Brain Anatomy Part III
Section XIII. Cerebellum
In a general sense, the basic anatomy of the cerebellum (little brain) mirrors that of the cerebrum. There is a peripheral cortex, central white matter, and deep gray nuclei. The deep gray nuclei communicate with the cortex and also send or relay information to or from the cerebellum (analogous to the supratentorial deep gray structures). There are also two hemispheres and different cerebellar lobes.
In distinction however, the cerebellar hemispheres are connected via a midline vermis. Each of the three lobes spans both hemispheres and the vermis. These lobes are separated by fissures. The lobes can be further subdivided into numerous lobules, which are further detailed in the full classic atlas. For most general radiology purposes, the precise lobule affected is not as important, although an understanding or reference for normal anatomy of the lobules of the vermis can be useful to assess vermian hypoplasia.
The cerebellum actually contributes to diverse functions as outlined in the full atlas and the bulk of the dedicated motor-related function seems to be found primarily within the anterior lobe (which is considerably smaller than the posterior lobe).
Illustrations are adapted from the following article that can be reviewed for additional detail:
Lehman VT et al. Current concepts of cross-sectional and functional anatomy of the cerebellum: a pictorial review and atlas. BJR 2020;93(1106)
Cerebellar Lobules and Fissures, Superior View
Illustration of the cerebellum superior view. The lobules span both hemispheres and vermis. The primary fissure separates the anterior lobe (lobules I-V) from the posterior lobe (lobules IV-IX).
Cerebellar Lobules and Fissures, Inferior View
3D Illustration of the cerebellum, inferior view. The posterior lobe is the largest and is separated from the flocculonodular lobe (lobule X) by the posterolateral fissure.
Cerebellar Lobules and Fissures, Posterior View
3D illustration of the cerebellum, posterior view. The most prominent fissure is the horizontal fissure followed by the superior posterior fissure. The horizontal fissure has potential to be confused with pathology such as infarct on axial images. These two fissures together produce a bowtie sign on coronal images around crus I (part of lobule VII).
Cerebellar Lobules and Fissures, Anterior View
3D illustration of the cerebellum, anterior view. The lobules form a ring, with the most expansive portion consisting of lobule VII (crus I/II), which is devoted largely to association functions. Lobules I-III of the anterior lobe are small and hidden from view from the posterior and surface perspective.
Lobules of the Vermis
Patterns of lobules of the vermis need not be memorized, but it is useful to have a reference for comparison when vermian hypoplasia is being considered.
Cerebellar Lobes
The anterior and posterior lobes are separated by the primary fissure. More directly, the primary fissure separates lobules V and VI. Note that the anterior lobe is considerably smaller and really superior/cranial in location rather than anterior in the upright position.
These lobules also have common names and have been classified in slightly different ways by different authors.
Clinical Correlate Cases
Joubert's Syndrome
Patient with Jourbert's Syndrome and a molar tooth appearance of the superior cerebellar peduncles. There was also absence of the decussation of the superior cerebellar peduncles.
MSA-C
Small middle cerebellar peduncles, in particular on the right, in the setting of multiple system atrophy type C.
Dentate Nuclei Gadolinium Accumulation
Patient with multiple prior doses of gadolinium and increasing T1 hyperintensity of the dentate nuclei on successive examinations. The dentate nuclei may be inconspicuous on gadolinium-naïve patients.
Acute Aphasia
Patient with acute aphasia and no abnormality in the cerebral hemispheres, including left presumed language areas.
Key Clinical Correlates of the Cerebellum
The anatomy of the cerebellum is complex. For most radiology purposes, it can be thought of as having two hemispheres and a connecting midline vermis. Together, the hemispheres and vermis are divided into an 'anterior' lobe, a 'posterior' lobe, and a flocculonodular lobe.
The lobes are subdivided into lobules by fissures, most of which need not be memorized for general purposes but can instead be determined by comparing to a reference when needed.
There is central white matter, peripheral cortex, and deep nuclei. The main nucleus that is recognized on imaging is the dentate nucleus.
The pattern of lobules in the vermis on a midline sagittal image though may be useful to understand for assessment of cases of vermian hypoplasia.
In general, cerebellar afferents arrive via the middle cerebellar peduncles (descending) and inferior cerebellar peduncles (ascending) and most efferents depart via the superior cerebellar peduncles.
The triangle of Mollaret is important to understand as lesions can result in hypertrophic olivary degeneration (HOD) and palatal myoclonus.
The function of the cerebellum is complex and diverse. To a first approximation, most motor function locates to the anterior lobe and truncal control locates medially. Much of the cerebellum is dedicated to associative functions.
Thus, lesions of the cerebellum can result in a wide array of clinical deficits, ranging from motor, affective, language, memory, oculomotor and others such as headache.
Clinical deficits may also reflect simultaneous lesion of the adjacent brainstem.
