Clinical Endocrinology (1992), 36, 333
Computed tomography and magnetic resonance imaging of pituitary microadenomas Ivan Moseley The National Hospitals for Nervous D i s e a s e s , Q u e e n Square, London W C l N 3BG, UK
Johnson et al. (1992) present a laudable attempt to compare surgical findings in cases of pituitary adenoma with blinded interpretaton of CT and MR images. Since either technique should give an unequivocal answer in macroadenomas, I shall comment only on the smaller adenomas: here, the results suggest that MRI better fulfilled some of the requirements of a useful test, in that there was a greater degree of interobserver agreement, that is, the images were more easily interpreted, and the interpretations were less often incorrect. It is difficult to extract from this paper just how reliable the radiologists’ interpretations were, but even after conferring, two of them arrived at a correct opinion on only eight of 14 CT studies. This should surprise no one who has followed the history of ‘microadenoma radiology’. First we were told that plain films and tomography were useful (McLachlan et al., 1970) and then unequivocally, that they were not (Turski et al., 1981). Similarly, initial raptures over CT (Bonafe et al., 1981) were greatly modified when it became clear that things were not so simple (Davis et al., 1985). In the current study there were six cases in which two expert radiologists, although agreeing about the site of the adenoma, were wrong. Enthusiasm for pituitary CT has never been as unbounded in Britain as it has been in countries predisposed to welcome new techniques, proven or otherwise (Payer, 1988). and it is difficult to resist the conclusion that for the surgeon to operate blind, once he knows no macroadenoma is present, would be no less beneficial for the patient than relying on CT. In the 14 patients studied by MRI who did not receive gadolinium (which adds about 530.00 to the cost of the examination), two incorrect joint interpretations were made; one cannot work out how many of these tumours were macroadenomas, and the possible frequency of misinterpretation of unenhanced MR images in microadenomas therefore ranges from 2/14 (14%) to 2/9 (22%);while the former, in line with previous claims (Kucharczyk & Montanera, 1991),is not too discouraging, the latter would give cause for concern. The desirability of locating the tumour within the pituitary gland of a patient with hyperprolactinaemia is predicated solely and absolutely on surgery being the treatment of choice, a fact not obviously appreciated by some physicians. If the surgeon has to inspect both sides of
the gland to find the adenoma in up to a quarter of patients (only one in four less than ifhe were always to go for the same side first) the cost-benefit ratio of this expensive imaging procedure is low; should he feel that the added dissection and operation time are not genuinely disadvantageous, the question arises as to whether radiological ‘localization’ of a microadenoma is genuinely useful. Scientific rigour has been notable for its absence in published CT/MRI comparisons, and this study does not escape all the criticisms levelled by Kent and Larson (1988). By its understandable reliance on surgical findings, it tells us nothing about false positive interpretations in asymptomatic subjects-very common with plain films (Turski e t al., 198 1) and by no means unknown with CT-r about false-negative MRI (Kucharczyk & Montanera, 19911, although only one patient out of the 25 examined in the present study, a very small proportion, was thought to have a normal MRI. On the other hand, the confirmation that CT is an inadequate test is helpful.
Reterences Bonafe, A., Sobel, D. & Manelfe, C. (1981) Relative value of computed tomography and hypocycloidal tomography in the diagnosis of pituitary adenoma. A radio-surgical correlative study. Neuroradiology, 22, 133-137. Davis, P.C., Hoffman, J.C., Tindall, G.T. & Braun, I.F. (1985) Prolactin secreting pituitary microadenomas:inaccuracy of highresolution CT imaging. American Journal of Roentgenology, 144, I5 1-1 56. Johnson, M.R.,Hoare, R.D.,Cox, T., Dawson, J.M., Maccabe, J.J., Llewelyn, D.E.H. & McGregor, A.A. (1992) The evaluation of patients with a suspected pituitary microadenoma: computer tomography compared to magnetic resonance imaging. C/inica/ Endocrinology, 36, 335-338. Kent, D.L. & Larson, E.B. (1988) Magnetic resonance imaging of the brain and spine: is clinical efficacy established after the first decade? Annnals of Internal Medicine, 108,402404. Kucharczyk, W. & Montanera, W.J. (1991) The sella and parasellar region. In Magnetic Resonance Imaging of rhe Brain and Spine (ed. S . W. Atlas), pp. 632-640. Raven Press, New York. McLachlan, M.S.F., Wright, A S . & Doyle, F.M. (1970) Plain film and tomographic assessment of the pituitary fossa in 140 acromegalic patients. British Journal of Radiology, 43, 360-369. Payer, L. (1988) Medicine and Culture: Varieties of Treatment in the United States. England, West Germany and France. Henry Holt, New York. Turski, P.A., Newton, T.H. & Horten, B.H. (1981) Sellar contour: anatomo-polytomographic correlation. American Journal of Roentgenology, 137,213-2 16.