In the current study, which compared the diagnostic yield and performance of the 25G FNB needle with the standard 22G FNA needle for the evaluation of pancreatic solid masses without on-site evaluation of specimens, the diagnostic yield, technical performance, and safety profile of the 25G FNB needle were comparable to those of the 22G FNA needle. Although our study failed to demonstrate the superiority of the 25G FNB needle over the 22G FNA needle in terms of the overall histological diagnostic yield, the 25G FNB group demonstrated a better histological diagnostic yield for specific tumor discrimination compared with the 22G FNA group.
Needle selection for EUS-guided sampling can be a complex process in clinical practice. The 22G FNA needle has been the most frequently used for EUS-FNA of pancreatic masses [
9,
11], but the 25G FNA needle could be particularly useful for targeting lesions requiring extreme scope bending, as its smaller caliber and greater flexibility allow it to puncture tissue in hard pancreatic masses more easily [
10]. This needle can also provide less bloody and less contaminated specimens, which may facilitate on-site interpretation [
9,
10]. However, one meta-analysis reported no significant differences in accuracy, complication rates, the number of needle passes, or needle visibility when comparing 22G and 25G FNA needles [
20]. In the present study, although there was no significant difference, there was a trend toward a higher score for background blood or clot in the samples from both the conventional smear and liquid-based preparations in the 25G FNB group compared with the 22G FNA group. Although cytological examination of EUS-FNA specimens enables us to detect malignancies, particular neoplasms such as lymphomas and gastrointestinal stromal tumors may be difficult to diagnose without histological specimens. Additionally, histology may be required for better, more specific characterization of pancreatic neoplasms other than adenocarcinomas [
21,
22]. In fact, Möller
et al. [
22] reported that combining EUS-FNA cytology and histology with the 22G FNA needle significantly increased the sensitivity of malignancy diagnosis compared with cytology or histology alone. The sensitivity of histology alone was only 60 %, and the sensitivity of cytology alone was 68.1 %. Combining cytology and histology improved sensitivity to 82.9 %. In our study, the overall diagnostic accuracy regarding pancreatic masses was consistent with the cytological diagnostic accuracy in both groups. There was no improvement in diagnostic accuracy with the combination of cytology and histology. In the study by Möller
et al. [
22], core specimens were harvested for histological analysis first, and the remaining material was examined cytologically; however, in our study, samples for histological analysis were collected after tissue acquisition for cytological analysis. This different order may have caused the difference in the results. Recently, FNB needles of various sizes with a reverse-bevel-sided hole were developed to acquire core specimens for histological assessment. In a study of the 19G FNB needle by Iglesias-Garcia
et al. [
16], sample quality for histology was adequate in 45/47 pancreatic lesions (95.7 %), and correct diagnosis based solely on histology was provided in 42/47 (89.4 %), with two technical failures in the transduodenal approach. The needle emerged from the echoendoscope with difficulty in 18 % of cases, and this technical difficulty was experienced when the transduodenal approach was performed because of the rigidity induced by its 19G caliber and the curved position of the echoendoscope in the duodenum. In another study, Bang
et al. [
23] compared the performance of the 22G FNA needle and the 22G FNB needle in 56 patients with solid pancreatic masses. The specimens obtained were reviewed by an on-site cytopathologist to ascertain sample adequacy after each pass. In that study, there was no significant difference in the median number of needle passes (1 vs. 1,
P = 0.21), technical failure (0 vs. 3.6 %,
P = 1.0), the rates of diagnostic sufficiency (100 % vs. 89.3 %,
P = 0.24), or the presence of diagnostic histological specimens (66.7 % vs. 80 %,
P = 0.66) between the FNA and the FNB cohorts. Although the small-caliber 22G FNB needle obtained an adequate sample for cytological analysis, the quantity and quality of the acquired tissue appeared to be unsatisfactory for histological assessment. The histological diagnostic yield of the 22G FNA needle in our study (34.2 %) was lower than that reported by the previous study (66.7 %). There is one explanation that may contribute to this difference. In the study of Bang
et al., the specimens obtained with the 22G FNA needle underwent cell block analysis for histological assessment, and some studies have shown that cell block is a valid technique for performing histological assessments and can improve the diagnostic accuracy of smears [
24‐
26]. In our study, the specimens for histological examination were placed in formalin solution, and the cell block technique was not used for histological assessment. In the present study, we observed no technical failure in either group, and there was no significant difference in cytological diagnostic accuracy between the groups. Although there was no statistically significant difference for CS, there was a trend toward higher scores for all categories in the sample quality analysis in the 25G FNB group compared with the 22G FNA group. Moreover, the 25G FNB group exhibited higher scores for the amount of diagnostic cellular material and the retention of appropriate architecture when LBP was used. In addition, there was a trend toward the 25G FNB needle exhibiting higher overall histological diagnostic accuracy than the 22G FNA needle (52.6 % vs. 34.2 %,
P = 0.105), and the 25G FNB group showed a better histological diagnostic yield in specific tumor discrimination compared with the 22G FNA group (60.6 % vs. 32.4 %,
P = 0.018). However, these results were unsatisfactory compared with those of previous studies, which used larger-gauge FNB needles [
16,
23]. In the present study, samples for histological analysis were collected after tissue acquisition for cytological analysis, which was somewhat biased against histology. We performed EUS-guided sampling in inoperable solid pancreatic lesions and solid pancreatic lesions, in which it was difficult to differentiate between malignant and benign lesions in other diagnostic tests. Because cytology is more sensitive than histology alone for the diagnosis of pancreatic malignancies [
27], we first obtained specimens for cytological examination. After the material for cytological examination was obtained, we restricted the number of needle passes for obtaining histological specimens to 2 to prevent procedure-related complications such as pancreatitis, bleeding, bile peritonitis or malignant seeding [
28]. These factors may be related to the relatively low histological diagnostic yield compared with previous studies, which used larger-gauge FNB needles [
16,
23]. A specimen obtained using a smaller-gauge needle may be less hemorrhagic and more adequate for cytological diagnosis. However, blood contamination does not decrease the histological diagnostic yield. Although we believe that the side bevel of the 25G FNB needle can allow cells to move into the needle more easily, larger-gauge FNB needles can offer a greater chance of obtaining an intact histological core. Prospective comparative studies are needed to evaluate the histological diagnostic yield of FNB needles of different sizes.