Inferior petrosal sinus sampling in differential diagnosis of ACTH-dependent hypercortisolism

Survival rate of patients with endogenous hypercortisolism, as well as complications reversibility and treatment effectiveness depends on on-time and precise diagnosis. In case of apparent clinical picture with all laboratory tests confirmation, the most challenging appears the differential diagnosis of ACTH-dependent hypercortisolism as none laboratory test can reveal the genesis of ACTH hypersecretion. When there is no visualization of the pituitary adenoma, the only method to confirm the diagnosis is bilateral inferior petrosal sinus sampling (BIPSS). Nevertheless, around 16% of patients have inactive pituitary incidentalomas in combination with carcinoid tumor of other localization. Epidemiologic researches show that the size of such incidentalomas tend to be less than 6 mm. According to clinical guidelines in case of such small neoplasms it’s recommended to perform bilateral inferior petrosal sinus sampling. This clinical case represent a rare exception to the rules when there is a pituitary adenoma more than 6 mm and mild hypercortisolism, possibly as the result of lung carcinoid tumor.