Radiology can have a major role to play not only in baseline assessment of pancreatic adenocarcinoma, but also it can potentially give more details that may be prognostically important, including prediction of surgical resection [6].
Both DWI visual analysis and ADC measurement can reliably distinguish PDAC from background pancreatic parenchyma. Pancreatic tumors, even if small in size, almost invariably show diffusion restriction, presenting as a focal high signal area on high b value DW images with low signal on ADC mapping [7].
In this study, we found that the pancreatic head is the most common site for pancreatic adenocarcinoma presented. In 41/50 cases, 11/15 are resectable lesions (73%), and in 30/35, non-resectable lesions (85%). This is also established in the study done by Greenlee. et al. [8], who found that 65% of pancreatic adenocarcinomas involved the pancreatic head and uncinate process and 15% in the body and tail. The remaining lesions were detected diffusely involving the pancreas.
In our study, males are more affected than females presented in 10/15 (67%) resectable and 22/35 (63) non-resectable lesions. Artinyan et al. 2008 [9] stated that the anatomic location of pancreatic cancer was a prognostic factor for survival. The age of resectable lesions was lower than the age of the patients having unresectable lesions.
In this study, the addition of DWI to the conventional MRI sequence increased significantly the tumor detection rate. Thirteen of fifty lesions could not be detected by conventional MRI and could clearly be detected by the addition of DWI, and their sizes ranged between 2 and 3 cm. So, the accuracy of detection raised from 74 to 100%. Park et al. [10] demonstrated that the addition of DW-MR imaging to conventional MR sequences helps increase significantly the sensitivity of MR imaging for the detection of small pancreatic adenocarcinoma with sensitivity values rising from 75–76% to 96–98%.
In this research, we have many associated findings with the non-resectable lesions such as biliary obstruction in 27/35 (77.1%), vascular encasement in 26/36 (74.3%), distant metastasis in 8/35 (22.8%), infiltration to adjacent structures in 3/35 (8.5%), and infiltrating spleen, duodenum, and left kidney. Jun et al. [11] stated that the most frequent sites of metastasis form carcinoma of the pancreas are the lymph nodes, lung, liver, adrenal glands, kidney, and bone.
Elsayes et al. [12] found that associated lesions should be described and can affect surgical decision-making. Peritoneal nodules or the presence of ascites suggest disseminated disease that would render the patient unsuitable for a curative resection. Also, the presence of enlarged lymph nodes can also affect surgical resectability and indicate a need for additional therapy.
In our study, 15/50 (30%) lesions are resectable and 35/50 (70%) lesions are non-resectable. Whipple’s operation was done in 6 cases, subtotal pancreatectomy in 3 cases, venous graft taken from the great saphenous vein in 2 cases, and from the internal jugular vein in 1 case. In non-resectable lesions, palliative procedures were done. Chen et al. [13], on a study done on 38 patients, found that 31 lesions were in the head or uncinate process, 5 in the body, and 2 in the tail. Twenty-four lesions were resectable and underwent Whipple’s (3 cases), child operation (13 cases), pylorus-preserving pancreaticoduodenectomy (7 cases), and distal pancreatectomy with splenectomy (7 cases). The lesion size is less than 2 cm in 10 patients and more than 2 cm in 14 patients (2–6 cm). Unresectable lesions underwent palliative procedures like choledechojejunostomy, gastrojejunostomy, and external biliary drainage.
In our study, the ADC value of both resectable and non-resectable lesions are seen with great overlap with a wide range and insignificant P value of 0.452. The ADC value from examined lesions ranged between 09 and 1.4 × 10−3 mm2/s.
Also, in this research, there is no significant difference between the ADC values of different grades of the pancreatic adenocarcinomas.
The mean ADC values of pancreatic adenocarcinoma extracted from published studies are 1.3 × 10−3 mm2/s (range 0.78 × 10−3 mm2/s to 2.32 × 10−3 mm2/s). In general, most of the studies reported that the mean ADC values of malignant pancreatic tumors were lower than those of normal pancreatic tissues and benign lesions [14].
Barral et al. [15] and Lee et al. [16], instead, did not report significant differences in ADC values between PDACs and other solid pancreatic tumors.
In addition, a considerable overlap of ADC values in the range of malignant lesions might be present. Moreover, benign pancreatic lesions such as pseudocysts can show some degree of diffusion restriction which is thought to be due to the high viscosity of its content [17]. Thus, quantitative ADC analysis alone may be not so accurate for characterization of pancreatic lesions [18].
Rosenkrantz et al. [19] did not report a significant difference in the mean ADC between poorly and well/moderately differentiated tumors. However, some authors postulated that the cell density is proportional to tumor aggressiveness as ADC values were lower in higher than lower-grade tumors in their studies. Also, other studies suggested a relation between tumors hyper-cellularity and increased metastatic capacity [18].
In this study, tumor size was a significant predictor for tumor resectability. This is logical as large tumors become more in contact with blood vessels and lymphatics, and therefore, more chance of tumor spread. Phoa et al. reported that a tumor diameter of > 3 cm showed poor survival after resection [20].
In fact, tumor size is a particularly important prognostic factor to examine as it is included in the American Joint Committee on Cancer (AJCC) staging of pancreatic adenocarcinoma [21].
However, it should be kept in mind that the effect of tumor size on prognosis is largely mediated through other biologic factors such as lymph node status and histologic differentiation rather than merely tumor size, especially when tumor size is < 5 cm [22].
This study had some limitations such as its retrospective design and the relatively small number of patients within each patient group. It is recommended to focus on clear classification of the groups, criteria of resectability, and ADC values and their relations to each other.