Giovannini et al. reported in the first study [39] this five-score classification based on different color patterns with a sensitivity of 100 % and a specificity of 67 % in differentiating benign from malignant lesions. Then the same group in the second study [12], basing on the same scoring system, proved that the accuracy was 89.2 % for the differential diagnosis, with both sensitivity and positive predictive value (PPV) over 90 % [34]. A second group, Iglesias-Garcia et al. [13], used a four-score classification (Table 3.2), and they prove that EUS elastography has diagnostic sensitivity, specificity, and overall accuracy of 100 %, 85.5 %, and 94 %, respectively, in diagnosing malignancy [34].

Itokawa et al. [11] showed in their study that at qualitative EUS elastography all pancreatic ductal adenocarcinomas had intense blue pattern (hardest color in their color map), whereas inflammatory masses had mixed colorations (green, yellow, and low-intensity blue). Again there are at least two studies that give disappointing results about qualitative endoscopic ultrasound elastography [9, 10, 34]. Hirche et al. [10] found in their study very low values in predicting the nature of pancreatic lesions, such as diagnostic sensitivity, specificity, and accuracy just 41 %, 53 %, and 45 %, respectively. Janssen et al. [9] instead conclude that it is not possible to distinguish chronic pancreatitis from hard malignant tumors with elastography, probably due to their similar fibrous structure. These different values of diagnostic accuracy in qualitative EUS elastography among different studies can be explained probably because of the subjective interpretation of the elastographic pattern [14, 34, 41]. By the way due to the desmoplasia of ductal adenocarcinoma, it is possible to exclude malignancy with high accuracy when in the ROI is seen a predominantly green pattern, so this examination have a negative predictive value usually higher than 90 % [10, 12, 31, 42–44]. With EUS elastography strain ratio (SR) that gives a relative quantitative value, Iglesias-Garcia et al. [40] proved that in differential diagnosis of pancreatic solid lesions quantitative EUS elastography with SR has an accuracy (97.7 %) and a specificity (92.9 %) higher than qualitative analysis and these data could be explained with comparing two regions of interest (ROI), one inside the lesion and one inside adjacent pancreatic parenchyma. They said that a lesion with a SR higher than 6.04 or a mass elasticity lower than 0.05 % has 100 % sensitivity to be classified as a malignant tumor [34, 40]. Furthermore, the specificity can reach 100 % value with a SR higher than 15.41 or a mass elasticity value below 0.03 %. So EUS elastography with SR could be an important tool in the differential diagnosis among pancreatic masses and could differentiate pancreatic cancers from inflammatory masses, with a sensitivity of 100 % and a specificity of 96 %, and pancreatic adenocarcinoma from neuroendocrine tumors, with 100 % sensitivity and 88 % specificity [34, 40]. Another study confirms different values with EUS quantitative techniques with a mean SR of 39.08 (±20.54) for pancreatic ductal adenocarcinoma and a mean SR of 23.66 (±12.65) for inflammatory masses [11, 34]. At the acoustic radiation force impulse (ARFI), being a rigid mass, stiffer than the adjacent pancreatic parenchyma for the pathological features previously described, pancreatic ductal adenocarcinoma is characterized by higher wave velocity values than normal parenchyma with predominately hard pattern at Virtual Touch Tissue Imaging (VTI) and at Virtual Touch Tissue Quantification (VTQ); shear wave velocities are usually >3 m/s, higher than ones measured in the adjacent parenchyma [2, 16, 29, 45]. Park et al. [30] concluded in their study that ARFI elastography identified relative stiffness values between the lesion and background pancreatic parenchyma using VTI and VTQ, which could be helpful in differentiating malignant tumors from benign inflammatory lesions, although there was a considerable degree of overlap between the ARFI values of the benign and malignant lesions. In D’Onofrio et al. experience, a wide range of wave velocity values results from ARFI analysis on pancreatic adenocarcinoma, but in any case a differential diagnosis with chronic pancreatitis is really difficult, and still now no cutoff values exist [2]. Pancreatic ductal adenocarcinoma usually presents at elastography, both qualitative and quantitative, as a harder mass than normal pancreatic adjacent parenchyma; it is also usually harder than benign lesions, but this last feature is not very simple to appreciate at elastographic study, and of course it is harder in relation to the adjacent parenchyma than benign lesions.