How to improve the diagnostic performance of endoscopic ultrasound-guided tissue acquisition for small gastric subepithelial lesions: Role of proper traction assistance

Gastric subepithelial lesions (SELs) are commonly identified during upper gastrointestinal endoscopy. These lesions are covered by normal mucosa and display diverse histological features, leading to a broad differential diagnosis. A key diagnostic consideration is distinguishing between mesenchymal tumors, such as gastrointestinal stromal tumors (GISTs), which require treatment,¹ and benign SELs, which typically do not necessitate intervention.

According to the Guidelines for GIST,^{2, 3} tumor size is a critical criterion for histopathological diagnosis, with a threshold of 20 mm. However, tissue diagnosis is advised for any tumor exhibiting irregular margins, ulceration, depression, or evidence of growth, regardless of size. Endoscopic ultrasound-guided tissue acquisition (EUS-TA) is the first-line diagnostic approach in such cases.

Since differentiating GISTs is critical in SEL diagnosis, obtaining high-quality tissue samples that preserve structure and enable immunohistochemical evaluation is essential. Recent advancements in needles used for EUS-TA have significantly improved diagnostic capabilities. Although traditional fine-needle aspiration (FNA) needles were commonly used, newer fine-needle biopsy (FNB) needles, such as the Franseen and fork-tip needles, have been developed, with innovative designs that enable the acquisition of high-quality specimens.⁴ These advancements have enhanced diagnostic accuracy.

A meta-analysis comparing FNB and FNA needles for gastrointestinal SELs showed that FNB needles achieved significantly higher diagnostic accuracy than FNA needles (odds ratio 4.10, 95% confidence interval 2.48–6.79; P < 0.0001).⁵ However, the unique tip design of FNB needles reduces puncture performance compared to FNA needles. While this limitation is usually not an issue for easily accessible lesions, it poses challenges in more difficult cases, such as small gastric SELs, where achieving adequate puncture with an FNB needle can be challenging and remains a practical limitation.

In gastric SETs, respiratory motion and the high mobility of the lesions often make puncture challenging. The lesion may shift during the attempt, complicating efforts to secure it for puncture. Positioning the lesion at approximately the 3 o'clock direction on the EUS screen, instead of the conventional 6 o'clock position, can sometimes help. Applying upward angulation to the scope and using the probe to “cradle” the tumor helps stabilize the lesion, reducing its movement and facilitating puncture. However, this technique requires the tumor to be sufficiently large to be cradled effectively. Consequently, smaller gastric SETs remain particularly challenging, underscoring the need for tailored diagnostic methods for these cases.

A forward-viewing echoendoscope equipped with a cap attached to its tip has been reported as a potential solution.^{6, 7} By suctioning the SET into the cap, this method enables effective tissue sampling even for small lesions measuring ≤15 mm.⁶ The approach aims to stabilize the lesion by pulling it into the cap and has shown promise in some cases. However, a randomized controlled trial comparing this method with conventional EUS-TA using an oblique-viewing echoendoscope found no significant difference in diagnostic yield.⁷ Therefore, despite its theoretical advantages, the effectiveness of this technique remains uncertain.

Against this backdrop, the randomized controlled trial by Minoda et al.,⁸ published in this issue of Digestive Endoscopy, investigated a novel approach to improving EUS-TA outcomes by enhancing lesion stability during puncture. The study employed the clip-with-thread technique, a traction method previously proven effective in endoscopic submucosal dissection.⁹ By stabilizing SET lesions, this technique minimizes movement during puncture and facilitates the use of FNB needles.

In a direct comparison with conventional EUS-TA without traction, both groups used the Franseen needle. The traction-assisted group achieved significantly higher rates of adequate tissue sampling (90% [27/30] vs. 66.7% [20/30], P = 0.028) and diagnostic yield (86.7% [26/30] vs. 63.3% [19/30], P = 0.037). Subgroup analysis revealed that when a forward-viewing echoendoscope was used, the traction-assisted group demonstrated a significantly higher adequate tissue sampling rate (100% [15/15] vs. 66.7% [10/15], P = 0.014) and diagnostic yield (100% [15/15] vs. 66.7% [10/15], P = 0.014). Conversely, with an oblique-viewing echoendoscope, no significant differences were observed between the groups in adequate tissue sampling rates (80% [12/15] vs. 66.7% [10/15], P = 0.409) or diagnostic yield (73.3% [11/15] vs. 60.0% [9/15], P = 0.439).

The authors noted that in the oblique-viewing scope group, clip detachment occurred in two cases, potentially contributing to the lack of significant differences. They speculated that lesions on the greater curvature of the upper stomach might be prone to clip dislodgement due to large scope movements. Additionally, misalignment between the needle trajectory and the thread pull direction in oblique-viewing scopes could increase the likelihood of clip detachment. However, the small sample size makes it difficult to draw definitive conclusions. Future research should focus on identifying cases where clip placement is most effective and where clip detachment is less likely.

Notably, the clip-with-thread technique requires additional preparation and placement time, and clip dislodgement renders this effort futile. Furthermore, removing the clip after the procedure may potentially affect the lesion. Therefore, for lesions where clip placement does not significantly improve outcomes, the technique may not be necessary.

Another critical consideration is the difference between forward-viewing and conventional oblique-viewing echoendoscopes, particularly the presence of a forceps elevator in the latter. Although not explicitly discussed in that study, the forceps elevator can enhance puncture performance and improve tissue acquisition through techniques such as the fanning method. This aspect should not be overlooked, and warrants further investigation to optimize EUS-TA outcomes.

Targeting during clip placement can also be a significant challenge. For SETs with intramural growth, targeting is relatively straightforward. However, for small SETs primarily growing extramurally, placing the clip in the appropriate location can be difficult, potentially limiting the effectiveness of this technique. Future studies should aim to clearly identify the lesion types for which the clip-with-thread traction-assisted method is most beneficial.

Additionally, some reports have suggested that mucosal incision biopsy achieves higher diagnostic accuracy than EUS-TA for small lesions.¹⁰ Comparative trials between these two approaches, along with studies clarifying their respective advantages, disadvantages, and optimal applications, are needed. Such research would help establish a more robust diagnostic strategy for small SETs.

In conclusion, EUS-TA is an invaluable diagnostic tool for SETs. However, achieving precise puncture and effective needle strokes within the lesion can be challenging, particularly for small lesions. One primary reason for this difficulty is the inherent mobility of SETs, which underscores the importance of stabilization. Implementing lesion fixation methods is a key strategy to address this challenge. The clip-with-thread technique, commonly used as a traction method in endoscopic submucosal dissection, offers a potentially effective approach to improving diagnostic outcomes in such cases.

Authors declare no conflict of interest for this article.

None.