|LETTER TO EDITOR
|Ahead of print publication
String sign: Can we make it more scientific?
Iyad Khamaysi1, Gadeer A'li Taha2, Efad Weishahi2, Eyal Zussman3
1 The Ruth and Bruce Rappaport Faculty of Medicine, Technion – Israel Institute of Technology; Department of Gastroenterology, Rambam Health Care Campus, Haifa, Israel
2 Department of Gastroenterology, Rambam Health Care Campus, Haifa, Israel
3 NanoEngineering Group, Faculty of Mechanical Engineering, Haifa, Israel
|Date of Submission||08-Mar-2021|
|Date of Acceptance||06-May-2021|
|Date of Web Publication||03-Sep-2021|
Department Gastroenterology and Hepatology, Rambam Health Care Campus, Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, POB 9602, Haifa 31096
Source of Support: None, Conflict of Interest: None
We read with great interest the study by Hakim et al., regarding the interobserver variability of string sign of pancreatic cysts among experienced endosonographers.
We agree with authors that string sign is a useful and reliable test that can be used to improve the diagnostic accuracy of other pancreatic cyst fluid studies when used in combination.
The study showed that while a good interrater agreement among different experienced endosonographers in assessing its positivity, was observed; a disagreement on the minimum length of the string sign to be considered positive and poor interrater agreement with marked interobserver variability (>5 mm) in the measured length of the formed string, was noticed also.
Therefore, the authors concluded that a positive string sign should be interpreted with caution and not used as a single test but in combination with other tests to differentiate mucinous from nonmucinous cysts.
String sign is inherently a subjective test and lacks a theoretical framework for predicting the viscoelastic nature of the fluid, which can be objectively characterized by the viscous and elastic response of a fluid under deformation (rheological behavior).
In order to overcome the subjective nature of the string sign, we developed a new rheological assay in which (using a rheometer) a wide array of viscoelastic properties (rheological curves) can be generated and recorded.
In our study, we found that the cutoff value of pancreatic cyst fluid viscosity, ηc, can serve as an independent marker to distinguish between mucinous and non-mucinous cysts. It was found that ηc >1.3 cP characterizes mucinous cysts, whereas ηc >1.3 cP is typical for non-mucinous cysts. Moreover, we could differentiate between three distinct flow curves of the rheological behavior of pancreatic cyst fluids according to dynamic viscoelastic properties. Types I and II hypothesized to correlate with non-mucinous cysts, and type III with mucinous cysts [Figure 1]. This simple and rapid diagnostic tool can be immediately implemented after EUS-FNA sampling, and provides for a low variability rate compared to the commonly used, subjective string sign technique. Although the findings are promising, they must be further confirmed in a large-scale study.
|Figure 1: Representative types I, II and III flow curves. The graph inset shows the values of infinite viscosity, ηc, depicting the difference between the minimal value of type III and the maximum value of types I and II|
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In conclusion, the string sign as it is currently performed, suffers from significant shortcoming due to its subjective nature. Rheological properties (“scientific” string sign), instead, can overcome the disadvantages of the standard string sign and replace it in clinical practice.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Hakim S, Coronel E, González GM, et al.
An international study of interobserver variability of “string sign” of pancreatic cysts among experienced endosonographers. Endosc Ultrasound
Khamaysi I, Abu Ammar A, Vasilyev G, et al
. Differentiation of pancreatic cyst types by analysis of rheological behavior of pancreatic cyst fluid. Sci Rep