P&S Journal: Winter 1995, Vol.15, No.1
Endoscopic Ultrasound in Gastroenterology
By Robin Eisner
Many technologies used by physicians to characterize disease have limitations, so doctors continually search for superior and-with increasing importance-cost-effective techniques for better diagnosis and treatment.
One new technology that fits both criteria is endoscopic ultrasonography (EUS), an imaging method that adds to a doctor's ability to see pathological changes in patients. One of the leading practitioners of gastrointestinal EUS in the United States joined P&S in July 1993-Dr. Charles Lightdale.
A 1966 P&S graduate, Dr. Lightdale is professor of clinical medicine and director of clinical gastroenterology. As director of endoscopic research at Memorial Sloan-Kettering Cancer Center, Dr. Lightdale began testing EUS in the late 1980s as a potential method for evaluating gastrointestinal cancer. "Better instruments were continually developed, and I became better at interpreting the images," he says.
He realized that high frequency ultrasound waves placed internally, rather than externally, would allow him to see the structures beneath the lining of the esophagus, stomach, or intestines-anatomical regions of his specialty-in more detail. Ultrasound from outside the body cannot penetrate the tissues in question. "With high frequency ultrasound inside you can see things not visible with any other system," Dr. Lightdale says. Combining ultrasound and endoscopy, which allows him to examine the surface of the GI tract, Dr. Lightdale has helped change the field of GI oncology. He now can find and stage early GI cancers more accurately, prevent unnecessary surgery, prepare patients better for surgery through new treatments, and monitor recurrence of cancer. He also performs research to increase knowledge about disease-causing changes in the GI tract.
EUS is done on an outpatient basis. The patient is sedated but requires no assistance breathing. A topical spray numbs the back of the throat so the endoscope-ultrasound probe that passes through the tract causes minimal discomfort. Both the endoscope and the ultrasound probes are hooked to video monitors that capture images for real-time or future analysis. The endoscope allows the physician to scan the epithelial lining for growths and abnormalities; the ultrasound penetrates below. Imaging can take 15 to 45 minutes, depending on the purpose.
"EUS can help to diagnose cancer but more often is used to stage the disease to determine how far it has spread locally," says Dr. Lightdale. Cancer starts on the surface lining of the GI tract and grows deeper as it progresses. Tumor depth determines the treatment: The deeper the tumor, the greater its tendency to spread. Before EUS was available, physicians relied on surgical biopsies and computerized tomography scans to stage GI cancers. CT scans remain important in diagnosing cancer that has spread but are less sensitive than EUS in detecting an early stage tumor.
The Health Care Financing Administration recognized the clinical value of EUS last year when it was agreed that Medicare would reimburse physicians for its use and analysis. "There is now enough data comparing EUS to surgical pathology to verify its accuracy in staging cancer," says Dr. Lightdale.
Dr. Lightdale also uses the endoscope portion of EUS aided by ultrasound images to treat tumors in some patients at risk for surgery or to prepare others for surgery. He uses the endoscope to remove cancerous tissue with an electrocautery device or laser. He can treat some tumors with chemical sensitizers that destroy tumors when exposed to low-dose laser light, a new treatment called photodynamic therapy.
EUS is now performed at about 120 medical centers in the United States, but Dr. Lightdale receives referrals from around the country. Some of the patients make good subjects for his research, including early detection of esophageal cancer, a form that now accounts for half of 11,000 new cases of esophageal cancer seen each year, up from 5 percent to 10 percent 20 years ago.
Dr. Lightdale studies the relationship of esophageal cancer to Barrett's esophagus, a condition in which patients have a 30 to 300 times greater risk of developing cancer. In Barrett's esophagus, squamous cells lining the epithelium are wrongly replaced by columnar cells. If patients develop cancer, treatment usually involves the removal of most of the esophagus. By following patients prospectively and monitoring them for any neoplastic changes, Dr. Lightdale hopes to identify a less drastic treatment.
In an attempt to diagnose and treat these cancers at the earliest possible stage to ensure their cure, he uses special endoscopic staining methods, magnification endoscopy, fluorescence spectroscopy (analyzing the light signals from illuminated tissue), and high-frequency EUS and he studies abnormal genes in biopsy specimens.
Dr. Lightdale also uses EUS to evaluate pancreas tumors and pancreatitis and to find gallstones lodged in the common bile duct. He believes EUS has great potential to replace more invasive tests for these purposes and may help explain the cause of abdominal pain in some patients where the diagnosis has been unclear.