lateral ventricle

**Anatomy (5 parts):** Each lateral ventricle has (1) a frontal (anterior) horn, (2) a body, (3) an atrium (trigone), (4) an occipital (posterior) horn, and (5) a temporal (inferior) horn. The C-shape follows the arc of the caudate nucleus and hemispheric development.

**Boundaries/relations (high-yield):** - Frontal horn: roof and anterior wall = corpus callosum (genu); lateral wall = head of the caudate nucleus; medial wall = septum pellucidum. - Body: roof = corpus callosum; floor = body of caudate laterally and thalamus; fornix runs along the medial floor. - Temporal horn: hippocampus forms the floor/medial wall; the tail of the caudate and amygdala are nearby (the amygdala lies at the tip of the temporal horn). - Occipital horn: contains no choroid plexus. Bulb of the corpus callosum and calcar avis (from the calcarine sulcus) indent it. - Atrium: site of the glomus (largest tuft of choroid plexus, often calcified on imaging in adults).

**CSF production and flow:** The choroid plexus (modified ependymal cells plus pia/capillaries with fenestrated endothelium) makes CSF in the body, atrium, and temporal horn, and in the 3rd and 4th ventricles. Flow: lateral ventricles → foramen of Monro (interventricular foramen) → third ventricle → cerebral aqueduct (of Sylvius) → fourth ventricle → foramina of Luschka (lateral) and Magendie (median) → subarachnoid space → arachnoid granulations → dural venous sinuses (superior sagittal sinus). CSF is made at about 500 mL/day, with a total volume of about 150 mL. Choroid plexus blood supply comes from the anterior choroidal artery (ICA) and the lateral posterior choroidal artery (PCA).

**Clinical correlations:** - **Obstructive (non-communicating) hydrocephalus:** Blockage at the foramen of Monro (for example, colloid cyst of the third ventricle) causes dilation of both lateral ventricles. It classically presents with positional headache, sudden drop attacks, or sudden death. A unilateral foramen of Monro obstruction causes asymmetric ventriculomegaly. Aqueductal stenosis causes dilated lateral and third ventricles with a normal-sized fourth ventricle. - **Communicating hydrocephalus:** Impaired reabsorption at arachnoid granulations (post-meningitis, subarachnoid hemorrhage) causes all ventricles to dilate. **Normal pressure hydrocephalus** (wet, wobbly, wacky: incontinence, gait apraxia, dementia) shows ventriculomegaly out of proportion to sulcal atrophy, and ex vacuo dilation is seen in Alzheimer disease or atrophy. Hydrocephalus ex vacuo has normal CSF pressure. - **Intraventricular hemorrhage:** Seen in premature infants from germinal matrix hemorrhage (fragile subependymal vessels near the caudate head/lateral ventricle floor) and in hypertensive hemorrhage that ruptures into the ventricles. - **Tumors:** Ependymoma (usually 4th ventricle in children), subependymal giant cell astrocytoma (tuberous sclerosis, near the foramen of Monro), central neurocytoma (young adults, lateral ventricle near the septum pellucidum), choroid plexus papilloma (lateral ventricle in children, 4th ventricle in adults; may cause hydrocephalus via CSF overproduction). - **Ventriculitis/infection:** Can follow shunts or meningitis and shows ependymal enhancement. - **Procedures:** A ventriculoperitoneal (VP) shunt is usually placed into the frontal or occipital horn of the lateral ventricle. An external ventricular drain (EVD) at Kocher's point is used for ICP monitoring/drainage. - **Development:** Lateral ventricles are derived from the cavity of the telencephalon (prosencephalon → telencephalon). The third ventricle derives from the diencephalon, the aqueduct from the mesencephalon, and the fourth ventricle from the rhombencephalon (metencephalon/myelencephalon). - **Septum pellucidum:** Absence is associated with septo-optic dysplasia (and holoprosencephaly spectrum disorders). A cavum septum pellucidum is seen in boxers (chronic traumatic encephalopathy). - **Imaging:** Normal frontal horn width is small and slit-like on CT/MRI. In Huntington disease, caudate atrophy leads to "boxcar" enlarged frontal horns with loss of the normal concave contour.

**Pearls:** Ependymal cells line the ventricles (ciliated cuboidal/columnar), and choroid plexus epithelium has tight junctions forming the blood–CSF barrier. The lateral ventricles are the largest ventricles, and CSF flows from them only through the foramen of Monro.