Calcar avis
Calcar avis, previously known as hippocampus minor, is a normal variant of the cerebral ventricular system.
Gross anatomy
It is a medial side indentation of the junction of the trigone and the occipital horn of the lateral ventricles by the calcarine fissure in the brain .
Radiographic features
Ultrasound
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 .
CT
On axial reconstructions, the calcar avis may mimic intraventricular hemorrhage in the occipital horns. This structure can also mimic grey matter heterotopia and schizencephaly .
