This 53-year-old patient presented with headaches. CT and MRI demonstrated a large non-enhancing thin-walled cyst following CSF signal in the lateral and 3rd ventricles, causing obstructive hydrocephalus. Histology of the excised lesion confirmed an ependymal cyst.

Ependymal cysts are benign neuroepithelial cysts lined by ependymal cells, thought to arise from sequestration of developing neuroectoderm during embryogenesis. They are thin-walled and contain clear serous fluid secreted by the lining ependyma. They are most commonly intraventricular, typically in the lateral ventricles, but rarely may be found in the periventricular white matter or subarachnoid spaces. Most are small and asymptomatic.

On imaging they are well-defined, thin-walled and do not contrast enhance. On CT they are isodense to CSF. On MRI they follows CSF signal on all sequences and do not demonstrate diffusion restriction. Occasionally the cyst may be hyperintense to CSF if there is a high
protein content.

The main differential diagnoses, which may be difficult to distinguish, are intraventricular arachnoid cyst and asymmetric ventricles. Other diagnoses to consider, although they have
distinguishing features, are choroid plexus cyst, epidermoid cyst, neurocysticercosis and porencephalic cyst.

1. Osborn A. & Preece M. Intracranial Cysts: Radiologic-Pathologic Correlation and Imaging Approach, Radiology 2006; 239:650-664
2. StatDx
Credit: Dr Donna D’Souza