The mucosa is the innermost layer of the wall of the oesophagus, stomach and bowel. Many precursors of bowel cancer and some very early tumours initially grow only in this layer. Endoscopic mucosal resection, or EMR for short, removes them precisely – through an endoscope and without an external incision.
For most polyps, forceps or a simple snare are sufficient during a colonoscopy. Large, flat or broad-based lesions, by contrast, lie close against the bowel wall and can hardly be captured completely in this way. EMR is intended for them – in the colon often for polyps from about two centimetres. It is also used in the oesophagus and stomach, for example for cell changes in Barrett’s oesophagus, a lining altered by stomach acid flowing back.
First, fluid is injected beneath the lesion. This cushion lifts the lining away from the deeper muscle layer and creates distance from the rest of the bowel wall. A snare then encircles the lesion and cuts it off using high-frequency current – smaller ones in one piece, large ones usually in several. The edges are then cauterised; areas at risk of bleeding can be closed with small clips.
Every piece removed is examined in the laboratory. The report shows whether it was a benign precursor or an early tumour and, if it was removed in one piece, whether the margin is clear. If there is already a suspicion before the procedure that a tumour reaches deeper into the wall, other options come into consideration: submucosal dissection, in which the lesion is detached in one piece, or surgery.