20 Neuroanatomy: Draw It to Know It
Cerebral Ventricles
Here, we will draw the cerebral ventricles in sagittal view.
First, draw the C-shaped appearance of one of the bilat-
eral lateral ventricles and include its posterior tail. Next,
label the individual horns of the representative lateral
ventricle. Label the supero-anterior-lying horn as the
frontal horn, the posterior-lying horn as the occipital
horn, and the infero-anterior-lying horn as the temporal
horn. Th e head of the caudate constitutes the majority of
the lateral wall of the frontal horn, the occipital horn
extends deep into the occipital lobe, and the hippocam-
pus constitutes the anterior medial wall of the temporal
horn (the amygdala sits just in front of it and forms the
anterior border of the temporal horn). Next, label the
long superior bend of the lateral ventricle as its body and
label the region where the temporal and occipital horns
and body come together as the atrium (aka trigone).
Now, show that through the bilateral foramina of Monro,
the lateral ventricles empty into the third ventricle,
which lies in the midline of the nervous system and
which is fl anked by the hypothalamus, inferiorly, and the
bilateral thalami, superiorly. Next, show that the third
ventricle empties into the narrow cerebral aqueduct (of
Sylvius), which empties into the diamond-shaped fourth
ventricle. Th en, show that at the inferior angle of the
fourth ventricle, at the level of the gracile tubercle (the
swelling formed by the gracile nucleus in the posterior
wall of the medulla), the fourth ventricle becomes the
obex, and descends as the central canal of the spinal
cord.^13
Next, let’s label the midline borders of the fourth ven-
tricle. First, label the anterior border as the fl oor of the
fourth ventricle. Th e fl oor of the fourth ventricle is an
important anatomic site because it forms the posterior
border of the tegmentum of the pons and medulla and
many important anatomic structures lie within or near
to it, including certain lower cranial nerve nuclei and
certain neurobehavioral cell groups (eg, the locus coer-
uleus and the area postrema). Next, label the superior–
posterior border of the fourth ventricle as the superior
medullary velum (aka anterior medullary velum) and
then the inferior–posterior border as the inferior medul-
lary velum (aka posterior medullary velum). Th e cerebel-
lar peduncles form the lateral borders of the fourth
ventricle and the cerebellum helps form the rest of the
posterior border (the roof ). Medulloblastoma tumors
oft en lie along the superior medullary velum.
Now, let’s include the choroid plexus. Show that it lies
within the central regions of the cerebral ventricles: in
the body and atrium of the lateral ventricle, temporal
horn of the lateral ventricle, third ventricle, and fourth
ventricle. Th e lack of choroid plexus in the frontal and
occipital horns allows neurosurgeons to place intraven-
tricular drains in these horns without injuring the highly
vascularized choroid plexus.
Th e shape of the lateral ventricles bears resem-
blance to many major cerebral structures — the cerebral
hemispheres, the caudate–putamen, and the fornix–
hippocampus. During embryogenesis, all of these
structures undergo a backward, downward, and forward
migration, which we will demonstrate with our arms,
now. First, create a coronal view of the developing brain
as follows. Hold your arms together with your elbows
bent and extend your wrists so you could set a plate on
your palms. Your hyper-extended palms represent the
fl at surface of the brain when it fi rst forms. Next, curl
your fi ngertips to demonstrate that during early develop-
ment, there is inrolling of the walls of the hemispheres.
Th en, continue to curl your fi ngers in so that they touch
your palms to form the bilateral lateral ventricles and the
small midline third ventricle. Next, initiate the backward,
downward, and forward evagination of the ventricles.
Bring your forearms back toward your chest, then fan your
elbows apart as you bring your hands downward, and then
extend your arms forward. Th is completes our demonstra-
tion. We can imagine how each of the horns takes shape
during the diff erent steps of lateral ventricular develop-
ment: the frontal horns take shape during the origination
of the ventricular system, the occipital horns are created
during the backward migration, and the temporal horns
form during the downward and forward migration.^4 – 8