258 Neuroanatomy: Draw It to Know It
Peduncles, Midline Structures, Arteries (Cont.)
II. Midline Structures
Now, in order to draw the fl occulonodular lobe and cer-
ebellar tonsils, fi rst label the fourth ventricle and indi-
cate that the midline portion of the cerebellum is the
vermis, and also show that the outer aspect of the cere-
bellum is the hemisphere. Next, include in our diagram
the two components of the fl occulonodular lobe: in the
hemisphere, show the fl occulus, and in the vermis, show
the nodule. We show these structures, here, because the
unfolded schematic of the cerebellum, which is so com-
monly used to represent the cerebellum, places the fl oc-
culonodular lobe at the bottom of the diagram, and we
need to appreciate that the fl occulonodular lobe actually
lies in anterior, mid-cerebellar position. Also, above the
fourth ventricle, include the lingula: the slender vermian
tip of the anterior cerebellar lobe. Th e lingula combines
with the fl occulonodular lobe to form the vestibulocer-
ebellum (or archicerebellum), which infl uences equilib-
rium and eye movements.
Next, include one of the paired cerebellar tonsils; we
include the cerebellar tonsils because this paired, midline
structure is an important aspect of a common neurologic
condition, Chiari malformation. Chiari malformation is
a wide-ranging syndrome divided into three diff erent
subtypes: types I, II, and III. Type I is the most mild
and type III is the most severe. Chiari malformation
always involves downward displacement of the cerebel-
lar tonsils through the foramen magnum, but what
determines its morbidity is the degree of cerebellar
displacement and the degree of displacement of addi-
tional brainstem structures. Also, what determines its
morbidity is the associated pathologic involvement
of other areas of the central nervous system. Notably,
type I Chiari malformation is found in roughly two
thirds of cases of syringomyelia (a central cavitation of
the spinal cord), and type II Chiari malformation (aka
Arnold-Chiari malformation) is almost universally asso-
ciated with myelomeningocele (a protrusion of the
spinal cord and meninges through a defect in the poste-
rior vertebral column). Patients with Chiari malforma-
tion range from being entirely asymptomatic (when the
malformation is only incidentally found on radiographic
imaging ) to being severely aff ected with considerable
developmental delay and substantial motor–sensory
defi cits.^12 – 15III. Arterial Supply
Lastly, let’s show the basic arterial supply of the cerebel-
lum. First, let’s draw the vertebrobasilar arterial arrange-
ment and then show its cerebellar perfusion pattern.
Show that paired vertebral arteries derive the basilar
artery, which branches into the paired posterior cerebral
arteries. Th en, indicate that the posterior inferior cere-
bellar arteries emerge from the vertebral arteries. Next,
at the base of the basilar artery, show that paired anterior
inferior cerebellar arteries emerge and, fi nally, at the
upper portion of the basilar artery, show that the paired
superior cerebellar arteries emerge. Now, show that on
the anterior surface of the cerebellum, the posterior infe-
rior cerebellar arteries perfuse the inferior cerebellum;
the anterior inferior cerebellar arteries perfuse the mid-
lateral cerebellum; and the superior cerebellar arteries
perfuse the superior cerebellum. We show the discrete
vascular cerebellar territories in Drawing 19-6.^1 – 11 , 16 , 17