INTRODUCTION

Preoperative evaluation of tumor consistency is important in patients with pituitary adenoma. Pituitary adenoma consistency was considered to be relevant to collagen content.¹ High-temporal resolution dynamic contrast enhanced MR imaging (DCE-MRI) can evaluated volume of the extravascular extracellular space per unit volume of tissue (v_e),² and fibrosis content was positively correlated to v_e in pancreatic cancer.³ Our aim was to evaluate the possible role of DCE-MRI in evaluation of tumor consistency in patients with pituitary adenoma. Furthermore, we evaluated the correlation between the v_e and collagen IV content of the pituitary adenoma.

METHODS

A prospective study was performed using 19 patients with pituitary adenoma (mean age, 57.2 ± 15.8 years). All patients underwent MR imaging with a 3T system (MAGNETOM Prisma; Siemens Healthcare, Erlangen, Germany). A 20-channel head/neck coil was used. Imaging protocol included a coronal prototype compressed sensing volumetric interpolated breath-hold examination (CS VIBE) sequence (TR/TE, 3.9/0.97 ms; in-plane resolution, 1.10 × 0.94 mm reconstructed into 0.9 × 0.9 mm; slice thickness, 0.9 mm; 48 slices; FOV, 180 mm; flip angle, 10.0°; bandwidth, 640 Hz/pixel; image matrix, 145 × 192; CS factor, 7; temporal resolution, 5.0 seconds; acquisition time, 200 seconds). Images were sent to the PACS and analyzed by using the software Vitrea (Canon Medical Systems Co.,Tochigi, Japan) to obtain volume of v_e (Fig 1).² Pituitary adenomas were classified into 2 groups according to the intraoperative findings: tumors with soft consistency and hard consistency. Region of interest measurements were performed in pituitary adenoma and normal white matter. We also evaluated ADC value and signal intensity ratios on T1-weighted images (rT1) and T2-weighted images (rT2). We compared v_e, ADC, rT1 and rT2 between soft adenoma and hard adenoma using Mann-Whitney U test. In addition, the diagnostic performances of the parameters were compared using receiver operating characteristic (ROC) curve analysis. Furthermore, we evaluated the correlation between the v_e and collagen IV content of the pituitary adenoma using Pearson correlation coefficient.

RESULTS

The hard adenoma showed significantly higher v_e (0.341±0.124 vs. 0.197±0.124, p=0.0326) than soft adenoma, whereas no significant difference was found in ADC (10^-3mm²/sec) (0.768±0.220 vs. 0.713±0.266, p=0.720), rT1 (0.816±0.057 vs. 0.864±0.102, p=0.400), or rT2 (1.80±0.57 vs. 1.72±0.42, p=0.968). The ROC curve analysis showed significance for v_e (AUC=0.762, significance level p = 0.0256), and no significance for ADC, rT1 and rT2 (AUC=0.556, 0.622, 0.511, significance level p = 0.6957, 0.3851, 0.9395; respectively) (Fig 2). The collagen IV content of pituitary adenoma ranged from 5.08 to 61.57%. Pearson correlation coefficient analysis revealed a strong positive correlation between the v_e and collagen IV content (r = 0.836, P < 0.0001) (Fig 3).

DISCUSSION

The current study exploited the potential of the prototype CS VIBE sequence in evaluating the pituitary adenoma with a high spatial (0.9 mm isotropic) and temporal (5.0 seconds) resolution, allowing for the quantitative pharmacokinetic analysis. The hard adenoma showed significantly higher v_e than the soft adenoma. Thus, this technique may be useful to predict the consistency of pituitary adenoma preoperatively. Our result of the significant positive correlation between the v_e and collagen IV content of the pituitary adenoma is consistent with a previously reported significant positive correlation between collagen content and v_e in pancreatic cancer.³ Collagen content was considered to be causally related to consistency of a pituitary adenoma.¹ Thus, it is conceivable that higher v_e in hard adenoma reflects higher collagen content.

CONCLUSION

The hard adenoma showed significantly higher v_e than soft adenoma. The v_e of pituitary adenoma correlated to the collagen IV content. The v_e derived from DCE-MRI can provide information about the consistency of pituitary adenomas.

Acknowledgements

The authors would like to thank Tomoko Takajo (technical assistant) who helped with immunohistochemical staining for collagen IV to obtain collagen content of pituitary adenomas and the staff of Kagoshima University Hospital for their support.