Ponction sous échoendoscopie

The development of endoscopic ultrasound (EUS) has allowed better identification of both parietal and lymph node extension of gastrointestinal and pancreatic tumours. Nevertheless, EUS cannot distinguish malignant forms of lymph nodes, pancreatic masses or extrinsic compression of the digestive tract from benign forms. The development since 7 years of the sectorial linear EUS allowed realizing guided biopsies of such lesions. It appears possible to perform a biopsy guided by EUS with both types of equipment (radial or linear, sector-based), but the technique of biopsy with the radial system is more time-consuming and technically more difficult and more dangerous, as it is impossible to completely follow the biopsy needle as it comes out of the operator channel, and to guide it into the lesion. The linear sector-based endoscopic ultrasound equipment includes a small diameter convex electronic probe, fitted on to a standard endoscope. This is an optic fibre device with a 60° field of vision fitted with an operating channel of 2 and 3.8 mm diameter, depending on the particular instrument, through which biopsy forceps, biopsy needle or accessories for therapeutic procedures can pass. Guided biopsies may be carried out with this type of sector-based probe, by following the biopsy needle at the exit of the operator channel and guiding it into the lesion. This is possible because the ultrasound beam is emitted longitudinally in the same axis than the axis of the endoscope and not perpendicularly as in radial ultrasound endoscopes. The principal indications for EUS-guided biopsies are the diagnosis of lymph nodes or mediastinal, coeliac and pelvic masses, of sub-mucosal tumours, of gastric linitis with negative endoscopic biopsies, and of pancreatic tumours. The best results are obtained with lymph nodes and mediastinal masses, anastomotic recurrences, extrinsic compressions of the gastrointestinal tract and pancreatic tumours. Besides, the efficacy of EUS-guided biopsies is higher in lesions of small diameter (< 4 cm). This is due to the fact that larger cancers are the site of necrosis and/or intra-tumour fibrosis, both of which prevent good sampling. If a “micro-biopsy” is obtained, it enables more accurate histological diagnosis to be made and accurate characterisation of the tissue in about 80% of malignancy diagnoses. The results quoted in the literature show an overall sensitivity of the technique varying between 76 and 91%, a specificity of 84 to 100%, and a reliability of 78 to 94%. A prospective study investigating 457 patients from 4 centres (Indianapolis, Copenhagen, Marseilles and Orange in California) showed a sensitivity of the biopsy statistically better for lymph nodes (94%) and extra-luminal tumours (86%) than for parietal lesions (sub-mucosal tumours and large gastric folds) (61% p<0.001).