Endoscopic Ultrasound
For endoscopic ultrasound of the upper digestive
tract, a probe is inserted into the esophagus, stomach
and duodenum during a procedure called
esophagogastroduodenoscopy. Among other uses, it allows
for screening for pancreatic cancer, esophageal cancer,
and gastric cancer as well as benign tumors of the upper
gastrointestinal tract. It also allows for
characterization and biopsy of any focal lesions found
in the upper gastrointestinal tract. This is done by
inserting a needle through the stomach lining into the
target.
Endoscopic ultrasound is performed with
the patient sedated. The endoscope is passed through the
mouth and advanced to through the esophagus to the
suspicious area. From various positions between the
esophagus and duodenum organs within and outside the
gastrointestinal tract can be imaged to see if they are
abnormal and they can be biopsied by a process called
fine needle aspiration. Organs such as the liver,
pancreas and adrenal glands are easily biopsied as are
any abnormal lymph nodes. In addition the
gastrointestinal wall itself can be imaged to see if it
is abnormally thick suggesting inflammation or
malignancy.
The technique is highly sensitive for
detection of Pancreatic Cancer (90-95% sensitivity)
particularly in patients who are suspected to have a
mass or present with jaundice. Its role in staging
patients with pancreatic cancer is limited to local
metastases; however, in combination with CT scan which
provides information on regional metastases, it provides
an excellent imaging modality for diagnosis and staging
of pancreatic carcinoma.
Endoscopic ultrasound
can also be used in conjunction with endoscopic
retrograde cholangio pancreatography (ERCP). The
ultrasound probe is used to locate gall stones which may
have migrated into the common bile duct. This occurrence
may cause obstruction of the drain shared by the liver
and pancreas which may lead to lower back pain, jaundice
and pancreatitis.
Echo-endoscopy can also be used
for imaging of the rectum and colon, although these
applications are lesser known. It is used primarily to
stage newly diagnosed rectal or anal cancer. EUS guided
fine needle aspiration may be used to sample lymph nodes
during this procedure. Evaluation of the integrity of
the anal sphincters may also be done during lower EUS
procedures.