The diagnostic accuracy of preoperative CT scanning in the evaluation of pituitary ACTH-secreting adenomas

Between 1980 and 1985, 35 patients (26 women and nine men) who had coronal CT scans of the sella turcica for suspected ACTH-secreting pituitary adenoma underwent transsphenoidal exploration. The CT examinations were performed with a fourth-generation EMI scanner (CT 7070). The reports of the preoperative CT examinations were compared with the findings at transsphenoidal exploration; in cases with negative CT scans, the decision to operate was based on biochemical evidence of Cushing's disease. In 27 patients, distinct adenomas were found at surgery; in the eight others, total hypophysectomy (four cases) or resection of the central core of the pituitary gland (four cases) was performed. Three patients had macroadenomas, all of which had been identified correctly on preoperative CT scan. Among the 24 microadenomas (less than 10 mm diameter), 14 had been correctly identified on preoperative CT scan while 10 were found in patients with negative scans. The CT examinations in these 35 patients showed probable adenomas in 20 cases, of which 17 (85%) were confirmed at surgery. In the other three cases (15%), adenomas were not found. Among the 15 patients with negative CT scans, 10 (66.6%) had distinct adenomas found at surgery. Coronal CT scans for ACTH-secreting adenomas had a sensitivity of 63%, a specificity of 62.5%, and an overall accuracy rate of 62.8%. Thus, in our experience, CT scanning with current state-of-the-art equipment has poor diagnostic accuracy in Cushing's disease. The possible reasons for this are that most of the adenomas in this series were microadenomas less than 6 mm in diameter, and that ACTH microadenomas probably show almost the same degree of enhancement with contrast medium as the surrounding normal pituitary tissue.
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