The U sign: tenth landmark to the central region on brain surface reformatted MR imaging

Abstract

Background and purpose: Identification of the central region is of special importance to avoid neurologic deficits in brain surgery. Brain surface reformatted images (Mercator view) map the frontoparietal brain surface in 1 view and provide a synopsis of the most important landmarks. In this view, the U-shaped subcentral gyrus appears as a distinctive anatomic structure enclosing the Sylvian end of the central sulcus. The purpose of this study was to add the subcentral gyrus as a new landmark to the central region (U sign) and to compare its frequency and applicability with common landmarks in healthy hemispheres.

Materials and methods: Mercator views of 178 hemispheres in 100 patients were generated from 3D MR imaging datasets. The hemispheres were evaluated on Mercator views for the presence or absence of each of the 9 common landmarks and the new U sign identifying the central region.

Results: The new landmark U sign was most common (96.6%), followed by the thin postcentral gyrus sign (95.5%). The least common landmark was the Ω-shaped handknob (54.5%). None of the landmarks could be identified in all hemispheres. All landmarks could be identified bilaterally in only 1.3% of patients.

Conclusions: On the Mercator view, the new U sign is an applicable and even the most frequent landmark to identify the central region. Considering the variability of the anatomic structures of the brain, including the motor hand area, the synopsis of all 10 landmarks on this surface-reformatting projection is a helpful adjunct to standard MR imaging projections to identify the central region.

Fig 1.

Example of the thin post cg sign, and the midline sulcus sign. The precentral gyrus has a thicker anteroposterior diameter (large white arrow) compared with the postcentral gyrus (small white arrow). The longest sulcus running horizontally and entering the interhemispheric fissure (black arrow) is the central sulcus.

Fig 2.

Variants of the handknob. In our study, we only considered the inverted Ω shape (white arrow) because other variants, such as inverted ε (continuous black arrows), and multiple bulgings (dotted black arrows) were not assessed.

Fig 3.

The U sign. Right hemisphere. Absence of the subcentral gyrus as a rare variant, the central sulcus (asterisk) terminates into the Sylvian fissure (white arrow). Gray arrows mark the precentral (continuous arrow) and postcentral (dotted arrow) gyri. Left hemisphere: The subcentral gyrus connects the pre- and postcentral gyri (U sign).

Fig 4.

Examples of all 10 landmarks in 1 single section: 1 indicates the upper T sign; 2, the L sign (duplicated as a variant); 3, the lower T sign; 4, the M sign; 5, the bracket sign; 6, the bifid post cg sign; 7, the thin post cg sign (fenestrated post cg as a variant); 8, the midline sulcus sign; 9, the subcentral gyrus sign; 10, the handknob. Only 1 hemisphere is depicted and was mirrored for better visualization.

Fig 5.

Barplots representing the frequency of landmark identification as a percentage of all (blue), right (purple), and left (yellow) hemispheres.