A modified protocol using half-dose gadolinium in dynamic 3-Tesla magnetic resonance imaging for detection of ACTH-secreting pituitary tumors

ACTH-secreting tumors represent 10% of functioning pituitary adenomas, and most of them are microadenomas. It is generally accepted that only half of these tumors are correctly identified with current magnetic resonance imaging (MRI) techniques. The objective of the paper is to report a method for detecting suspected ACTH-secreting pituitary tumors undetectable by conventional dynamic MRI using dynamic 3-Tesla MRI (3T MRI) and half-dose gadopentetate dimeglumine (0.05 mmol/Kg). Eight patients were included (5 men and 3 women) with a mean age of 29.12 years. Each of them had a confirmed diagnosis of Cushing disease and a negative dynamic MRI for microadenoma using full-dose gadopentetate dimeglumine. A second MRI was then performed using only half the usual dose of contrast material. Images from the second MRI where compared with the first study. Microadenomas were detected in 100% of the patients using a half dose of the contrast. All were recognized on the basis of the presence of a hypointense nodular lesion surrounded by normal contrast-enhanced tissue. Six patients were submitted to surgery, and the results were confirmed by immunohistochemistry in all of them. The remaining subject had a sinus sample catheterization coincident with the MRI results. Conclusion: A half dose of dynamic resonance imaging contrast material increases the sensitivity of MRI detection of ACTH-secreting pituitary tumors.