J Neurosurg 100:820–824, 2004

Surgical considerations regarding giant dilations of the
perivascular spaces
PAUL HOUSE, M.D., KAREN L. SALZMAN, M.D., ANNE G. OSBORN, M.D.,
JOEL D. MACDONALD, M.D., RANDY L. JENSEN, M.D., PH.D.,
AND WILLIAM T. COULDWELL, M.D., PH.D.
Departments of Neurological Surgery and Radiology, University of Utah Health Sciences Center, Salt
Lake City, Utah
Object. Dilations of brain perivascular spaces (PVSs), also known as Virchow–Robin spaces, are routinely identified on
magnetic resonance imaging studies of the brain and recognized as benign normal variants. Giant dilations occur only
rarely and can be easily misdiagnosed as central nervous system tumors. The relevant surgical literature was reviewed to
help establish indications for surgical intervention in these typically benign lesions.
Methods. Giant dilations of the PVSs in 12 patients who had undergone surgery for several different indications were
identified. Both clinical and radiographic presentations of these patients were reviewed along with the surgical procedures.
Conclusions. Dilations of the PVSs can become giant lesions that may necessitate surgical intervention to relieve mass
effect or hydrocephalus. The relationship of these lesions to neurological symptoms such as tremor and seizures remains
unclear.

KEY WORDS • perivascular space • Virchow–Robin space

T

HE PVSs in the brain are complex pia mater–lined

areas that follow penetrating arteries and arterioles
into the cerebral cortex. They are lined by a single
layer of pia in the cerebral hemispheres and two layers of
pia along the lenticulostriate arteries.17 The spaces are usually small (1–2 mm in diameter), but can be easily visualized on thin-section T2-weighted MR imaging studies.19
Perivascular spaces are filled with interstitial fluid, not CSF,
and are thought to be a major pathway for interstitial fluid egress from the brain.21 Furthermore, they play a role in
immunological regulation because they harbor resident microglia.13
Giant dilations of the PVS are unusual anatomical variants that can be misdiagnosed as central nervous system tumors. Often these dilations are found in patients with nonspecific neurological complaints. The relationship between
tumefactive PVS dilations and a variety of neurological
symptoms has yet to be firmly established. Here, we reviewed the surgical literature regarding PVS dilations with
an emphasis on the indications for intervention.
Clinical Material and Methods
The clinical, radiological, and pathological records of patients with giant dilations of the PVS were reviewed. We
identified 12 patients harboring tumefactive dilations of the
PVS who had undergone a variety of surgical procedures,
and these patients constitute the largest group of such patients in the medical literature to date (Table 1). Most (11
patients) had undergone either primary treatment or review
Abbreviations used in this paper: CSF = cerebrospinal fluid;
FLAIR = fluid-attenuated inversion-recovery; MR = magnetic resonance; PD = Parkinson disease; PVS = perivascular space; VP =
ventriculoperitoneal.

820

at the University of Utah Hospital at the request of the treating physicians. One additional patient was treated primarily at the University of Southern California Hospital. All patients had dilations of at least 1.5 cm in diameter, which
produced local mass effect.
Patients, seven of whom were men, ranged in age from
21 to 57 years, with a mean age of 42 years. Dilated PVSs
were located in the thalamus, midbrain, and subcortical
white matter. Lesions were situated in the left hemisphere in
seven patients, right hemisphere in three, and both hemispheres in two. The majority of patients presented with
headaches, and eight had obstructive hydrocephalus.
Six patients underwent biopsy. Eight patients required
CSF diversion because of hydrocephalus. Three patients
underwent VP shunt placement, whereas a fourth experienced a cystoperitoneal shunt placement. Four patients underwent ventriculocisternostomy. One patient had a cyst
catheter-reservoir implanted to enable serial aspiration. Follow-up imaging studies from 2 to 9 years after the initial diagnosis were available in all patients. No enlargement of
a cystic dilation was noted, except in the two patients described later.
Illustrative Cases
Case 1

This 39-year-old man presented with a 1-year history of
severe headaches, which had become progressively more
debilitating. These headaches initiated behind the left eye
and evolved to encompass the entire head. Additionally, the
patient experienced a coarse tremor of the right upper and
lower extremities. Magnetic resonance images of the brain
revealed a nonenhancing cystic lesion in the left insula and
basal ganglia together with significant local mass effect
(Fig. 1).
J. Neurosurg. / Volume 100 / May, 2004

Giant dilations of the perivascular spaces
TABLE 1
Characteristics in 12 patients with giant dilations of the PVS
Case
No.

Age (yrs),
Sex

Primary
Symptom(s)

1

39, M

headache

biopsy

2
3
4

35, M
57, M
44, F

biopsy, ventriculocisternostomy
biopsy, ventriculocisternostomy
ventriculocisternostomy

5

46, M

headache, poor vision
lethargy, poor memory
poor balance,
poor concentration
headache

6
7
8
9

56, F
40, M
21, M
47, F

headache, poor memory
headache
seizure
headache

fenestration, shunt placement
biopsy
biopsy
shunt placement

10
11
12

35, M
49, F
31, F

headache, confusion
headache
headache, hemiparesis

shunt placement
ventriculocisternostomy
cyst catheter aspiration

Procedure(s) Performed

biopsy

Craniotomy was performed for cyst fenestration and diagnostic purposes. A healthy small artery could be identified centrally in some of the cysts. The patient experienced
resolution of headaches and improvement in tremor (Fig.
2). Histological analysis showed cystic dilations of healthy
brain tissue with some reactive gliosis at the cyst edges.
Five months following his surgery the patient was involved in a motor vehicle accident and experienced a recurrence of the headaches. Brain imaging studies revealed reexpansion of the fenestrated cysts with some hemorrhage.
Along with the headaches, the patient also developed some
intermittent dystonic movements of the right arm. Endoscopically assisted placement of a VP shunt was performed
because of the symptomatic enlargement of the cysts. The
patient again experienced relief of the headaches and resolution of the movement abnormalities. He remains asymptomatic 1 year following shunt placement.

PVS
Location

thalamus,
white matter
midbrain
midbrain
midbrain
midbrain,
thalamus
thalamus
midbrain
white matter
thalamus,
midbrain
thalamus
thalamus
midbrain

Laterality

Hydrocephalus

lt

no

lt
lt
rt

yes
yes
yes

rt

no

lt
rt
lt
bilat

yes
yes
no
yes

bilat
lt
lt

yes
yes
no

Discussion
Dilations of the PVS could be visualized on T2-weighted
MR imaging in up to 95% of patients in a recent study.19 It
has been asserted that PVS dilations are a normal part of aging and occur primarily in the elderly.9 Such dilations have
been noted in nearly 30% of healthy children, however,

Case 6

This 56-year-old woman presented on multiple occasions
to local emergency rooms and to her primary physician with
a variety of complaints. She had suffered headaches and
gait instability. These were accompanied by new memory
and intermittent speech difficulties. She also had a history
of panic attacks and depression. Her symptoms were believed to be nonspecific and were originally managed using
medical therapy. After several episodes of worsening symptoms, brain imaging studies were performed.
Both computerized tomography scanning and MR imaging studies revealed that the patient had a left posterior thalamic cyst causing obstructive hydrocephalus (Fig. 3). The
patient underwent cyst fenestration via a supracerebellar,
subtentorial approach. Initially, she had a good response to
surgery; 4 months later, however, many of her symptoms
returned. Imaging studies demonstrated that the cyst had returned to its original size with resultant hydrocephalus. The
patient therefore underwent placement of a ventriculoatrial
shunt. Again, initially she responded well, with improvement in her hydrocephalus. Unfortunately, despite this improvement in the hydrocephalus, some of her symptoms,
including headache and dizziness, persisted.
J. Neurosurg. / Volume 100 / May, 2004

FIG. 1. Case 1. Axial FLAIR-weighted (upper left), T2-weighted
(upper right), and contrast-enhanced T1-weighted (lower left) and
coronal contrast-enhanced T1-weighted (lower right) MR images
revealing the tumefactive dilations of the PVS in the left basal ganglia and insula. Note that the lesion follows CSF signal intensity and
does not enhance following administration of a contrast agent. This
large multilocular lesion produces mass effect on the basal ganglia,
thalamus, and third ventricle. The thin rim of high signal on the T2and FLAIR-weighted images surrounding the enlarged PVS is consistent with the small amount of gliosis identified on histological examination.

821

P. House, et al.

FIG. 2. Case 1. Axial T1- (left) and T2-weighted (right) MR images obtained following cyst biopsy and fenestration, demonstrating
greatly reduced mass effect with reexpansion of the third ventricle
to normal dimensions.

and have been associated with normal development, even in
macrocephalic children.2,18 Small dilations of the PVS are
now considered to be a normal imaging variant with a benign prognosis. In fact, small PVS dilations are now visualized in nearly all patients when 3-tesla imaging is used
(AG Osborn, unpublished data).
Case reports of extreme dilations of the PVSs have been
published previously and will be described later. Often the
cases of tumefactive PVS dilation come to surgical attention because of their unusual appearance and concerns regarding possible pathological features. A variety of indications for surgical intervention exist in association with these
lesions. To help clarify these issues, we review the surgical
indications regarding treatment of hydrocephalus, treatment
of tremor or seizure, and the need to perform biopsy.
Treatment of Hydrocephalus

Cystic dilation of the PVS within the midbrain can cause
obstructive hydrocephalus by limiting CSF flow through
the cerebral aqueduct. In 1983 Poirier, et al.,15 described a
54-year-old patient with mesencephalic lacunae who had
experienced neurological deterioration with symptoms similar to those in normal-pressure hydrocephalus, including
progressive gait disturbance, incontinence, and worsening
mental status. Improvement occurred after ventriculocisternostomy. Similarly, Homeyer, et al.,10 reported on a 42year-old man who had experienced worsening headache in
association with 10 years of progressive diplopia and paresthesias in both upper extremities. On MR imaging, PVS
dilations in the right mesencephalon and thalamus with
resultant hydrocephalus were visualized. Eventually, a VP
shunt was placed, with improvement in the patient’s paresthesias and headaches, although his diplopia remained. No
change in the PVS dilation was noted on MR imaging studies performed at 6 months.
As these two cases illustrate, patients become symptomatic from hydrocephalus very slowly and the symptoms
may mimic those that occur in normal-pressure hydrocephalus. More recent literature confirms these initial reports.
Mascalchi, et al.,14 have described two patients. The first, a
58-year-old woman, presented with a decreased mental status (as documented on the Mini-Mental State Examination),
Parinaud phenomena, gait difficulty, and rubral tremor. All
symptoms improved after a shunt was placed to relieve
hydrocephalus. The second patient, a 55-year-old man, re822

FIG. 3. Case 6. Coronal T2- (upper left) and FLAIR-weighted
(upper right) and contrast-enhanced T1-weighted (lower left) MR
images of the dilated PVS revealing severe compression of the third
ventricle with resultant hydrocephalus. Transependymal edema is
demonstrated, but there is no evidence of contrast enhancement.
The coronal contrast-enhanced T1-weighted image (lower right) obtained after cyst fenestration reveals a decrease in both the size of
the giant PVS and hydrocephalus.

ceived a diagnosis of a “frontal lobe syndrome” consisting
of memory loss, decreased mental status, and ataxic gait. A
ventriculocisternostomy was performed and the patient’s
symptoms improved. Again, the size of PVS dilation was
unchanged on MR images obtained 6 months later. In a
more recent study,11 a 35-year-old man was described as experiencing slowly developing symptoms of forgetfulness,
confusion, and somnolence. Aside from these symptoms,
results of his neurological examination were unremarkable.
He was found to have left midbrain PVS dilations with
hydrocephalus, although his symptoms improved with the
placement of a shunt.
The development of hydrocephalus necessitated surgery
in the majority of patients included in our study. Eight patients required CSF diversion procedures. Three patients
underwent insertion of VP shunts, one patient received a
cystoperitoneal shunt, and four patients underwent ventriculocisternostomy procedures. One patient had small serial
aspirations of a midbrain cyst with no further treatment.
In all cases the cystic PVS dilation remained stable or decreased in size on subsequent MR imaging studies.
Although PVSs are filled with interstitial fluid and not
CSF, one might postulate that CSF drainage alone could decrease the size of dilated PVSs. In all cases published to
date in which CSF drainage was used to treat hydrocephalus, the PVS dilations remained stable in size. In the patients in this study the PVS dilations only decreased in size
when they were directly fenestrated or subjected to shunt
placement.
Clearly, some degree of enlargement of the cystic PVS
dilation occurred in each patient who later developed hydrocephalus. Longitudinal studies of PVS dilations have
not been performed, but follow-up imaging studies in cases
J. Neurosurg. / Volume 100 / May, 2004

Giant dilations of the perivascular spaces
published to date have yet to demonstrate an increase in
PVS size. Given that the number of patients who harbor undiagnosed tumefactive dilations of the PVS is likely to be
large, the few published cases of lesions causing hydrocephalus indicate that lesion growth is rare.
Tremor and PVSs

When multiple small dilations of the PVSs are present
in the striatum, they can be classified as état criblé or type
III lacunae in the classification system of Poirier and Derouesné.16 These were first described in 1843 and in 1929.
Critchley5 described this condition as being a form of arteriosclerotic parkinsonism. The contribution of multiple
small PVS dilations to symptoms of PD is still a matter of
debate. This subject is reviewed by Fénelon and associates,8
who also reported on two patients with état criblé, based on
imaging and histological studies. Although both patients
displayed signs of PD, only one patient had the usual changes in the substantia nigra, indicating that dilated PVSs may
play a role in causing or modifying PD.
The surgical implications of état criblé have also been
investigated recently. Desaloms and colleagues7 prospectively studied the outcome of posteroventral medial pallidotomy in patients with PD, noting that patients who had
status cruciformis or lacunae prior to surgery had less improvement in their off-medication condition at 6 months
posttreatment. Patients with both conditions had a higher
incidence of transiently altered mental status. Nonetheless,
Laitinen, et al.,12 reported no difficulty or lack of effect of
pallidotomy in patients harboring dilated PVSs. In fact, the
majority of their patients harbored dilated PVSs predominately in the posteroventral regions of the globus pallidus.
The patients’ preoperative motor symptoms were noted to
be more severe on the side of the body contralateral to the
side of the brain having the least number of dilated PVSs.
These findings indicate that there may be a functional consequence to multiple PVSs. When the majority of dilations
are in the posteroventral pallidum, however, they may lessen the effects of PD.
The effect of a massive PVS dilation on tremor is unknown. The case of a patient harboring mesencephalic cystic dilations with resultant triventricular hydrocephalus was
presented by Mascalchi and colleagues.14 This patient displayed a right-sided rubral tremor along with symptoms of
hydrocephalus. Although many of the hydrocephalic symptoms improved with CSF diversion, the patient’s tremor
did not. In contrast, one of the patients in the present study
displayed upper- and lower-extremity coarse tremor that
dramatically improved with decompression. In this case, the
extensively dilated PVS was causing mass effect on the
basal ganglia, which, according to neuroimaging studies,
improved following shunt placement. The experience of
this patient demonstrates that tremor may sometimes be improved if it is caused by basal ganglia compression.
Seizure and PVSs

The functional relationship between tumefactive dilation
of the PVS and seizures is unclear. Only one case report
demonstrates a causal link.3 This patient, a 64-year-old man,
experienced right temporal lobe seizures very late in life.
Evaluation revealed a large PVS dilation in the right hippocampus. It is possible that this lesion expanded over years
J. Neurosurg. / Volume 100 / May, 2004

FIG. 4. Magnetic resonance imaging performed in a patient with
multiple cystic dilations of the PVS demonstrating a pattern that
could at first appear to be a neoplasm. Axial FLAIR- (upper left) and
T2-weighted (lower left) images reveal abnormal increased signal
within the adjacent white matter; however, the signal characteristics
of the giant PVS always follow CSF signal intensity and no contrast
enhancement is demonstrated. Right: The T1-weighted images.

and led to the development of seizure. Other case reports indicating a link between dilations and seizures are unable to
offer clear causal explanations.1,4
One patient in our series experienced seizures. This patient, a 21-year-old man, had a history of generalized seizures with no clear origin. Magnetic resonance imaging
studies revealed cystic dilations in the cortical and subcortical white matter on the left side. The patient underwent biopsy sampling for what proved to be PVSs. The patient was
also found to have cortical dysplasia, a known contributory
factor to seizures. Follow-up imaging performed 6 years after biopsy revealed the PVS dilations to be unchanged.
It is unclear whether there is any functional consequence
to PVS dilations. As discussed earlier, there is some evidence indicating that the condition of état criblé may contribute, in either a positive or negative way, to parkinsonian symptoms. The functional consequence of extreme
PVS widening has been studied in only one patient.20 This
60-year-old woman with extreme widening of subcortical
PVSs in the right frontal and parietal areas underwent somatosensory evoked potential and transcranial magnetic
motor evoked potential monitoring. No laterality of testing
or other functional consequences could be demonstrated.
Analysis of data currently available indicates that PVS dilations do not often contribute to seizure activity. Patients harboring dilated PVSs and demonstrating seizures should be
thoroughly evaluated for a more common cause of seizure.
Biopsy for Tissue Diagnosis

The ominous appearance of tumefactive PVS dilations
will often lead to a differential diagnosis that includes neoplasm. The majority of case reports published to date fea823

P. House, et al.
ture patients who have undergone a brain biopsy procedure.
A typical case was recently reported from Australia; MR
imaging results revealed large right frontal cystic structures
with mass effect. A biopsy was performed, revealing the
masses to be dilated PVSs.6 Six of the patients in our series
had undergone biopsy procedure for diagnostic purposes.
With the high-resolution capability of modern 1.5-tesla
MR imaging, there is now little need for tissue biopsy sampling to diagnose even a dramatically enlarged PVS. Note
that PVSs are filled with interstitial fluid,21 which has the
imaging characteristics of CSF on all MR imaging and
computerized tomography scanning sequences.19 Enhancement does not occur following administration of a contrast
agent (Fig. 4). Evaluation of this series of patients reveals
consistent imaging characteristics, as described earlier, in
all lesions subject to biopsy sampling.
In patients with small dilations of the PVS the surrounding brain parenchyma has normal imaging characteristics.
In some patients with massive dilations of the PVSs, however, increased T2 and FLAIR signals are noted surrounding
the dilations (Figs. 2 and 4). The presence of the increased
T2 signal has been viewed as a worrisome finding and in
some cases has prompted the performance of tissue biopsy.
In patients who have been followed up with serial imaging
we have not identified a case in which this T2 signal worsened over time or masked an underlying malignancy. Our
series of patients indicates that this abnormal signal stems
from reactive gliosis surrounding the enlarged PVS and is
not an ominous finding.
After reviewing this series of patients and the relevant
surgical literature, we adopted the following approach to
patients presenting with massive dilations of the PVS. Patients presenting with symptomatic hydrocephalus are treated with the aid of CSF diversion. Patients presenting with
focal symptoms related to PVS mass effect undergo cyst
drainage and fenestration. If the cyst symptomatically recurs, shunt placement is undertaken. Incidentally noted
PVS dilations are evaluated using high-resolution MR imaging and are not subject to biopsy sampling.
Conclusions
Extreme or tumefactive dilations of the PVS are unusual
anatomical variants often found during imaging evaluation for a variety of neurological symptoms. These lesions
are benign and do not require biopsy sampling for diagnosis when high-resolution MR imaging studies can be performed. Nonetheless, a rare subset of these lesions will
slowly expand over time and may produce neurological sequelae or hydrocephalus if they arise in critical areas. Cerebrospinal fluid diversion procedures successfully alleviate
symptomatic hydrocephalus. The relationship of these unusual dilations to seizures or tremor remains unclear.

3. Bastos AC, Andermann F, Melancon D, et al: Late-onset temporal lobe epilepsy and dilatation of the hippocampal sulcus by an
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671–675, 1999
5. Critchley M: Arteriosclerotic parkinsonism. Brain 52:23–83,
1929
6. Davis G, Fitt GJ, Kalnins RM, et al: Increased perivascular spaces
mimicking frontal lobe tumor. J Neurosurg 97:723, 2002
7. Desaloms JM, Krauss JK, Lai EC, et al: Posteroventral medial pallidotomy for treatment of Parkinson’s disease: preoperative magnetic resonance imaging features and clinical outcome. J Neurosurg 89:194–199, 1998
8. Fénelon G, Gray F, Wallays C, et al: Parkinsonism and dilatation
of the perivascular spaces (état criblé) of the striatum: a clinical,
magnetic resonance imaging, and pathological study. Mov Disord 10:754–760, 1995
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Manuscript received September 30, 2003.
Accepted in final form January 13, 2004.
Address reprint requests to: William Couldwell, M.D., Ph.D., Department of Neurosurgery, University of Utah, 3B-409 SOM, 30
North 1900 East, Salt Lake City, Utah 84132-2303. email: william.
couldwell@hsc.utah.edu.

J. Neurosurg. / Volume 100 / May, 2004