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Flocculonodular lobe

The flocculonodular lobe is a small, phylogenetically ancient part of the cerebellum located on its inferior surface. It consists of two lateral flocculi and a central nodule, connected by thin pedicles. This lobe plays a crucial role in balance and eye movements, forming the core of the vestibulocerebellum. It is situated anteriorly, adjacent to the fourth ventricle, and is closely associated with the brainstem and the vestibular system.

Anatomy

  • Composed of two flocculi (one on each cerebellar hemisphere) and a central nodule (part of the vermis).

  • Located on the inferior surface of the cerebellum.

  • Bordered posteriorly by the posterior lobe of the cerebellum.

  • The flocculi are connected to the brainstem by the peduncle of the flocculus.

  • Forms the vestibulocerebellum, the oldest part of the cerebellum (archicerebellum).

Synonyms

  • Vestibulocerebellum

  • Archicerebellum (when referring to its phylogenetic classification)

  • Sometimes called the Flocculo-nodular lobe

Arterial Supply

  • Posterior inferior cerebellar artery (PICA): Main supply to the flocculonodular lobe.

  • Anterior inferior cerebellar artery (AICA): May contribute to the flocculus.

  • Superior cerebellar artery: Usually does not supply the flocculonodular lobe.

Venous Drainage

  • Superior and inferior cerebellar veins drain blood from the flocculonodular lobe.

  • Venous blood eventually drains into the transverse sinus and straight sinus via the cerebellar veins.

Function

  • Balance and posture: Integrates vestibular input to maintain equilibrium.

  • Coordination of eye movements: Coordinates smooth pursuit and vestibulo-ocular reflexes.

  • Regulation of muscle tone: Especially in axial and proximal muscles.

MRI Appearance

  • Location: Seen on sagittal and coronal MRI as a small lobe on the inferior surface, anterior to the fourth ventricle.

  • Signal: Normal cerebellar cortex—gray matter (intermediate signal on T1, isointense on T2); white matter (hypointense on T1, isointense on T2).

  • Distinguishing features: Flocculi appear as small bulges lateral to the nodulus; nodule appears at the midline.

  • Atrophy or lesions: May appear as volume loss or abnormal signal in vestibulocerebellar disorders.

CT Appearance

  • Difficult to distinguish from other cerebellar structures due to limited soft tissue contrast.

  • Location: May be inferred by anatomical landmarks (anterior to the fourth ventricle).

  • Lesions: Calcification or hemorrhage can sometimes be seen; otherwise, the flocculonodular lobe is not well visualized on CT.

MRI images

Flocculonodular lobe MRI 3T axial image

MRI images

Flocculonodular lobe MRI 3T coronal image

MRI images

Flocculonodular lobe MRI 3T sagittal image

CT image

Flocculonodular lobe CT sag anatomy image -img-00001-00001