Assessment of SMI (Superb Microvascular Imaging) for Characterising the Endocystic Material of Papillary Intraductal Mucinous Pancreatic Tumours (PIMPT)

Pancreatic cysts are becoming increasingly common in the general population. They are most often discovered incidentally during an imaging scan.

There are many types of pancreatic cystic lesions, but the most common are papillary intraductal mucinous pancreatic tumours (PIMPTs), serous cystadenomas (SCAs), mucinous cystic tumours (MCTs) (formerly known as mucinous cystadenomas), cystic neuroendocrine tumours, and solid and pseudopapillary tumours.

PIMPTs carry a risk of degeneration, which may arise from an initially benign wall-bound nodule (polyp) that can subsequently progress to a malignant lesion. The average rates of high-grade dysplasia/invasive carcinoma in surgical specimens of PIMPT from the secondary ducts and the main duct are 31% and 62% respectively. The presence of a wall-adherent nodule \> 1 cm is a clear indication for pancreatic surgery to prevent neoplastic progression (or to treat it if it is already present within the nodule). However, PIMPTs also secrete mucus, which most often presents as a globule adhering to the wall, thus resembling a wall-adherent nodule.

The key examination for assessing a PIMPT is echoendoscopy, which enables the type of material present within the cyst to be characterised. The most sensitive standard Doppler technique (e-flow) is often unsuccessful (no visible vessels) or yields an inconclusive result, as the vessels present in the tissue nodules are very fine and have a very slow flow.

Currently, to distinguish mucus from a tissue nodule, an ultrasound contrast agent (Sonovue) is routinely used to detect microvascularisation. A tissue nodule takes up the contrast agent, whereas a mucus ball is avascular (no contrast uptake).

Superb Microvascular Imaging (SMI) is a new ultrasound mode that broadens the range of visible blood flow by revealing low-velocity microvascular flow. SMI is capable of visualising microvascular flow without the injection of contrast medium, unlike the current gold standard technique based on the injection of Sonovue.

The Mermoz Endoscopy Centre will be equipped with an ultrasound console enabling SMI to be performed during an echoendoscopy examination. This technology is now available on the new Aplio i800 EUS console (Canon-Olympus).

To date, no data have been published on the potential of SMI to characterise the endocystic material of PIMPTs. This is why this clinical investigation is being conducted.