Reply to Wijmans et al.

We thank Drs. Wijmans and Annema for their interest in our work, and their position and opinions are well received. We shall try to summarize our motivations for this research as well as answer their specific questions.

Needle-based confocal laser endomicroscopy (nCLE) is an exciting imaging technology that in essence allows us to deliver a confocal microscope through a standard 19 G needle, and potentially into any organ or space identifiable by endoscopic ultrasound (EUS). The concept and the flexibility of a probe-based system may allow for a paradigm shift in the way we diagnose and stage malignancy. Questions remain, however, about its applicability, functionality, and our ability as endoscopists to interpret and compare the visual information with traditional histology. While there must be a healthy amount of skepticism, we believe that this technology is in fact revolutionary, and the current criticisms are reminiscent of initial criticisms of other emerging imaging technologies over the years – even EUS. 

As with all new imaging technology, there will be barriers to acceptance and validation. To that end, we along with others, are working hard to produce large registries and to accurately ascertain the accuracy of interpretation for all applications including lymph nodes. At the moment, in vivo endomicroscopy has added tremendous value to the management or Barrett’s esophagus [1], early gastric neoplasia [2], and perhaps biliary strictures [3]. In addition, nCLE is gaining acceptance for its value in the diagnosis of pancreatic cysts [4].

With regard to nCLE of lymph nodes, we have found it to be invaluable to our staging algorithm for many malignancies. Our experience is unique in that we were able to achieve robust images readily, and we believe this is related to our technique, which we outlined in great detail in the article. We scanned the entire diameter of the lymph nodes in question several times by moving the needle, and finally removed the probe and acquired a core biopsy. An important criticism arose that we could not make one-to-one comparisons with histology and therefore cannot identify histological structures with certainty. This is a limitation of how core biopsies are acquired in general. We took core biopsies of all of our lymph nodes and processed them accordingly in formalin without making cell blocks or slides. Unlike probe-based CLE (pCLE) of endoscopically visible lesions, however, in nCLE of lymph nodes it is impossible to compare optical biopsies with their histological counterpart on a one-to-one basis. It is not possible to biopsy the exact location of optical biopsy at the current moment of imaging and with the current technology. Correlations can still be made, however, based on identifiable features, the size of the various elements in the optical biopsy, and prior experience with endomicroscopy in general. This approach was successfully employed in past studies of nCLE in pancreatic cysts [4], and even pancreatic solid masses [5]. In our study, we attempted to do this, and were intentional in not overstating our conclusions. Our best and most conclusive correlations, however, were in regard to carcinomatous deposits in the subcapsular region of the lymph node cortex. We explained further in our discussion that metastatic deposits are most likely to appear in the subcapsular cortex. We can identify the capsule readily by distinct features and by correlating with EUS. We can also capture optical biopsies as we scan the diameter of the lymph node working backwards from the inside of the capsule. Many elements are recognizable and repeat often. In nCLE, as with all optical biopsy, pattern recognition is important and this comes with experience.

It is also clear that endomicroscopy is valuable as long as abnormal or pathological specimens have distinct imaging characteristics, even if we cannot identify a histological correlate but simply resort to using descriptive terminology. The best example of this is the application of pCLE for biliary strictures; there is a very high negative predictive value of a normal-appearing optical biopsy [3] and often very clear features of malignancy in abnormal optical biopsies, and yet to date, the optical biopsy findings remain descriptive for lack of concrete histological correlations.

Finally, although we are not yet at a point where we can make management decisions based solely on endomicroscopy of lymph nodes, I believe we can agree that the images, and the facility with which they can be obtained, are certainly intriguing. As such, this is nothing more than a feasibility study and we were very careful to not overstate these findings, but are extremely optimistic of the potential.

• References

• 1 Xiong YQ, Ma SJ, Zhou JH. et al. A meta-analysis of confocal laser endomicroscopy for the detection of neoplasia in patients with Barrett’s esophagus. J Gastroenterol Hepatol 2016; 31: 1102-1110
• 2 Bok GH, Jeon SR, Cho JY. et al. The accuracy of probe-based confocal endomicroscopy versus conventional endoscopic biopsies for the diagnosis of superficial gastric neoplasia (with videos). Gastrointest Endosc 2013; 77: 899-908
• 3 Meining A, Chen YK, Pleskow D. et al. Direct visualization of indeterminate pancreaticobiliary strictures with probe-based confocal laser endomicroscopy: a multicenter experience. Gastrointest Endosc 2011; 74: 961-968
• 4 Napoleon B, Lemaistre AI, Pujol B. et al. In vivo characterization of pancreatic cystic lesions by needle-based confocal laser endomicroscopy (nCLE): proposition of a comprehensive nCLE classification confirmed by an external retrospective evaluation. Surg Endosc 2016; 30: 2603-2612
• 5 Konda VJ, Aslanian HR, Wallace MB. et al. First assessment of needle-based confocal laser endomicroscopy during EUS-FNA procedures of the pancreas (with videos). Gastrointest Endosc 2011; 74: 1049-1060