Imaging of the Sella Turcica
May 1, 1999 5 minutes read
Special Feature
Imaging of the Sella Turcica
By Leon Speroff, MD
Over the years, the screening approach i have recommended for patients with galactorrhea and amenorrhea is the combination of a prolactin level and the lateral coned-down view of the sella turcica. With the availability of more sophisticated (and more expensive) imaging techniques, the coned-down view of the sella turcica fell out of favor with radiologists. In some areas, it is even difficult to find a radiologist who is experienced in reading the lateral coned-down view. Modern endocrinologists have supported this movement away from the coned-down view, citing the greater accuracy of the more modern techniques. Let me make an argument for the continued use of the coned-down view, and for some of you, a return to the coned-down view.
There has been growing conservatism in the management of small pituitary tumors because of an appreciation that the majority of these tumors never change.1-3 I recommend a conservative approach of close surveillance, advocating dopamine agonist treatment for those prolactin-secreting tumors that display rapid growth or for those tumors that are already large, and reserving surgery only for those tumors that are unresponsive to medical therapy. This means that small tumors (microadenomas that are < 10 mm in diameter) need not be treated at all. Hence, the initial x-ray evaluation for amenorrheic patients with or without galactorrhea can be the coned-down lateral view of the sella turcica. This will detect the presence of a large tumor, although an incredibly rare suprasellar extension might escape this method. The coned-down lateral view of the sella is also a good screen for other lesions, such as a craniopharyngioma. Combining this screening technique with the prolactin assay, we are able to select those few patients who require more sensitive sellar imaging.
For the greatest accuracy, the diagnostic modality of choice is either thin-section coronal computed tomography (CT scan) with intravenous contrast enhancement or magnetic resonance imaging (MRI) with gadolinium enhancement. CT scanning (capable of high-resolution 1.5 mm cuts) is able to evaluate the contents of the sella turcica as well as the suprasellar area; however, total accuracy is not achieved.4 MRI is even more sensitive than the CT scan, but it is also more expensive and it requires a lengthy period of time to obtain the images. MRI provides highly accurate assessments without biologic hazard, and it is better for evaluation of extrasellar extensions and the empty sella turcica.5 Most neuroradiologists and neurosurgeons prefer MRI, as do I. My intention, however, is to be conscious of cost and to isolate those few patients who require sophisticated but expensive imaging.
If the prolactin level is greater than 100 ng/mL or if the coned-down view of the sella turcica is abnormal, I recommend CT scan evaluation or MRI. A double floor of the sella is often seen on the coned-down view and, in the absence of enlargement and/or demineralization, is interpreted as a normal variation rather than asymmetrical depression of the sellar floor by a tumor. The presence of visual problems and/or headaches should also encourage CT scan or MRI evaluation. Headaches are definitely correlated with the presence of a pituitary adenoma.6 Although they are usually bifrontal, retro-orbital, or bitemporal, no locations or features are specific for pituitary tumors.
The prolactin level of 100 ng/mL for determining a more aggressive approach has been empirically chosen. Both in my own experience and that of others, large tumors are most frequently associated with prolactin levels greater than 100 ng/mL. Large masses associated with prolactin levels less than 100 ng/mL are more likely to be tumors other than prolactin-secreting adenomas, causing stalk compression and interruption of the normal dopamine regulation of prolactin secretion. These tumors will be associated with abnormal changes present in the coned-down view of the sella turcica.
If imaging rules out an empty sella syndrome or a suprasellar problem, treatment is dictated by the patient’s desires, the size of the tumor, and the rapidity of growth of the tumor. The above approach to the problem of pituitary tumors implies that patients with prolactin levels less than 100 ng/mL and with normal coned-down views of the sella turcica can be offered a choice between treatment and surveillance. An annual prolactin level and a periodic coned-down view (at first annually and then at increasing intervals) are indicated for continued observation to detect an emerging and slow-growing tumor. Dopamine agonist therapy is recommended for patients wishing to achieve pregnancy and for those patients who have galactorrhea to the point of discomfort. Thus far, long-term therapy with a dopamine agonist has not been proven to be successful in producing a complete reversal of the problem (with either permanent suppression of elevated prolactin levels or elimination of small tumors). Thus, a strong argument can be made for a "need not to know" the presence of a pituitary microadenoma. If treatment and management are not changed, it is not necessary to document the presence of a microadenoma.
Reasons why the diagnosis of microadenoma is not necessary include:
• Microadenomas are common.
• Microadenomas rarely grow during pregnancy.
• Microadenomas rarely progress to a macroadenoma ( > 10 mm in diameter )
• There is a significant recurrence rate after surgery.
• The natural course is unaffected by dopamine agonist treatment.
• There is no contraindication to hormone therapy or oral contraception.
• It is better to avoid the problem of the pituitary incidentaloma.
Contemporary reviews point out the shortcomings of the coned-down view of the sella turcica, citing the limitation of excluding only macroadenomas.7 Indeed, reviews of my textbook have faulted the chapter on amenorrhea for being less than state-of-the-art, emphasizing that where I use the coned-down view, MRI should be uniformly obtained. I would argue that the state-of-the-art approach is to use the MRI when necessary (to avoid the compulsion to document the presence of a microadenoma for the reasons stated above) to be cost-effective. This takes strength of conviction when your radiologist reports that a coned-down view of the sella turcica is not sufficient.
References
1. Schlechte J, et al. J Clin Endocrinol Metab 1989;68:412-418.
2. Reincke M, et al JAMA 1990;263:2772-2776.
3. Donovan LE, et al. Arch Intern Med 1995;155:181-183.
4. Teasdale E, et al. Clin Radiol 1986;37:227-232.
5. Stein AL, et al. Obstet Gynecol 1989;73:996-999.
6. Strebel PM, Obstet Gynecol 1986;68:195-199.
7. Yazigi RA, et al. Fertil Steril 1997;67:215-225.
Correction
An error appeared in the April 1999 issue of OB/GYN Clinical Alert. On page 92 in Dr. Berga’s abstract and commentary, the headline should have read: "Estrogen Supplementation Attenuates Glucocorticoid and Catecholamine Responses to Mental Stress in Perimenopausal Women." We regret any confusion this may have caused.
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