7-Tesla Diffusion-Weighted MRI Apparent Diffusion Coefficient for Preoperative Evaluation of Pituitary Adenoma Consistency

Background: Endoscopic surgery is an effective treatment strategy for pituitary adenomas; however, intrinsic tumor properties, including tumor consistency, can preclude gross total resection. Preoperative characterization of tumor consistency is useful and can guide surgical approach and help predict extent of resection. Advanced radiological modalities, such as 7-Tesla (T) diffusion-weighted imaging (DWI), may be useful in probing biological tissue properties of pituitary adenomas. The objective of the present study was to examine 7-T DWI as a novel method of measuring pituitary adenoma consistency ([Fig. 1]).

Methods: Thirteen patients with pituitary adenoma were scanned at 7-T MRI, which included a DWI acquisition. Regions of interest were drawn to calculate average tumor apparent diffusion coefficient (ADC). Tumor ADC was normalized to adjacent temporal gray matter ADC. All patients underwent surgical resection, and a single neurosurgeon rated tumor firmness from 1 (least firm) to 5 (most firm). Tumor specimens were evaluated for cellularity (H&E), collagen content (trichrome), and vascularity (CD31 stain) by a neuropathologist. Extent of resection was determined through intraoperative observation and postoperative MRI. Tumor ADC was correlated with intraoperative consistency rating, histopathology, and extent of resection ([Fig. 2]).

Results: Corrected ADC values were significantly correlated with both tumor firmness (r = −0.60, p = 0.029) and extent of trichrome staining (r = −0.72, p = 0.009) such that greater ADC values were associated with decreased tumor firmness and decreased staining, respectively. Correlations between ADC values and tumor vascularity were not significant (r = −0.09, p = 0.78). Corrected ADC values in totally resected tumors (1.54) were greater than in subtotally resected tumors (0.85; p = 0.02) and greater for moderate cellularity (1.51) relative to high tumor cellularity (0.8; p = 0.035). There was a trend-level association for partial resections to exhibit greater tumor firmness rating (3 vs. 1.7; p = 0.051). Finally, the degree of trichrome staining was also found to correlate positively with tumor firmness (r = 0.60; p = 0.04; [Figs. 3] and [4]).

Conclusion: Our results suggest that high resolution ADC of pituitary adenomas is a sensitive measure of tumor consistency. The 7-T DWI may hold clinical value in the preoperative workup and surgical management of patients with pituitary adenomas.