What are the two main types of ACTH depended Cushing syndrome?
Cushing syndrome, when due to excessive levels of ACTH, is usually due to a pituitary adenoma (85%), or less frequently ectopic production of ACTH (15%) e.g. small cell lung cancer.
What is the difference between Cushing syndrome and Cushing disease?
Cushing syndrome is the clinical constellation of findings due to the effects of excessive glucocorticoids, from any source. Cushing disease is a specific cause of Cushing syndrome, caused by excessive ACTH production by a pituitary adenoma (usually a microadenoma).
As the patient has had a normal CT, what test can be performed to try and confirm a pituitary origin for the excessive ACTH and to try and identify which half of the pituitary it comes from?
Inferior petrosal sinus sampling.
Two 3-millimetre areas of delayed enhancement are seen in the pituitary gland, one on the right just posterior to the level of the stalk and the other more centrally at the same level. The pituitary stalk is midline. The optic chiasm and cavernous sinuses are uninvolved, with normal cavernous carotid flow voids.
Conclusion:
Two possible microadenomas. Whether both of these are microadenomas and if so whether both are functional is uncertain.