The lateral ventricles are the largest in the series of four interconnecting fluid-filled cavities within the brain. These cavities and theirs interconnecting channels, constitute the cerebral ventricular system. The other two cavities of this system are the third and fourth ventricles, while the cerebral aqueduct of Sylvius is one of the interconnecting channels, and it ensures the communication between the third and fourth ventricle.
The ventricular system is a well organized interconnecting system spanning every region of the brain. The channels connecting the lateral ventricles to the third (the midline ventricle) are called the interventricular foramen (or foramen of Monro). The cerebral aqueduct connects the third and fourth ventricles. The system is then made continuous with the central canal of the spinal cord, which originates from the floor of the fourth ventricle. The ventricles produce and contain cerebrospinal fluid (CSF), and the entire surface of the ventricular system is lined by an epithelial layer called the ependyma. Also, there is a vascular pia mater in the roofs of the third and fourth ventricles, and in the medial wall of the lateral ventricle along the line of the choroid fissure. This pia mater is directly apposed to the ependyma, and forms the tela choroidea, which gives rise to the highly vascularised choroid plexuses. However, the CSF is secreted by the choroid plexuses located within the lateral, third and fourth ventricles alone, but reaches the entire ventricular system and beyond by flowing from the lateral to the third ventricle through the foramen of Monro. It then flows through the cerebral aqueduct into the fourth ventricle, and from there into the central canal starting just inferior to the fourth ventricle. The CSF finally leaving the fourth ventricle through the foramen of Magendie and the foramina of Luschka to reach the subarachnoid space surrounding the brain.
Each lateral ventricle lies within a cerebral hemisphere. The lateral ventricle, when viewed from the lateral aspects of the brain, has a roughly C – shaped profile which follows the arrangement and shape of each hemisphere. Thus, the lateral ventricles span the cerebrum, including the occipital, frontal and parietal lobes. The lateral ventricle has a body or central part and three extensions, namely the anterior, posterior and inferior horns.
Body of Lateral Ventricle
The central part of the lateral ventricle is elongated anteroposteriorly. Anteriorly, it becomes continuous with the anterior horn at the level of the interventricular foramen. Posteriorly, the body reaches the splenium of the corpus callosum. It is triangular in cross section and has a roof, floor, and a medial wall; the roof and floor meeting on the lateral aspects. The roof is formed by the trunk of the corpus callosum, while the medial wall is formed by the septum pellucidum and by the body of the fornix, which is common to two lateral ventricles. The floor is formed mainly by the superior surface of the thalamus, medially, and by the caudate nucleus laterally. Between these two structures are the stria terminalis and the thalamostriate veins.
Extensions of The Central Part of Lateral Ventricle
The inferior horn is the largest component of the lateral ventricle. It begins at the posterior end of the central region, and runs anteroinferiorly into the temporal lobe. It has an anterior end that reaches close to the uncus of the cerebrum, a floor, and a roof. The roof of the inferior horn is formed by the floor of the central region. In cross section, the inferior horn has a narrow cavity which is bounded above, and laterally, by the roof, and below, and medially by the floor. Because of this orientation, the lateral part of the roof is sometimes referred to as the lateral wall, and the medial part of the floor, the medial wall.
The lateral part of the roof (lateral wall) is formed by fibres of the tapetum, while the medial part of the roof is formed by the tail of the caudate nucleus and the stria terminalis. These structures are continuous into the roof of the inferior horn from the floor of the central part. Anteriorly, the tail of the caudate nucleus and the stria terminalis end in relation to the amygdaloid complex, which lies in the most anterior part of the roof. The floor of the inferior horn is formed mainly by the hippocampus, along with the alveus and fimbriae. In the lateral part of the floor is an elevation called the collateral eminence, produced by inward bulging of the white mater which lies deep to the collateral sulcus. The anterior horn of the lateral ventricle lies anterior to the central part, from which it is separated by an imaginary vertical line that runs at the level of the interventricular foramen. This extension is triangular in cross section and has a roof, floor and medial wall. It is closed anteriorly by the genu and rostrum of the corpus callosum. Its roof is formed by the most anterior part of the trunk of the corpus callosum while the floor is formed by the head of the caudate nucleus. A small part of the floor near the midline is formed by the upper surface of the rostrum of the corpus callosum. The medial wall is formed by the septum pellucidum. Thirdly, the posterior horn of the lateral ventricle extends posteromedially into the occipital lobe, and like other parts of the lateral ventricle it has a roof, lateral wall and a medial wall.
The roof and lateral wall are formed by the tapetum, while the medial wall shows two elevations, one superior and the other inferior and referred to as the calcar avis. Superior to those elevations is a structure called the bulb of the posterior horn. This bulb is formed by fibres of the forceps major as they run backwards from the splenium of the corpus callosum.