Overview
This lecture covers key methods for identifying the central sulcus on brain MRI, a crucial skill for neuroanatomy and neuroradiology.
Importance of the Central Sulcus
- The central sulcus separates the frontal and parietal lobes of the brain.
- It also divides the precentral (motor) and postcentral (sensory) gyri.
- Accurate identification is essential for neuroimaging interpretation.
Methods to Identify the Central Sulcus
1. Midline Sulcus Sign
- Look for a sulcus intersecting the interhemispheric fissure and extending toward the lateral brain surface and Sylvian fissure.
2. Upper T Sign
- The superior frontal sulcus meets the precentral sulcus, forming an upside-down T; the central sulcus lies just posterior.
3. Upper L Sign
- The superior frontal gyrus continues laterally into the precentral gyrus, forming an L shape; the central sulcus is just behind.
4. Bracket/Mustache (Pars Marginalis) Sign
- The pars marginalis appears as a bracket or mustache on axial slices; the first sulcus anterior is the central sulcus.
5. U Sign (Sagittal Plane)
- The central sulcus is surrounded by brain tissue, forming a U-shape and not reaching the Sylvian fissure.
6. Bifid Postcentral Gyrus Sign
- The pars marginalis splits the postcentral gyrus into two, with the central sulcus just anterior.
7. Inferior Frontal Gyrus and X/Lower T Sign
- The inferior frontal sulcus meets the precentral sulcus in a T shape; the next sulcus posteriorly is the central sulcus.
8. Thin Postcentral Gyrus Sign
- The postcentral gyrus is noticeably thinner than the precentral gyrus on axial images.
9. Sigmoid Hook/Omega Sign
- The precentral gyrus forms an upside-down omega or sigmoid hook (hand knob) near the central sulcus.
10. T1 Gray-White Sign
- Gray-white matter differentiation is visible on both pre- and postcentral gyri, but less so where they meet at the central sulcus.
Key Terms & Definitions
- Central Sulcus — groove separating the frontal and parietal lobes, and the precentral and postcentral gyri.
- Precentral Gyrus — anterior to the central sulcus; primary motor cortex.
- Postcentral Gyrus — posterior to the central sulcus; primary sensory cortex.
- Interhemispheric Fissure — deep groove dividing the two cerebral hemispheres.
- Sylvian (Lateral) Fissure — separates the frontal and parietal lobes from the temporal lobe.
- Pars Marginalis — superior extension of the cingulate sulcus, helps locate the central sulcus.
Action Items / Next Steps
- Review and practice identifying the central sulcus using 2–3 preferred signs on MRIs.
- Read the referenced Radiopaedia article for further review.
- Revisit specific signs as needed for exam preparation.