Published online Oct 28, 2019. doi: 10.3748/wjg.v25.i40.6116
Peer-review started: July 23, 2019
First decision: August 27, 2019
Revised: September 17, 2019
Accepted: September 27, 2019
Article in press: September 28, 2019
Published online: October 28, 2019
Processing time: 96 Days and 21.3 Hours
The histological heterogeneity of periampullary adenocarcinoma is high as it comprises adenocarcinomas of the ampulla, distal common bile duct, pancreas, and duodenum. Misclassification of the original tumor site occurs in clinical practice, which causes inappropriate postoperative treatment and incorrect prediction of the overall survival. Recently, the histopathological subtype of periampullary adenocarcinomas is demonstrated to be a better prognostic predictor than the site of origin. According to the endoscopic morphological characteristics of tumor tissue, periampullary adenocarcinoma can be classified into two histological subtypes. One is intestinal-type periampullary adenocarcinoma (IPAC) and the other is pancreatobiliary-type periampullary adenocarcinoma (PPAC). IPAC is reported to have a better prognosis than PPAC.
The classification of histological subtypes is difficult to determine before surgery. Limitations still exist for contrast-enhanced computed tomography or multiparameter magnetic resonance imaging to help differentiating between IPAC and PPAC. Diffusion-weighted imaging (DWI) is a noninvasive functional imaging method. It calculates the apparent diffusion coefficient (ADC) to reflect random motion of water molecules, which could add information pertinent to tissue structure. Based on DWI, ADC histogram analysis has been used in the diagnosis of diseases of many other abdominal organs and is demonstrated to have high reproducibility. It may have the ability to differentiate IPAC from PPAC.
The aim of this study was to investigate the diagnostic value of ADC volumetric histogram analysis in differentiation of IPAC and PPAC. Accurate preoperative differentiation between IPAC and PPAC can help predict the prognosis and make treatment strategy for patients with periampullary adenocarcinoma.
Patients who were confirmed with a periampullary adenocarcinoma and underwent MRI at 3.0 T with diffusion-weighted images (b-values = 800 and 1000 s/mm2) before surgery were analyzed. The mean, 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles of ADC values and ADCmin, ADCmax, kurtosis, skewness, and entropy were then obtained from the volumetric histogram analysis. Comparisons were made with an independent Student's t-test or Mann-Whitney U test. Multiple-class receiver operating characteristic curve analysis was performed to determine and compare the diagnostic value of each significant parameter.
The mean, maximum, and various percentiles ADC values derived from b1000 were lower in the PPAC group than in the IPAC group with statistical significance. The 75th percentile of ADC values achieved the highest area under the curve (AUC) (AUC = 0.781; sensitivity, 91%; specificity, 59%; cut-off value, 1.50 ×10-3 mm2/s).
Our study showed that volumetric ADC histogram analysis could help classify histopathological subtypes of periampullary adenocarcinoma. In addition, a b-value of 1000 s/mm2 has higher diagnostic value than b-value of 800 s/mm2. The 75th percentile ADC1000 value achieved the best diagnostic performance.
Although volumetric ADC histogram analysis has been demonstrated to have the ability to distinguish between IPAC and PPAC, the optimal b-value is still not confirmed. Besides, multiple b-value DWI studies may provide more differential diagnostic value. Thus, further investigations are needed.