Endosonography in gastric lymphoma and large gastric folds

Abstract

To establish a correct preoperative differential diagnosis between gastric lymphoma and cancer is essential but can be difficult as endoscopic biopsies can sometimes provide a low diagnostic yield. By EUS, infiltrative carcinoma tends to show a vertical growth in the gastric wall, while lymphoma tends to show mainly a horizontal extension. EUS provides an accurate staging of gastric lymphoma, showing the exact level of infiltration and the presence of perigastric lymph nodes, thus the physician can obtain an accurate prognosis for each patient and select the best form of treatment accordingly. The response to chemoradiotherapy can also be investigated very accurately by EUS. Large gastric folds are seen in a great number of benign and malignant conditions. Diagnosis represents a clinical challenge because etiology may be extremely varied and standard biopsies are often inconclusive. Different diseases show different levels of infiltration of the gastric wall, thus a characteristic echo-pattern helps for the differential diagnosis. Endosonography, used always in combination with biopsy, allows to rule out malignancies and to select the most appropriate treatment for each patient (medical or surgical).

Introduction

Endoscopic ultrasonography (EUS) has made remarkable advances during the last 18 years, and it is now the most accurate imaging technique in gastrointestinal endoscopy. Many papers reported its value in the investigation of a large variety of gastrointestinal disorders, but at the moment the only established diagnostic indications are: the staging of malignant tumors, the characterization of submucosal lesions and of large gastric folds, the detection of small pancreatic tumors and the investigation of the biliary tree.

Many instruments, equipped with different scanning frequencies, are available. Up to now, the videoechoendoscopes with a radial scan of 360°, perpendicular to the long axis of the instrument, are most frequently used. The radial scanning provides an easier understanding of the anatomy and a faster scanning of the gastrointestinal tract. Frequencies are available ranging from 7.5 MHz to 20 MHz (Olympus GF-UM130 and GF-UMQ130). Lower frequencies (7.5 MHz) are useful to explore gross lesions in and outside the gut wall, while higher frequencies (20 MHz) are useful to explore accurately the wall layers and detect subtle changes in the mucosa.

Convex or linear scanning echoendoscopes, with respect to the anatomic orientation and to the general overview of the structures, appear to be inferior to the radial method. This is due to the limited scanning field (90°–120°), parallel to the long axis of the instrument. However, since the needle can be followed on the ultrasonographic screen, it is possible to perform EUS-guided fine needle aspiration (FNA) of target lesions located within and beyond the gastric wall.

Furthermore the incorporation of a Doppler signal, with or without color, makes understanding of the anatomical and vascular structures easier, thus performing FNA can be even safer (Olympus GF-UC30P), (Binmoeller et al., 1998a).

The Olympus GF-UM 30P is designed on the basis of the current mechanical radial scanning EUS scope but changing the direction of scanning into sector by using reflection of a rotatable mirror. Therefore it is possible to use the scope together with current EU-M30 observation unit and also perform the fine needle puncture under sonographic control. The available frequency is 7.5 MHz, but the most important feature is that the scanning range reaches 250°, thus allowing a larger field of exploration and an easier orientation, not-possible with other sector scanning instruments (Binmoeller et al., 1998b).

Several types of small ultrasonic probes have been designed for the imaging of gastrointestinal structures (Olympus UM-2R and UM-3R), (Yasuda, 1994). The main advantage of these probes, with a 7.5–30 MHz frequency range, is that they can be passed through the working channel of conventional endoscopes during upper and lower endoscopy, as well as in ERCP. High frequency miniprobes allow the visualization of mural gastrointestinal structures with much greater resolution, so that they can be useful to evaluate small and flat lesions such as early cancers. Anyway the depth of penetration is low, thus making the assessment of large tumors and extramural lesions difficult.

EUS appearance of the intestinal wall consists of a five-layer structure (1st, interface echo-mucosa; 2nd, deep mucosa; 3rd, submucosa; 4th, muscularis propria; and 5th serosa and subserosal fat) of different echogenicity (Kimmey et al., 1989) (Fig. 1). EUS diagnosis of gastrointestinal diseases relies on the detection of changes in the layer structure of the gastrointestinal wall. Neoplasms are usually detected as a disruption in the continuity of a layer or by diffuse layer thickening. A change in the echogenicity of the layers is another evidence of tissue pathology. Moreover, EUS is able to display the relationship of the tumor to neighboring organs, and early lymph node metastasis.