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Foramen of Monro (interventricular foramen): an opening between the lateral ventricle and third ventricle through which CSF flows from the lateral ventricle to the third ventricle.

Fourth Ventricle: a cavity within the brain that is situated between the brainstem and the cerebellum. The fourth ventricle receives CSF from the cerebral aqueduct, and CSF exits the fourth ventricle via the foramina of Luschka and Magendie into the subarachnoid space.

Hematoma: a localized collection of blood, usually clotted.

Hemorrhage: the escape of blood from blood vessels.

Hydrocephalus: an abnormal condition that occurs when there is an imbalance between the rate of CSF production and the rate of absorption, leading to gradual accumulation of CSF.

Hygroma: a sac, cyst or bursa distended with fluid. A subdural hygroma is a collection of fluid between the brain and the skull.