Holes in the brain: answer

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Giant perivascular spaces (PVS) are very rare, non-neoplastic brain cysts. These cysts can reach very dramatic and atypical sizes and can be confused for neoplastic or other lesions, leading to unnecessary interventions. PVS are smoothly demarcated fluidfilled structures, and are thought to derive from the accumulation of interstitial fluid between penetrating vessels and pia mater [1]. As the interstitial fluid cannot exit, PVS enlarge, forming cyst-like structures, although they do not communicate directly with the subarachnoid space. These can cause localised mass effect and be mistaken for more sinister pathologies. Recognising their distinctive appearances on imaging is imperative, as biopsying these vascular lesions can have disastrous consequences [2]. PVS are usually asymptomatic, found incidentally on imaging or autopsy, or present with vague non-localising symptoms. There is no known age or sex predilection and they can be found in most parts of the brain parenchyma. ‘‘Normal’’ small PVS are present in up to 30% of children and are often found around the basal ganglia [1,2]. In contrast, the giant variant tends to present later