Superb Microvascular Imaging (SMI) and Two-Dimensional Endoscopic Ultrasound Guided Shear Wave Elastography (2D-SWE-EUS) in Differential Diagnosis of Pancreatic Adenocarcinoma (PA) From Other Pancreatic Solid Lesions (PSLs) and Pancreatic neuroendocrinE Tumors (pNETs) Malignancy

Pancreatic adenocarcinoma (PA) diagnosis

Pancreatic adenocarcinoma (PA) is the most common tumor of the pancreas, representing more than 90% of all solid pancreatic neoplasia and 55% -73% of solid pancreatic masses. Given its poor prognosis and the major therapeutic consequences, the discrimination between PA and other pancreatic solid lesions is mandatory.

Endoscopic ultrasound (EUS) is admitted as the most sensitive imaging procedure for the detection and characterization of pancreatic tumors. Based on only endosonographic features, it remains difficult to differentiate PA from other solid masses, the specificity (Spe) and accuracy of EUS for the diagnosis of pancreatic tumor malignancy range from 53-69% and 72-83%, respectively.

Over the past 30 years, EUS-guided tissue acquisition (EUS-TA), or more recently fine needle biopsy (EUS-FNB), has demonstrated its efficiency for tissue sampling and remains the gold standard for the pathologic diagnosis of pancreatic lesions.

Although several prospective randomized studies and meta-analyses have shown that FNB needles are significantly superior to FNA needles for the diagnosis of solid pancreatic tumors, the overall accuracy remains insufficient to rule out malignancy. Additional diagnostic criteria are then required.

The assessment of pancreatic tumor enhancement using ultrasound contrast agents (UCAs) in real time with imaging specific methods seems useful to improve their characterization either by contrast-enhanced EUS (CE-EUS) or, more recently, by contrast-harmonic EUS (CH-EUS). Contrast harmonic EUS (CH-EUS), was already demonstrated useful to differentiate pancreatic adenocarcinoma from other pancreatic lesions.

EUS-Elastography (EUS-E) is another EUS image enhancement technique, which rational based on the difference in elasticity between the tissues. There are two types of elastographies: strain elastography (SE) and shear wave elastography (SWE). Strain elastography has proved useful for the characterization of pancreatic lesions and lymph nodes. However, this technique was demonstrated difficult to perform with adequate accuracy and reproducibility for pancreatic lesions and have many limitations. In some recent publications SWE was demonstrated moderate reliability.

Pancreatic neuroendocrine tumors (pNETs)

Pancreatic neuroendocrine tumors (pNETs) are rare tumors, but according to the last epidemiological data, their incidence and prevalence are steadily rising.

Surgical resection is generally performed for pNETs due to their malignant potential. However, with increasing use of high-resolution conventional imaging, the significant incidence of small (≤ 2 cm) pancreatic neuroendocrine incidentaloma (pNET) has risen in recent decades. Given their unknown natural history due to the lack of literature, the significant morbidity and mortality of pancreatic surgery, the current French and European Neuroendocrine Tumor Society (ENETS) Guidelines suggests that conservative management may also be considered for the small size (≤ 2 cm) nonfunctional, asymptomatic and without criteria for malignancy pNETs, classified as G1 or low G2 according to the 2019 World Health Organization (WHO) classification system lesion, after multidisciplinary discussion and patient counseling.

EUS is recognized as the most sensitive procedure for the detection and characterization of pNETs. Overall sensitivity of EUS-TA for the diagnosis of pNETs is high, reaching 95.1% in recently published study, appearing higher in small lesions (≤ 20 mm) than in large lesions (> 20 mm).

The overall concordance rate for EUS-TA and surgical specimens grading varies from 58% to 86.4% and is higher for lesions ≤ 10 mm, 10-20 mm, comparing to lesions > 20 mm. These results confirm the risk of under or over-grading of pNETs on the EUS-TA specimen, independently of the needle size which used for the TA.

CH-EUS was also demonstrated accurate in the prediction of pNETs malignancy and useful for decision-making management of these tumors.

Hypothesis

Two new image enhancement EUS technologies were recently developed, able to assess precisely tumor microvascular density and the stiffness of pancreatic lesions, that is correlated to tumor's stroma fibrosis, and thus help to characterize and predict the malignancy, and accordingly, the management of the pancreatic solid lesions. It's particularly useful in overcoming EUS false-negative cases of PA and small pNETs malignancy diagnosis.

Superb Microvascular Imaging (SMI) is a novel doppler technique that enhances the range of visible blood flow, by revealing low velocity microvascular flow, enabling the capture of a higher-quality microvascular flow images. Based on the same principle as CH-EUS, which assesses tumor microvascularization, this technique is expected to be also useful for the PSLs malignancy diagnosis.

Shear Wave Elastography (SWE) relies on the properties of shear-wave propagation to offer an advanced assessment of their velocity and tissue elasticity, presenting the results quantitatively in a dynamic display.

The new developed image enhancement EUS technologies, SMI and 2D-SWE-EUS now available on the new Aplio i800 EUS unit (Canon-Olympus).

Given the lack of published data in the literature regarding the utility of SMI and 2D-SWE-EUS, it is essential to assess the performance of these two techniques in the differential diagnosis of SPLs and pNETs malignancy