Mega cisterna magna, arachnoid cyst, and Dandy Walker variant | First Look MRI
An 18-year-old male with the diagnosis of MCM presented with headache. a T2-weighted axial image (7400/115/1 TR/TE/excitations) reveals an intact vermis. b T2-weighted sagittal image (7400/115/1 TR/TE/excitations) demonstrates a widened retrocerebellar cistern. The tentorium is not elevated, but there is scalloping in the occipital bone. The fourth ventricle has a normal shape. c CSF flow MR image (70/15.8/10° TR/TE/flip angle) shows pulsatile CSF flow that can be seen in only one image and shown in early systole of the cardiac cycle. The flow is present throughout the dilated MCM and the flow during early systole is in the normal cranial direction (arrows)
Yildiz, H., Yazici, Z., Hakyemez, B. et al. Evaluation of CSF flow patterns of posterior fossa cystic malformations using CSF flow MR imaging. Neuroradiology 48, 595–605 (2006). https://doi.org/10.1007/s00234-006-0098-8