Cerebellar Lobes, Lobules, and Zones

At the most general level, it is common to divide the cerebellum into a narrow midline vermis and expansive lateral hemispheres. The cerebellum is further divided into anterior, posterior, and flocculonodular lobes by the primary and posterolateral fissures, respectively. The lobes of the cerebellum are composed of yet smaller divisions called lobules. The lobules of the vermis are identified by Roman numerals I to X; the corresponding lateral (hemisphere) portion of each vermis lobule is identified by the same Roman numeral but with the prefix H. Vermis lobules II to X have hemisphere portions HII to HX; lobule I does not have a hemisphere part in humans. The anterior lobe comprises lobules I to V and HII to HV, and the posterior lobe, lobules VI to IX and HVI to HIX. The flocculonodular lobe consists of the nodulus (lobule X) and its hemisphere counterpart, the flocculus (lobule HX). In turn, each lobule consists of a series of individual ridges of cortex called folia (singular, folium).

The individual folia are continuous from one hemisphere to the other, across the midline on the superior cerebellar surface. This pattern, obvious on the superior cerebellar surface, is disrupted on the inferior surface by the enlargement of the lateral parts of the cerebellum and consequent infolding of the midline area.

Superimposed on the lobes and lobules of the cerebellum are rostrocaudally oriented cortical zones that are defined on the basis of their connections. There are three principal zones on each side: the medial (vermal), intermediate (paravermal), and lateral (hemisphere) zones. On the basis of their afferent and efferent connections, these three larger cortical zones can be subdivided further into nine smaller zones. In general, these zone patterns are the basis for the modules. The clinical deficits that result from a cerebellar lesion depend mainly on which of the three principal zones is involved; consequently, the three-zone terminology is used.

The medial (vermal) zone is a narrow strip of cortex adjacent to the midline that extends throughout anterior and posterior lobes and includes the nodulus. This zone is widest in lobule VI and tapers rostrally and caudally. The intermediate (paravermal) zone lies adjacent to the medial zone and extends throughout anterior and posterior lobes but has little representation in the flocculonodular lobe. The lateral (hemisphere) zone occupies by far the largest part of the cerebellar cortex. It includes large portions of anterior and posterior lobes and the flocculus.