Stomach Anatomy

The stomach is the widest part of the gastrointestinal (GI), or digestive, tract. It is a muscular, highly vascular bag-shaped organ that is distensible and may take varying shapes, depending on the build and posture of the person and the state of fullness of the organ (see the image below). The stomach lies in the left upper quadrant of the abdomen, specifically in the left hypochondriac, epigastric, and umbilical regions. ^{[1, 2, 3]}

The stomach performs several important functions, including temporary storage of ingested food, mechanical breakdown of solid food, enzymatic digestion of proteins, regulation of the passage of chyme into the duodenum, secretion of intrinsic factors for vitamin B12 absorption, microbial defense, and secretion of gut hormones and acid (to aid in digestion and iron absorption). ^[3]

Stomach and duodenum, coronal section.

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The thoracic esophagus enters the abdomen via the esophageal hiatus of the diaphragm at the level of T10. The abdominal portion of the esophagus has a small intra-abdominal length (1-2.5 cm). The gastroesophageal junction therefore lies in the abdomen below the diaphragm to the left of the midline at the T11 level. The stomach region adjacent to the esophagus is called the cardia. This junction is marked by transition from esophageal squamous epithelium to gastric columnar epithelium known as the Z-line. ^[4]

The cardiac notch (incisura cardiaca gastri) is the acute angle between the left border of the abdominal esophagus and the fundus of the stomach, which is the part of stomach above a horizontal line drawn from the cardia. The body (corpus) of the stomach leads to the pyloric antrum (at the incisura angularis). The pyloric antrum narrows toward the right to become the pyloric canal, surrounded by the pyloric sphincter, which joins the duodenum at the L1 level (transpyloric plane) to the right of the midline (see the image below).

Stomach regions, in situ.

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The anterior surface of the stomach is related to the left lobe (segments II, III, and IV) of the liver, the anterior abdominal wall, and the distal transverse colon. The posterior surface of the stomach is related to the left hemidiaphragm, spleen, left kidney (and adrenal), and pancreas (stomach bed).

The omental bursa (lesser sac) lies behind the stomach and in front of the pancreas; it communicates with the greater sac (main peritoneal cavity) via the omental (epiploic) foramen (of Winslow) behind the hepatoduodenal ligament (the free edge of the lesser omentum).

The convex greater curvature of the stomach begins from the cardiac notch, formed between the lateral border of the abdominal esophagus and the fundus of the stomach, and arches upward, posterolaterally and to the left. Its highest convexity is almost at level with the left sixth rib anteriorly; however, it varies among individuals and during respiration. ^[3] . The concave lesser curvature starts at the right side of the cardia as a continuation of the right border of the abdominal esophagus and runs a short distance along the right border of the body of the stomach and the superior border of the pylorus. The junction of the vertical and horizontal parts of the lesser curvature is called incisura angularis. Lesser curvature is shorter in length than the greater curvature.

The stomach and the first part of the duodenum are attached to the liver by the hepatogastric ligament (the left portion of the lesser omentum) containing right and left gastric vessels, to the left hemidiaphragm by the gastrophrenic ligament, to the spleen by the gastrosplenic/gastrolienal ligament containing short gastric vessels, and to the transverse colon by the gastrocolic ligament (part of the greater omentum) containing epiploic (omental) vessels. Few peritoneal bands may be present between the posterior surface of the stomach and the anterior surface of the pancreas. Part of the greater omentum hangs like an apron from the transverse colon, with four layers of the peritoneum (often fused): two layers go downward from the stomach and then run upward to be attached to the transverse colon.

Blood supply

The celiac trunk (axis) arises from the anterior surface of the abdominal aorta at the level of L1. It has a short length (about 1 cm) and trifurcates into the common hepatic artery (CHA), the splenic artery, and the left gastric artery (LGA).

The LGA runs toward the lesser curvature of the stomach and divides into an ascending branch (supplying the abdominal esophagus) and a descending branch (supplying the proximal stomach). The CHA runs toward the right on the superior border of the pancreas and gives off the gastroduodenal artery (GDA), which runs down behind the first part of the duodenum. After giving off the GDA, the CHA continues as the proper hepatic artery.

The right gastric artery (RGA), a branch from the proper hepatic artery or CHA, runs along the lesser curvature from right to left and joins the descending branch of the LGA to form an arcade along the lesser curvature between the two leaves of peritoneum of the lesser omentum. This arcade gives off multiple small arteries to the body of the stomach. The GDA gives off the posterior superior pancreaticoduodenal artery and then divides into the right gastro-omental (gastroepiploic) artery (RGEA) and the anterior superior pancreaticoduodenal artery; it also gives off the small supraduodenal artery (of Wilkie). The RGEA runs along the greater curvature from right to left.

The splenic artery runs toward the left on the superior border of the distal body and tail of pancreas and gives off the left gastro-epiploic (gastro-omental) artery, which runs from left to right along the greater curvature and joins the RGEA to form an arcade along the greater curvature between the two leaves of peritoneum of the greater omentum. This arcade gives off multiple small arteries to the body of the stomach.

The greater curvature arcade formed by the RGEA and the left gastro-epiploic artery provides several omental (epiploic) branches to supply the highly vascular greater omentum. The splenic artery also gives off 3-5 short gastric arteries that run in the gastro-splenic (gastrolienal) ligament and supply the upper part of the greater curvature and the gastric fundus. Few small posterior gastric arteries may arise from the splenic artery. The stomach has a rich network of vessels in its submucosa.

The left gastric (coronary) vein drains into the portal vein at its formation (by the union of the splenic and superior mesenteric veins). The right gastric and right gastro-omental veins drain into the hepatic portal vein. The left gastro-omental vein drains into the splenic vein, as do the short gastric veins.

The pylorus is marked by a prepyloric vein (of Mayo), which lies on its anterior surface. The gastrocolic trunk of Henle is present in a large number of cases and lies at the junction of the small bowel mesentery and the transverse mesocolon. It may drain branches from the middle colic, anterior superior pancreaticoduodenal vein, and right gastro-omental veins.

The short gastric arteries and veins are sometimes collectively referred to as the vasa brevia.

Lymphatic drainage

Lymph nodes (LNs) draining the stomach can be systematically categorized into distinct levels based on their anatomical locations and drainage pathways. This classification is crucial for understanding the metastatic spread of gastric malignancies and for planning surgical interventions. LNs are classified into stations numbered 1-20 along with stations 110, 111, and 112. ^[5]

Station number 1 (right paracardial nodes): Located on the right side of the cardia, along the first ramification of the ascending branch of the LGA (cardio-esophageal branch)

Station number 2 (left paracardial nodes): Located on the left side of the cardias, along the cardio-esophageal branch of the left inferior phrenic vessels

Station number 3 (lesser curvature nodes): LNs are located along the descending branch of the LGA and along the RGA distal to the first gastric branch.

Station number 4 (greater curvature nodes): Divided into two groups separated by the Von Ghoete point, where the right and left gastroepiploic arteries meet each other at full channel: a left group (4s) and a right group (4d).

Station number 5 (suprapyloric nodes): Located at the lesser curvature, immediately above the pylorus, along the RGA and its origin

Station number 6 (infrapyloric nodes): Located at the greater curvature, immediately below the pylorus, at the confluence of the right gastroepiploic vein with the anterior inferior pancreaticoduodenal vein

Station number 7 (LGA nodes): Located along the LGA, between its roots from the celiac trunk till the origin of its ascending branch on the lesser curvature.

Station number 8 (CHA nodes): Located around the CHA from its root from the celiac trunk to the branching off of the GDA. These LNs are distinguished into an anterior part (8a) and a posterior part (8p).

Station number 9 (celiac trunk nodes): Located immediately near the origins of the LGA, CHA, and splenic artery

Station number 10 (splenic hilum nodes): Located at the splenic hilum, distal to the end of the pancreatic tail. The vascular boundary between the 10 and 4sb LNs is represented by the first gastric ramification of the left gastroepiploic.

Station number 11 (splenic artery nodes): Located along the splenic artery and are distinguished into a proximal group (11p) and a distal group (11d)

Station number 12 (hepatoduodenal ligament nodes): Located in the context of this ligament and include three separate groups (12a, 12b, and 12p)

12a: Left hepatoduodenal ligament LNs; located along the proper hepatic artery in the caudal half between the confluence of the right and left hepatic ducts and the upper pancreatic margin

Station number 13 (retropancreatic nodes): Located on the posterior surface of the head of the pancreas cranial to Vater's ampulla along the superior and inferior branches of the posterior pancreaticoduodenal artery. The left lateral border of this location is marked by the portal vein, while the upper border is represented by the origin of posterior hepatoduodenal ligament LNs.

Station number 14 (superior mesenteric vein and artery nodes): Located along the confluence of the superior mesenteric vein (14v) into the portal vein and along the origin of the AMS (14a) — at the root of the mesenterium.

Station number 15 (middle colic nodes): Located in the transverse mesocolon around the middle colic artery and vein, from their origin/confluence from/into the superior mesenteric vessels, till the mesocolic hedge of the transverse colon.

Station number 16 (aortic hiatus - a1, middle - a2/b1, and caudal - b2 para-aortic nodes):

16a1: Para-aortic LNs in the diaphragmatic aortic hiatus

16a2: Para-aortic LNs between the upper margin of the origin of the celiac artery and the lower border of the left renal vein

16b1: Para-aortic LNs between the lower border of the left renal vein and the upper border of the origin of the inferior mesenteric artery

16b2: Para-aortic LNs between the upper border of the origin of the inferior mesenteric artery and the aortic bifurcation

Station number 17 and 18 (peripancreatic nodes): Peripancreatic LNs are located along the pancreaticoduodenalis superior anterior vessels on the anterior surface of the pancreatic head beneath the pancreatic sheath (station 17) and along the inferior border of the pancreatic body (station 18).

Station number 19 (infradiaphragmatic): Located in the infradiaphragmatic space predominantly along the subphrenic vessels

Station number 20 (paraesophageal): Located in the paraesophageal region in the diaphragmatic esophageal hiatus

Station number 110, 111, and 112 (lower thorax): These LNs are located in the lower thorax [110], in the supradiaphragmatic space separate from the esophagus [111], and in the posterior mediastinal space separate from the esophagus and the esophageal hiatus [112], respectively

Nerve supply

The esophageal plexus of vagus (para-sympathetic) nerves lies in the posterior mediastinum below the hila of the lungs. It divides into two vagal trunks that enter the abdomen along with the esophagus through the esophageal hiatus in the left dome of diaphragm. The right (posterior) vagus is behind and to the right of the intra-abdominal esophagus, whereas the left vagus is in front of the intra-abdominal esophagus.

The right vagus gives off a posterior gastric branch called the criminal nerve of Grassi, which traverses to the left and supplies the cardia and fundus of the stomach; the nerve is so called because it is often missed during vagotomy and is then responsible for recurrence of peptic ulcers. The right vagus gives off a celiac branch (which supplies the pancreas and the small and large bowel), and the left vagus gives off a hepatic branch (which supplies the liver and the gallbladder).

After giving off the celiac and hepatic branches, respectively, the right and left vagal trunks continue along the lesser curvature of the stomach (in close company with the vascular arcade formed by the left and right gastric vessels) as the posterior and anterior gastric nerves of Latarjet, which supply the corpus (body) of the stomach, antrum, and pylorus.

Sympathetic nerve supply to the stomach comes from the thoracic spinal cord segments 5-12 and is mainly distributed via the greater and lesser thoracic splanchnic nerves and the celiac plexus. ^[3]

Anatomy on diagnostic imaging

The stomach and duodenum are evaluated radiologically with barium studies using fluoroscopy. It should be noted that on computed tomography, the cardia is on a lower horizontal plane than the dome of the fundus.

Endoscopic anatomy

Cardia (esophagogastric junction), incisura angularis, and pylorus are very well seen on upper GI endoscopy.

Physiological anatomy

Stomach is a reservoir; its size and shape changes from time to time depending on the volume of its contents (food/fluid). The shape and position of the stomach also changes with the position of the patient, whether erect or supine. A large J-shaped stomach can descend as low as into the pelvis.

Severe pain in any part of the body (e.g., headache, ureteric colic due to stone) may give rise to pylorospasm and reflex vomiting.

The esophagus is lined with nonkeratinized stratified squamous epithelium, which changes into columnar epithelium in the stomach. The columnar cells in the stomach secrete mucin; the chief (zymogenic) cells in the fundus secrete protein-digesting pre-enzyme pepsinogen; the parietal (oxyntic) cells in the body (corpus) of the stomach secrete acid (H+ ions) and intrinsic factor; and the G cells in the antrum secrete gastrin (which in turn acts on parietal cells).

The innermost lining of the stomach wall is mucosa, which consists of columnar epithelium, lamina propria, and muscularis mucosa. Submucosa contains a rich network of blood vessels and Meissner's nerve plexus. The smooth muscles of the stomach are arranged in three layers: inner oblique (unique to stomach), middle circular (forms the pylorus), and outer longitudinal. These muscles are supplied by the Auerbach's nerve plexus. Serosa is the visceral peritoneum that covers most of the stomach. Mucosa and submucosa are thrown into several longitudinal folds called rugae.

The lower esophageal sphincter, or gastroesophageal sphincter, is not a true (anatomic) sphincter; however, the pylorus is a true sphincter composed of circular muscles.

Wall layers on ultrasonography

Endoscopic ultrasonography (EUS) is a newer technical tool for evaluating the stomach. An ultrasound probe is mounted at the tip of an upper GI endoscope, which is passed into the stomach. The wall of the stomach is seen as five alternating layers as follows:

• Mucosa (hyperechoic)
• Lamina propria (hypoechoic)
• Submucosa (hyperechoic)
• Muscularis propria (hypoechoic)
• Serosa (hyperechoic)

EUS is very helpful in the diagnosis and staging of early gastric cancer and for evaluation of gastric varices in portal hypertension.

Congenital hypertrophic pyloric stenosis seen in infants presents as pyloric obstruction at 2-4 weeks of life.

Common diseases of the stomach include peptic (gastric) ulcers and gastric tumors/cancers (e.g., adenocarcinoma, lymphoma, and GI stromal tumor). Historically, the most common operations performed on the stomach were those for peptic ulcer disease. Today, the most common procedures performed on the stomach include bariatric procedures (e.g., gastric band, sleeve gastrectomy, and gastric bypass). Various types of gastrectomies are performed for gastric tumors and cancers.

Types of vagotomies include truncal, selective, and highly selective.

In truncal vagotomy, both anterior and posterior vagal trunks are divided as they enter the abdomen. In selective vagotomy, the anterior and posterior vagi are divided below their hepatic and celiac branches, respectively. The nerve supply to the viscera (e.g., liver, gallbladder, common bile duct, pancreas, and small and large bowel) is preserved. In highly selective vagotomy (also referred to as proximal gastric vagotomy or parietal cell vagotomy), the anterior and posterior nerves of Latarjet are preserved, which maintains the nerve supply to the antrum and pylorus. Truncal vagotomy and selective vagotomy denervate the antrum and pylorus and necessitate a drainage procedure (gastrojejunostomy or pyloroplasty); highly selective vagotomy does not require drainage.

Parietal cell mass is increased in patients with Zollinger-Ellison syndrome, resulting in hypersecretion of acid. Antrectomy removes the G cells and results in reduction of acid production by taking away stimulation of parietal cells by gastrin.

The artery involved in a bleeding duodenal ulcer is GDA, which runs vertically down behind (posterior to) the first part of the duodenum.

Pseudocyst of the pancreas is a collection of fluid that develops in the lesser sac behind the stomach. The anterior wall of the pseudocyst is in close approximation to the posterior wall of the stomach; the pseudocyst can be easily drained into the stomach (cystogastrostomy) either surgically or endoscopically.

Because of the shorter length of the lesser curvature, obtaining adequate proximal and distal margins in a growth situated along the lesser curvature may be difficult without performing total gastrectomy.

The stomach can be mobilized after division of the LGA (proximal to its bifurcation) and left gastroepiploic artery and can survive on the RGA and right gastroepiploic artery, to be taken through the mediastinum into the neck (even as high as the pharynx) after total esophagectomy. The vascular arcades on the lesser and greater curvatures have to be preserved.

Esophagogastric anastomosis is done to the fundus — the highest point of the mobilized stomach.

During gastrotomy (surgical procedure involving making an incision in the wall of the stomach), vessels are encountered in the submucosal plane — these must be controlled with suture, diathermy, or any other energy-based device.

The lesser sac is opened by dividing the gastrocolic omentum between the greater curvature of the stomach and transverse colon — this exposes the body and tail of the pancreas, with splenic artery running on its upper (cranial) border. The gastrocolic omentum is opened toward its left, away from the middle colic vessels, where it is thinner and broader.

The spleen is at risk for injury when short gastric vessels are divided during mobilization of the fundus and the upper part of the greater curvature of the stomach. Similarly, the fundus of the stomach can be injured when short gastric vessels are divided during splenectomy.

The transverse mesocolon, containing middle colic vessels, or the transverse colon itself may be involved in stomach cancer. Posterior infiltration of stomach cancer occurs into the pancreas.

A vascular flap of greater omentum based on an epiploic artery can be used to provide cover to an anastomosis in the abdomen (e.g., esophagogastric, biliary enteric, and pancreaticoenteric).