Is whole-lung CT scanning still necessary in all cases of ACTH-dependent Cushing's syndrome in the era of petrosal sinus sampling?

We reviewed 31 patients in whom both bilateral inferior petrosal sinus samp ling without CRH stimulation, and a CT scan of the lungs were done. Twenty- five had normal lung CT scans, of whom 23 had a higher inferior petrosal si nus:peripheral ACTH ratio greater than or equal to 1.5. After careful follo w-up, none was subsequently shown to have ectopic ACTH syndrome. Six had ab normal lung CT scans, of whom two had ratios greater than or equal to 1.5. In these two patients, other investigations suggested pituitary disease, an d pituitary surgery led to apparent cure. Of the remaining four patients, w ho had ratios <1.5, two had incidental lung findings, and pituitary abnorma lities were demonstrated at pituitary surgery. The third underwent bilatera l adrenalectomy, and no evidence of ectopic ACTH syndrome has emerged as ye t after 4 years follow-up. The fourth had a small-cell carcinoma of the lun g, confirmed histologically. Our series suggests that whole-lung CT scannin g is only necessary in cases of ACTH-dependent Gushing's syndrome where bil ateral inferior petrosal sinus sampling has not demonstrated a significant increase in petrosal sinus ACTH levels as compared with the peripheral leve l. Thus, in our experience the test is now only necessary in those patients (approximately 25%) where the ratio is less than or equal to 1.5.