Endoscopic ultrasound combines two procedures: an endoscopy and an ultrasound scan. The instrument resembles the endoscope used for a gastroscopy but is slightly thicker and carries a small ultrasound probe at its tip. It is passed through the mouth into the oesophagus, stomach and duodenum – or through the anus for questions concerning the rectum.
The advantage lies in proximity. With ultrasound through the abdominal wall, air in the bowel and the tissue in between get in the way; deep-lying organs such as the pancreas are often only partly visible. From the inside, only a few millimetres separate the probe from the stomach wall, pancreas, bile duct and lymph nodes. The image shows the individual layers of the wall and even small changes – without X-rays.
Common reasons include a bulge beneath the lining noticed during a gastroscopy, cysts or nodules in the pancreas, and a suspected stone in the bile duct when conventional ultrasound does not provide clarity. After an inflammation of the pancreas with no apparent cause, endoscopic ultrasound looks for tiny stones. With tumours of the oesophagus, stomach or rectum, the examination shows how deep they reach into the wall and whether nearby lymph nodes are affected; further treatment depends on this.
If a finding remains unclear, a fine needle can be guided through the wall into the abnormal area under ultrasound guidance. This fine-needle aspiration obtains tissue or fluid for the laboratory, without an incision and by a short route. Endoscopic ultrasound differs from ERCP in its aim: it is mainly used for diagnosis, whereas ERCP treats the bile duct. If endoscopic ultrasound finds a bile duct stone, ERCP can often follow immediately.