Giant tumefactive perivascular spaces: A further case.

Virchow-Robin spaces (VRS) or the perivascular spaces are small pial lined, cystic structures in the brain and are filled with interstitial fluid. They are normal spaces, identified in all age groups and are common in places where the penetrating vessels enter into the substance of brain. Occasionally, these spaces can be enlarged and are termed as giant tumefactive perivascular spaces (GTPVS). When enlarged, these cysts are commonly confused with other lesions such as cystic neoplasms. The pathognomonic imaging appearance helps in the diagnosis of this condition in most instances and invasive management is unwarranted. We report a 4-year-old male with GTPVS. In our patient, GTPVS were diagnosed incidentally on brain imaging ordered for a head trauma and he was managed conservatively. During 1-year follow-up, he remained asymptomatic and the size of the cysts was virtually unchanged.

Introduction

Virchow-Robin spaces (VRS) or the perivascular spaces (PVS) are normal interstitial fluid filled cystic structures in the brain.[1] They are about 1-2 mm in size, typically lined by pia mater and are common in places where the penetrating arteries and arterioles enter into the substance of the brain.[1234] In this article, we report a child with incidentally detected giant tumefactive perivascular space (GTPVS).

Case Report

A 4-year-male was referred to us for further management of cystic lesions which were initially mistaken for cystic neoplasm. He had a recent minor head trauma subsequent to a fall. He never lost consciousness and did not have neurological symptoms including headaches, vomiting and seizures. A computer tomogram done at an outside facility showed cystic lesions. He did not travel outside the United States and has no exposure to pets or farm animals. Physical examination including neurological system was within the limits. No evidence of papilledema was found on fundus examination.

A magnetic resonance imaging (MRI) showed three clustered cystic areas in subcortical white matter near the atrium of left lateral ventricle. The larger cyst (ovoid shaped lateral cyst) was located in the left temporo-parieto-occipital region, measured 34 × 32 × 42 mm and was located just lateral to the atrium of the left lateral ventricle [indicated by number ‘1’ in the Figures 1-3]. Two smaller cysts were also identified. One of them measured 8.1 mm (spherical shaped medial cyst) in diameter, and was located medial to the posterior horn of the left lateral ventricle in the occipital region [indicated by number ‘2’ in the Figures 1 and 3]. The other smaller cyst (ovoid shaped central cyst) was located in between the two above mentioned cysts [indicated by number ‘3’ in the Figures 1 and 3]. This cyst measured 8.3 × 20 × 24 mm, and the choroid plexus was noticed in the periphery. The posterior horn and atrium of left lateral ventricle were distorted due to the pressure effect from these cysts. All the three cysts were hypointense in the T1-weighted sequences and hyperintense in the T2-weighted sequences. The intensity signals of the cysts were isointense to the cerebrospinal fluid (CSF) in all the sequences. No evidence of hydrocephalus or midline shift was found. There was no enhancement of the cystic wall after the administration of gadolinium [Figures 1b, 2b and 3a]. There were no restricted diffusion [Figure 3b] and there were also no areas of calcification.

Figure 1

(a) Axial T1-weighted image of the brain without contrast showing all the three cysts, noted as ‘1’, ‘2’ and ‘3’; (b) Axial T1-weighted image of the brain with contrast. There is no enhancement of the wall of the cysts after the administration of gadolinium

Figure 3

(a) Coronal T1-weighted image with gadolinium showing all the three cysts (noted as ‘1’, ‘2’ and ‘3’) and no enhancement of the wall of the cysts; (b) Axial diffusion weighted image showing the lateral and central cysts without restricted diffusion

Figure 2

(a) Sagittal T1-weighted image of the brain without contrast showing the large lateral cyst identified as ‘1’; (b) Sagittal T-1 weighted image of the brain with gadolinium showing no enhancement of the wall of the lateral cyst

From the asymptomatic nature and classical radiological appearance, GTPVS was diagnosed. The patient was initially referred to pediatric neurology service. A decision to follow conservatively was made and he was seen a year later. In the interval period, he did not develop any symptoms. A repeat MRI was done a year later and showed the same findings without any increase in size or number of the cystic spaces. The patient was also referred to neurosurgery consultation and a conservative long-term follow-up was advised.

Discussion

The PVS or the VRS were initially reported by Virchow in 1851 and Robin in 1859. These spaces are normal interstitial fluid filled spaces that accompany the penetrating vessels of the brain.[1] The PVS directly communicate with the subpial space; but are separated from the cerebrospinal fluid filled subarachnoid space by a single layer of the pia mater.[5]

The appearance of the normal PVS in the MRI of the brain is typical. They are round or oval in shape, have smooth margins, are generally less than 2 mm (some authors considered less than 5 mm as normal) in diameter and are located along the path of penetrating blood vessels.[5678] They do not enhance with contrast administration and the lesions are isointense with the cerebrospinal fluid.[78] Small PVS occur in all age groups and the size is generally larger with advancing age.[9] The most common location of the PVS is along the lenticulostriate arteries, just above the anterior perforated substance and adjacent to the anterior commissure.[124] Other common locations include subcortical white matter, midbrain, subinsular region and cerebellum.[46] PVS has been commonly noted in many genetic and metabolic conditions such as mucopolysaccharidosis, mannosidosis, Lowe syndrome, Coffin-Lowry syndrome, megalencephaly and ectodermal dysplasia.[10] Furthermore, children with developmental delay, epilepsy, attention deficit hyperactive disorder or benign macrocephaly tend to have enlarged PVS.[11] The precise etiology and function of these spaces is still unknown.[56] Occasionally the PVS can expand and mimic a cystic neoplasm.[6] Various names such as GTPVS, “cavernous dilatation” or Poirier's Type IIIb “expanding lacunae” are given for these enlargements.[61213] Authors define GTPVS as PVS equal to or greater than 1.5 cm, occurring as either a solitary lesion or in clusters of multiple contiguous cysts.[2] GTPVS are relatively rare in the pediatric population. Out of 37 patients with GTPVS reported by Salzman et al., four were less than 18 years of age.[2]

The most common site for the GTPVS is along the penetrating vessels of the mesencephalothalamic region.[2] The pathogenesis for this enlargement is not clearly known. Various possibilities such as increased cerebrospinal fluid pulsations, the ex vacuo phenomenon, or an abnormality of arterial wall permeability and the spiral elongation of the penetrating blood vessels, have been cited as contributing factors.[24] In most instances, the giant PVS are incidentally diagnosed when the imaging is done for various other reasons.[14] In one series of 37 patients with GTPVS, 15 patients reported with headache.[2] The other less common symptoms reported include dizziness, dementia, visual changes, seizure, syncope, stroke, memory problems, poor balance and poor concentration.[2] Surgical or neuroendoscopic interventions are not required unless until these cysts have associated complications such as hydrocephalus.[5]

In view of its rarity, the most important consideration in the GTPVS is the diagnostic confusion with other conditions.[15] The differential diagnosis includes cystic neoplasms, parasitic cysts, ventricular diverticula, cystic infarction, non-neoplastic neuroepithelial cysts, and deposition disorders such as mucopolysaccharidosis.[245714] The prompt recognition of the pathognomonic radiological features of GTPVS prevents unnecessary investigations such as biopsies or surgical resection.[15] The typical location along and at the site of the penetrating blood vessel, the lack of enhancement with gadolinium, and the isointensity with the CSF in all sequences are the pathognomonic features of the GTPVS.[67] Furthermore, there will not be any calcifications with normal adjacent brain parenchyma. There may be an associated mass effect depending on the size and location of the GTPVS.[2]

We conclude that physicians need to be aware of the typical imaging characteristics of GTPVS so that unwanted invasive neurosurgical procedures or frequent repeated imaging of the brain can be prevented.