Surg Neurol
1993 ;39 ;385-91

385

Spontaneous Regression of Intracranial Arteriovenous Malformation
Franco Marconi, M .D., Giuliano Parenti, M.D., and Michele Puglioli, M .D.
Institute of Neurosurgery (F.M ., G .P .), University of Pisa ; and Department of Neuroradiology (M .P .), Hospital S . Chiara,
Pisa, Italy

Marconi F, Parent' G, Puglioli M . Spontaneous regression of
intracranial arteriovenous malformation. Surg Neurol
1993 ;39 :385-91 .

Spontaneous regression of an arteriovenous malformation
is rare . When complete or partial regression occurs, an
associated factor is usually involved, such as intracranial
hemorrhage, surgery, radiation therapy, or a new neurological deficit . Another case in which the resolution was
totally spontaneous is presented here . We discuss the importance of transcranial doppler revealing the hemodynamic changes in the cerebral arteries in the presence
of an AVM and when the latter is thrombosed . Several
mechanisms for regression are considered, and we focus
on the dissection of the afferent vessel, pointing out the
role of such an event in the natural history of AVM .
WORDS : Arteriovenous malformation ;
thrombosis ; Transcranial doppler
KEY

Spontaneous

Introduction
Spontaneous regression of an arteriovenous malformation (AVM) without intracranial hemorrhage, embolic
phenomena of the afferent vessels, coagulopathies, radiation therapy, traumas, or appearance of a neurological
deficit is a rare event [24,37,44] .
A case of spontaneous and complete disappearance of
an intracranial AVM 20 years after diagnosis is reported
here . The regression can be confirmed by means of
angiographic, tomographic, and doppler sonographic
studies .
We emphasize the importance of transcranial doppler
(TCD) in the evaluation of the hemodynamic modifications of the AVMs [22] . Analyzing the possible pathogenic mechanisms reported in literature, we point out
the likelihood of such an event and its role in the natural
history of AVM .

Addreis reprint requeststa .. Dr . Franco Marconi, Istituto di Neurochirurgia, University di Pisa, Via Roma, 67, 56100 Pisa, Italy .
Received August 26, 1991 ; accepted December 9, 1992 .
0 1991 by Elsevier Science Publishing Co ., Inc.

Case Report
B.B ., a 22-year-old man hospitalized in our institute
for the first time, had been experiencing generalized
seizures with a frequency of two to three times a week
for 3-4 months . Neurological examination was negative .
Left carotid angiography showed an AVM of 3 x 2 cm
(medium-size AVM) [44] in the left rolandic area fed
by the sylvian artery (MCA) of the same side (Figure 1) .
Due to location and size of the angioma, a conservative treatment was chosen and the patient was discharged
with antiepileptic treatment (phenobarbital 200 mg/
day) . "Minor" seizures such as absences were subsequently reported, and, therefore, phenytoin (150 mg/
day) was added to the treatment .
At age 36 (14 years later), the patient suffered a fur
ther generalized seizure and was readmitted to a hospital .
At that time angiography was carried out : the result
showed almost no change when compared to the previous one . The patient was discharged with clonazepam
(1 mg daily) added to his treatment and no further major
or minor seizures occurred .
For the following 5 years the patient underwent periodic controls with computed-tomographic (CT) scan and
TCD . Hemodynamic study by TCD regularly revealed
high-flow velocity on both the left MCA and left anterior
cerebral artery (ACA) with vascular resistance (pulsatility index) decreased compared to normal values [22] .
The flow direction on the A1 segment of left ACA is
inverted, whereas the direction of contralateral flow appears normal but with increased flow velocity . The hyperpnea test did not show any further substantial velocity
modifications on the vessels examined (Figure 2) .
At 41 years of age the last control of the CT scan
exam revealed an area of subcortical impregnation in
the left rolandic site with an irregular and partially serpiginous feature (Figure 3) .
At age 42, 10 months after the last control, the patient
reduced his antiepileptic treatment on his own initiative
and was consequently rehospitalized due to the reappearance of generalized seizures . Neurological examination was still negative . CT scan without contrast medium
did not reveal any hemorrhage . A TCD control revealed
0090-3019'93!36 .00

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A

Surg Neurol
1993 ;39 :385-91

B
Figure 1 . (A, B) The left carotid angiography showing an AVM in the left rolandic area fed by a hypertropbic sylvian artery of the same side .

Figure 2 . The TCD exam shows increased floe velocities
(Vm) and decreased pulsatility index (PI) values on the left
MCA ln.v. Vm 65 .6 ± 8 .4 cml sec. P1 0 .75 ± 0 .131 and
on the ACA (n .v . Vm 46 .6 ± 10 .2 cmlset PI 0 .68- 0 .17)
of the same side . The flow direction on A1 segment of the
left ACA is inverted.

Surg Neurol
1993 ;39 :385-91

Spontaneous regression of AVM

387

Figure 3 . (A, B) The CT scan reveals an
area of subcortical impregnation in the left
prerolandic site, attributable to the AVM nidus . with irregular and partially serpiginous
feature and double images of vessel impregnation which represent the drainage veins toward the superior longitudinal sinus,

A

B

normal values of mean flow velocity (Vm) and pulsatility
index (PI) on the left MCA and ACA (Figure 4) . With
the presence of such TCD values, he underwent cerebral
angiography through the femoral artery which showed
the complete regression of the AVM . A gradually taper-

Figure 4. The TCD exam shows normal values of Vm and PI on the left
MCA and ACA .

ing occlusion of the large feeding branch of the MCA
near the nidus of the angioma was, in fact, present (Figure 5) . He was then discharged with antiepileptic treatment consisting of 200 mg of phenobarbital, 300 mg of
phenytoin, and 1 .5 mg of clonazepam daily .
At 10 months following his readmission to hospital,
TCD exam confirmed normal values of Vm and PI on
the left MCA and ACA . A tomographic aspect of a
thrombosed AVM [2,3,26,36) was evident in the CT
scan (Figure 6) . Magnetic resonance imaging (MRI) carried out after 12 months showed in the angioma a small
area of linear or ribbon-like aspect with a hypointense
signal in every sequence examined (Figure 7) . With antiepileptic treatment, the seizures were controlled .
Discussion
The incidence of partial or complete spontaneous regression in the natural history of AVM is uncertain ; according to other authors the percentage value is between
2% and 3% [29,37) .
Moreover a complete spontaneous regression has
been reported for both intracranial and dural AVM
[7,13,21] .
Most reported cases of spontaneous regression of
AVM have occurred in adults between the ages of 30
and 60 years, at intervals ranging from 6 months to 21
years after diagnosis; in most cases the regression has
been acute, whereas a gradual regression (angiographic)
of AVM is seen in others [44) .
In the literature spontaneous regression has been explained by several mechanisms : Pool and Potts suggest
that arteriosclerosis of the feeding vessels could be a
possible cause for the spontaneous regression of AVM
[32). Sukoff et al ascribe the disappearance of AVM,
in the reported case, to the acute occlusion of the sylvian

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Surg Neurol
1993 ;39 : 3 85-91

Figure 5 . (A, B) The cerebral angiography shows the complete regression

of AVM . The feeding vessel of AVM seems to be progressively decreased in
caliber (arrows)
.

artery on an embolic basis [38} . Omoyola et al . state
that the partial regression of AVM, in one patient out
of the three reported, is a consequence of the embolism
starting from an associated thrombosed aneurysm of the
feeding vessels [281 . Eisenman et al thought that intra-

Figure 6 . CT scan before and after infusion of contrast medium: the

characteristic impregnation relative to AVM is no longer evident in the left
precentral frontal site.

Marconi et al

cranial hemorrhage could lead to the disappearance of
an AVM by exerting a compressive force on the AVM
directly by the hematoma or indirectly through local
edema. The compression reducing the blood flow in the
feeding vessels can, in fact, favor thrombosis [6] . Lakke
reports a gradual reduction in the size of the afferent
vessels observed on serial angiograms . The author hypothesizes that frequent microbleedings with the consequent organization and gliosis of the clot caused kinking
of the feeding vessels facilitating thrombosis of the AVM
[16] . Conforti suggests that the probability of thrombosis of the dural venous sinuses which has followed a
phlebostasis due to an increase of intracranial pressure,
could be a mechanism of spontaneous regression of a
dural AVM [4) .
However, reviewing the cases reported in the literature, the exact mechanisms involved in spontaneous
AVM regression are uncertain ; the most common is
almost certainly that of compression of the vascular nid us
from intracranial hemorrhage, either when it is an intracranial hematoma [4,18,20,21,24,30,41] or a subarachnoid hemorrhage [6,7,15,16,40} .
On the other hand, other authors say that a total
spontaneous regression can occur without hemorrhage
and thrombotic phenomena [28,29,33,34,421 . In such
cases the partial or total regression of AVM may be
demonstrated as an incidental finding on CT or cerebral
angiography, either of which is usually carried out for
persistent headache or intracranial epileptic seizures .
Even in our patient, the complete disappearance of
an AVM diagnosed about 20 years previously was an
incidental finding that occurred during a dopplersonographic and angiographic control for seizures . Such a

Surg Neurol
1993 ;39 :385-91

Spontaneous regression of AVM

A

389

B

Figure 7 . (A, B) Magnetic resonance DP- and T2-weighted images (SE . TRITE 1876/30 and TRITE 18761100) : on the left precentral frontal region

with sulcal distribution a small long area of hypointense signal, prevalently in T2-weighted images, is present (arrowsi . Vascular-type images cannot be
documented.

phenomenon, in the absence of any other "favoring factor" should be considered a spontaneous regression .
It is difficult to specify the mechanism by which AVM
thrombosis occurred and only hypotheses can be suggested . The CT scan without contrast medium performed on the patient upon his admission to the hospital
for epileptic seizures did not give any signs of hemorrhage ; angiography revealed a thrombosed AVM . About
10 months prior to this, the AVM had very clearly
showed up on both the CT scan and TCD . During the
interval of time following these examinations, no neurologic symptomatology was observed to make us suspect
hemodynamic modifications in AVM . As a matter of fact,
once the seizures had been controlled by antiepileptic
treatment and once CT scan had ruled out the possibility
of hemorrhage, angiographic study would not have been
performed to verify a disappearance of the arteriovenous
shunt if TCD had not revealed a normal velocity flow
on the left MCA and ACA which fed the AVM .
Nevertheless, MR imaging carried out 12 months
after this period of seizures showed a small area, linear
in aspect, and of hypointense signal in every sequence
examined that could be interpreted as a hemorrhage in
the AVM . Such a hemorrhage, however, it came about,
must have been of a small dimension considering that
no neurologic manifestations or even headache were
reported . However, it must be noted that the hemorrhage evolves toward a "cyst-like" MR aspect [10] .
Moreover the small hypointense area revealed by MR
imaging, due to hemosiderin deposits, could be mistaken
for two other entities : dense calcifications and flow void
(lack of signal) in vessels [10] . Calcium deposits are
excluded by CT scan, and flow void is excluded by angiographic findings .
The angiographic picture of a progressive narrowing
of the feeding vessel lumen up to its obstruction in the
nidus of the angioma is very interesting for a mechanism

of feeding vessel dissection . This pathogenic mechanism
is quoted elsewhere by various authors, who point out
in the "hemodynamic stress" that the angioma vessels
must bear the primum movens of the histopathological
alterations of the walls themselves . The high blood flow,
often characterized by turbulent movement, would, as
a matter of fact, determine hypertrophy and successive
vessel dilatation 11,8,12,23,25 1 . Stress would also imply
endothelial alterations and dissection of the intima with
consequent stenosis, vessel obstruction, or the formation of aneurysms on the afferent vessel to the angioma
[11,17,24,35,39] . This case is interesting not only because of the phenomenon of spontaneous thrombosed
AVM of such dimension and with such high blood flow
in the feeding vessels, but also because it underlines the
usefulness ofTCD in the evaluation of the hemodynamic
situation of an arteriovenous shunt and its eventual modifications [14,19] . TCD examination had already proved
to be useful for measuring increases in flow velocity on
the left MCA and ACA (in which the flow was inverted)
for the presence of shunt with reduced cerebrovascular
resistance which were not modifiable at hyperpnea due
to the vasoparalysis phenomena [22] . This hemodynamic situation remained unaltered for 5 years at least .
TCD exam, however, proved to be more useful in revealing normalization in flow velocity on the vessels that fed
the AVM to such an extent as to make us suspect a
thrombosis of the shunt, and suggest that angiographic
study should be performed to confirm the phenomenon .
Without the TCD exam finding the normalization of
the right hemisphere's cerebral hemodynamic situation,
after the control of the seizures and exclusion of hemorrhage at CT scan, there would have been no reason to
perform angiography .
The almost complete disappearance of epileptic seizures after the setup of the treatment, taking into account the rarity of bleeding in the natural history of

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1993 ;39 :385-91

thrombosed AVM [44], led us to decide against surgical
removal as suggested by Wharen et al for these cases
with intractable seizure disorders [421 .
On the other hand the criteria for advising surgery
for an arteriovenous malformation must prescind from
the possibility of spontaneous regression which is a rare
event ; the age and general status of the patient as well
as the site and size of the AVM are important [5,6,9,27,
31,43] .
We considered it important to report this case because
a careful study of the spontaneous regression can help
establish the possible treatment . Additionally, in the follow-up of patients with a non-treated AVM, the importance of TCD, a bloodless and repeatable exam, for the
evaluation of spontaneous regression is pointed out .
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