Primary motor cortex

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Frontal lobe

U-shaped fibres of the central sulcus

• U shaped fibres connecting the pre and post central gyrus.
• seen on functional MRI and nTMS.

• Function: sensorimotor integration for fine hand movements.

Identification of central sulcus

• Continuous sulcus with cingulate sulcus

• Sigmoidal hook (handknob, omega) sign:
• The precentral gyrus bulges posteriorly at the hand motor area

• Midline sulcus sign:
• The central sulcus is the longest sulcus in a roughly coronal plane intersecting the interhemispheric fissure

• Upper T sign:
• The superior frontal sulcus intersects the precentral sulcus in a "T" junction. The central sulcus is the next posterior sulcus.

• L sign:
• The superior frontal gyrus intersects precentral gyrus in an "L" junction. The central sulcus is immediately posterior.

• Lower T sign:
• The inferior frontal sulcus terminates posteriorly in the precentral sulcus in a "T" junction. The central sulcus is the next posterior sulcus.

• M sign:
• The inferior frontal gyrus has a characteristic "M" configuration and terminates posteriorly in the precentral gyrus. The central sulcus is immediately posterior.

• Bracket sign:
• The marginal sulcus is visible immediately posterior to the central sulcus, and is easily identifiable of sagittal paramedian images as the continuation of the cingulate sulcus

• Thin postcentral gyrus sign:
• The postcentral gyrus is thinner than the precentral gyrus

• Bifid postcentral gyrus sign:
• The postcentral gyrus is split medially by the pars marginalis of the cingulate sulcus

• U sign:
• The most inferolateral extent of the central sulcus is capped by a U-shaped gyrus – the subcentral gyrus – which abuts the lateral fissure