Brain Anatomy Part II
Section VI. Central Sulcus Overview
Identification of the central sulcus is one of the most important anatomy-related tasks in clinical neuroradiology.
The central sulcus can be identified by 4 general methods:
Directly by intrinsic properties of the sulcus
Secondarily after identification of an adjacent sulcus with a known relationship to the central sulcus
Secondarily after identification of an adjacent gyrus with a known relationship to the central sulcus
By using left-right hemispheric symmetry
This section reinforces and builds upon the prior sections, although this section emphasizes intrinsic features of the central sulcus not yet introduced (most material has already been covered!).
It is useful to learn all of these numerous methods of central sulcus identification since any one sign may be absent due to variation or pathology in any given patient and since the signs also facilitate understanding of the anatomy of the frontal lobe, parietal lobe, and Sylvian fissure.
3D surface images show many key signs formed from the central sulcus features and the adjacent gyri and sulci.
Key Signs
The central sulcus extends medially near midline, has a posteriorly-directed termination, and a characteristic omega sign curve.
Key Signs
The central sulcus is continuous and terminates inferolaterally above (not at) the Sylvian fissure. The central sulcus can also be identified secondarily by first identifying adjacent sulci or gyri with a known relationship.
There is a complete ring of gyri that encircles the continuous central sulcus. The primary somatomotor and somatosensory cortex does not like to be disrupted by sulci.
The 'Central Lobe' Circle
The 'central lobe' circle. The precentral gyrus and postcentral gyrus are bridged superior-medially by the paracentral lobule and inferior-laterally by the subcentral gyrus, forming a complete ring around the central sulcus, sometimes referred to as the ‘central lobe.’ The central sulcus does not usually extend through the subcentral gyrus to the Sylvian fissure, contributing to the subcentral ‘U sign.’
AP-directed sulci (SFS, IFS, IPS) typically terminate in T-bone fashion at the precentral sulcus and postcentral sulcus and do not violate the complete central ring. The primary somatomotor and somatosensory cortex does not like to be disrupted. These terminations constitute signs (big T, little t, and IPS intersection signs) to identify anatomy in the central region.
The hand-knob region often has a characteristic curve but the exact appearance of this region can be quite variable.
Handknob Variants: Inverse Omega, Epsilon, and Triplet Signs
The image on the left shows the inverse omega sign of the central sulcus in the right cerebral hemisphere and a double focal curve on the left, which has been called the epsilon sign. Although not well depicted at this level, note that these features are located just posterior to the big T junction of the superior frontal sulcus and precentral sulcus. The image on the right shows a less common configuration in the right central sulcus of three adjacent focal curves, which we will call a triplet sign (note changes related to glioma treatment left frontal lobe which obscure many of the signs of the central sulcus).
Lopsided Epsilon Sign
Lopsided epsilon on the left. There are two focal curves, unequal in size with the lateral curve more prominent than the medial one.
Null Hand Knob Curve
Although there is slight curvature in the central sulcus, there is no true dominant hand know or epsilon sign. Yet another variant configuration of this region. Many variant configurations of the 'hand knob' region are possible.
The Alladin's Lamp Sign: A Compilation of Features
Aladdin's lamp (or teapot) configuration of the central sulcus: the combined effect of a continuous sulcus, a focal handknob curve, a slightly oblique orientation relative to, the medial extent, and the posterior pointed orientation of the medial termination create this configuration. In fact, this appearance can be likened to a lamp or teapot pouring water into the bracket of the pars marginalis at more superior levels.
It is useful to learn numerous signs to identify the central sulcus as each sign can be variable or altered by pathology.
Variant Postcentral Sulcus
In this case, the postcentral sulci (orange arrows) extend medial to the central sulci (red arrowhead) and extend anterior to the pars marginalis of the cingulate sulcus (not fully shown). However, the central sulcus could still be positively identified by the handknob sign on the left, big T sign, symmetry, and Alladin's Lamp appearance.
Variant False L/Big T Signs
False L/Big T signs due to anatomic variation, including discontinuous superior frontal sulcus.
The central sulcus can also be identified on midline and far-lateral sagittal images. As a continuous sulcus, it can be traced while scrolling in-between. In distinction, the central sulcus will be more difficult to identify directly on coronal images.
Near-Midline Sagittal Image of Central Sulcus Signs
Signs related to the central sulcus. The central sulcus is immediately anterior to the pars marginalis of the cingulate sulcus, embedded within the paracentral lobule region. The paracentral lobule typically has a Y-shape in this imaging plane. The central sulcus typically has a posterior convex appearance (posterior bowing sign). The paracentral lobule/pars marginalis of the cingulate sulcus are just anterior to the quadrilateral-shaped precuneus.
Key Central Sulcus Signs, Lateral Convexity
At this level, the central sulcus is best identified by the relationship to other identifiable adjacent sulci and gyri. The central sulcus usually will not extend inferiorly all the way to the Sylvian fissure as there is a subcentral gyrus (with the U sign); however, if you scroll to the extreme lateral image, there may appear to be a superficial communication between the central sulcus and the Sylvian fissure.
Normal 7T SWI appearance
The cortex along the anterior bank of the central sulcus (M1 motor region) is normally mildly hypointense on SWI. This feature may be more marked with increasing MRI field strength. This is within the range of normal due to microscopic features such as intrinsic iron content and is more marked at higher field strengths. This appearance must not be confused with pathology.
ALS
Susceptibility weighted imaging at 3T shows a more sharply etched hypointense rim of the anterior bank of the central sulcus, more marked in the right cerebral hemisphere. This is abnormal and is compatible with this patient's diagnosis of ALS.
Peri-Rolandic Cortex on 7T DIR
The decreased signal of the peri-Rolandic cortex is particularly marked on 7T double inversion recovery (DIR), which effectively combines properties of T2 FLAIR and white matter nulling; both of these lead to relatively decreased signal of the cortex compared to surrounding cortex.
Gray-White Sign
3T MPRAGE demonstrates that the peri-Rolandic cortex is relatively hyperintense compared to cortex elsewhere, with less distinct gray-white differentiation. The M1 and S1 areas are more heavily myelinated than the surrounding cortical regions, which largely accounts for this finding. This has been referred to as the gray-white sign.
