Interpeduncular fossa

At a glance

English

Interpeduncular fossa

Latin (TA2)

Fossa interpeduncularis

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the interpeduncular fossa

The interpeduncular fossa is a depression on the underside of the brain at the junction of the forebrain and midbrain. In the strict sense it is the deep cleft between the two cerebral peduncles of the midbrain as they diverge forward from the upper border of the pons. In a wider, older sense the name covers the whole rhomboid area bounded in front by the optic chiasm, at the front sides by the optic tracts, at the back sides by the cerebral peduncles and behind by the upper border of the pons.

Taken in that wider sense, its floor contains a sequence of structures that can be read from back to front: the posterior perforated substance, pierced by small arteries; the paired mammillary bodies; the tuber cinereum, a grey bulge of the hypothalamus; and the infundibulum, the stalk that leads down to the pituitary gland. The deep part between the peduncles overlies the interpeduncular nucleus of the midbrain tegmentum.

The fossa matters because of what passes through it. The oculomotor nerve emerges from the medial side of each cerebral peduncle into the fossa and runs forwards between the posterior cerebral and superior cerebellar arteries. The fossa is filled with cerebrospinal fluid in the interpeduncular cistern, and the arteries of the cerebral arterial circle (of Willis) lie in and around it: the terminal basilar artery and its bifurcation into the posterior cerebral arteries, the posterior communicating arteries and the start of the posterior circulation. Paramedian branches from these vessels enter the posterior perforated substance to supply the midbrain and thalamus.

An aneurysm at the tip of the basilar artery or of the posterior communicating artery here can compress the oculomotor nerve, giving a dilated pupil and drooping eyelid. Blood from a ruptured aneurysm collects in the interpeduncular cistern, where it is easily seen on CT. Neurocutaneous melanosis, a rare condition of pigment cells in the meninges, often involves this area. The fossa is also a route for endoscopic third ventriculostomy, which opens the floor of the third ventricle into it.

Function and supply

Function

A landmark space that contains the interpeduncular cistern, the emerging oculomotor nerves and the terminal basilar artery with its branches.

Blood supply

The posterior perforated substance in its floor is pierced by paramedian branches of the basilar, posterior cerebral and posterior communicating arteries.