Presentation
Brought in by parents post absence seizure
Patient Data







Images significantly degraded by motion artefact.
Allowing for this, the posterior horn of the left lateral ventricle shows asymmetric distension.
No other abnormality seen.

















Cystic, well-defined lesion in the posterior (occipital) horn of the left lateral ventricle (however separate from its walls) following CSF signal on all sequences in keeping with a simple (most likely arachnoid) cyst. Asymmetric prominence of the temporal horn of the left lateral ventricle, ?obstructive hydrocephalus due to the site of the cyst at the trigone.
Case Discussion
The case shows the typical appearance of an arachnoid cyst in an atypical location, so-called intraventricular arachnoid cysts (although strictly-speaking they are not all true arachnoid cysts histologically, please see article for more detail).
It is rarely symptomatic however may cause seizures, especially if localized to the trigone of the lateral ventricle and causing obstructive hydrocephalus of the temporal horn.