This photo gallery presents the anatomy of fornix by means of MRI (T1-weighted sagittal, axial and coronal views).
The fornix, which means “arch” in Latin, is a C-shaped bundle of white matter (nerve fibers) in the brain.
The fornix is an essential part of the limbic system and represents the hippocampus’ most extensive single pathway, connecting it to different subcortical structures.
This part of the brain originates from the hippocampus in the mesial (medial) temporal lobe and stretches longitudinally to the diencephalon and basal forebrain to form an arch over the thalamus(1).
The fornix is a part of the limbic system associated with various cognitive processes, emotions, memory consolidation, and sexual responses(2).
Structures and Parts of the Fornix
The fornix’s bundle of white matter fibers are prominent on the cerebral hemispheres’ medial aspects.
The fornix starts in the hippocampus as the alveus, a collection of myelinated fibers found medially to the floor of the lateral ventricle’s temporal horn.
The alveus’ fibers travel posteromedially and aggregate to form the hippocampus’ fimbria (fringe) of the hippocampus. The fimbriae’s main bulk continues on each side of the cerebral hemisphere and forms the fornix’s crus (crus cerebri).
The two posterior pillars (crura) arch anterosuperiorly under the splenium of the corpus callosum, one for each hemisphere(3). The two posterior pillars (crura) arch anterosuperiorly under the corpus callosum’s splenium, one for each hemisphere.
The crura both establish a connection with each other across the midline by the partially crossing fibers known as the hippocampal commissure (David’s lyre)(4).
The crura continue anteriorly and merge in the midline to form the fornix body. This body arches over the thalamus and under the septum pellucidum (thin vertical membrane), connecting it to the corpus callosum.
The fornix body extends anteriorly and divides into the right and left halves known as the columns of the fornix.
Each column turns downwards in front of the interventricular foramen of Monro. Then, the column passes through the hypothalamus to reach the mammillary body.
The fornix columns divide at the anterior commissure’s level and form the precommissural and postcommissural fornix.
The precommissural fornix consists of the fibers that descend in front of the anterior commissure. These fibers relay onto the medial olfactory area (septal nuclei), the ventral striatum, and the cingulate gyrus (band of cortex).
Meanwhile, the postcommissural fornix comprises the fibers that pass behind the anterior commissure. These fibers relay onto the mammillary bodies and the thalamus’ anterior nuclei.
A small number of fornical fibers pass above the corpus callosum’ splenium to reach the structures above the corpus callosum. These fibers constitute the dorsal fornix(5).
Functions of the Fornix
As the hippocampus’s primary output tract, the fornix’s primary function is transmitting information from the hippocampus to the mammillary bodies and the anterior nuclei of the thalamus.
Experts believe that fornix plays a crucial role in some aspects of memory, specifically in recalling long-term memory and details from past events(6).
The fornix is largely involved in regulating episodic memories, a type of declarative memory encompassing autobiographical information(7).
The fornix is also a critical part of the Papez (medial limbic) circuit. It is a closed circuit consisting of the following pathways(8):
- The Papez circuit starts in the hippocampal formation (subiculum). The subiculum projects to the mammillary bodies via the postcommissural fornix through the subiculothalamic tract.
- The mammillary bodies project to the anterior thalamic nuclei through the mammillothalamic tract.
- The anterior thalamic nuclei project to the cingulate gyrus, which then projects to the parahippocampal gyrus.
- Finally, the parahippocampal gyrus projects to the entorhinal cortex and the hippocampal formation to complete the circuit.
The Papez circuit is involved in memory and learning, emotion, and social behavior. This circuit was originally thought to be the anatomical substrate of emotional experience.
However, the amygdala, basal forebrain, and prefrontal cortex have recently been recognized as additional components that play a more profound role in emotions.
Anomalies of the Fornix
Since the fornix is part of the limbic system, it is sometimes implicated in the limbic system’s anomalies. Below are some anomalies of the fornix:
Herpes Simplex Encephalitis
Herpes simplex encephalitis is an infection involving the limbic system, and thus the fornix. This infection predominantly affects the limbic system’s gray matter components(9).
Herpes simplex encephalitis results in abnormalities of the fornix’s fimbria, which is adjacent to the acutely involved hippocampus and the forniceal crus. There are also marked swellings of the forniceal body(10).
Although rare, the holoprosencephaly spectrum describes congenital absence as one of its findings(11).
This anomaly involves a malformation of the forebrain in humans, resulting from incomplete or failed forebrain division(12).
The fornix is well-involved in the spread of tumors of the white matter tract, such as hypothalamic glioblastoma multiforme. Patients with this condition present a memory deficit(13).
Glioblastoma multiforme is the most common primary intracranial neoplasm (tumor) in adults. It accounts for 12-15% of all intracranial neoplasms and ~50% of astrocytomas(14).
• Harnsberger HR, Osborn AG, Ross JS, Moore KR, Salzman KL, Carrasco CR, Halmiton BE, Davidson HC, Wiggins RH. Diagnostic and Surgical Imaging Anatomy: Brain, Head and Neck, Spine. 3rd ed. Salt Lake City, Utah. Amirsys. 2007. • Bourjat P, Veillon F. Imagerie radiologique tête et cou. Paris, Vigot. 1995. • Gouazé A, Baumann JA, Dhem A. Sobota. Atlas d’Anatomie humaine. Tome 3. Système nerveux central, système nerveux autonome, organe des sens et peau, vaisseaux et nerfs périphériques. 1er éd. Paris, Maloine. 1977. • Kahle W, Cabrol C. Anatomie. Tome 3: Système nerveux et organe des sens. 1er éd. Paris, Flammarion. 1979.
- Senova, S., Fomenko, A., Gondard, E., & Lozano, A. M. (2020). Anatomy and function of the fornix in the context of its potential as a therapeutic target. Journal of Neurology, Neurosurgery & Psychiatry, 91(5), 547-559.
- Rajmohan, V., & Mohandas, E. (2007). The limbic system. Indian journal of psychiatry, 49(2), 132.
- Senova, S., Fomenko, A., Gondard, E., & Lozano, A. M. op. cit.
- Rajmohan, V., & Mohandas, E. op. cit.
- Lövblad, K. O., Schaller, K., & Vargas, M. I. (2014, October). The fornix and limbic system. In Seminars in Ultrasound, CT and MRI (Vol. 35, No. 5, pp. 459-473). WB Saunders.
- Dubourg, C., Bendavid, C., Pasquier, L., Henry, C., Odent, S., & David, V. (2007). Holoprosencephaly. Orphanet journal of rare diseases, 2(1), 1-14.
- Hanif, F., Muzaffar, K., Perveen, K., Malhi, S. M., & Simjee, S. U. (2017). Glioblastoma multiforme: a review of its epidemiology and pathogenesis through clinical presentation and treatment. Asian Pacific journal of cancer prevention: APJCP, 18(1), 3.