The central sulcus joins the Sylvian Fissure in only 2 % of cases .
In 98 % there is a subcentral gyrus.
The precentral gyrus and postcentral gyrus are consistently united inferiorly by the subcentral gyrus (Broca’s inferior frontoparietal pli de passage, or rolandic operculum).
A single axial DWI image – obtained in the anterior commissure–posterior commissure plane – was selected from each scan just above the subcentral gyrus such that it included the most inferolateral portion of the central sulcus. These single images were given to 10 readers (neuroradiologists, a neuroradiology fellow and radiology trainees) who marked the central sulcus based on the presence of the ‘invisible cortex sign’. Their accuracy in identifying the central sulcus was compared with that of the principal investigators, who used tri-planar T1 volumetric MRI sequences.
One hundred and eight consecutive patients (55 female, 53 male) were selected, ranging from 18 to 81 years old (mean = 40.5, σ = 18.2). The central sulcus was correctly identified in 95.5% of cases (σ = 3.7%; range 89.4-99.1%).
The ‘invisible cortex sign’ is a highly accurate method of identifying the inferolateral central sulcus on a single axial DWI slice without relying on the more superior aspects of the sulcus 1).
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 distinct anatomic structure enclosing the Sylvian end of the central sulcus. The purpose of a 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.
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.
The 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.
On the Mercator view, the 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 2).
Subcentral gyrus approach
Maesawa et al. reported on a patient presenting with secondary somatosensory cortex epilepsy with a tumor in the left deep parietal operculum. The patient was a 24-year-old man who suffered daily partial seizures with extremely uncomfortable dysesthesia and/or occasional pain on his right side. MRI revealed a tumor in the medial aspect of the anterior transverse parietal gyrus, surrounding the posterior insular point. Long-term video electroencephalography monitoring with scalp electrodes failed to show relevant changes to seizures. Resection with cortical and subcortical mapping under awake conditions was performed. A negative response to stimulation was observed at the subcentral gyrus during language and somatosensory tasks; thus, the transcortical approach (specifically, a transsubcentral gyral approach) was used through this region. Subcortical stimulation at the medial aspect of the anterior parietal gyrus and the posterior insula around the posterior insular point elicited strong dysesthesia and pain in his right side, similar to manifestation of his seizure. The tumor was completely removed and pathologically diagnosed as pleomorphic xanthoastrocytoma. His epilepsy disappeared without neurological deterioration postoperatively. In this case study, 3 points are clinically significant. First, the clinical manifestation of this case was quite rare, although still representative of secondary somatosensory cortex epilepsy. Second, the location of the lesion made surgical removal challenging, and the transsubcentral gyral approach was useful when intraoperative mapping was performed during awake surgery. Third, intraoperative mapping demonstrated that the patient experienced pain with electrical stimulation around the posterior insular point. Thus, this report demonstrated the safe and effective use of the transsubcentral gyral approach during awake surgery to resect deep parietal opercular lesions, clarified electrophysiological characteristics in the secondary somatosensory cortex area, and achieved successful tumor resection with good control of epilepsy 3).