Diagnosis And Tumor Localization

Accurate diagnosis and differential CS diagnosis is crucial for selection of appropriate therapy. Despite major recent advances, the diagnosis of CS continues to challenge the diagnostic skills of physicians. The goal of the clinician should be to identify individuals with CS as early in the course of the disease as possible to maximize the chance for cure and to avoid the chronic complications of hypercortisolism (8).

Once there is clinical suspicion of CS, the first step is the biochemical documentation of endogenous hypercortisolism (7,14). This step can usually be accomplished by outpatient tests. Measurement of 24-h urinary-free cortisol (UFC) and/ or 17-hydroxysteroid excretion and the 1-mg overnight dexamethasone suppression test are frequently employed as the first step. Contemporary diagnostic assays (e.g., immunoradiometric plasma ACTH concentrations before and after CRH) and imaging modalities (high-resolution magnetic resonance imaging [MRI]) have dramatically improved the diagnosis of ACTH-dependent CS.

After confirmation of ACTH-dependent CS, the challenge is to localize the ACTH-secreting source by MRI, inferior petrosal or cavernous sinus sampling,

Hypercortisolism Before And After

Fig. 1. (A) Catheter placement for bilateral simultaneous blood sampling of the inferior petrosal sinuses. (From Oldfield EH, Chrousos GP, and Schulte HM. Preoperative lateralization of ACTH-secreting pituitary microadenomas by bilateral and simultaneous inferior petrosal venous sinus sampling. N Eng J Med 1985;312:100.) (B) The maximal ratio of ACTH concentration in plasma from either petrosal sinuses and a peripheral vein at baseline (panel A) and after administration of oCRH (panel B). The asterisks represent five patients with primary adrenal disease in whom adrenocorticotro-pin was undetectable in peripheral-blood plasma before and after CRH administration.

Fig. 1. (A) Catheter placement for bilateral simultaneous blood sampling of the inferior petrosal sinuses. (From Oldfield EH, Chrousos GP, and Schulte HM. Preoperative lateralization of ACTH-secreting pituitary microadenomas by bilateral and simultaneous inferior petrosal venous sinus sampling. N Eng J Med 1985;312:100.) (B) The maximal ratio of ACTH concentration in plasma from either petrosal sinuses and a peripheral vein at baseline (panel A) and after administration of oCRH (panel B). The asterisks represent five patients with primary adrenal disease in whom adrenocorticotro-pin was undetectable in peripheral-blood plasma before and after CRH administration.

computed tomography, octreoscan, or positron emission tomography (Fig. 1). If ACTH dependency has been established and the pretest probability of CD is high, the next step should be a pituitary MRI. If the pituitary MRI is normal, inferior petrosal or cavernous sinus sampling should be performed. Only rarely in a patient with ACTH-dependent CS does pituitary MRI show a pituitary adenoma that is not ACTH producing (incidentaloma), as demonstrated by the lack of a central-to-peripheral ACTH gradient on inferior petrosal sinus sampling.

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