Uncus

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Structures seen from a basal view of the brain with the brainstem removed, showing the cut surface of the mesencephalon.

The uncus (plural: unci) is a hook-shaped limbic structure located on the anteromedial aspect of the parahippocampal gyrus, in the mediobasal region of the temporal lobe. It lies lateral to the mammillary bodies, posterior perforated substance and cerebral crus (crus cerebri), and just anterior to the lateral geniculate body.

It is composed of two parts: an anterior and posterior segments.

• The anterior segment bears two gyri that overlie the amygdala. The first, the ambient gyrus, forms two small projections on the anteromedial surface of the segment. The second is a lateral extension of the lateral olfactory stria called the semilunar gyrus. Both gyri are separated by the semi-annular sulcus which contains the anterior choroidal artery. The anteriormost part of the uncus forms the entorhinal cortex.

• The posterior segment of the uncus contains the head of the hippocampus. This region lies just above uncal sulcus which separates it from the parahippocampal gyrus located inferiorly.

The inferior surface of the uncus is buried within the uncal sulcus. This surface bears an important anatomical landmark called the band of Giacomini, which separates the uncinate gyrus anteriorly from the uncal apex (intralimbic gyrus and hippocampus inversus) located posteriorly. The band of Giacomini represents the rostral continuation of the dentate gyrus and may also be referred to as the tail of the dentate gyrus.

The blood supply of the uncus is primarily from branches of the anterior choroidal artery, but it also receives blood from branches of the internal carotid artery, middle cerebral artery and the posterior cerebral artery.

The uncus forms part of the limbic and olfactory cortices and thus plays a role in olfaction, emotions, and memory.