SURVEY OF OPHTHALMOLOGY VOLUME 39. NUMBER5. MARCH-APRIL1995

AFTERI MAGES,

JONATHANWlRTSCHAFTER, EDITOR

Value of Parasagittal Magnetic Resonance Images in
Visualizing the Vascular Territories of the Cerebellum
CHIN-SANG CHUNG, MD, CLAUDIA J. CHAVES, MD, AND LOUIS R. CAPLAN, MD

Department of Neurology, Tufts-New England Medical Center, Boston, Massachusetts
Abstract. The outcomes of infarctions of the cerebellar arteries may range from self-limited
neuro-ophthalmic symptoms to sudden death. Identification of the affected territory may
assist in clinical management because the vascular syndromes, as well as vascular mechanisms of cerebellar infarcts, are different according to the involved cerebellar arteries.
However, it is usually difficult to tell the exact vascular territories using only transaxial
imagings. Magnetic resonance imaging is a good tool for obtaining parasagittal and coronal images of the cerebellum, which are better for showing the vascular territories. To
illustrate this point we report a 61-year-old woman with bilateral cerebellar infarcts (right
posterior inferior cerebellar artery and left superior cerebellar artery who had vertigo,
vomiting, headache, intermittent vertical diplopia, and difficulty walking. The clinical
value ofparasagittal imaging of the cerebellum in this case is discussed. (Surv Ophthalmol
39:399-402, 1995)

Key words, cerebellum 9 magnetic resonance imaging ~ parasagittal images 9
vascular territories

s u d d e n severe vertigo and vomiting. She had
difficulty walking, veering to the right. She had
an occipital headache and intermittent vertical
diplopia. T h e symptoms were maximal at onset
and gradually i m p r o v e d over the next week.
T h e r e were no h e a r i n g disturbances, no tinnitus;
no history o f vertigo, headache, syncope, tinnitus, amaurosis fugax, or o t h e r neurologic symptoms. She was r e f e r r e d to N E M C H because of
bilateral cerebellar infarcts on CT scan and for
f u r t h e r evaluation and m a n a g e m e n t . She had no
history of hypertension, diabetes mellitus, or
heart diseases. On examination her blood pressure was 130/70. T h e r e was no ocular or carotid
bruit. She was alert, oriented, and aware o f current events. H e r speech was normal. Mental
status was normal. Cranial nerve examination
revealed n o r m a l optic n e r v e h e a d s and visual

During the last decade advances in neuroimaging, particularly magnetic resonance imaging (MRI), have revolutionized in vivo study of
the posterior fossa structures. Different from C T
scan, which allowed only axial views, MRI has
m a d e it possible to obtain three-dimensional
images o f the brainstem and cerebellum using
transaxial, parasagittal and coronal imaging. 7
We r e p o r t a patient with bilateral cerebellar infarcts to illustrate the value o f parasagittal MRI
images in evaluating the vascular territories of
the cerebellum.

Case Report
A 61-year-old white woman, a past cigarette
smoker, awakened at 3 a.m. 10 days before admission to the New England Medical C e n t e r
Hospitals (NEMCH), Boston, MA, when she had
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Surv Ophthahnol 39 (5) March-April 1995

CHUNG ET AL

Fig. 1. A: A transaxial Tu-weighted MRI section through the midpons shows the high signal intensity in the central

portion of the left cerebellar hemisphere. The plane of the section does not permit certain differentiation ~)f1he
territory of the left superior cerebellar artery which is involved fi-om the territory c)fthe left cerebellar artery which
is uninvolved. B: A parasagittal Tz-weighted MRI section through the left cerebellar hemisphere (2 cm fiom the
midline) shows the high signal intensity lesion in the territory of the superior cerebellar artery. C: A parasagittal Ieweighted MRI section through the right cerebellar hemisphere (2 cm from the midline) shows the high signal
intensity lesion in the territory of the posterior inferior cerebellar artery.

fields bilaterally and there was no visual neglect.
Extraocular movements were normal, but horizontal nystagmus was noted on horizontal gaze
bilaterally. There was no vertical nystagmus. Facial sensation was normal and smile was symmetric. The soft palate elevated symmetrically. Sternocleidomastoid and trapezius muscles had
good strength bilaterally. Tongue p r o t r u d e d in
the midline. Motor power, tone, and bulk were
normal and symmetric. Sensory system was intact to light touch, pinprick, temperature, vibration, and position throughout. Deep tendon
reflexes were normal and symmetric with
downgoing toes bilaterally. Cerebellar examination showed slight right limb incoordination with
rapid alternating movements. Finger-to-nose
and heel-to-shin tests were intact. Gait was widebased and ataxic with veering to the right (lateropulsion). She was unable to walk unassisted or
without learning on something.
All admission blood tests were within normal
ranges. Electrocardiogram showed normal sinus
r h y t h m and slight ST depression in leads II and
III but no significant defects. An echocardiogram showed normal left ventricular size and
ejection fraction of 50%. The valves were normal.
Mild aortic insufficiency was noted. Brain computerized tomographic (CT) scanning showed
bilateral cerebellar infarcts. MRI scanning revealed an infarct in the left superior cerebellar

artery (SCA) territory (Figs. 1Aand B) and another
in the right posterior inferior cerebellar artery
(PICA) territory (Fig. 1C). The patient had ultrasound studies of the neck. In the right internal
carotid artery (ICA) there was irregular calcified
plaque on Duplex scan and mild to moderate
stenosis on Doppler study. Left ICA showed
55-65% stenosis. The right vertebral artery had
markedly diminished flow and the left vertebral
artery was normal. Transcranial Doppler study
was done on the vertebrobasilar system. Mean
velocities were slightly diminished in the basilar
artery and left vertebral artery and normal in the
right vertebral artery. Angiography of the posterior circulation revealed a tight stenosis at the
origin of the right vertebral artery. The right
PICA was not well seen.
Neurologically the patient improved gradually in terms of her ataxia. She was able to ambulate very well with the use of a cane. It was felt
that an embolism from a tight stenosis at the
origin of the right vertebral artery was the etiology of her bilateral cerebellar strokes. She was
placed on Coumadin and was also encouraged to
stop smoking. She was ambulatory with the help
of a cane at the time of discharge.

Discussion
The clinical syndromes are different according

PARASAGITTAL MRI FOR VASCULAR TERRITORIES OF CEREBELLUM

Fig. 2. Diagrammed vascular territories of the cerebellum on the parasagittal section of the Trweighted
MRI scan (2 cm from the midline). A: anterior inferior
cerebellar artery. S: superior cerebellar artery. P: posterior inferior cerebellar artery.

to the vascular territory of cerebellar infarcts)
Cerebellar infarcts caused by the occlusion of the
SCA are commonly associated with dysarthria,
headache, dizziness, vomiting, ataxia, dysmetria,
axial lateropulsion, and delayed coma. Superior
cerebellar infarcts can cause the rapid onset of
cerebellar swelling or hematoma producing
compression of the brainstem, hydrocephalus,
upward herniation of the cerebellum compressing the tectum at the diencephalic/mesencephalic junction, thus impairing upward gaze, or
downward herniation of the cerebellar tonsils.
Acute neurosurgical intervention to treat the hydrocephalus or evacuate the clot can be life-saving. In comparison to the other cerebellar arteries SCA infarction has the lowest incidence of
specific neuro-ophthalmological findings.
By comparison, AICA infarction has the most
frequent and specific pattern of neuro-ophthalmological findings and perhaps the fewest cerebellar hemisphere symptoms unless the ipsilateral PICA happens to be hypoplastic. Occlusion
of the anterior inferior cerebellar artery (AICA)
usually affects the lateral area of the lower pons,
causing ipsilateral cranial nerve dysfunctions
(trigeminal, abducens, facial and vestibular cranial nerves), ipsilateral Horner's syndrome, and
contralateral pain and temperature sensory loss
of the body regions below the neck. When the
pons is not involved, the AICA infarct causes a
pure vestibular syndrome.
Caudal cerebellar, or PICA territory, infarcts
cause vertigo, headache, vomiting, ataxia, and

401

delayed coma. Occlusion of the medial branch of
the PICA ocasionally involves the dorsolateral
medullary area and causes a modified Wallenberg syndrome with symptoms such as lateropulsion of saccadic eye movements, oblique saccades
on attempted vertical gaze, impaired smooth
pursuit, nystagmus, eyelid nystagmus, and skew
deviation.
Stroke mechanisms of cerebellar infarcts also
differ according to the vascular territories. 2"4-6
SCA and PICA territory infarctions are most frequently caused by embolic mechanisms, either
intraarterial (artery to artery) or cardiac. AICA
territory infarcts are usually caused by /n situ
thrombosis of the atherosclerotic intracranial
vessels. 2'3 Thus, precise localization of the vascular territory is now one of the essential steps in
evaluation of patients with cerebellar infarction.
We always refer to the parasagittal images to confirm the exact vascular territories, which vary
according to the angle of scanning on the conventional axial scans. It sometimes is difficult to
tell the exact vascular territory if only the axial
scan is available, as shown in Fig. 1A. The vascular distribution of lesions is often more apparent
on images obtained in the parasagittal or coronal
planes. For imaging of patients with suspected
cerebellar infarcts, we always obtain parasagittal
and coronal views as well as axial images to identify the vascular territory. Parasagittal sections
are better for the vertical distribution (superior
versus inferior cerebellar arteries) of the vascular
territory ofcerebellar infarction and coronal sections are better for visualizing the medial and
lateral branches of the SCA and PICA. T~weighted images are particularly helpful in identifying the affected vascular territories (Figs. 1B
and C).
On the parasagittal plane, the SCA territory
comprises the superior aspect of the cerebellar
hemisphere, the ipsilateral superior vermis, and
the largest part of the deep white matter, including most or all of the dentate nucleus (Figs. 1B
and 2). 8'~~The typical PICA territory includes the
entire inferoposterior surface of the cerebellar
hemisphere and the ipsilateral part of the inferior vermis. The posterior extent of the PICA distribution is the great horizontal fissure (or slightly above it in the semilunar lobule) near the
posterolateral margin of the cerebellum (Figs.
1C and 2). 9 The penetrating branches of PICA
reach only the inferior part of the deep cerebellar white matter, most of which is supplied by the
SCA. The course and vascular supply of the
AICA is quite variable, 9'll but it usually supplies

the lateroinferior part of the pons, the middle
cerebellar peduncle, and the floccular region.
The AICA also supplies the whole anterior surface of the cerebellar hemisphere.
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There has been no financial support for this work.
Corresponding authors: Chin-Sang Chung, MD, Neurology, Chungnam National Univ. Hospital, 640 Daesa-dong,
Joong-ku, Taejon, Korea 301-040, or Louis R. Caplan, MD,
Tufts-England Medical Center, 750 Washington St., Boston,
MA 02111.