Lateral aperture of fourth ventricle

[TA] one of the two lateral openings of the fourth ventricle into the subarachnoid space (the lateral cerebellomedullary cistern) at the cerebellopontine angle. SYN: apertura lateralis ventriculi quarti [TA], foramen lateralis ventriculi quarti, foramen of Key-Retzius, foramen of Luschka, foramen of Retzius.