Gastrointestinal Pathology. Группа авторов

      Major indications for tissue sampling of the small intestine include celiac disease as well as resection of early neoplasia.

      Diagnostic Sampling

      Currently established protocols for sampling for celiac disease recommend four to six biopsies from the duodenum including the duodenal bulb and distal duodenum.

      All other suspicious areas should be sampled using routine biopsy technique. Sampling of the papilla should be performed with caution as biopsy in this area can cause pancreatitis. When a suspected neoplastic lesion is seen in the region of the papilla, it is preferred to take a biopsy that does not immediately injure the orifice of the bile duct or the pancreas duct.

      Therapeutic Sampling

Adenomatous polyps of the duodenum are handled in a similar manner to adenomatous lesions anywhere in the gastrointestinal tract. Endoscopic mucosa resection can be performed with injection followed by snare. There appears to be higher risks of bleeding and perforation associated with endoscopic resection of duodenal lesions. This is particularly true were using cap‐assisted devices where the thin wall of the duodenum is suctioned into the cap leading to inadvertent full‐thickness resection.

      Special attention is required for resection of lesions involving the ampulla of Vater. In these cases, typically the lesion is resected followed by placement of a stent in the pancreatic and bile duct orifice to prevent stricturing of these and acute pancreatitis.

      Another special situation is polypoid lesions in the distal small intestine, which can now be accessed with deep enteroscopy methods. Polyps are generally removed in the same manner as polypoid lesions elsewhere in the gastrointestinal tract by snare polypectomy. Special circumstances include numerous polyps such as those developed in patients with Peutz–Jeghers syndrome. These can be particularly large and numerous. It may not be possible to resect and retrieve all tissues. Because of the laborious process of deep enteroscopy, it is often not feasible to extract the endoscope with each large polypoid tissue. Thus diagnostic sampling can be performed by biopsy of the lesion or fragmentation of the lesion with a snare followed by complete therapeutic excision of the lesion.

      Colon

      Major indications for diagnostic sampling of the colon include detection of both overt and microscopic colitis and surveillance for dysplasia in inflammatory bowel disease.

      Perhaps the most commonly performed tissue sampling in the field of gastroenterology involves removal of colorectal polyps and tissue sampling of more advanced colorectal neoplasia.

      Diagnostic Sampling

      In patients with chronic diarrhea and suspected microscopic colitis, random biopsies should be taken throughout the colon including at least two biopsies from the right, transverse, descending, and sigmoid colon. For limited sampling the flexible sigmoidoscopy is also a reasonable approach. In this case at least two biopsies should be obtained from the sigmoid and descending colon as well as transverse colon if this can be reached with the sigmoidoscope.

      In the setting of inflammatory bowel disease, biopsy sampling should be performed to establish the diagnosis and to assess the extent. For the initial diagnosis, the American Society for gastrointestinal endoscopy recommends two biopsies from each of five sites including the ileum and rectum.

      Surveillance of inflammatory bowel disease is a special circumstance and is evolving. Traditionally, random biopsies were obtained throughout the colon. Current guidelines recommend biopsy of each colonic segment with four‐quadrant biopsies every 10 cm from the cecum to the rectum for a minimum total of 33 biopsy samples. In cases where the entire colon is not affected, four samples should be obtained every 10 cm of the affected areas. More recently, it has been shown that using dye spray such as indigo carmine or methylene blue can identify areas of dysplasia with high accuracy and thus guide directed sampling without the need for random biopsy. Biopsies should however also be assessed from each colonic segment to assess for inflammation.

      Therapeutic Sampling

Endoscopic resection methods of flat and lateral spreading colorectal polyps has expanded rapidly over last 10 years. Most noninvasive neoplastic lesions of the colon can now be removed through advanced endoscopic methods such as EMR or ESD avoiding the need for surgery. Lesions less than 2 cm can typically be removed en bloc with endoscopic mucosal resection involving injection of a fluid cushion under the lesion followed by snare resection. Where there is suspected early (mucosal or superficial submucosal) invasive carcinoma, en bloc resection should be performed using either EMR or ESD depending on the size of the lesion. The tissue processing should be the same as for other neoplastic lesions with orientation of the specimen and pinning of the specimen to assess the lateral and deep margins (Figure 1.14).

The final histological analysis allows for detailed staging, as well as matching the corresponding histological and endoscopic findings; note the lavender line overlays indicating sites of advanced neoplasia. The close collaboration between pathologists and endoscopists further improves the accuracy of each procedure (Figure 1.15).

Summary

      The role of pathology in gastrointestinal endoscopy remains critical. Gastroenterologists should have a thorough knowledge of optimal methods of tissue removal and initial processing to allow optimal diagnosis and therapeutic results. Advances in endoscopic resection have allowed complete resection of many early cancers but require closer cooperation between the endoscopist and pathologist to ensure the tissue is properly handled and staged. With EUS‐FNA, the direct interaction of pathologist with rapid on‐site cytological evaluation has led to higher accuracy, and reduced the need for repeat procedures. Finally, advances in imaging will continue to improve the targeting of tissue sampling and reduce the need for low‐yield random sampling methods.

Figure 1.14 Endoscopic submucosal dissection (ESD) procedure. A flat neoplastic lesion is seen in panel 1–2 after staining with cresyl violet. The margins are incised (panel 3) with the endoscope retroflexed (black tube). The submucosal plane is dissected with a needle knife (panel 4). The final resection site (panel 5) and corresponding resection specimen prepared for pathology processing (panel 6).

Figure 1.15 Endoscopically resected en bloc well‐differentiated adenocarcinoma 28 × 17 mm with superficial submucosal invasion and no lymphovascular invasion and negative horizontal and vertical margins. This sample meets criteria for endoscopic curative resection.

Figure 1.16