Clinical Value of Dynamic MRI in the Diagnosis of Pituitary Microadenoma

Abstract

MRI is today the first-choice technique for detection of pituitary microadenomas. The combination of T1-weighted spin-echo, T2-weighted spin-echo and T1-weighted spin-echo after intravenous gadolinium administration gives a clearly positive result in about 70% of cases. In the remaining 30% the hypersignal generated by the contrast agent can hide the smallest lesions. Dynamic MRI is considered capable of visualizing some of the smallest pituitary microadenomas not visible on conventional MRI, and has therefore become the most promising technique to image pituitary lesions. The purpose of this study is to compare the effectiveness of conventional and dynamic MRI.

Fifty patients were examined with dynamic contrast-enhanced MRI of the pituitary gland. They were thought to have pituitary adenoma on the basis of clinical and biological data. MRI was performed at 1.5T (Siemens SP 63) with the acquisition of three sequences:

1) T2-weighted sequence

2) Dynamic study: (temporal resolution 17 s)

3) T1-weighted postcontrast sequence.

In 10 cases (20%) no pathological findings were seen. In 32 cases (64%) pathological findings were seen both in dynamic and in SE T1 and T2-weighted images. In 8 cases (16%) pathological findings were observed only in the dynamic study.

In 8 studies out of 50 (16%) dynamic MRI showed small (less than 7 mm) focal relatively hypointense areas in the pituitary gland, visible neither on SE T2-weighted pre-contrast nor on SE T1-weighted postcontrast images, leading to a diagnostic sensitivity from 64% to 80%. Dynamic MRI did not miss any lesions although in 3 cases the picture was more clear on SE sequences. We can conclude that dynamic MRI study of the pituitary gland improves accuracy in the diagnosis of pituitary microadenomas.