Localizing Procedures

The adrenal imaging techniques used as localizing procedures are adrenal scintigraphy, computed tomography (CT),

FIGURE 70-2. Different clinical appearances of patients with Cushing's syndrome in relation to early diagnosis. A to C, The faces of some patients observed in 1982, 1987, and 1995, respectively.

FIGURE 70-2. Different clinical appearances of patients with Cushing's syndrome in relation to early diagnosis. A to C, The faces of some patients observed in 1982, 1987, and 1995, respectively.

and magnetic resonance imaging (MRI) scanning. Radiocholesterol scintigraphy is very useful in patients with Cushing's syndrome because it evaluates both adrenals simultaneously.8 9 In patients with adrenocortical hyperplasia resulting from a corticotropin-dependent syndrome, scintigraphy shows bilateral uptake (Fig. 70-4A). In the presence of a cortisol-secreting adenoma, focal uptake is observed, and scintigraphy accurately depicts the suppression of the contralateral adrenal gland (Fig. 70-4B). When an adrenal tumor is present, either CT or MRI scanning localizes the tumor and documents the size of the mass and its relationship to the surrounding structures (Fig. 70-4C and D). In selected patients with a unilateral adrenal mass, image-guided fine-needle aspiration cytology may be performed when requested for surgical planning.10

MRI scanning is preferable to CT scanning for identifying pituitary adenomas. MRI scanning, however, may fail to localize pituitary tumors smaller than 5 mm, and nonfunctioning micropituitary tumors occur in up to 25% of the population. Bilateral selective venous catheterization of the inferior petrosal sinus with CRH stimulation is the most sensitive test for confirming the presence of a pituitary adenoma and in most cases can identify the side of the microadenoma.11 Furthermore, plasma values of corticotropin (ipsilateral, peripheral) with a ratio higher than 1.5:1 rule out ectopic corticotropin secretion.7 Selective venous catheterization of other veins is occasionally helpful for identifying ectopic corticotropin-secreting tumors, as is MRI with Tl- and T2-weighted images for bronchial adenomas in the chest or pancreatic carcinoid tumors in the abdomen. Figure 70-5 shows a useful algorithm for the evaluation of a patient with Cushing's syndrome, as suggested by Kaye and Crapo.7

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