Utility of Diffusion-Weighted MRI for Detection of Locally Recurrent Pancreatic Cancer After Surgical Resection.

Abstract

<b>BACKGROUND.</b> Overlapping imaging findings between local tumor recurrence and postsurgical fibrosis represent a major clinical challenge after pancreatic ductal adeno-carcinoma (PDAC) resection. <b>OBJECTIVE.</b> The purpose of this study was to compare the diagnostic performance of MRI with and without DWI for differentiating locally recurrent tumor and postsurgical fibrosis after PDAC resection. <b>METHODS.</b> This retrospective study included 66 patients (35 men, 31 women; mean age, 60.5 years) who underwent PDAC resection between January 2009 and March 2016, postoperative surveillance CT showing a soft-tissue lesion at the operative site or at the site of peripancreatic vessels, and subsequent MRI with DWI for further evaluation. CT at least 6 months after MRI served as the reference standard, with increase in size of the soft tissue by 5 mm or more differentiating locally recurrent tumor (<i>n</i> = 26) and postsurgical fibrosis (<i>n</i> = 40). Two observers in consensus evaluated MRI characteristics of the soft-tissue lesions. Two additional observers independently reviewed MRI examinations in two separate sessions (conventional MRI alone vs MRI with DWI), recording likelihood of recurrent tumor using a 1-5 scale. ROC analysis was performed, considering scores of 4 or 5 as positive. <b>RESULTS.</b> Subjective diffusion restriction was more common in locally recurrent tumor than postsurgical fibrosis (88.5% vs 25.0%, <i>p</i> = .01). Median ADC was lower for locally recurrent tumor than postsurgical fibrosis (1.3 vs 1.7 × 10^-3 mm²/s, <i>p</i> < .001). For both observers, MRI with DWI in comparison with conventional MRI alone showed higher AUC for diagnosis of locally recurrent tumor (observer 1: 0.805 vs 0.707, <i>p</i> = .048; observer 2: 0.898 vs 0.637, <i>p</i> < .001) and higher sensitivity (observer 1: 88.5% vs 61.5%, <i>p</i> = .008; observer 2: 84.6% vs 42.3%, <i>p</i> = .001) but no difference in specificity (observer 1: 72.5% vs 80.0%, <i>p</i> = .08; observer 2, 95.0% vs 85.0%, <i>p</i> = .10). Interobserver agreement was moderate for conventional MRI (κ = 0.41) and good for conventional MRI with DWI (κ = 0.62). <b>CONCLUSION.</b> The addition of DWI to conventional MRI improves the differentiation of locally recurrent tumor and postsurgical fibrosis after PDAC resection, primarily because of improved sensitivity for recurrence. <b>CLINICAL IMPACT.</b> The findings indicate a potential role for MRI with DWI in surveillance protocols after PDAC resection.