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JUNE,
COMPUTERIZED VASCULAR By
PART
I:
BARRY
D.
TRANSVERSE LESIONS
OF
ARTERIOVENOUS PRESSMAN,
M.D., 0.
J. ROBERT DAVIS, M.D.
WASHINGTON,
C
OMPUTERIZED transverse tomography (CTT) of the brain is a recently developed method which allows non-invasive roentgenologic evaluation of intracranial disease. Since its inception, major attention has been given to the diagnosis and evaluation of tumors, clots, infarcts, yentricular size and orbital lesions. The purpose of this report is to discuss the application of CTT to the diagnosis and evaluation of intracerebral arteriovenous malformations. CTT as developed by EMI, Ltd. has been recently well described in the literature.’-4 It is important to note that the absorption coefficients of tissue are expressed by an arbitrary convention with that of water designated as 0, air as - oo and bone as + zoo. Intermediate absorption coefficients of importance include approximately + II to + 14 for white matter, + 17 to + 20 for gray matter and greater than +20 for calcium. The absorption coefficients for blood are not clearly established, although it is known that hematomas have absorption coefficients of greater than +20. Recent data indicate that the absorption coefficients of blood may range from approximately +6 to the mid 20’s and may be dependent on the hematocrit.5
CASE
I
(Fig.
history
than +20, sugA radionuclide brain scan was positive in both the dynamic and static phases and a cerebral angiogram demonstrated an arteriovenous malformation in the right occipital lobe. sorption
coefficients
gesting
a hematoma.
CASE
sented
after
was
of
right
year
of migraine
contiguous *
ton,
From
several
area the
of
Department
(Fig. 2). A 3 I year old female preprolonged headaches and stiff neck head trauma. The spinal fluid was
II
with minor
xanthochromic.
The
tively sorption
the initial CTT scan (ab+19 to +23). On repeat immediately after the injection
scan,
radiodense coefficients:
performed
splenial
showed
region
was
rela-
on
iothalamate,
increased
density The
this
(absorption radionuclide
cients: +20 to +30). scan was positive in this region and venous malformation of the splenial demonstrated on cerebral ‘angiography.
region
coeffibrain an arterioregion was
CASE III. A 28 year old female with a known right parietal arteriovenous malformation measuring approximately 3 cm. in size was studied by CTT. The lesion was indistinctly seen as a slightly lucent region (absorption coefficients:
to
+12
on the
+14)
A right
IV.
CASE
formation
in this
a relatively
dense
to
+20
+34)
scan. parietal year
region
with
arteriovenous
old female (absorption
surrounding
mal-
was seen
as
coefficients:
slight
lucency
CTT.
known splenial
(Fig. 3). A 13 year old female with a large right posterior thalamic and arteriovenous malformation was seen
later,
to have
a region
density
tion coefficients: +20 to +25) in this region on CTT. This became denser (absorption coefficients: +20 to +33) after the intravenous injection of 6o cc. of meglumine iothalamate. The
old
female
with
experienced
periorbital
evaluated
of greater
of 6o cc. of meglumine
a
CASE
sudden
When she the spinal fluid was xanthochromic. On CTT, there was a right occipital lucent region with absorption coefficients in the range of +5 to +9. There was a onset
M.D.,
OF CASES
A 6
I).
KIRKWOOD,
D.C.
on the
38 year
OF
MALFORMATIONS
and DAVID
REPORT
TOMOGRAPHY THE BRAIN*
1975
headaches.
days
increased of Radiology,
with
Neuroradiology
abSection,
D. C. 208
The
George
v
Washington
of increased
University
density
Medical
Center,
(absorp-
Washing-
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VOL.
No.
524,
Computerized
2
Transverse
radionuclide brain scan was positive. Several months later she was restudied when hemorrhage was suspected. CTT again revealed the lesion
but
density ventricles.
orrh
also
demonstrated
interpreted The
in
tricular
traven
as hemorrhage cerebrospinal fluid
into
the
was
Tomography:
(absorption
on
This
grand
17
mal
old
year
male
seizure.
tion ance
experienced
The
radionuclide
brain scan indicated a left frontal vascular lesion. A left frontal arteriovenous malformation was demonstrated with cerebral angiography. CTT was performed immediately after angiography and demonstrated a dense lesion (absorption coefficients: +2! to +4c) with contiguous lucency in the same location. The patient was not scanned in the absence of circulating contrast material. CASE
+23) of
in
A
the
high
following
absorption
72 year subdural
was
(absorption
meglumine
creased
4).
a chronic CTT there
of
the initial dense region formed
(Fig.
VII
suspected
left the
old female hematoma.
an ill-defined coefficients:
iothalamate coefficients
was On
slightly +59
parietal lobe. administration
to
CTT perof 6o cc.
demonstrated in
this
+20
radionuclide a large left malformation
to
+45).
Static
brain scans were parasagittal parietal was demonstrated
arteriography. viii
CASE
VI.
first
209
hema known
CASE
I
coefficients:
and dynamic positive and arteriovenous
agic.
his
Part
inregion
(Fig.
left
#{231}). This
cerebellar
was studied because and coordination.
marked
density
27
year
old
arteriovenous
of deterioration On CTT
(absorption
male
with
malformathere
in balwas
coefficients:
+20
to +40) in the left cerebellum which became greater (absorption coefficients: +20 to +6) after the administration of meglumine iothalamate. Massive hydrocephalus was also demon s t rated. DISCUSSION
In the formations
majority we
creased density coefficients) as normal Three 2
of
creased
The
of the arteriovenous have studied, relative (i.e., increased compared to
malin-
absorption surrounding
brain tissue was present (Table cases did show relative radiolucency, these also demonstrated areas of density.
possible
explanations
for
increased
i).
in-
B.
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210
D.
Pressman,
J.
R.
Kirkwood
and
D. 0.
Davis
JUNE,
1975
2. Case ii. (A) There is an area of ill-defined increased density (arrow) in the region of the splenium of the corpus callosum. (B) Obviously increased density is present in the same area after intravenous radiographic contrast material injection. The linear density behind this (arrow) is frequently seen in patients who have received contrast material, and is believed to be the straight sinus. (C) Splenial arteriovenous malformation seen on vertebral angiogram.
FIG.
density include:
of an arteriovenous (a) mural thrombus
within the formation;
malformation or calcification
vessels of the arteriovenous mal(b) the presence of an associated
hematoma (Case I); gliosis of the intervening
(c)
calcification brain tissue.6
thermore, if intravascular blood shown to have a high absorption
or Fur-
is in fact coefficient
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
3. Case
FIG.
v. (A)
tricle
(arrow).
mine
iothalamate.
multiple
draining
formation. indicative lower
An area
(B) ‘I’his
(D)
There veins. C’l’l’
of intraventricular transverse
plane.
of slightly
area
increased density is visualized is markedly increased in density after
is also
density
(C) Vertebral performed
after hemorrhage.
more
posteriorly,
angiography symptoms
‘l’he
which
demonstrates of
hemorrhage
arteriovenous
of the posterior of intravenous
to the right administration the
angiogram
a posterior reveal
malformation
showed
thalamic
to
density
again
ven-
megluan
area
arteriovenous
intraventricular
was
he
third
seen
of
mal(arrow)
on a scan
at a
B.
D.
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212
J.
Pressman,
R.
Kirkwood
and
D. 0.
Davis
-
JUNE,
1975
I
-
‘1
(greater
than
density
malformations
counted
ever,
the
+20),
teriovenous for
the
b
explanation
the
of may
large
for
blood
the
pool.
lucencies
the
ar-
be
acHow-
seen
in the 3 cases accounted for absorption
is in
fact
is difficult.
by the
coefficient
lower
than
It
large
might
blood
of intravascular
that
of
normal
also pool
be
if the blood
brain.
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
VOL.
524,
Computerized
No.
Transverse
Tomography:
Part
I
213
&
In the
all
patients
who
mine
iothalamate,
formation
of increased were scanned
were
scanned
administration
intravenous
the
was
easily
density. prior
of
after meglu-
arteriovenous visualized
as
an
istration scan
of
meglumine
performed
following
mal-
trast
material
injection
area
able
increase
in
In the patients who to and after the admin-
lesion
and
scan,
whereas
all
were three
iothalamate,
the
intravenous
con-
showed
the
a consider-
radiodensitv
very had
obvious been
of
the
on
the
questionably
J.
B. D. Pressman,
214
R.
Kirkwood namic
TABLE!
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
SUMMARY
Total
No. of Cases.
Cases
studied
contrast Cases
to
material
studied
contrast
RESULTS
after
7
intravenous
administration. contrast Dense Dense
and
Lucent
Lucent Definitely
abnormal
abnormal
2
I
2
I
4
2
-
Total
I
on the routine CTT. It is reasonable to assume that this increased radiodensity is accounted for by the circulating iodine with a resultant increase in the absorption coefficient of blood. Therefore, in a vascular lesion such as an arteriovenous malformation or a vascular tumor, an increase in the absorption coefficients on the CTT would be expected, as was seen in the cases presented herein. Scaning after the positive
administration terial
of intravenous
accordingly
may
contrast offer
very
that
high
rate
malformations. indicate
CTT
that
(that
unsuspected
this
of detection It is also the
regimen
is, without arteriovenous
iodine
of
in
a
routine
injection)
as
Barry The
intracranial
lesion
all
is nega-
D. Pressman, M.D. of Radiology George Washington University
Medical
Center
23rd
Street D. C.
20037
REFERENCES
J.
Computerized
I.
AMBROSE,
2.
ning (tomography): Brit. 7. Radiol., DAvis, D. 0., and tomography
ica, 3.
1974,
46,
1973,
axial
Clinical
scan-
application.
1023-1047.
PRESSMAN,
G. of
2.
Radiol.
B. D. Computerized C/in. North Amer-
297-313.
12,
HOUNSFIELD,
tion
transverse
Part
of brain.
axial scanning
N.
Computerized
transverse
(tomography) Part Brit. 7. Radiol., 1973,
system.
i.
Descrip46, ioi6-
1022.
P. F. J., Scoi-r, W. R., SCHNUR, J. A., DAVIS, K. R., and TAvERAS, J. M. Computerized axial tomography with EM! scanner. Radiology,
4. NEW,
110,
1974, .
Scorr,
W.
SCHNUR,
for
of
malformations
high as would be desirable for a simple non-invasive screening examination. Therefore, we recommend static and dyis not
scanning in CTT performed
a routine
a suspected
1975
Department
for arteriovenous true that our data
sensitivity
brain
in whom
Washington,
information
results
JUNE,
It is valuable to perform CTT in all patients with known arteriovenous malformations. Ventricular size and configuration as well as the appearance of the lesion will thereby be established. As in Case viii, the necessity of a ventricular shunt may be demonstrated. Furthermore, such data are useful for a baseline, so that the patients may be followed by CTT. In cases with recurrent seizures, increasing headaches or other suggestions of hemorrhage of the arteriovenous malformation, CTT will allow rapid demonstration of an intracerebral hematoma (Case i) or of an intraventricular hemorrhage (Case v). The need for arteriography or for surgery can thereby be rapidly determined. Of course, if another unsuspected lesion is the cause of the new symptomatology this may also be demonstrated.
90!
ma-
concerning the vascularity of a lesion visualized by routine CTT. In 3 cases, the arteriovenous malformation was difficult to recognize on the scan prior to the injection of contrast material (Table i). Therefore, all patients with the clinical suspicion of arteriovenous malformation or the history of subarachnoid hemorrhage should be given intravenous contrast agent and again scanned after a routine CTT has been performed. Our data demonstrate
Davis
tive.
intravenous
prior to intravenous administration.
Questionably
for
D. 0.
radionuclide
patients
______
administration.
material
Appearance material
OF
8
prior
and
STEHBENS,
Blood
Louis,
J.,
P. F.
NEW,
DAVIS,
J. A. Computerized
intracerebral
rhage. 6.
109-123.
R.,
and
Radiology, W. 1972,
ff2,
p. 5cI.
hemor-
73-80.
Pathology
C.
K. R., and tomography
intraventricular
1974,
E.
Vessels.
axial
V.
Mosby
of
the
Cerebral
Company,
St.
JUNE,
COMPUTERIZED VASCULAR By
PART
I:
BARRY
D.
TRANSVERSE LESIONS
OF
ARTERIOVENOUS PRESSMAN,
M.D., 0.
J. ROBERT DAVIS, M.D.
WASHINGTON,
C
OMPUTERIZED transverse tomography (CTT) of the brain is a recently developed method which allows non-invasive roentgenologic evaluation of intracranial disease. Since its inception, major attention has been given to the diagnosis and evaluation of tumors, clots, infarcts, yentricular size and orbital lesions. The purpose of this report is to discuss the application of CTT to the diagnosis and evaluation of intracerebral arteriovenous malformations. CTT as developed by EMI, Ltd. has been recently well described in the literature.’-4 It is important to note that the absorption coefficients of tissue are expressed by an arbitrary convention with that of water designated as 0, air as - oo and bone as + zoo. Intermediate absorption coefficients of importance include approximately + II to + 14 for white matter, + 17 to + 20 for gray matter and greater than +20 for calcium. The absorption coefficients for blood are not clearly established, although it is known that hematomas have absorption coefficients of greater than +20. Recent data indicate that the absorption coefficients of blood may range from approximately +6 to the mid 20’s and may be dependent on the hematocrit.5
CASE
I
(Fig.
history
than +20, sugA radionuclide brain scan was positive in both the dynamic and static phases and a cerebral angiogram demonstrated an arteriovenous malformation in the right occipital lobe. sorption
coefficients
gesting
a hematoma.
CASE
sented
after
was
of
right
year
of migraine
contiguous *
ton,
From
several
area the
of
Department
(Fig. 2). A 3 I year old female preprolonged headaches and stiff neck head trauma. The spinal fluid was
II
with minor
xanthochromic.
The
tively sorption
the initial CTT scan (ab+19 to +23). On repeat immediately after the injection
scan,
radiodense coefficients:
performed
splenial
showed
region
was
rela-
on
iothalamate,
increased
density The
this
(absorption radionuclide
cients: +20 to +30). scan was positive in this region and venous malformation of the splenial demonstrated on cerebral ‘angiography.
region
coeffibrain an arterioregion was
CASE III. A 28 year old female with a known right parietal arteriovenous malformation measuring approximately 3 cm. in size was studied by CTT. The lesion was indistinctly seen as a slightly lucent region (absorption coefficients:
to
+12
on the
+14)
A right
IV.
CASE
formation
in this
a relatively
dense
to
+20
+34)
scan. parietal year
region
with
arteriovenous
old female (absorption
surrounding
mal-
was seen
as
coefficients:
slight
lucency
CTT.
known splenial
(Fig. 3). A 13 year old female with a large right posterior thalamic and arteriovenous malformation was seen
later,
to have
a region
density
tion coefficients: +20 to +25) in this region on CTT. This became denser (absorption coefficients: +20 to +33) after the intravenous injection of 6o cc. of meglumine iothalamate. The
old
female
with
experienced
periorbital
evaluated
of greater
of 6o cc. of meglumine
a
CASE
sudden
When she the spinal fluid was xanthochromic. On CTT, there was a right occipital lucent region with absorption coefficients in the range of +5 to +9. There was a onset
M.D.,
OF CASES
A 6
I).
KIRKWOOD,
D.C.
on the
38 year
OF
MALFORMATIONS
and DAVID
REPORT
TOMOGRAPHY THE BRAIN*
1975
headaches.
days
increased of Radiology,
with
Neuroradiology
abSection,
D. C. 208
The
George
v
Washington
of increased
University
density
Medical
Center,
(absorp-
Washing-
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
VOL.
No.
524,
Computerized
2
Transverse
radionuclide brain scan was positive. Several months later she was restudied when hemorrhage was suspected. CTT again revealed the lesion
but
density ventricles.
orrh
also
demonstrated
interpreted The
in
tricular
traven
as hemorrhage cerebrospinal fluid
into
the
was
Tomography:
(absorption
on
This
grand
17
mal
old
year
male
seizure.
tion ance
experienced
The
radionuclide
brain scan indicated a left frontal vascular lesion. A left frontal arteriovenous malformation was demonstrated with cerebral angiography. CTT was performed immediately after angiography and demonstrated a dense lesion (absorption coefficients: +2! to +4c) with contiguous lucency in the same location. The patient was not scanned in the absence of circulating contrast material. CASE
+23) of
in
A
the
high
following
absorption
72 year subdural
was
(absorption
meglumine
creased
4).
a chronic CTT there
of
the initial dense region formed
(Fig.
VII
suspected
left the
old female hematoma.
an ill-defined coefficients:
iothalamate coefficients
was On
slightly +59
parietal lobe. administration
to
CTT perof 6o cc.
demonstrated in
this
+20
radionuclide a large left malformation
to
+45).
Static
brain scans were parasagittal parietal was demonstrated
arteriography. viii
CASE
VI.
first
209
hema known
CASE
I
coefficients:
and dynamic positive and arteriovenous
agic.
his
Part
inregion
(Fig.
left
#{231}). This
cerebellar
was studied because and coordination.
marked
density
27
year
old
arteriovenous
of deterioration On CTT
(absorption
male
with
malformathere
in balwas
coefficients:
+20
to +40) in the left cerebellum which became greater (absorption coefficients: +20 to +6) after the administration of meglumine iothalamate. Massive hydrocephalus was also demon s t rated. DISCUSSION
In the formations
majority we
creased density coefficients) as normal Three 2
of
creased
The
of the arteriovenous have studied, relative (i.e., increased compared to
malin-
absorption surrounding
brain tissue was present (Table cases did show relative radiolucency, these also demonstrated areas of density.
possible
explanations
for
increased
i).
in-
B.
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210
D.
Pressman,
J.
R.
Kirkwood
and
D. 0.
Davis
JUNE,
1975
2. Case ii. (A) There is an area of ill-defined increased density (arrow) in the region of the splenium of the corpus callosum. (B) Obviously increased density is present in the same area after intravenous radiographic contrast material injection. The linear density behind this (arrow) is frequently seen in patients who have received contrast material, and is believed to be the straight sinus. (C) Splenial arteriovenous malformation seen on vertebral angiogram.
FIG.
density include:
of an arteriovenous (a) mural thrombus
within the formation;
malformation or calcification
vessels of the arteriovenous mal(b) the presence of an associated
hematoma (Case I); gliosis of the intervening
(c)
calcification brain tissue.6
thermore, if intravascular blood shown to have a high absorption
or Fur-
is in fact coefficient
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
3. Case
FIG.
v. (A)
tricle
(arrow).
mine
iothalamate.
multiple
draining
formation. indicative lower
An area
(B) ‘I’his
(D)
There veins. C’l’l’
of intraventricular transverse
plane.
of slightly
area
increased density is visualized is markedly increased in density after
is also
density
(C) Vertebral performed
after hemorrhage.
more
posteriorly,
angiography symptoms
‘l’he
which
demonstrates of
hemorrhage
arteriovenous
of the posterior of intravenous
to the right administration the
angiogram
a posterior reveal
malformation
showed
thalamic
to
density
again
ven-
megluan
area
arteriovenous
intraventricular
was
he
third
seen
of
mal(arrow)
on a scan
at a
B.
D.
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
212
J.
Pressman,
R.
Kirkwood
and
D. 0.
Davis
-
JUNE,
1975
I
-
‘1
(greater
than
density
malformations
counted
ever,
the
+20),
teriovenous for
the
b
explanation
the
of may
large
for
blood
the
pool.
lucencies
the
ar-
be
acHow-
seen
in the 3 cases accounted for absorption
is in
fact
is difficult.
by the
coefficient
lower
than
It
large
might
blood
of intravascular
that
of
normal
also pool
be
if the blood
brain.
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
VOL.
524,
Computerized
No.
Transverse
Tomography:
Part
I
213
&
In the
all
patients
who
mine
iothalamate,
formation
of increased were scanned
were
scanned
administration
intravenous
the
was
easily
density. prior
of
after meglu-
arteriovenous visualized
as
an
istration scan
of
meglumine
performed
following
mal-
trast
material
injection
area
able
increase
in
In the patients who to and after the admin-
lesion
and
scan,
whereas
all
were three
iothalamate,
the
intravenous
con-
showed
the
a consider-
radiodensitv
very had
obvious been
of
the
on
the
questionably
J.
B. D. Pressman,
214
R.
Kirkwood namic
TABLE!
Downloaded from www.ajronline.org by 118.99.164.113 on 06/23/16 from IP address 118.99.164.113. Copyright ARRS. For personal use only; all rights reserved
SUMMARY
Total
No. of Cases.
Cases
studied
contrast Cases
to
material
studied
contrast
RESULTS
after
7
intravenous
administration. contrast Dense Dense
and
Lucent
Lucent Definitely
abnormal
abnormal
2
I
2
I
4
2
-
Total
I
on the routine CTT. It is reasonable to assume that this increased radiodensity is accounted for by the circulating iodine with a resultant increase in the absorption coefficient of blood. Therefore, in a vascular lesion such as an arteriovenous malformation or a vascular tumor, an increase in the absorption coefficients on the CTT would be expected, as was seen in the cases presented herein. Scaning after the positive
administration terial
of intravenous
accordingly
may
contrast offer
very
that
high
rate
malformations. indicate
CTT
that
(that
unsuspected
this
of detection It is also the
regimen
is, without arteriovenous
iodine
of
in
a
routine
injection)
as
Barry The
intracranial
lesion
all
is nega-
D. Pressman, M.D. of Radiology George Washington University
Medical
Center
23rd
Street D. C.
20037
REFERENCES
J.
Computerized
I.
AMBROSE,
2.
ning (tomography): Brit. 7. Radiol., DAvis, D. 0., and tomography
ica, 3.
1974,
46,
1973,
axial
Clinical
scan-
application.
1023-1047.
PRESSMAN,
G. of
2.
Radiol.
B. D. Computerized C/in. North Amer-
297-313.
12,
HOUNSFIELD,
tion
transverse
Part
of brain.
axial scanning
N.
Computerized
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(tomography) Part Brit. 7. Radiol., 1973,
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i.
Descrip46, ioi6-
1022.
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Scorr,
W.
SCHNUR,
for
of
malformations
high as would be desirable for a simple non-invasive screening examination. Therefore, we recommend static and dyis not
scanning in CTT performed
a routine
a suspected
1975
Department
for arteriovenous true that our data
sensitivity
brain
in whom
Washington,
information
results
JUNE,
It is valuable to perform CTT in all patients with known arteriovenous malformations. Ventricular size and configuration as well as the appearance of the lesion will thereby be established. As in Case viii, the necessity of a ventricular shunt may be demonstrated. Furthermore, such data are useful for a baseline, so that the patients may be followed by CTT. In cases with recurrent seizures, increasing headaches or other suggestions of hemorrhage of the arteriovenous malformation, CTT will allow rapid demonstration of an intracerebral hematoma (Case i) or of an intraventricular hemorrhage (Case v). The need for arteriography or for surgery can thereby be rapidly determined. Of course, if another unsuspected lesion is the cause of the new symptomatology this may also be demonstrated.
90!
ma-
concerning the vascularity of a lesion visualized by routine CTT. In 3 cases, the arteriovenous malformation was difficult to recognize on the scan prior to the injection of contrast material (Table i). Therefore, all patients with the clinical suspicion of arteriovenous malformation or the history of subarachnoid hemorrhage should be given intravenous contrast agent and again scanned after a routine CTT has been performed. Our data demonstrate
Davis
tive.
intravenous
prior to intravenous administration.
Questionably
for
D. 0.
radionuclide
patients
______
administration.
material
Appearance material
OF
8
prior
and
STEHBENS,
Blood
Louis,
J.,
P. F.
NEW,
DAVIS,
J. A. Computerized
intracerebral
rhage. 6.
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and
Radiology, W. 1972,
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Pathology
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K. R., and tomography
intraventricular
1974,
E.
Vessels.
axial
V.
Mosby
of
the
Cerebral
Company,
St.
