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Abstract
The diagnosis of Cushing's syndrome (CS) is still one of the most challenging problems in endocrinology. In ACTH-dependent CS, bilateral inferior petrosal sinus sampling (BIPSS) is a useful method for distinguishing between pituitary and ectopic sources of ACTH secretion. BIPSS is an interventional radiology method, in which ACTH levels obtained from petrosal sinuses are compared to peripheral venous blood ACTH levels at basal conditions and after corticotropin-releasing hormone (CRH) or desmopressin (DDAVP) stimulation. A gradient between central and peripheral sources of ACTH indicates Cushing's disease (CD), whereas the absence of a gradient suggests ectopic CS. In some cases, intrapituitary gradients from side-to-side may also help to predict the side of the adenoma within the pituitary. However, anatomical variations may lead to false lateralization of the lesion in the pituitary gland during BIPSS. We report the case of a 51-year-old woman with CD in whom BIPSS indicated a central source of secretion of ACTH, but it was not compatible with the side of the adenoma on MRI. The laboratory results after BIPSS were inconsistent with the radiological findings of the patient. The hypoplastic right petrosal sinus, which was discovered during angiography, was the cause of the abnormality. To avoid false interpretation of BIPSS results due to such anatomical variations, angiographic imaging is a commonly used technique before this procedure. As in our case, if laboratory results after BIPSS are not compatible with the earlier radiological findings, possible anatomical variations seen in angiography procedure before BIPSS should be taken into consideration.