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The brain

The sellar region

Modalities for examination


CT and MRI allow good demonstration and analysis of pathological processes in the region of the sella. The relative positions of the anatomical structures within this region allow optimal visualization in the coronal plane. However, the sagittal plane has certain advantages. The examination should include visualization of the region of the hypothalamus and also the part of the sphenoid sinus nearest the sella. With MRI, greater contrast differences between the tissues are achieved than with CT and in addition artefacts caused by the base of the skull, the sinuses and tooth fillings are avoided. Another advantage of MRI is that it is multiplanar. One of the disadvantages of MRI as opposed to CT is that calcifications are not shown or are difficult to assess and this is also true of bone lesions. In summary, MRI is regarded as the examination of choice in this region. The posterior lobe has a higher signal intensity than the anterior lobe on T1-weighted images.

The need for computed cisternography has decreased with the technical development of CT and MRI which allow improved geometrical resolution. Plane X-ray examination of the sella region and tomography have become more or less obsolete.

Anatomy

The sella turcica is bordered superiorly by diaphragma sellae and laterally by the cavernous sinus. Above the sella turcica is the chiasmatic cisterna and this contains the upper part of the infundibulum, the optic nerves and chiasm, the supraclinioid parts of the carotid siphons and the circle of Willis. The normal height of the pituitary gland is 3-8 mm and its width 10-17 mm. The upper surface is normally flat or somewhat concave, seldom convex. A convex upper surface occurs, however, more often

 

/upload/book of radiology/chapter09/nic_k9_8.6.jpg a

Figure 4. Normal pituitary gland.
a) MRl in the sagittal plane. Above the pituitary gland the stalk of the pituitary gland can be seen (horizontal arrow) as can the optic chiasm (vertical arrow).
b) CT in the coronal plane through the pituitary gland. lnferiorly the base of the sella and the sphenoid sinus are seen, superiorly the stalk of the pituitary gland and on each side of this is the anterior clinoid processes (vertical arrow) and in addition the cavernous sinus (star). The contrast medium-filled left carotid siphon can also be seen (horizontal arrow).

/upload/book of radiology/chapter09/nic_k9_8_2.jpg b

in young patients or pregnant women but symmetry is pre served, although the height can increase to 9-10 mm. Slight asymmetry, less than 1.5 mm, of the bottom of the sella is relatively common. The correlation between the size of the pituitary gland and the volume of the sella is poor The normal anatomy of the sellar region is shown in Fig. 4

 

Kjell Bergstrom and Giuseppe Scotti