The interpeduncular cistern is the subarachnoid CSF space between the two cerebral peduncles of the midbrain, bounded anteriorly by the posterior perforated substance, laterally by the cerebral peduncles, and posteriorly by the pons. It contains the basilar artery tip, the posterior cerebral arteries (P1 segments), the posterior communicating arteries, the superior cerebellar arteries, and both oculomotor nerves (CN III) as they course from the midbrain to the cavernous sinus.
| Location | Between the cerebral peduncles of the midbrain, in front of the pons |
|---|---|
| Parts |
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| Connections |
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| Blood Supply | Basilar artery; Posterior cerebral arteries |
Holds the top of the basilar artery and the oculomotor nerves. An aneurysm here can press on the oculomotor nerve and cause a droopy eyelid and dilated pupil.
The interpeduncular cistern is the key surgical field for basilar tip aneurysms, which are the most complex cerebrovascular lesions approached through the pterional or subtemporal craniotomy to reach this cistern. CN III passes through the interpeduncular cistern between the PCA and SCA, an acute CN III palsy (dilated pupil, ptosis, exodeviation) in a patient with thunderclap headache indicates subarachnoid haemorrhage from a posterior communicating or basilar tip aneurysm compressing CN III as it traverses the cistern.
Posterior communicating artery aneurysm expanding downward into the interpeduncular cistern compresses the oculomotor nerve as it exits the midbrain, producing a painful acute CN III palsy with pupil dilation, ptosis, and exodeviation; this is a neurosurgical emergency as the CN III palsy indicates aneurysm mass effect and imminent rupture risk.
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