EUS stands for Endoscopic Ultrasound. It is an endoscopic technique that combines endoscopy and ultrasound. This allows the endoscopist to examine the walls of the digestive tract, as well as the adjacent organs including the pancreas, bile ducts, liver and gallbladder.
The endoscopist passes an echoendoscope through the mouth into the digestive tract to the area to be examined. The echoendoscope has a built in miniature ultrasound probe that allows the doctor to use sound waves to create visual images of the digestive tract wall and its adjacent organs. Given the proximity of the ultrasound probe in the gut to these structures, EUS is the most accurate way to examine these structures. EUS can also be used to perform sampling and treatment as follows:
- Fine needle aspiration (FNA): A needle is passed under EUS guidance into the area of interest to obtain cells for analysis. EUS helps to avoid blood vessels and other vital structures, and allows precise and safe sampling of cells from the area of interest. FNA can also be used to withdraw fluid from a cyst
- Fine needle biopsy (FNB): Similar to FNA, this technique allows the doctor to obtain a large tissue sample called a core biopsy to obtain tissue for analysis. This is required when cell analysis alone is not diagnostic, and the architecture of the tissue is required for diagnosis.
- Celiac axis treatment: EUS can visualize the celiac axis accurately, and allows precise injection of medication to control pain that is mediated by this important nerve bundle.
- Cancer treatment: EUS can be used to place markers (fiducials) into cancers to enable accurate and safe (stereotactic) radiotherapy. EUS can also be used to inject medication or alcohol accurately into cancers for treatment
- Metal stent placement: EUS can be used to place a special stent that joins 2 spaces together. This is often done for pancreatic pseudocyst treatment, but can also be done to drain the bile duct through the stomach or duodenum.
EUS is most commonly used for the following cases:
- Evaluation and sampling of submucosal masses in the digestive tract. These are masses that are detected on general endoscopy, but are located in the deeper layers of the gut wall such that normal biopsy is unable to obtain the tissue sample for analysis.
- Evaluation of the bile ducts for stones, to determine whether ERCP is required. EUS is the only modality that can accurately detect very small stones.
- Evaluation and sampling of cysts and masses in adjacent organs such as the pancreas and lymph nodes.
- Evaluation of the pancreas for chronic pancreatitis when other radiologic tests are inconclusive.
- Staging of digestive cancers, including pancreatic, bile duct, stomach, esophagus and rectal cancers. This allows the doctor to make better decisions about surgery, chemotherapy and radiotherapy.
- Celiac plexus treatments such as nerve blocks to stop pain from the upper abdomen. This is particularly is pain due to pancreatic cancer and chronic pancreatitis.
- Drainage of pancreatic fluid collections, and endoscopic treatment of severe acute pancreatitis.
You should fast for at least 6 hours prior to your endoscopic ultrasound. Longer fasting may be needed if your doctor suspect that your stomach is not emptying properly. You may drink clear fluid up to 2 hours before the procedure but milk is not allowed during the fasting.
In general, most medication should be continued before the gastroscopy with the exception of diabetes medication and blood thinners. Diabetic medication should be omitted during the fasting. You should check with your doctor if your blood thinner needs to be discontinued prior to the procedure.
As you will be given medication to make you sleepy, you must not drive, work or make any important decision after the procedure. Medical Certificate will be issued if needed and you should rest at home for the rest of the day.
Before the EUS
A nurse will conduct final checks, and bring you into the procedure room. An intravenous line will be inserted.
During the EUS
A throat spray will be administered to lessen the discomfort of the procedure.
You will be lying on your left, with your legs curled up and a plastic bite will be placed between your teeth to protect your teeth.
Sedation will then be given. After you have fallen asleep, the procedure will begin. You will likely not remember any of the procedure. You will be breathing on your own and monitored closely during the procedure.
You will wake up gradually after the procedure is done. All the medication used for sedation have a duration of action of a few minutes.
After the EUS
You will be cared for in a recovery area or room. The nurses will give you food and drink when they assessed that you are ready. You should arrange for a family member to take discharge instruction and take you home. You should only resume working and driving the following day.
Sometimes, you may have a mild sore throat, bloating and cramping. This normally goes away after 24 hours.
EUS is an advanced endoscopic technique. Very few specialists and endoscopists undergo additional training after specialization to do this properly. Typically, it takes about an additional 1-2 years of dedicated EUS training after completing specialist and general endoscopy training in order to perform EUS competently. There are various levels of difficulty in EUS. Most EUS specialists are able to perform routine cases such as simple diagnostic evaluation and FNA. However, only top EUS experts are able to perform difficult cases successfully. It is important to ensure that the doctor performing the EUS has the correct level of expertise to match the difficulty of the case.
EUS is safe when performed by properly trained doctors. The risk of diagnostic EUS is equivalent to a simple gastroscopy. Complications and failures increase significantly when EUS is performed by Inadequately trained doctors or those with insufficient cases to maintain their skill. Hence, it is important to ensure that the doctor performing the EUS has the appropriate expertise for the case. The doctor should welcome questions regarding their training, credentials and experience. Simple questions such as the following are useful:
- Which public institution where you formally certified to do EUS independently?
- How many cases have you performed?
- What is your FNA yield (or successful diagnosis rate)?
- What is your complication rate?
- How will you detect complications and how have you managed these before?
- How many difficult EUS cases have you done, and what are some examples?
- Advanced Endoscopy