Cerebral peduncle

The cerebral peduncle is a broad structural term encompassing two main parts of the midbrain: the basis pedunculi and the tegmentum. The basis pedunculi includes the crus cerebri and the substantia nigra.

The cerebral peduncles are paired structures that resemble cylindrical masses emerging from the upper surface of the pons, diverging as they extend upward and forward. When viewed from the base of the brain, these structures are mostly obscured by the temporal lobes of the cerebrum, which must be retracted to reveal them.

Anatomical relationships:

• Interpeduncular fossa: The depressed area between the anterior ends (crura cerebri) of the two cerebral peduncles is termed the interpeduncular fossa. The medial surface of each peduncle forms the lateral boundary of this fossa, from which the oculomotor nerve emerges. The fossa contains the posterior perforated substance, a layer of gray matter pierced by numerous small blood vessels. Additionally, the interpeduncular nucleus, associated with the limbic neuronal circuitry, is located within this fossa near the pons.

• Superior relations: Superiorly, the cerebral peduncles, primarily the tegmentum, contribute to the floor of the third ventricle.

• Ventral relations: The ventral surface of each peduncle is related to the terminal branches of the basilar artery, including the superior cerebellar and posterior cerebral arteries, as they cross from the medial to the lateral side.

• Lateral relations: The lateral surface of each cerebral peduncle is associated with the parahippocampal gyrus of the cerebral hemisphere. The trochlear nerve crosses this surface from behind to the front. Higher up, near the point where the cerebral peduncle merges into the cerebral hemisphere, the optic tract winds backward around its ventrolateral surface.

• Lateral sulcus and associated structures: On the lateral surface of each cerebral peduncle, there is a longitudinal furrow called the lateral sulcus, marking the boundary between the crus cerebri and the tegmentum. Fibers of the lateral lemniscus surface in this sulcus and course upward and backward, disappearing beneath the inferior colliculus.