerve (small arrow, B–D) and
vestibulocochlear nerve (large arrow, B–D) are seen in
distance as juxtaposed parallel bundles that disappear into internal auditory
canal (arrowheads, B–D). On axial thin-section
constructive interference in steady-state source image, fly-through volume is
depicted as pyramid, representing field of vision of virtual camera with
imaginary viewpoint at top (black arrow).
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Fig. 1B. —Normal anatomy of left cerebellopontine angle (CPA) in
58-year-old woman as seen on source MRI (A) and on virtual MR endoscopy
images (B–D). Projection was anterior to posterior and medial to
lateral. On virtual MR endoscopy images, pons (P) is on left, and trigeminal
nerve (V) is easily recognized as thick straight structure in upper part of
CPA. Facial nerve (small arrow, B–D) and
vestibulocochlear nerve (large arrow, B–D) are seen in
distance as juxtaposed parallel bundles that disappear into internal auditory
canal (arrowheads, B–D). Abducent nerve (VI) is much
smaller than trigeminal nerve and, in some cases, can be difficult to
visualize.
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Fig. 1C. —Normal anatomy of left cerebellopontine angle (CPA) in
58-year-old woman as seen on source MRI (A) and on virtual MR endoscopy
images (B–D). Projection was anterior to posterior and medial to
lateral. On virtual MR endoscopy images, pons (P) is on left, and trigeminal
nerve (V) is easily recognized as thick straight structure in upper part of
CPA. Facial nerve (small arrow, B–D) and
vestibulocochlear nerve (large arrow, B–D) are seen in
distance as juxtaposed parallel bundles that disappear into internal auditory
canal (arrowheads, B–D). Same region seen in B is
displayed but virtual camera has been rotated slightly upwards around fixed
viewing point. On anterior-to-posterior projection, CPA cistern is seen
through diamond-shaped window bordered superiorly by trigeminal nerve,
medially by pons, inferiorly by abducent nerve, and laterally by posterior
wall of petrous bone. VI = abducent nerve.
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Fig. 1D. —Normal anatomy of left cerebellopontine angle (CPA) in
58-year-old woman as seen on source MRI (A) and on virtual MR endoscopy
images (B–D). Projection was anterior to posterior and medial to
lateral. On virtual MR endoscopy images, pons (P) is on left, and trigeminal
nerve (V) is easily recognized as thick straight structure in upper part of
CPA. Facial nerve (small arrow, B–D) and
vestibulocochlear nerve (large arrow, B–D) are seen in
distance as juxtaposed parallel bundles that disappear into internal auditory
canal (arrowheads, B–D). Same region seen in B
and C is displayed with virtual camera zoomed in, so that abducent
nerve is no longer visible.
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Fig. 2A. —Normal anatomy of right cerebellopontine angle (CPA) in
61-year-old woman as seen on source MRI (A) and virtual MR endoscopy
images (B–D) from surgical perspective, mimicking
retrosigmoidal approach. Projection was posterior to anterior and lateral to
medial. Virtual MR endoscopy images show posterior aspect of facial nerve
(VII), which lies in front of vestibulocochlear nerve (VIII). Blood vessel
(open arrows, B and C; solid arrows, D)
makes turn around facial and vestibulocochlear nerves near entrance of
internal auditory canal. Trigeminal nerve (V) is seen in upper part of CPA,
with pons (P) on left. Flocculus (F) partially obscures view. Abducent nerve
is indicated by arrowheads (B–D). On axial thin-section
constructive interference in steady-state source image, fly-through volume is
depicted as pyramid, representing field of vision of virtual camera with
imaginary viewpoint at top (black arrow).
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Fig. 2B. —Normal anatomy of right cerebellopontine angle (CPA) in
61-year-old woman as seen on source MRI (A) and virtual MR endoscopy
images (B–D) from surgical perspective, mimicking
retrosigmoidal approach. Projection was posterior to anterior and lateral to
medial. Virtual MR endoscopy images show posterior aspect of facial nerve
(VII), which lies in front of vestibulocochlear nerve (VIII). Blood vessel
(open arrows, B and C; solid arrows, D)
makes turn around facial and vestibulocochlear nerves near entrance of
internal auditory canal. Trigeminal nerve (V) is seen in upper part of CPA,
with pons (P) on left. Flocculus (F) partially obscures view. Abducent nerve
is indicated by arrowheads (B–D). Abducent nerve and blood vessel
(solid arrow) are seen in close proximity in distance.
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Fig. 2C. —Normal anatomy of right cerebellopontine angle (CPA) in
61-year-old woman as seen on source MRI (A) and virtual MR endoscopy
images (B–D) from surgical perspective, mimicking
retrosigmoidal approach. Projection was posterior to anterior and lateral to
medial. Virtual MR endoscopy images show posterior aspect of facial nerve
(VII), which lies in front of vestibulocochlear nerve (VIII). Blood vessel
(open arrows, B and C; solid arrows, D)
makes turn around facial and vestibulocochlear nerves near entrance of
internal auditory canal. Trigeminal nerve (V) is seen in upper part of CPA,
with pons (P) on left. Flocculus (F) partially obscures view. Abducent nerve
is indicated by arrowheads (B–D). Same region seen in B is
displayed, but virtual camera has been rotated slightly upwards around fixed
viewing point. Glossopharyngeal nerve (solid arrow) becomes visible
in lower part of CPA and disappears into jugular foramen. CPA cistern is seen
through trapezoidal window that is bordered superiorly by trigeminal nerve,
medially by pons, inferiorly by facial and vestibulocochlear nerve complex,
and laterally by posterior wall of petrous bone. Long diagonal line of
abducent nerve is seen in distance.
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Fig. 2D. —Normal anatomy of right cerebellopontine angle (CPA) in
61-year-old woman as seen on source MRI (A) and virtual MR endoscopy
images (B–D) from surgical perspective, mimicking
retrosigmoidal approach. Projection was posterior to anterior and lateral to
medial. Virtual MR endoscopy images show posterior aspect of facial nerve
(VII), which lies in front of vestibulocochlear nerve (VIII). Blood vessel
(open arrows, B and C; solid arrows, D)
makes turn around facial and vestibulocochlear nerves near entrance of
internal auditory canal. Trigeminal nerve (V) is seen in upper part of CPA,
with pons (P) on left. Flocculus (F) partially obscures view. Abducent nerve
is indicated by arrowheads (B–D). Same region seen in B
and C is displayed, but virtual camera has been zoomed in to depict
relationship between abducent nerve and looping blood vessel more clearly.
Abducent nerve disappears into opening of Dorello's canal. P = pons.
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Neurogenic Tumors of the CPA
Acoustic schwannomas are the most common CPA tumors, representing
75–80% of all neoplasms found in this location and typically arising in
the internal auditory canal. Although schwannomas can display a variety of
growth patterns, in most cases, a mass is identified in the CPA. The
relationship between the tumor and the adjacent nerves can be shown on virtual
MR endoscopy (Fig. 3A,
3B,
3C,
3D). The information can be
manipulated to replicate the view the surgeon will have when using a
retrosigmoidal approach for tumor resection.
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Fig. 3A. —Right acoustic nerve schwannoma in 39-year-old man. Coronal
gadolinium-enhanced T1-weighted image obtained with fat saturation shows
enhancing ovoid lesion in right cerebellopontine angle (CPA).
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Fig. 3B. —Right acoustic nerve schwannoma in 39-year-old man. Axial
thin-section constructive interference in steady-state source image shows
fusiform mass (asterisk) in right internal auditory canal extending
into right CPA cistern. Note close relationship between tumor and juxtaposed
facial nerve (arrow).
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Fig. 3C. —Right acoustic nerve schwannoma in 39-year-old man. Virtual
MR endoscopy image of right CPA as seen in cranial-to-caudal projection was
obtained with patient's nose pointing downward. Tumor (T) is seen as ovoid
lesion in right CPA. Pons (P) is on right.
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Fig. 3D. —Right acoustic nerve schwannoma in 39-year-old man. Virtual
MR endoscopy image of right CPA in anterior-to-posterior projection reveals
that facial nerve (VII) is displaced and compressed over anterior surface of
tumor (T).
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Trigeminal nerve schwannomas are rare lesions, representing 1–8% of
all intracranial neuromas and less than 0.5% of all intracranial tumors. They
can involve various portions of the trigeminal nerve and exhibit different
patterns of growth. Surgical resection of these tumors presents great
technical difficulties, and virtual MR endoscopy can help the surgeon to gain
understanding of the anatomic extension of the lesion preoperatively.
Involvement of the prepontine segment of the trigeminal nerve is best
visualized with a posterior-to-anterior perspective, mimicking the
retrosigmoidal surgical view (Fig.
4A,
4B,
4C,
4D).
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Fig. 4A. —Dumbbell-shaped left trigeminal schwannoma in 62-year-old
woman. Axial gadolinium-enhanced T1-weighted image obtained with fat
saturation shows extension of tumor along left trigeminal nerve from brainstem
to Meckel's cave. Tumor has bilobular appearance and contains two cystic
components.
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Fig. 4B. —Dumbbell-shaped left trigeminal schwannoma in 62-year-old
woman. Axial thin-section constructive interference in steady-state source
image shows close relationship of posterior pole of tumor to entry and exit
zone of roots of facial and vestibulocochlear nerves.
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Fig. 4C. —Dumbbell-shaped left trigeminal schwannoma in 62-year-old
woman. Virtual MR endoscopy images show left cerebellopontine angle as seen
from perspective of retrosigmoidal surgical approach (posterior-to-anterior
and lateral-to-medial projections). Posterior aspect of vestibulocochlear
nerve (VIII) is seen with trigeminal schwannoma (T) in distance. Flocculus (F)
partly obscures field of view on C. On D, virtual camera has
been rotated upwards around fixed viewing point so that relationship of
posterior pole of tumor (arrowheads) to facial (VII) and
vestibulocochlear nerves can be assessed.
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Fig. 4D. —Dumbbell-shaped left trigeminal schwannoma in 62-year-old
woman. Virtual MR endoscopy images show left cerebellopontine angle as seen
from perspective of retrosigmoidal surgical approach (posterior-to-anterior
and lateral-to-medial projections). Posterior aspect of vestibulocochlear
nerve (VIII) is seen with trigeminal schwannoma (T) in distance. Flocculus (F)
partly obscures field of view on C. On D, virtual camera has
been rotated upwards around fixed viewing point so that relationship of
posterior pole of tumor (arrowheads) to facial (VII) and
vestibulocochlear nerves can be assessed.
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Microvascular Compression Syndrome
Mechanical vascular compression of cranial nerves in the CPA has been
reported to cause a wide range of symptoms, including trigeminal and
glossopharyngeal neuralgia, hemifacial spasm, positional vertigo, tinnitus,
and hearing loss [8]. Although
the pathophysiology of these disorders is complex, there is growing evidence
of the efficacy of microvascular decompression surgery. The decision of
whether to perform surgery on patients with microvascular compression syndrome
remains difficult, especially without radiologic evidence. Even on
high-resolution T2-weighted images, which provide excellent contrast between
cerebrospinal fluid and nerves, finding conclusive evidence of vascular
compression can be challenging. In such cases, virtual MR endoscopy provides
3D information concerning the spatial relationship between nerves and vessels
that is far superior to the information provided by 2D images
[2] (Figs.
5A,
5B,
5C,
5D,
5E,
5F,
6A,
6B,
6C,
6D,
7A,
7B,
7C,
7D). Moreover, 3D imaging can
be used to replicate the surgical field of view and is therefore useful in
presurgical planning.
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Fig. 5A. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A).
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. On axial thin-section constructive
interference in steady-state source image, fly-through volume is depicted as
pyramid, representing field of vision of virtual camera with imaginary
viewpoint at top (black arrow). Curved blood vessel is seen in left
CPA, with first hairpin (180°) turn pointing toward left internal auditory
canal.
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Fig. 5B. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A).
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. Small tortuous blood vessel, corresponding
to left anterior inferior cerebellar artery, is seen in close proximity to
facial and vestibulocochlear nerves. Blood vessel makes three hairpin turns
(arrows). Meatus of internal auditory canal is readily identifiable
(arrowheads).
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Fig. 5C. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A).
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. Same region seen in B is shown, but
virtual camera has zoomed in on tortuous blood vessel and on facial and
vestibulocochlear nerves. Second and third hairpin turns of blood vessel
(arrows) are easily recognized in close proximity to facial and
vestibulocochlear nerve complex. Meatus of internal auditory canal is visible
(arrowheads).
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Fig. 5D. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A),
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. Same region seen in B and C
is shown, but virtual camera has been zoomed in to depict second hairpin turn
of blood vessel and facial nerve in medial-to-lateral projection. Distance
between looping blood vessel (arrow) and facial nerve is
visualized.
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Fig. 5E. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A),
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. In image of same region seen in
B–D, virtual camera has been rotated backwards around
facial and vestibulocochlear nerve bundles in medial-to-lateral projection to
show gap between inferior part of second hairpin turn of blood vessel
(arrows) and vestibulocochlear nerve.
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Fig. 5F. —Vascular loop in close vicinity to left vestibulocochlear
(VIII) and facial (VII) nerves in 73-year-old woman. Neurovascular conflict
was presumed to be present on basis of findings on source MRI (A),
However, virtual MR endoscopy images (B–F) of left
cerebellopontine angle (CPA) (in anterior-to-posterior and medial-to-lateral
projections) show conclusively that there is no neurovascular contact between
nerves and vessels. F = flocculus. Virtual camera has been zoomed in to show
third hairpin turn of blood vessel and vestibulocochlear nerve in
medial-to-lateral projection image of same region seen in
B–E. Gap between anterior part of third hairpin turn of
blood vessel (arrow) and vestibulocochlear nerve is visible.
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Fig. 6A. —Microvascular compression syndrome in 76-year-old man as seen
on source MRI (A) and virtual MR endoscopy images (B–D) of
right cerebellopontine angle (CPA) in anterior-to-posterior and
medial-to-lateral projections. On virtual endoscopy images, small artery
(open arrows, B–D) is seen, as well as facial (VII) and
vestibulocochlear (VIII) nerves. Internal auditory canal (arrowheads,
B–D) is well depicted. On axial thin-section constructive
interference in steady-state source image of right CPA, fly-through volume is
depicted as pyramid, representing field of vision of virtual camera with
imaginary viewpoint at top (black arrow).
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Fig. 6B. —Microvascular compression syndrome in 76-year-old man as seen
on source MRI (A) and virtual MR endoscopy images (B–D) of
right cerebellopontine angle (CPA) in anterior-to-posterior and
medial-to-lateral projections. On virtual endoscopy images, small artery
(open arrows, B–D) is seen, as well as facial (VII) and
vestibulocochlear (VIII) nerves. Internal auditory canal (arrowheads,
B–D) is well depicted. Image reveals small artery running between
facial and vestibulocochlear nerves.
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Fig. 6C. —Microvascular compression syndrome in 76-year-old man as seen
on source MRI (A) and virtual MR endoscopy images (B–D) of
right cerebellopontine angle (CPA) in anterior-to-posterior and
medial-to-lateral projections. On virtual endoscopy images, small artery
(open arrows, B–D) is seen, as well as facial (VII) and
vestibulocochlear (VIII) nerves. Internal auditory canal (arrowheads,
B–D) is well depicted. Image shows same region seen in B,
but virtual camera has been rotated upwards around fixed viewing point.
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Fig. 6D. —Microvascular compression syndrome in 76-year-old man as seen
on source MRI (A) and virtual MR endoscopy images (B–D) of
right cerebellopontine angle (CPA) in anterior-to-posterior and
medial-to-lateral projections. On virtual endoscopy images, small artery
(open arrows, B–D) is seen, as well as facial (VII) and
vestibulocochlear (VIII) nerves. Internal auditory canal (arrowheads,
B–D) is well depicted. Same region seen in B and C
is shown with virtual camera rotated further upwards around fixed viewing
point. Vestibulocochlear nerve (solid arrow) is seen as slightly
displaced and buckled.
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Fig. 7A. —Microvascular compression syndrome in 65-year-old man with
right hemifacial spasm due to dolichoectatic vertebrobasilar trunk. Axial
T2-weighted image obtained through posterior fossa shows dolichoectatic
basilar artery (arrowheads) coursing horizontally across anterior
surface of pons, from right to left.
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Fig. 7B. —Microvascular compression syndrome in 65-year-old man with
right hemifacial spasm due to dolichoectatic vertebrobasilar trunk. Axial
thin-section constructive interference in steady-state source image shows that
vertebrobasilar confluence is displaced to right. Fly-through volume is
depicted as pyramid, representing field of vision of virtual camera with
imaginary viewpoint at top (black arrow).
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Fig. 7C. —Microvascular compression syndrome in 65-year-old man with
right hemifacial spasm due to dolichoectatic vertebrobasilar trunk. C
and D, Virtual MR endoscopy images show right cerebellopontine angle in
two projections. In anterior-to-posterior and medial-to-lateral projections
(C), facial (VII) and vestibulocochlear (VIII) nerves are seen in
distance through window formed by vertebral arteries (VA). In projection
showing surgical (retrosigmoidal) perspective (D), tortuous
vertebrobasilar system is seen in distance, displacing facial and
vestibulocochlear nerve complex to posterior. Smaller vessel (open
arrow) makes contact (solid arrow) with right facial nerve.
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Fig. 7D. —Microvascular compression syndrome in 65-year-old man with
right hemifacial spasm due to dolichoectatic vertebrobasilar trunk. C
and D, Virtual MR endoscopy images show right cerebellopontine angle in
two projections. In anterior-to-posterior and medial-to-lateral projections
(C), facial (VII) and vestibulocochlear (VIII) nerves are seen in
distance through window formed by vertebral arteries (VA). In projection
showing surgical (retrosigmoidal) perspective (D), tortuous
vertebrobasilar system is seen in distance, displacing facial and
vestibulocochlear nerve complex to posterior. Smaller vessel (open
arrow) makes contact (solid arrow) with right facial nerve.
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Conclusion
Virtual MR endoscopy projections provide unique insight into the anatomy of
the CPA. The technique improves the understanding of the complex spatial
relationships between cranial nerves and blood vessels and between tumors and
adjacent structures. By providing this information, virtual MR endoscopy
contributes information useful in deciding the indication for surgery (e.g.,
microvascular compression syndrome) and is an important tool for neurosurgeons
and otolaryngologists in planning and optimizing surgical procedures in the
CPA.
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Introduction
Principles and Methods
