Limbic lobe

Blood supply

Superior hypophyseal arteries, which arise from each internal carotid artery immediately after it pierces the dura, supply the hypothalamus and the infundibulum. A capillary bed in the infundibulum gives rise to portal vessels to the anterior lobe. The posterior lobe is supplied by inferior hypophyseal arteries from the internal carotid arteries in the cavernous sinus.

Venous drainage is to the cavernous and intercavernosal sinuses.

Radiological features of the pituitary gland

Skull radiographs The appearance of the pituitary fossa is affected by disease processes in the gland. This is dealt w i th in the section on the skull.

CT and MRI (Fig. 2. 11) Sagittal and coronal images are most useful. The posterior pituitary has high signal intensity on unenhanced T1 weighted images. The dura above the sella should be horizontal, not convex. The diameter of the infundibulum should be no bigger than the adjacent basilar artery. The sella itself is delineated by signal void of the bony cortex and by the high-intensity signal of marrow in the clivus. The optic nerves and chiasm and the intracranial carotid vessels above, and the sphenoid sinus below, are seen clearly on coronal sections. LIMBIC LOBE (Fig. 2. 12) This is not an anatomical lobe as such but functionally related structures that surround the corpus callosum on the medial surface of the cerebral hemisphere. It includes cingulate splenial and parahippocampal gyri, the hippocampus, the dentate gyrus and the fornix.

The cingulate gyrus curves around the genu and body of the corpus callosum and continues around the splenium as the splenial gyrus. This, in turn, is continuous w i th the dentate gyrus and the hippocampus.

Also included in the limbic lobe are grey matter on the corpus callosum - called the induseum griseum - and white fibres that run along its length - the medial and lateral longitudinal striae.

Hippocampus (Fig. 2. 13) This is a curved elevation in the floor of the inferior horn of the lateral ventricle. Its enlarged, ridged anterior end has the appearance of a paw - the pes hippocampi. The hippocampus consists of grey matter, w i th a fine covering of white matter called the alveus. Its function is concerned w i th behaviour patterns, emotion and recent memory.

Fornix (see Fig. 2. 12) This is an efferent pathway from the hippocampus to the mamillary bodies. Fibres of the alveus converge on the medial border of the hippocampus as a band of fibres called the fimbria of the hippocampus. This becomes free of the hippocampus as the crus of the fornix (the posterior pillar of the fornix).