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An interruption of the pre-central sulcus at the level of the middle frontal gyrus allows the middle frontal gyrus to merge with the anterior margin of the pre-central gyrus. Sometimes the middle frontal gyrus is subdivided into superior and inferior sections by an inconstant middle frontal sulcus. The middle frontal gyrus is the largest frontal gyrus and is separated from the inferior frontal gyrus by the inferior frontal sulcus. The superior frontal gyrus is separated from the middle frontal gyrus by the superior frontal sulcus, which extends posteriorly to dead end or end in a “T” at the superior precentral sulcus. Over the lateral convexity surface are 3 main gyri oriented longitudinally: superior, middle, and inferior frontal gyri ( Figures 1, 4-10). The largest lobe is the frontal lobe extending from the frontal pole to the central sulcus and inferiorly bordered by the cingulate gyrus (part of limbic lobe) along its medial surface ( Figure 3A, 3B). Typical Patterns of Cerebral Gyri and Sulci Typical Pattern – Frontal Lobe The temporal lobes sit upon the floor of the middle cranial fossa and the occipital lobes lie atop the tentorium cerebelli above the posterior cranial fossa. The basal portion of the anterior frontal lobes sits atop the orbital plates of the frontal bones in the anterior cranial fossa. The midline interhemispheric fissure separates one cerebral hemisphere from the other. In a significant portion of individuals, the posterior ascending ramus of the sylvian fissure on the right has a steeper, more vertical orientation than on the left ( Figures 2A, 2B). A common normal hemispheric asymmetry involving the sylvian fissure exists. A small posterior descending ramus is often present ( Figure 1). The sylvian fissure has various branches including the anterior horizontal and anterior ascending ramus, the anterior and posterior subcentral sulci, and the posterior ascending ramus. The frontal, parietal, temporal, occipital and insular lobes surround the sylvian fissure (lateral sulcus) along the lateral convexity in an anterior to posterior orientation. 1 The limbic lobe/system refers to a functional unit of the brain involved with emotions and instinctual behaviors. Current concepts and nomenclature have expanded the number of lobes to 6, which now includes the insular and limbic lobes. The traditional concept has been that the brain consisted of 4 lobes: the frontal, temporal, parietal, and occipital lobes. The typical patterns of surface anatomy will be presented along with functional attributes when pertinent. Despite this, there is a general schema (pattern) from which the interpreter can call upon to adapt to unexpected individual variances that may not look exactly like the textbook picture. There are also certain normal asymmetries of the cerebral hemispheres that one will often encounter. Variability in gyral/sulcal anatomy is the rule, as no two individuals have the exact same pattern.

The MRI and CT images in this pattern approach will be supplemented with high-resolution, computer-generated 3-D images. This pictorial review will provide the basic tools a radiologist needs to generate an accurate and precise description of neurologic-based diseases by providing a pattern recognition approach and will focus on gyral and sulcal anatomy. Localization is not only critical for the neurosurgeon/neurologist but having this knowledge and being cognizant of the functional deficits related to a specific anatomic location allows the interpreting radiologist to focus attention on specific regions of the brain.

Moore, MD, medical illustrator.Įvaluation of CT and MRI studies of the brain in routine clinical practice >not only requires an accurate identification and description of abnormal findings, but precise localization is essential as well. Note: Figures 3A, 4, 5, 6, 7, 8, 16 and 18 are reprinted with permission from Alastair J.E.