The value of high-field MRI (3T) in the assessment of sellar lesions

The aim of this study was the evaluation of the normal sellar anatomy in vitro and in vivo with high-field MRI and its application in the diagnosis of sellar pathologies in comparison to standard MRI.

All high-field MR images were obtained using a 3T Bruker Medspec 30/80 Scanner with a head birdcage transmit/receive coil and an actively shielded gradient system with a maximum gradient strength of 45mT/m. Firstly an in vitro study of the sella turcica was performed to depict normal pituitary and sellar anatomy at high field. After a pilot-study this sequence-protocol was established: A RARE sequence (TR/TE = 7790/19ms; matrix size, 512 × 512; RARE factor = 8, FOV, 200mm) was used for T2-weighted coronal, axial and sagittal images. A 3D gradient echo sequence with magnetization-preparation (MP-RAGE, TR/TE/TI = 33.5/7.6/800ms, matrix size, 512 × 512; FOV, 200mm, effective slice thickness, 1.88mm; 3 averages) was used for acquisition of T1-weighted pre- and post-contrast images. Between January 2002 and March 200458 patients were enrolled in this study. Seven patients were examined for suspected microadenoma and in 51 patients 3T MRI was used to obtain additional information about the sellar lesion already known to be present from standard MRI.

In 21 cases the accuracy of the imaging findings was assessed afterwards by comparison with intraoperative findings. The infiltration of the medial cavernous sinus wall was suspected on standard MRI on 15 sides (47%), on high-field MRI on 9 sides (28%) and could be verified by intraoperative findings on 6 sides (19%). Accordingly, sensitivity to infiltration was 83% for 3T and 67% for standard MRI. Specificity was 84% for 3T and 58% for standard MRI. Moreover, high-field MRI revealed microadenomas in 7 patients with a median diameter of 4mm (range 2–9mm). The segments of the cranial nerves were seen as mean 4 hypointense spots (range 2–5 spots) on high-field MRI in contrast to 3 spots (range 0–4 spots) on standard MRI. This difference was considerably significant (P < 0.001, Wilcoxon rank sum test). The histopathological results revealed pituitary adenoma in 16 patients and non-adenomatous sellar pathologies such as Rathke's cleft cyst, sarcoidosis, meningeoma and metastasis in 5 patients.

High-field MRI is superior to standard MRI for the prediction of invasion of adjacent structures in patients with pituitary adenomas and improves surgical planning of sellar lesion.