We present the MR imaging findings in a patient who developed tetraventricu
lar hydrocephalus after massive rupture of dermoid cysts with generalized s
ubarachnoid and ventricular spread of cyst contents. The development of tet
raventricular hydrocephalus due to ruptured dermoid is a very unusual compl
ication, and was attributed to cyst contents interfering with passage of ce
rebrospinal fluid through the arachnoid granulations and fourth ventricular
outlet foramina.