S. Z. Wennmacker1, E. De Savornin Lohman1, P. De Reuver1, J. Drenth3, J. Hermans2, C. Van Laarhoven1 1Radboudumc,Surgery,Nijmegen, Netherlands 2Radboudumc,Radiology,Nijmegen, Netherlands 3Radboudumc,Gastroenterology And Hepatology,Nijmegen, Netherlands
Introduction: Preoperative evaluation of gallbladder (GB) polyps is commonly done by transabdominal ultrasound (TAUS). However, reported sensitivities of TAUS to detect GB polyps vary greatly and diagnostic accuracy for differentiating neoplastic polyps remains suboptimal. Therefore, additional preoperative imaging modalities should be considered. We aimed to identify imaging characteristics of (different types) of GB polyps on MRI, to verify previously identified TAUS characteristics of different GB polyp types, and to assess diagnostic accuracy of both modalities.
Methods: We performed a prospective, exploratory study including patients ≥18 years of age with GB polyp(s) identified on previous ultrasound, who were considered to undergo cholecystectomy. Preoperatively, patients underwent a dedicated, standardized TAUS examination (evaluating presence, size, number, shape, surface, echogenicity, internal structure and subtype of gallbladder polyps), and a high b-value diffusion weighted (DWI-)MRI. Characteristics of polyp subtypes on MRI (presence, size, number, shape, internal pattern, signal intensity on T1, T2 and DWI, contrast enhancement on T1, and ADC-value on DWI) were described. Histopathology (PA) after cholecystectomy was used as reference standard. Polyp characteristics on TAUS were compared to characteristics from literature. Polyp size on TAUS and MRI were compared to PA using McNemars’ test, and sensitivity and specificity for presence and neoplastic nature of polyps were calculated.
Results: In total 27 patients were included of whom 20 (74%) had a polyp on PA (14 cholesterol polyps, 3 adenomyomatosis, and 3 adenomas). On MRI, all hyper intense polyps on T1 weighted image were cholesterol polyps, and none of the hyper intense polyps on DWI were cholesterol polyps. Two out of three adenomas showed a specific intensity pattern on DWI and ADC. However, five polyps were too small to establish polyp type on MRI, and small size and artifacts prohibited optimal analysis of several polyps. Polyp characteristics on dedicated TAUS from this study and literature are shown in Table 1. Sensitivity and specificity for presence of GB polyps were 95% and 57% for both MRI and TAUS, and for neoplastic nature these were 67% and 76% for TAUS, and 67% and 83% for MRI, respectively. Polyp size on TAUS, but not MRI, significantly differed from PA (p=0.03 and p=0.32, respectively).
Conclusion: Diagnostic accuracy of dedicated TAUS and MRI is similar. In larger polyps MRI might of additional value regarding polyp size evaluation, and differentiation of polyps based on signal intensity on T1 weighted images and DWI, and ADC patterns. MRI characteristics illustrated in this study should be confirmed in a large prospective cohort study.
