Giant tumefactive perivascular spaces mimicking a brain mass lesion: Report of three cases

Abstract

Virchow–Robin spaces or perivascular spaces are pial-lined fluid-filled interstitial spaces recognized throughout brain parenchyma along the path of penetrating vessels. Occasionally, they may become enlarged, cause mass effect, and be mistaken for cystic neoplasms or infections. We report three cases of giant tumefactive perivascular spaces (GTPVS) incidentally found at brain magnetic resonance imaging (MRI). The lesions were multilocular cystic-appearing, isointense to cerebrospinal fluid on all pulse sequences, and did not enhance. They were located both in typical and atypical locations and in one case associated with hydrocephalus. We describe the key features of GTPVS on MRI and illustrate the need to acknowledge and promptly recognize these entities in daily practice in order to avoid unnecessary treatment.

Introduction

Perivascular spaces (PVS) also known as Virchow-Robin spaces (VRS) surround and accompany the course of penetrating arteries throughout brain parenchyma in typical locations. ^1,2 Small VRS (<2 mm) appear in all age-groups and are typically asymptomatic. ³ Occasionally they may expand and increase in size, cause mass effect and mimic neoplastic lesions including dysembryoplastic neuroepithelial tumors (DNET) or cystic infections such as neurocysticercosis or toxoplasmosis. ^1,4

We report three cases of giant tumefactive perivascular spaces (GTPVS) and describe their radiologic features and possible locations within brain parenchyma, both typical and atypical. Awareness of the features of such entities is extremely important to prevent unnecessary treatments in the form of biopsy or surgical excision.

Case 1

A 27-year-old male was referred for frontal headache of new onset since 1 month. The patient had no history of neurologic disease or malignancy. On examination, he had no neurological signs.

Brain magnetic resonance imaging (MRI) (Figure 1(a) to (f)) showed a large multilocular cystic mass in the right frontal lobe involving the subcortical white matter of medial, anterior, and lateral orbital gyri and the anterior portion of the straight gyrus. There were associated gyral expansion and scalloping of adjacent frontal bone.

Figure 1.

Case 1. Brain MRI. Multilocular micro- and macro-cystic structure of an expansile subcortical right frontal mass, with signal isointense to CSF on T1-W (a) and T2-W (b) images. The frontal lobe is expanded, overlying gray matter seems not involved but stretched and displaced over the multilocular giant perivascular spaces. Axial T2-W FLAIR images (c) show gliotic changes in the intermingled parenchymal septi and overlying cortex (arrows on (c)). Diffusion-weighted image (d) and corresponding ADC map (e) demonstrate unrestricted diffusion. No contrast-enhancement is present on enhanced T1-W images (f). MRI: magnetic resonance imaging; CSF: cerebrospinal fluid.

The multilocular cysts showed MRI signal isointense to cerebrospinal fluid (CSF) in T1-W, T2-W, and T2-FLAIR images. T2-FLAIR images demonstrated high signal in the septi and in the overlying cortex likely related to gliotic changes. There was no vasogenic edema nor restricted diffusion on apparent diffusion coefficient (ADC) map. No contrast-enhancement was noted within the mass after gadolinium intravenous administration.

Differential diagnosis included a DNET, for its “bubbly appearance” related to multiple small-sized cysts, but the sparing of the cortex and a negative history for seizure favored the alternative, and in our opinion more likely diagnosis of GTPVS in an atypical location. The patient was treated conservatively and further clinical follow-up was performed. His headache resolved, and he remained asymptomatic thereafter. One-year follow-up brain MRI showed the lesion to be stable in size, morphology, and signal intensity.

Case 2

A 64-year-old woman presented to our emergency room with complaints of progressive headache and dizziness for the past 3 months and a long-standing history of vertigo and gait disturbances. Clinical examination revealed a high-grade fever (39°C) and a subtle motor deficit of the right arm. A brain MRI study excluded an intracranial or subdural hemorrhage but demonstrated a giant multilocular cystic mass involving the right midbrain and thalamus with mass effect on the third ventricle and Sylvian aqueduct (Figure 2(a) to (f)). In addition, there was enlargement of lateral ventricles with subtle signs of subependymal CSF resorption. The lesion was CSF-isointense on all pulse sequences and showed no enhancement following i.v administration of contrast medium. No signal intensity abnormalities were identified in the adjacent brain parenchyma. The typical location and radiologic features favored the diagnosis of GTPVS associated with obstructive supratentorial hydrocephalus. The patient was subsequently referred to our neurosurgery department and scheduled for a ventriculo-peritoneal shunt.

Figure 2.

Case 2. Brain MRI. Giant multilocular cystic mass involving right midbrain and thalamus consistent with GTPVS. The cysts follow CSF signal intensity on T2-W (a), FLAIR (b), and T1-W (c) images with no signal abnormalities in the adjacent brain parenchyma. Enlargement of lateral ventricles is observed on coronal FLAIR image with subtle signs of subependymal CSF resorption (b). Sagittal 3-D CISS and reformatted coronal images (d, e) demonstrate mass effect on the third ventricle with a cyst in right midbrain displaying posteriorly the tectal plate and causing Sylvian aqueduct stenosis. No contrast-enhancement is present on axial enhanced T1-W images (f). MRI: magnetic resonance imaging; CSF: cerebrospinal fluid; GTPVS: giant tumefactive perivascular spaces.

Case 3

A 67-year-old woman with no history of malignancies presented with a 6 months history of recurring episodes of severe right hemifacial pain, consistent with trigeminal neuralgia, unresponsive to medical treatment. Physical examination revealed no neurological deficits. A brain MRI with MR-angiography was performed to rule out intracranial masses and neurovascular conflicts. The exam excluded significant findings along the course of the right trigeminal nerve in the pons, at the root entry zone, in the cisternal spaces, and Meckel’s cave. However, MRI incidentally demonstrated mass-like well-defined round CSF-isointense lesions clustered within the right dorso-lateral aspect of the mesencephalon (tegmen) partially extending to the cerebral peduncle (Figure 3). The cystic, multilocular mass had a tumefactive appearance with mild expansion of the dorso-lateral midbrain profile. There were no signs of adjacent gliosis or vasogenic edema, nor contrast-enhancement after gadolinium administration. In addition, the cysts were localized along the expected course of the perforating mesencephalo-thalamic arteries. The multilocular cyst cluster, the signal intensity following CSF on all pulse sequences, the absence of contrast-enhancement, and the typical location suggested the diagnosis of GTPVS. The symptoms were judged to be unrelated to this mass, whose diagnosis was considered incidental.

Figure 3.

Case 3. Brain MRI. Mass-like multilocular cysts cluster in the right dorso-lateral aspect of midbrain tegmen extending to the cerebral peduncle. The cysts demonstrate CSF-like signal intensity on axial T2FLAIR (a) and 3-D axial and coronal T2-weighted CISS (b–d) and causes remodeling of right dorso-lateral midbrain profile without mild mass effect. The adjacent brain parenchyma does not show signal abnormalities suggestive of gliosis or vasogenic edema. No contrast-enhancement is noted on contrast-enhanced axial T1-W image (c). MRI: magnetic resonance imaging; CSF: cerebrospinal fluid.

Discussion

PVS or VRS represent pial-lined fluid-filled structures surrounding the walls of penetrating vessels within brain parenchyma. ^1,2 At MRI, normal PVS are typically round, oval, or tubular in shape; have smooth, well-defined margins; and are generally seen in clusters, often with a range of different sizes. ³ Small PVS (<2 mm) occur in all age-groups and tend to increase in frequency and size with advancing age. ³

PVS contain interstitial fluid and on MRI are isointense to CSF on all pulse sequences. ^4,5 They demonstrate no restricted diffusion and no enhancement after contrast medium administration. ³ Typically, there are no signs of gliotic changes at their periphery, differentiating them from sequelae of lacunar infarcts. ⁴

PVS are divided into three subtypes according to their location. Type I occur along lenticulostriate arteries entering the basal ganglia through the anterior-perforated substance. Type II are found along the path of perforating medullary arteries as they enter cortical gray matter over the high convexities, extending into the white matter. Type III appear in midbrain at the pontomesencephalic junction surrounding penetrating branches of the collicular and accessory collicular arteries. ^3,4

The exact etiology of these PVS has yet to be delineated. Multiple theories including perivascular myelin loss, fibrosis/obstruction of lymphatic drainage pathways, alterations of arterial wall permeability, and ex-vacuo dilatation secondary to brain atrophy have been proposed. ^5,6

Typical PVS are asymptomatic. Occasionally, they become enlarged and cause specific clinical manifestations, mass effect, or even hydrocephalus, ⁷ depending on their location and degree of compression. PVS greater than 1.5 cm either unilocular or in clusters are called giant tumefactive perivascular spaces, cavernous dilatation, or Poirier’s Type III b expanding lacunae. ^7,8 Headache is the most common presenting feature of GTPVS. ¹ Less common symptoms reported include dizziness, dementia, visual changes, seizure, syncope, stroke, and memory problems.

As we reported, GTPVS may occur in a typical location—the mesencephalothalamic region ³ —and possibly cause hydrocephalus or they can be seen in less typical locations, including the frontal lobes. ⁹ Occasionally, GTPVS may be associated with abnormally increased FLAIR signal intensity in the adjacent white matter. According to recent literature, this imaging finding may be either related to advanced chronic ischemic changes due to mass effect or chronic mechanical stress caused by high blood pressure on the brain arterioles. ¹ GTPVS may present mass effect and mimic more worrisome entities including cystic neoplasms, such as DNET, infections (toxoplasmosis and neurocysticercosis), infarction, and metabolic deposition disorders like mucopolysaccharidosis. ^4,5 The presence of adjacent frontal bone scalloping, seen in our case of frontal GTPVS, suggested a chronic, long-standing process. Understanding the pathognomonic imaging features of GTPVS—typical location along penetrating blood vessels, absence of enhancement after gadolinium administration, and isointensity relative to CSF on all pulse sequences—might prevent unnecessary investigations such as biopsies or surgical resection and associated risks.