Mills Ch22 Stomach

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CHAPTER 22:  Stomach

that lie adjacent to the esophagogastric junction. Shortly after entering the abdomen, the anterior vagus nerve gives off a hepatic branch, and the posterior vagus nerve gives off a celiac branch. Therefore, truncal vagotomy above these branches results in denervation of not only the stomach but also the entire intestinal tract. Sectioning below these nerves results only in gastric denervation. A highly selec- tive vagotomy (gastric corpus denervation) is achieved by sectioning lateral branches as the two main gastric nerves pass along the lesser curvature, with preservation of the ter- minal portions of the vagi that supply the antrum. No true nerve plexuses occur on either subserosal layer of the stom- ach but instead are concentrated in Meissner plexus in the submucosa and Auerbach plexus between the circular and longitudinal fibers of the muscularis propria. Lymphatics Recent studies (5,6) have disproved the former view that lymphatic channels are present at all levels of the lamina propria. By using careful ultrastructural techniques, lym- phatics have been shown to be limited to the portion of the lamina propria immediately superficial to the muscularis mucosae. From there, efferents penetrate the muscle and communicate with larger lymphatic channels running in the submucosa. This arrangement implies that gastric cancer may have lymph node metastases, even though the primary tumor is entirely superficial to the muscularis mucosae. The lymphatic trunks of the stomach generally follow the main arteries and veins. Four areas of drainage can be identi- fied, each with its own group of nodes. The largest area com- prises the lower end of the esophagus and most of the lesser curvature, which drains alongside the left gastric artery to the left gastric nodes. From the immediate region of the pylo- rus, on the lesser curvature, drainage is to the right gastric and hepatic nodes. The proximal portion of the greater cur- vature drains to pancreaticosplenic nodes in the hilum of the spleen, and the distal portion of the greater curvature drains to the right gastroepiploic nodes in the greater omentum and to pyloric nodes at the head of the pancreas. Efferents from all four groups ultimately pass to celiac nodes around the main celiac axis. Pathologists need to be aware of the location of differ- ent groups of lymph nodes and their nomenclature. A system based on location has been devised by the Japanese Gastric Cancer Association (7) and recognizes the following stations: perigastric along the greater curvature, perigastric along the lesser curvature, right and left paracardial (cardioesophageal), suprapyloric, infrapyloric, left gastric artery, celiac artery, com- mon hepatic artery, hepatoduodenal (portal), splenic artery, and splenic hilum. Nodes at these locations are regarded as regional and if positive are counted in the N category of the TNM system. However, at the present time, the TNM system does not require the location of the nodes to be recorded in order to derive the pathologic stage of a neoplasm (8). This is still based on the number of positive nodes.

FIGURE 22.4  Diagrammatic representation of gastric oxyntic mucosa. Zymogenic (chief) cells are seen mainly in the basal portion of the glands and parietal cells mainly in the isthmic portion. The neck portion contains zymogenic cells, parietal cells, and mucous neck cells. A small number of endocrine cells are present in the basal zone.

GENERAL HISTOLOGIC FEATURES Histologically, the mucosa has a similar pattern throughout the stomach. It consists of a superficial layer containing foveolae (pits), which represent invaginations of the surface epithelium, and a deep layer consisting of coiled glands that empty into the base of the foveolae (Fig. 22.4). The glandu- lar layer differs in structure and function in different zones of the stomach that correspond roughly, but not precisely, to the gross anatomic regions (Fig. 22.1). Adjacent to the GEJ is the cardiac mucosa, where the glands are mucus secreting. Extending proximally from the pylorus is the pyloric mucosa (sometimes called the antral mucosa), where the glands are also mucus secreting. This zone is triangular, extending much further (5 to 7 cm) proxi- mally along the lesser curvature than it does along the greater curvature (3 to 4 cm). The pyloric mucosal zone is not iden- tical to the antral region, although some accounts use these terms interchangeably. Also, contrary to what is implied in some descriptions, the incisura has no fixed relationship to the proximal margin of the pyloric mucosal zone. Else- where within the stomach (corpus and fundus), the mucosa is specialized to secrete acid and pepsin (oxyntic mucosa). Histologic transition between pyloric and oxyntic muco- sae is gradual rather than abrupt, with intervening junctional mucosae (1 to 2 cm in width) having a mixed histologic appearance. A broad mucosal transition zone is also present at the pylorus itself, where gastric and duodenal mucosae merge. However, at the lower end of the normal esopha- gus, the change from nonkeratinizing squamous epithelium to columnar epithelium is abrupt, both grossly and micro- scopically. The position of this squamocolumnar junction is variable and may not always coincide precisely with the