Displacement of the quadrigeminal plate in tumors of the fourth ventricle: MR appearance.

Magnetic resonance studies of 12 fourth ventricle tumors were reviewed. The relationship between the tumor and surrounding structures, such as the corpus medullare, the superior medullary velum, and the quadrigeminal plate, was assessed on midsagittal inversion recovery images. Two of the 12 tumors displaced the superior medullary velum superiorly. Seven of the 12 tumors displaced the corpus medullare posteriorly. The superior medullary velum was not recognized in 10 cases and the corpus medullare in 5. Ten of 12 quadrigeminal plates were displaced superoposteriorly due to focal enlargement of the cerebral aqueduct secondary to large intraventricular tumors. In the remaining two cases the tumor was not large enough to enlarge the cerebral aqueduct. The larger the tumor was, the more frequent was the displacement of the quadrigeminal plate. On T2-weighted images, CSF flow-void sign was seen around the tumor in 5 of 12 cases. We consider superoposterior displacement of the quadrigeminal plate to be a relatively constant and reliable sign accompanying fourth ventricle tumors.