Calcar avis

Last revised by Frank Gaillard on 12 Jan 2023

Calcar avis is an elevation of white matter projecting from the medial wall of the occipital horn of the lateral ventricle. It is variably conspicuous, depending on how deep the calcarine sulcus is.

The calcar avis is located on the medial wall of the occipital horn, near the junction with the trigone of the lateral ventricles. It is formed by white matter separating the ventricle from the calcarine sulcus and, thus, is more prominent if the sulcus is deep 1-3. It is located below the bulb of the occipital horn, formed by forceps major, and above the collateral eminence, formed by white matter separating the ventricle from the collateral sulcus 2.

In a coronal plane of the neonatal brain, the calcar avis can mimic an intraventricular hemorrhage. Continuation of it as an echogenic fissure as the calcarine fissure and normal vascularity aids in differentiating the calcar avis from a blood clot 1

On axial reconstructions, the calcar avis may mimic intraventricular hemorrhage in the occipital horns. This structure can also mimic grey matter heterotopia and schizencephaly ref.

The calcar avis was previously known as the hippocampus minor (in contrast to hippocampus major, now simply the hippocampus) 1.

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Cases and figures

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