EUS — Endoscopic Ultrasound

Advanced imaging

Why EUS exists

The pancreas and bile ducts sit deep in the abdomen, surrounded by bowel, blood vessels and other organs. Ultrasound from the skin outside the body has to travel through all of that, which limits how clearly these structures can be seen. EUS solves this by putting the ultrasound probe at the tip of an endoscope and placing it directly inside the stomach or duodenum — only millimetres away from the pancreas and bile duct.

The result is the highest-resolution imaging available for the pancreas and biliary tree, combined with the ability to take tissue samples through the same instrument using a fine needle. This is why EUS is considered the most accurate test for many pancreatic and biliary questions.

When EUS is useful

• Unexplained or recurrent pancreatitis
• Suspected pancreatic mass
• Pancreatic cysts
• Submucosal gut wall lesions
• Bile duct stones (equivocal imaging)
• Bile duct strictures of uncertain cause
• Staging of oesophageal, gastric and pancreatic cancer
• Lymph node assessment
• Autoimmune pancreatitis
• Fine-needle aspiration or biopsy

How EUS is performed

EUS uses a specialised echoendoscope — an endoscope with an ultrasound transducer at its tip. It is performed under sedation, similar to a standard endoscopy, and usually takes 30–60 minutes. After examining the relevant area, the endoscopist may decide that a tissue sample is needed.

• FNA (fine-needle aspiration) — a very fine needle passes through the gut wall under real-time ultrasound guidance to sample the lesion, with no external incision.
• FNB (fine-needle biopsy) — a slightly different needle that obtains a small core of tissue, often giving a more definitive answer.
• Cyst fluid analysis — where a pancreatic cyst is being assessed, fluid may be aspirated for analysis.
• EUS-guided drainage — in selected patients, used to drain a fluid collection or bile duct when the usual route is not available.

A pathologist works alongside the clinical team so that the specimen obtained is adequate — this reduces the need for a repeat procedure.

Preparation

• Fasting: nothing to eat or drink for 6–8 hours, because a full stomach impairs imaging and increases risk.
• Blood thinners: these need particular attention if a fine-needle sample is planned, and must be discussed in advance.
• Blood tests: recent count and coagulation studies are usually required when sampling is anticipated.
• Escort: required, as the procedure is performed under sedation.

After the procedure

Recovery is similar to a standard upper GI endoscopy: a short period of observation, a sore throat, and in some cases a few hours of monitoring if a needle sample was taken. Most patients go home the same day. If a tissue sample was taken, the report usually takes a few days and is discussed at a follow-up visit, where the pathologist’s findings are put together with the images to reach a conclusion.

Risks

• Sore throat and mild sedation effects — common and temporary.
• Bleeding — uncommon, more relevant when a needle sample is taken, especially in patients on blood thinners.
• Infection — particularly after cyst sampling; preventive antibiotics are used.
• Pancreatitis — uncommon, mostly when the pancreas itself is sampled.
• Inconclusive result — occasionally the sample is insufficient, and a repeat or alternative test is needed.

EUS is generally very well tolerated. Because it can provide a definitive answer where other tests are inconclusive, it often replaces longer, more invasive and less accurate diagnostic pathways.