Semilunar Lobules

Description

Semilunar lobules of the cerebellar hemispheres occupy much of the posterior lobe, expanding laterally from the vermian region into broad, leaf-like folia of cerebellar cortex. On the superior and posterior surface, the lobulus semilunaris superior blends anteriorly with Crus I of the ansiform lobule, while more inferiorly the lobulus semilunaris inferior approaches Crus II and the biventral region, with the horizontal fissure separating superior from inferior aspects along the hemisphere’s margin. Cortical folia run in tightly packed, curved lamellae, and their depth implies the underlying cerebellar white matter (arbor vitae) converging medially toward the cerebellar peduncles. Spatially, these lobules sit posterior to the primary fissure-defined anterior lobe and lateral to the midline vermis, emphasizing the cerebellum’s hemispheric, cerebrocerebellar territory. Lateral posterior lobe anatomy matters because it maps closely to planning and coordination of complex, learned movements, and it is a common locus for deficits in posterior circulation pathology. Infarction in the posterior inferior cerebellar artery (PICA) or superior cerebellar artery (SCA) territories can involve the posterior hemispheres, producing limb ataxia, dysmetria, and impaired rapid alternating movements that localize away from the anterior lobe gait-dominant presentations. Mass effect from a cerebellar hemisphere tumor or hemorrhage can compress the fourth ventricle and brainstem at the level of the cerebellar peduncles. Small structures, big consequences. Use this illustration in neuroanatomy teaching on cerebellar lobular organization (posterior lobe, Crus I and Crus II, cerebellar cortex foliation) and in clinical education that links cerebellar stroke syndromes and posterior fossa lesions to surface landmarks. It also suits neurosurgical and neuroradiology publications that need consistent surface nomenclature when correlating operative approaches or MRI segmentation of the cerebellar hemispheres. Anatomical accuracy verified by SciePro's Medical Advisory Board.