There is evidence of increased size of all vents (lateral, 3rd, 4th) for age indicating external hydrocephalus.

There is evidence of specific ventricular obstruction at the level of the 3rd ventricle and/or the foramen of Monroe (including hyperintense colloid cyst on T1-w).

There is evidence of specific ventricular obstruction at the level of the cerebral aqueduct.

There is evidence of specific ventricular obstruction at the level of the 4th ventricle.

There is evidence of early (hyperacute) obstructive hydrocephalus affecting only the anterior temporal horn configuration and expansion of the hypothalamic-segment, 3rd vent.

There is evidence of grade 1.0/4 to grade 1.6/4 acute obstructive hydrocephalus.

There is evidence of grade 1.8/4 acute obstructive hydrocephalus likely with impending incisural herniation.

There is evidence of grade 2/4 acute obstructive hydrocephalus with downward central incisural herniation (displacement of supratentorial structures into the tentorial hiatus).

There are primary imaging features of elevated intraventricular CSF pressure (subependymal edema, tightened appearance of the ependymal surface, upward bowing the lamina terminalis, downward bowing the tuber cinereum/mammillary bodies (corresponding to the rostral and caudal walls of an expanded lower (hypothalamic portion) of the 3rd vent) distention of the optic and infundibular recesses, and abnormal rotation of the ventrally displaced optic chiasm/visual pathway.

There may be additional (secondary) imaging features of elevated CSF pressure including optic hydrops, hyperdynamic CSF pulsations, cerebellar tonsillar sagging, and ventricular diverticula.

Given there is obstructive 4th ventricular enlargement (sequestered vent or obstructing mass), there is now upward incisural herniation.

There is evidence of epencymal cicatrix with sequestered ventricle under pressure.

There is evidence of grade 1-4 ex vacuo ventriculomegaly without progressive hydrocephalus.

There is evidence of subarachnoid or intraventricular acute or subacute blood products with some degree of hydrocephalus.

There is evidence of arrested or normal pressure hydrocephalus: has stable ventriculomegaly with at least some features of elevated CSF pressure.

There is unexplained downward incisusal and tonsillar herniation, with or without ventriculomegaly, which is most consistent with intracranial hypotension (ICH).

Other significant imaging findings are present.