Paracentral lobule

The paracentral lobule is located on the medial surface of the cerebral hemisphere, and includes parts of both the frontal and parietal lobes. It is the medial continuation of the precentral and postcentral gyri. It has motor and sensory functions related to the lower limb.

Gross Anatomy

Relations and boundaries

The paracentral lobule is bounded anteriorly by the paracentral sulcus, which is usually an ascending branch of the cingulate sulcus. This sulcus separates the paracentral lobule form the medial frontal gyrus (the medial continuation of the superior frontal gyrus) and the supplementary motor area (the posterior part of the medial frontal gyrus) ^1-4.

Posterior the paracentral lobule bounded by the pars marginalis, which is the ascending termination of the cingulate sulcus, and separates the paracentral lobule form the precuneus^1-4.

Inferiorly the cingulate sulcus separates the paracentral lobule from the cingulate gyrus. 

The central sulcus extends into the posterosuperior aspect of the paracentral lobule in most cases. Hence, the portion lying anterior to the sulcus is frontal lobe, while the portion lying posterior is parietal lobe ^1,4.

It is important to note, that the medial continuation of the precentral sulcus (which is often interrupted), is not the anterior border of the paracentral lobule, as this is located posterior to the paracentral lobulesulcus ^3,4. As a result of this, the superior frontal gyrus extends further posteriorly than the medial frontal gyrus, and the paracentral lobule includes not just the medial continuation of the precentral and postcentral gyri, but also an additional gyrus anteriorly ^3,4.  

Function

The anterior two-thirds are part of the primary motor area controlling the leg, foot and urinary bladder. 

Blood supply

It is supplied by branches of the anterior cerebral artery.

Variant anatomy

Approximately 95% of paracentral lobules are of continuous type. Continuous paracentral lobule describes incomplete separation of the precentral and postcentral gyri, such that they merge together. The remaining 5% are of segmented type , with complete separation of the precentral and postcentral gyri ². In this latter type, an additional small gyrus, known as the lobulo-limbic transitional gyrus is found between the lower border of the paracentral lobule and cingulate gyrus ².