Rare Case of Tricompartmental Arachnoid Cyst Spanning Infratentorial, Supratentorial, and Extracranial Compartment and Presenting as Posterior Parietal Meningocele

This case of arachnoid cyst involves multiplestructures. But interestingly, all these structures (arachnoid, dura, veins,and bone) are of mesodermal origin. So we would like to suggest that thispathology may be a result of developmental deviation during mesodermal differentiationrather than a simple expanding arachnoid cyst.