Brain Anatomy Part I
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Section I. Essential Neuroanatomy Overview
Color-coding of anatomic structures is consistent throughout this section, whether officially labelled or not.
We will start with the brain. Brain structures are depicted as patterns of size, location, orientation/configuration, and/or relationship wherever possible—referred to as ‘anatomic signs.’
Basic function, clinical significance, and examples of pathologically deranged anatomy are highlighted to reinforce key anatomy.
Although brief figure legends and text are provided, images are intended to be stand-alone and self-explanatory in quality and detail.
There is logical progression of concepts. To reduce redundancy of depiction of identical images in different sections, the contents of a given section may spill-over slightly into others without strict boundaries.
The first several sections (focused on the Sylvian fissure, cingulate sulcus, frontal lobe, and parietal lobe) briefly mention some methods to identify the central sulcus via recognition of the relationship of the central sulcus to sulci and gyri in these areas and build to the central sulcus section.
Later sections focus on structures beyond the central sulcus region, including further demonstration of the structures of the midline sagittal image-another key concept in clinical neuroanatomy of the brain.
Later sections on the head/neck, spine, and neurovascular anatomy also emphasize patterns and clinical significance.
Section II. Properties and Patterns of the Sulci Overview
Recognition of the properties of sulci is key to understanding surface anatomy.
The dominant features of the major sulci used to identify major signs of surface anatomy are reasonably constant.
Important properties of sulci to understand include the:
–Location
–Orientation
–Curvature
–Depth
–Continuity (continuous or discontinuous)
–Termination (blind, bifurcated, end-to-end, end-to-side)
Understanding sulcal patterns is key to recognition of the signs of cerebral surface anatomy. Here are some basic properties:
Throughout, we will see that these properties help define many patterns, or signs, that typically allow us to instantly recognize all majory sulci and gyri of the brain.
Major Sulci and Features
3D surface view shows some key examples. We will learn that the superior frontal sulcus (dark red) terminates at the precentral sulcus (yellow) with an 'end-to-side' junction. Unlike the precentral and postcentral sulci, the central sulcus (dark blue) is continuous without gaps. The central sulcus has characteristic curvatures, orientation, and blind terminations. Other sulci like that postcentral sulcus (red) often end with a short bifurcation.
Sulci that are perpendicular to an imaging plane are well-seen. Those that are 'in-plane' are usually poorly seen in that plane, although may be associated with a 'sheet-like' or 'highly-convoluted' appearance of lining gyri. The sheet-like/convoluted appearance is the basis of some of the signs we will learn.
In-plane vs. Orthoganol-plane depiction of the superior frontal and middle frontal sulci
The superior frontal sulcus courses within the sagittal plane. It is well visualized only in the coronal and axial planes. On sagittal images, it is in-plane and would not be well-seen.
The middle frontal sulcus courses within the axial plane and is only well visualized in the coronal and sagittal planes. On axial images, it is in-plane and would not be well seen.
Calcarine Sulcus
The calcarine sulcus courses closest to within the axial plane. However, it is oblique to all 3 standard planes and thus readily identified in all 3 planes. The location on axial images can be approximated by the convoluted sheet-like appearance of the surrounding cortex (and associated protuberance into the ventricular atria (the calcar avis). We will see that the overall appearance leads to a 'heart-shape' or 'caduceus appearance' of the sulcus.
Lateral Occipito-Temporal Sulcus
The lateral occipital temporal sulcus, which courses in the sagittal plane and divides the inferior temporal gyrus laterally from the lateral occipital temporal gyrus medially is seen as 'sheet-like' area of cortex. This results in a 'plateau' or 'double plateau' appearance.
Here are a just a few correlate cases to show utility of understanding sulcal properties focusing on the Sylvian fissure. The Sylvian fissure is the first sulcus to form and its characterization is key to identification of many congenital abnormalities.
Normal Variant Disproportionately Prominent Sulci
The parieto-occipital fissure is focally prominent relative to the other sulci. Various sulci can be focally prominent as a normal variant; this finding increases with age. Be cautious over-interpreting such a finding as supporting focal volume loss, encephalomalacia or necessarily supportive (in isolation) of NPH.
DESH
Focally-prominent sulci [Disproportionately Enlarged Subarachnoid Space Hydrocephalus-DESH] can also lend support to the possibility of NPH. In this case, the medially-convex left intra-parietal sulcus is focally-widened. This patient also had disproportionately enlarged ventricles, crowding of sulci near the vertex, prominent Sylvian fissures in the setting of walking difficulty.
Polymicrogyria
The Sylvian fissure region is a common location for polymicrogyria. Such polymicrogyria typically lines clefts or unnamed fissures that do not correspond to named sulci. This image demonstrates and unnamed cleft along the lateral convexity (i.e. not a normal named sulcus) lined with thickened abnormal cortex with an irregular border with the adjacent white matter.
Classic Lissencephaly
Even in this condition with nearly absent gyri/sulci throughout (and thickened layered cortex), the Sylvian fissures are still identified as shallow indentations. The overall appearance can be described as a 'figure 8' or 'hourglass' appearance. The Sylvian fissure is the first major sulcus to form and thus a reasonably constant and prominent feature of surface anatomy.
Alobar Holoprosencephaly
Although the Sylvian fissures are usually present in some form, they still are absent in alobar holoprosencephaly. Note the large monoventricle with a thin rim of smooth peripheral 'pancake' cortex without evidence of Sylvian fissures.
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