AN56.1-2 | Meninges & CSF — Glossary

Outermost meningeal layer; thick and tough; forms dural folds (falx, tentorium) and contains the dural venous sinuses

Middle meningeal layer; thin and avascular; the subarachnoid space between it and pia mater contains CSF

Innermost meningeal layer; thin, vascular, closely adherent to the brain surface, dipping into every sulcus

Sickle-shaped vertical dural fold separating the two cerebral hemispheres; contains the superior and inferior sagittal sinuses

Tent-shaped horizontal dural fold separating the cerebrum from the cerebellum; the tentorial notch allows passage of the midbrain

Gap in the free edge of the tentorium cerebelli through which the midbrain passes; site of uncal herniation in raised ICP

Transtentorial herniation of the medial temporal lobe (uncus) through the tentorial notch, compressing CN III (dilated pupil) and the midbrain

Pacchionian bodies — tufted projections of arachnoid into the superior sagittal sinus; main site of CSF absorption into venous blood

Specialised ependymal cells and capillary tufts in the ventricles producing CSF at approximately 500 mL/day

Interventricular foramen connecting each lateral ventricle to the 3rd ventricle; blockage causes unilateral hydrocephalus

Cerebral aqueduct through the midbrain connecting the 3rd to the 4th ventricle; the narrowest part of the ventricular system and most common site of obstruction

Median aperture of the 4th ventricle opening into the cisterna magna; one of three exits for CSF into the subarachnoid space

Lateral apertures (×2) of the 4th ventricle opening into the pontine cistern lateral recess

Abnormal accumulation of CSF causing ventricular dilation and raised intracranial pressure; obstructive or communicating

Ventriculoperitoneal shunt — tubing from the lateral ventricle to the peritoneal cavity with a pressure valve for draining excess CSF

Blood collection between the skull and dura from rupture of the middle meningeal artery; classically has a lucid interval

Blood collection between the dura and arachnoid from rupture of bridging veins; common in elderly and infants after trauma

Bleeding into the subarachnoid space, most commonly from rupture of a berry aneurysm at the circle of Willis; causes thunderclap headache

Dural venous sinus on either side of the sella turcica containing CN III, IV, V1, V2, VI, and the internal carotid artery

Cerebellomedullary cistern — enlarged subarachnoid space between the cerebellum and medulla; receives CSF from the foramen of Magendie

Lateral projections of spinal pia mater that anchor the spinal cord to the dura, preventing excessive movement