SELF TEST

The Limbic System Self Test

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Answer to Question 1:

Regarding the basal forebrain, all the
following are true except,

a. The main portion of the basal forebrain is found in the subcallosal area.
b. It is located immediately superior to the suprasellar cistern.
c. On transaxial images, it forms a bulge posterior to the gyrus rectus.
d. On coronal images, it can be identified at the level where the anterior temporal lobe becomes continuous with the rest of the brain.
e. It lies anterior to the mammillary bodies.

Discussion:

This question concerns the location of the basal forebrain as seen on MR and CT images. The basal forebrain has relatively few distinctive internal features. The main portion of the basal forebrain is located on the ventral surface of the brain immediately superior to the suprasellar cistern. A portion of the basal forebrain which contains the septal nucleus and the vertical portion of the diagonal band of Broca lies lateral to the subcallosal area on the medial surface of the inferior frontal lobe. The most anterior portion of basal forebrain is the anterior perforated substance which lies posterior to the gyrus rectus. The anterior perforated substance lies directly below the nucleus accumbens in the ventral striatum. See CT image 6 and MR image 5. The main portion of the basal forebrain is relatively featureless. It is seen as a heterogeneous collection of white and gray matter on coronal CT images. On way of locating this region on coronal images is to start with anterior sections of the temporal lobe in which the temporal lobe is seen as a structure completely separated from the rest of the brain as in MR coronal image 3. The image in which the temporal lobe lobe becomes joined to the rest of the brain is at the level of the mid portion of the basal forebrain. The posterior portion of the basal forebrain is at the coronal level of the mammillary bodies, MR image 10. See also the entry in Neuroanatomy Glossary.