The sagittal midline of the brain is one of the most important sectional planes in neuroimaging. A good working knowledge of the normal neuroanatomy of the sagittal midline is essential so that the subtle abnormalities that may manifest here can be recognized.
The neuroembryological development of the brain results in a striking symmetry that is evident throughout the majority of the brain. The sagittal midline in neuroimaging provides a unique opportunity to observe in a single slice, the continuity of the cerebrospinal fluid pathway, to observe if there are any abnormalities of the brainstem and diencephalon such as agenesis or hypoplasia and to observe if there is any displacement of the midline.
Viewing the sagittal midline is often an appropriate starting point when reading an MRI of the brain:
- the sagittal midline is observed when the cerebral aqueduct can be seen draining the third ventricle into the fourth ventricle
- then starting inferiorly, the reading commences by systematically reviewing the midline structures and noting if there is:
- any displacement, of the cerebellar tonsils, or crowding of the foramen magnum
- a review of the cisterns is important to note any displacement of the midline
- moving superiorly, the cerebral aqueduct is observed for patency
- the superior aspect of the midbrain is observed for its normal convex contour forming the posterior floor of the third ventricle
- the fornix and corpus callosum are inspected to note any agenesis, dysplasia or hypoplasia