What is the value of radionuclide scanning in the surveillance of patients with Barrett's esophagus?
E.M. Smith, K.H. Gladden, S. Fink, T.K. Chaudhuri (Hampton)
Barrett's esophagus (BE) is an acquired condition in which reflux of gastric and duodenal contents results in columnar epithelial replacement of the normal squamous mucosa of the lower esophagus [1, 2]. BE has a malignant potential, since the progression from squamous epithelium to Barrett's metaplasia continues to invasive esophageal carcinoma in a subgroup of patients [3, 4]. Prevalence rates for BE range from 8-15%, although some reports approach 20% in the general population  and 50% in patients with gastroesophageal reflux disease . The incidence of adenocarcinoma of the esophagus is rising worldwide  and the incidence rate of cancer development in patients with BE ranges from one adenocarcinoma per 46 to one per 441 patient year follow-up. This may also be expressed as representing a 30 to 125-fold increased risk for esophageal cancer over that of the general population [8, 9]. This evolution takes at least two years, with the vast majority of BE patients never progressing past normal mucosa or low-grade dysplasia . These data have raised the question of how best to survey patients with BE, so that their chance of early cancer diagnosis may be maximized [8, 11].
The double-contrast barium esophagogram represents the most readily available means to evaluate BE. Few patients with BE will have normal radiologic findings, but many patients are not referred for radiologic examination because the procedure may fail to demonstrate uncomplicated mucosal dysplasia in up to 60% of patients with BE . The presence of midesophageal stricture, mucosal reticular pattern and deep esophageal ulceration suggest BE. Other findings, such as hiatal hernia, thickened mucosal folds and gastroesophageal reflux are also frequently seen but not as specific. The finding of focal mural deformities associated with fixed transverse folds and minimal distensibility of the esophagus at
least 4 cm. proximal to the esophagogastric junction also suggests BE . When adenocarcinoma supervenes, its morphology is similar to that of squamous cell carcinoma of the esophagus .
Computed tomography (CT) is most helpful when BE has progressed to adenocarcinoma, wherein CT assists in staging of the cancer and in evaluating direct invasion or distant metastases . The radiologic appearance of esophageal adenocarcinoma on CT is similar to that of squamous cell carcinoma. CT is reliable in detecting local tumor invasion and metastases in the liver or adrenal glands [15, 16].
Radionuclide imaging takes advantage of the fact that the BE mucosa can secrete acid . Since 1973 the selective concentration of 99mTc-pertechnetate in gastric mucosa has been used to diagnose BE [1, 18, 19]. This technique allows for simple reproducible studies as these patients are followed clinically. Figure 1 shows a scintiscan obtained in a patient with BE. Radionuclide imaging has a high specificity but sensitivity is low, with only eight of 17 patients (47%) giving positive images in one study . Swallowed saliva can give a false positive test and patients are asked to drink a glass of water after initial imaging. This eliminates any saliva. A gradual decline in Tc99m-04 uptake as noted by serial scintigraphy in a a patient with BE may suggest either healing of the BE or transformation of the BE to malignancy.
Figure 1. Radionuclide scintigraphy showing a positive scan for Barrett's esophagus.
Endoscopic ultrasound (EUS) allows a detailed circumferential image of the esophageal wall. As measured by EUS the esophageal wall is significantly thickened in the columnar-lined portion of BE, so that EUS can be used to follow patients with BE . However, a study designed to test this function of EUS found that the current generation of echo-endoscopes does not reliably differentiate between benign and malignant wall thickening in patients with BE .
Primarily because none of these imaging studies provides material for a histologic diagnosis, endoscopy is the current surveillant tool of choice for most gastroenterologists [15, 22, 23]. This practice prevails despite the fact that from one endoscopic examination to another inconsistencies in the ability to detect specialized columnar epithelium are common and complicate the accurate endoscopic diagnosis of BE [24, 25]. Endoscopy also has a higher morbidity and expense than the imaging techniques. It has been suggested that yearly endoscopy is appropriate if length of life is the only criterion, whereas endoscopy every 2-3 years will provide the greatest quality-adjusted life expectancy . A way to provide histologic surveillance without endoscopy is provided by balloon cytology, a technique now being evaluated [27-29].
Clinicians have many ways in which to diagnose and follow the course of BE. The many therapeutic modalities available for the treatment of BE underscore the value of detecting and following these patients. Today's care includes profound acid suppression with proton pump inhibitors, laser ablation of Barrett's epithelium, and photodynamic therapy [22, 30] in addition to surgery. Hopefully, proper surveillance will increase the incidence of cure when carcinoma intervenes, as well as assist in the long-term care of the basic disease process.
10. Reid BJ, Blount PL, Rabin CE, et al. Flow-cytometric and histologic progression to maligancy in Barrett's esophagus: prospective endoscopic surveillance of a cohort. Gastroenterology 1991;102:1212-1219.
17. Mangla JC. Acid and pepsin production by Barrett's epithelium: role of radionuclide imaging in diagnosis. In: Spechler SJ, Goyal RK, eds. Barrett's esophagus. New York: Elsevier Science Publishing Co, 1985.
18. Chaudhuri TK, Chaudhuri TK, Fink S. In radionuclide scans of Barrett's esophagus, what is the involvement of mucoid and parietal cells in pertechnetate excretion? In: Giuli R, ed. OESO. The esophageal mucosa. Paris: Elsevier, 1994:860-863.