Fornix (brain)

The fornix is the main efferent system of the hippocampus and an important part of the limbic system. It is a curvilinear bundle of white matter fibers that begins as a group of myelinated fibers called the alveus. The alveus alveus joins to form the fimbria of the hippocampus. Transection of the fornix at the level of its body can lead to memory loss ^1,2. 

Gross anatomy

It is formed of four parts: 

• crura: best seen at the splenium of the corpus callosum at the level of the superior superior colliculus on coronal images

• hippocampal commissure: The fimbria of each hippocampus thickens and then splits off from the hippocampus to form the crus (leg) of the fornix; the two crura unite to form the hippocampal commissure, which provides one of two two major paths through which the hippocampi communicate with each other

• body: after the hippocampal commissure it is called body of the fornix

• columns (anterior pillars): curves anteriorly and dives into the hypothalamus (mamillary bodies)

Relations

At the level of the anterior commissure the fornix divides into posterior fibers and anterior fibers. The posterior fibers (called the postcommissural postcommissural fornix) end through through the mammillary body of the hypothalamus. The anterior fibers (called precommissural fibers) end in the septal region and nucleus accumbens ^1,2.