Upper GI Tract Anatomy

The gastrointestinal (GI) or digestive tract extends from the mouth to the anus (see the image below). The GI system comprises the GI tract and various accessory organs. The division of the GI tract into upper and lower is a matter of some confusion and debate. On embryologic grounds, the GI tract should be divided into upper (mouth to major papilla in the duodenum), middle (duodenal papilla to mid-transverse colon), and lower (mid-transverse colon to anus) according to the derivation of these three areas from the foregut, midgut, and hindgut, respectively.

Nevertheless, the GI tract is conventionally divided into upper (mouth to ileum) and lower (cecum to anus). However, from the point of view of GI bleeding, the demarcation between the upper and lower GI tract is the duodenojejunal (DJ) junction (ligament of Treitz); bleeding above the DJ junction is called upper GI bleeding and that below the DJ junction is called lower GI bleeding.

In addition to these anatomic landmarks, the GI tract can be further divided by the nature of its blood supply and spinal innervation. The foregut, primarily supplied by the celiac artery/trunk, extends from the esophagus to the major duodenal papilla. The foregut receives sympathetic innervation from spinal levels T5-T9 by the greater splanchnic nerve, with parasympathetic innervation from the vagus nerve. The midgut, primarily supplied by the superior mesenteric artery (SMA), spans from the major duodenal papilla to the mid transverse colon. It receives sympathetic innervation from T10-T12 by the lesser splanchnic nerves, with parasympathetic innervation from the vagus nerve. The hindgut, primarily supplied by the inferior mesenteric artery, extends from the mid-transverse colon to the anus. The hindgut receives sympathetic innervation from L1-L2 by lumbar splanchnic nerves, with parasympathetic input shifting to pelvic splanchnic nerves (S2-S4). These divisions are based partly on embryologic origins and the neurovascular anatomy gives hints into which arteries are ligated or preserved based upon resection of parts of the foregut, midgut, or hindgut.

While traditional video esophagogastroduodenoscopy (EGD) has been a standard for both diagnosing and treating upper GI tract disorders, virtual chromoendoscopy (VCE) techniques have significantly enhanced the visualization of mucosal abnormalities and subtle features. Unlike dye-based chromoendoscopy, VCE uses optical and digital filtering (pre- or post-processing) on white light endoscopy images to improve contrast. These high-definition resolution endoscopes employ multiple colour enhancement techniques and are complemented by automated endoscopic assessment systems powered by artificial intelligence, providing better management of upper GI diseases. ^[1]

A study confirmed the safety and feasibility of tethered capsule endomicroscopy (TCE) for imaging the esophagus, stomach, and duodenum, indicating its potential for broader upper GI tract applications, particularly in conditions such as Barrett's esophagus, and celiac disease. Its less invasive nature, absence of sedation, and higher patient acceptability could make it a viable option to screen for Barrett's esophagus and for the initial diagnosis of celiac disease, especially in patients who are hesitant to undergo frequent endoscopic follow-ups. ^[2]

Embryology:

Overview: The gut develops from three embryonic tissue layers: the endodermal inner epithelium, splanchnopleuric mesenchyme, and splanchnopleuric celomic epithelium. Caudal to the developing respiratory diaphragm, the primitive enteric gut is divided by head and tail, folding into three embryological regions: foregut, midgut, and hindgut, which give rise to organs and accessory organs of the GI tract. Blood vessels and lymphatics develop from local angiogenic mesenchymal cells, while the neural crest gives rise to the nerves in the enteric and autonomic systems. All the events in the developing primitive gut are executed by epithelial-mesenchymal interactions controlled by sequential gene expression, developmental clock, intrinsic regulatory mechanisms, and environmental factors. ^[3] At the microstructural level, the three embryonic layers give rise to the following structures:

• Endodermal epithelium: Mucosal epithelial layer, connected ducts and glands
• Splanchnopleuric mesenchyme: Lamina propria and muscularis mucosa, the connective tissue of the submucosa, the muscularis externa, and the future serosal lamina propria
• Splanchnopleuric celomic epithelium: Epithelial component of the serosa (peritoneum, a mesothelium)

The cranial end of the foregut (embryonic pharynx) is related to the development of the head and neck, while the caudal part of the foregut and a significant portion of the midgut undergo a series of changes to develop into organs of the upper GI tract. ^[3] (See Table 1.)

Table 1. Summary of the Developmental Changes During the Upper GI Organogenesis at Various Stages ^[3] (Open Table in a new window)

 

Mouth, oral cavity, and pharynx

The mouth (the opening between the upper and lower lips) extends from the lips and cheeks externally to the anterior pillars of the fauces internally, where it continues into the oropharynx. It is subdivided into the vestibule external to the teeth and the oral cavity proper internal to the teeth. The roof of the mouth is formed by the palate, which separates the oral and nasal cavities. The mylohyoid muscle primarily forms the floor of the mouth. The tongue occupies a majority of this space. The lateral walls of the mouth are defined by the cheeks and retromolar regions. Three pairs of major salivary glands (parotid, submandibular, and sublingual) and numerous minor salivary glands (labial, buccal, palatal, lingual) open into the mouth. The oral cavity primarily facilitates the ingestion and mastication of food (predominantly done by the teeth) and also plays a role in phonation and ventilation. ^[3]

The pharynx extends from the base of the skull above to the cricoid cartilage (at the level of C6) below. It has three parts: the nasopharynx (from the base of the skull above to the soft palate below), the oropharynx (from the soft palate above to the hyoid bone below), and the laryngopharynx (from the hyoid bone above to the cricoid cartilage below). The nasal cavity, oral cavity, and larynx open into the nasopharynx, oropharynx, and laryngopharynx, respectively. The laryngopharynx also has a piriform fossa on either side.

Esophagus

The esophagus is one of the few organs traversing three regions of the body: the neck, thorax, and abdomen. Accordingly, it is divided into three parts: cervical, thoracic, and abdominal. The esophagus is a 25-cm-long (other 25-cm-long organs are the duodenum and the ureter) vertical muscular tube that normally remains collapsed and runs from the laryngopharynx (throat or hypopharynx) in the neck (at level with the body of the sixth cervical vertebra in females and the body of the seventh cervical vertebra in males) through the superior and posterior mediastina (chest), passes through the esophageal hiatus in the respiratory diaphragm, and ends at the gastric cardiac orifice in the abdomen. ^[3]

Features: Generally, the esophagus is vertical in its course but also shows two shallow curves. It starts in the median plane, inclines to the left as far as the inferior neck, returns to the median plane near the fifth thoracic vertebra, and deviates leftward again at the seventh thoracic vertebra. ^[3] It is the second narrowest part of the alimentary tract, with multiple constriction points along its course. These constrictions are measured relative to the incisor teeth during esophagoscopy.

Cervical Esophagus: The cervical esophagus begins at the lower border of the cricoid cartilage (at the level of C6); it is very short (only 5 cm long) and lies in front of C6 and C7 (covered with prevertebral fascia), slightly to the left of the midline. It is located posterior to the trachea, to which it is attached by loose connective tissue. In the neck, the esophagus, along with the trachea and the thyroid (covering the trachea and the esophagus), is enclosed in a sheath of visceral (deep cervical) fascia.

Relations: Recurrent laryngeal nerves ascend on each side in or near the tracheo-esophageal groove.

Posteriorly: Vertebral column, longus colli, anterior longitudinal ligament, and prevertebral layer of cervical fascia

Laterally: Common carotid arteries and posterior part of the thyroid gland on each side.

Inferior neck: The esophagus deviates to the left, closer to the left carotid sheath and thyroid gland than the right; the thoracic duct ascends for a short distance along its left side. ^[3]

Thoracic Esophagus: The cervical esophagus continues as the thoracic esophagus at the suprasternal notch. In the superior mediastinum, the esophagus is situated a little to the left of the midline, between the trachea and the vertebral column. As the esophagus descends, its relations are: ^[3]

• Anteriorly: Trachea, tracheal bifurcation, right pulmonary artery, left main bronchus, fibrous pericardium (separating it from the left atrium), and the diaphragm
• Posteriorly: Vertebral column, longus colli muscles, right posterior intercostal arteries, thoracic duct, azygos vein, and the terminal parts of the hemiazygos and accessory hemiazygos veins, as well as the descending thoracic aorta near the diaphragm
• Recesses in the pleural cavity: The aortic-esophageal recess on the left side, between the esophagus and the descending thoracic aorta, and the azygo-esophageal recess on the right side, between the esophagus and the azygos vein and vertebral column

It passes posterior and to the right of the aortic arch to descend into the posterior mediastinum along the right side of the descending thoracic aorta. Here, the esophagus continues behind the left main bronchus and right pulmonary artery and comes to lie in front of the descending thoracic aorta at the esophageal hiatus of the diaphragm. The thoracic duct lies to the left of the esophagus in the superior mediastinum and behind it in the posterior mediastinum. Mediastinal pleurae lie laterally, and the pericardial sac lies anterior to the esophagus. The relations of the thoracic esophagus can be summarized in Table 2.

Table 2. Left and Right Lateral Relations of Thoracic Esophagus in Superior and Posterior Mediastina ^[3] (Open Table in a new window)

The thoracic esophagus enters the abdomen via the esophageal hiatus in the diaphragm at the level of T10 (see the image below) and has a small (2-3 cm) intra-abdominal length. The esophagogastric junction (cardia) therefore lies in the abdomen below the diaphragm to the left of the midline at the level of T11.

Abdominal part of the esophagus: It is 1-2.5 cm long, lying to the left of the midline at the level of the 11th thoracic (T11) vertebra and ends at the gastro-esophageal junction, where it is continuous with the cardiac orifice of the stomach. ^[4]

Relations: It lies posterior to the left lobe of the liver and anterior to the left crus of the respiratory diaphragm, the left inferior phrenic vessels, and the left greater and lesser thoracic splanchnic nerves. ^[4]

Ligaments: It has the following ligaments, which anchor it to the neighboring structures.

• Phrenico-esophageal ligament - The abdominal esophagus is firmly tethered to the margins of the esophageal hiatus by the phrenico-esophageal ligament, which limits its mobility. It is of crucial during fundoplication surgery as locating the phrenico-esophageal ligament on the thinner section of the left crus is crucial for safely mobilizing the esophagus during surgery. Once this ligament is breached, the esophagus can be easily mobilized, allowing for a clear view of the aorta posteriorly. ^[4]
• Gastrophrenic ligament: It is a short peritoneal reflection posterior to the abdominal part of the esophagus that continues directly onto the posterior surface of the fundus of the stomach. It encloses the esophageal branches of the left gastric vessels and the celiac branches of the posterior vagal trunk. ^[4]

Vascular Supply and Lymphatics:

The blood supply to the different segments of the esophagus is summarized below (see Table 3).

Table 3. Arterial Supply and Venous Drainage of the Esophagus ^[3] (Open Table in a new window)

Esophageal varices: The left gastric vein, which drains into the portal venous system, travels along the lesser curvature of the stomach to the esophageal opening in the diaphragm. Here, it receives several lower esophageal veins, making this a key site for porto-caval (porto-systemic) venous anastomoses and is an important site for development of esophageal varices in portal hypertension. ^[3]

Azygous varices develop as a result of portosystemic collateral circulation in response to portal hypertension, commonly due to liver cirrhosis. When portal pressure rises, blood is redirected through the left gastric vein into the esophageal veins, which drain into the azygous system, leading to their dilation. These varices are particularly significant because they can become engorged and fragile, increasing the risk of rupture and life-threatening upper gastrointestinal bleeding. Clinically, patients may present with hematemesis, melena, or signs of hemorrhagic shock, necessitating urgent intervention. Endoscopic evaluation is the gold standard for diagnosis, with endoscopic variceal ligation being a primary treatment for bleeding control. Pharmacologic management, including non-selective beta-blockers and vasoactive agents like octreotide, helps reduce portal pressure and prevent rupture. In severe or refractory cases, transjugular intrahepatic portosystemic shunt may be necessary to decompress the portal system. Due to the high morbidity and mortality associated with azygous variceal bleeding, early screening and prophylactic management are crucial in at-risk patients.

Lymphatic Drainage: It has a vast, longitudinally continuous submucosal lymphatic system where the flow can be bidirectional and therefore plays a key role in the lymphatic spread of esophageal carcinoma. Different segments of the esophagus drain in different groups of lymph nodes (see Table 4).

Table 4. Lymphatic Drainage of Cervical, Thoracic, and Abdominal Esophagus ^[3] (Open Table in a new window)

Innervation:

It possesses a well-developed intrinsic nervous system, inclusive of a ganglionated myenteric plexus and a sparsely ganglionated submucosal plexus, both of which are regulated by extrinsic autonomic nerves. ^[3] (See Table 5.)

Table 5. Innervation of Cervical, Thoracic, and Abdominal Esophagus ^[3] (Open Table in a new window)

The vagus nerve supplies motor fibers to the striated and smooth muscle of the esophageal wall travel along with secretomotor fibers to mucous glands in the esophageal mucosa, and mucosal afferent (sensory) fibers that terminate mainly in the nucleus of the solitary tract. ^[3]  

Stomach

Location: The stomach is located in the upper abdomen, extending from the left upper quadrant downward, forward, and to the right. It lies in the left hypochondriac, epigastric, and umbilical regions, occupying space beneath the respiratory diaphragm and anterior abdominal wall, and is bordered by the upper abdominal organs on either side. ^[3]

Parts of the stomach: The cardiac notch (incisura cardiaca gastri) is the acute angle between the left border of the intra-abdominal esophagus and the gastric fundus (the part of the stomach above a horizontal line drawn from the cardia). The fundus of the stomach is dome-shaped and projects above and to the left of the esophageal opening (cardiac orifice) to lie in contact with the left side of the respiratory diaphragm. The body (corpus) of the stomach extends from the fundus to the angular incisure, a constant external notch at the lower end of the lesser curvature. ^[3] It leads to the pyloric antrum (at the incisura angularis), which joins the duodenum at the pylorus, lying at the L1-L2 level (transpyloric plane) to the right of the midline. The stomach has a shorter concave lesser (right) curvature and a longer convex greater (left) curvature. The lesser curvature is attached to the undersurface of the liver by the lesser (gastrohepatic) omentum and the greater curvature is attached to the transverse colon by the greater (gastrocolic) omentum.

Gastric curvatures: The stomach has two curvatures with the following features (see Table 6).

Table 6. Features of the Lesser and Greater Curvatures of the Stomach ^[3] (Open Table in a new window)

Surfaces: When the stomach is empty and contracted, the anterior and posterior surfaces tend to face superiorly and inferiorly, but as the stomach distends, they face progressively more anteriorly and posteriorly. ^[3]

Anterior Surface: It has the following relation with the neighboring viscera/structures: ^[3]

• The entire anterior surface of the stomach is covered by peritoneum.
• The lateral part lies posterior to the left costal arch, in contact with the respiratory diaphragm, which separates it from the left parietal pleura, the base of the left lung, pericardium, and left 7th-9th ribs and costal cartilages.
• The superior left part curves posteriorly and contacts the visceral surface of the spleen.
• The right half is related superiorly to the left lobe of the liver and inferiorly to the anterior abdominal wall, through which it can be accessed by a needle for placement of a gastrostomy tube.

Posterior Surface: It has the following relations with neighboring viscera/structures: ^[3]

• It is covered by the peritoneum, except near the cardiac orifice, where it contacts the left crus of the diaphragm and sometimes the left suprarenal gland.
• Gastrophrenic ligament extends from the lateral aspect of this bare area to the inferior surface of the diaphragm.
• The posterior surface lies anterior to the left crus and inferior fibers of the diaphragm, left inferior phrenic vessels, left suprarenal gland, superior pole of the left kidney, splenic artery, anterior surface of the pancreas, and superior layer of the transverse mesocolon.
• The upper left part of the posterior surface curves anterolaterally and contacts the visceral surface of the spleen.
• The transverse mesocolon separates the stomach from the DJ flexure and proximal jejunum.

Gastric orifices: The stomach has the following two orifices, namely: ^[3]

1. Cardiac orifice: The esophagus opens into the stomach at the cardiac orifice lying left of the midline at the level of the T11 vertebra. It contains the lower esophageal sphincter that includes clasp-like semicircular smooth muscle fibers on the right side of the esophagus and sling-like oblique gastric muscle fibers on the left side. Internally, it is the site of gastro-esophageal junction.
2. Pyloric orifice: The stomach opens into the duodenum at the pyloric orifice lying right of the midline in the transpyloric plane, which passes through the lower border of the body of the L1 vertebra. It is formed by a circumferential thickening of circular muscle intertwined with connective tissue septa and some longitudinal muscle fibers.

Vascular Supply and Lymphatics: Arteries: The main arterial supply of the stomach is provided by the celiac trunk and its branches, i.e., the common hepatic, splenic, and left gastric arteries (see Table 7).

Table 7. Arterial Supply of Different Parts of the Stomach ^[3] (Open Table in a new window)

Veins: The veins draining the stomach usually accompany the corresponding named arteries and drain into either the splenic or superior mesenteric veins that ultimately empty into the hepatic portal vein. Some veins may drain directly into the hepatic portal vein. ^[3]

Lymphatic drainage: Usually, the lymphatics follow the course of the arteries supplying the stomach and are connected with lymphatics draining other organs in the proximal abdomen. The lymphatics at the gastro-esophageal junction are continuous with those draining the distal esophagus, while lymphatics from the pylorus are connected with those draining the duodenum and pancreas. ^[3]

Innervation: The stomach is innervated by the sympathetic and parasympathetic nerves.

• Sympathetic nerve supply - Originates from the 5th-12th thoracic spinal cord segments. It is mainly distributed via the greater and lesser thoracic splanchnic nerves and the celiac plexus. It causes vasoconstriction, inhibits gastric motility, and constricts the pylorus. ^[3]
• Parasympathetic nerve supply - It is from the vagus nerves via its anterior and posterior vagal trunks and their corresponding branches. The parasympathetic nerve supply is secretomotor to the gastric mucosa and motor to the gastric musculature. It is also responsible for coordinated relaxation of the pyloric sphincter during gastric emptying. A majority of fibers within the vagus nerves are afferent and convey gut sensation, including fullness, nausea, and probably pain. ^[3]  

Duodenum

Location: The duodenum is approximately 25 cm long and forms an elongated "C" shape that lies between the level of the L1 and L3 vertebrae in the supine position. The proximal 2.5 cm of the duodenum is intraperitoneal, and the remainder is retroperitoneal. ^[3] It has four parts: superior, descending, horizontal, and ascending (see Table 8).

Table 8. Location, Length, and Relations of the Four Parts of the Duodenum ^[3] (Open Table in a new window)

Superior Part: The first (superior) part or bulb (5 cm) is the most mobile part of the duodenum. It is connected to the undersurface of the liver (porta hepatis) by the hepatoduodenal ligament, which contains the proper hepatic artery, portal vein, and common bile duct; the quadrate lobe of the liver and gallbladder are in front and the common bile duct, portal vein, and gastroduodenal artery are behind.

The second (descending) part, or C loop (10 cm), which has an upper and a lower genu (flexure), is composed of the transverse mesocolon and colon in front and the right kidney and inferior vena cava (IVC) behind; the head of the pancreas lies in the concavity of the C loop.

The third (horizontal) part (7.5 cm) runs from right to left in front of the inferior vena cava and aorta, with superior mesenteric vessels (the vein on the right and the artery on the left) in front.

The fourth (ascending) part (2.5 cm) continues as the jejunum. The duodenum continues into the jejunum at the DJ flexure.

The rest of the small bowel (jejunum and ileum) is a convoluted tube about 4-6 m long that occupies the center of the abdomen and the pelvis, surrounded on two sides and above by the colon. The ileum continues into the large intestine at the ileocecal junction.

Vascular supply and lymphatic drainage

Arteries: The C-shaped duodenum shares its blood supply with the head of the pancreas as it receives blood from the superior and inferior pancreaticoduodenal arteries. Additionally, the superior and descending parts of the duodenum receive blood from several other arteries, including the right gastric, supraduodenal, right gastro-omental, common hepatic, and gastroduodenal arteries. ^[3] (See Table 9.)

Table 9. Arterial Supply of the Four Parts of the Duodenum ^[3] (Open Table in a new window)

Veins: Submucosal and intramural veins give rise to small veins that accompany the corresponding named arteries. The superior pancreaticoduodenal vein and small veins from the superior part and a portion of the descending part of the duodenum drain directly into the hepatic portal vein. The inferior pancreaticoduodenal vein and veins from the horizontal and ascending parts can drain directly into the superior mesenteric vein. ^[3]

Lymphatic Drainage: Duodenal lymphatics drain into the nodes related to superior and inferior pancreaticoduodenal vessels and ultimately into lymph nodes along the common hepatic and superior mesenteric arteries and celiac trunk. ^[3]

Innervation: The duodenum is innervated by both parasympathetic and sympathetic nerves.

• Parasympathetic supply - The preganglionic fibers from the celiac plexus are carried by the vagus nerve to synapse with neurons in the duodenal wall. It is secretomotor to the duodenal mucosa and motor to the duodenal musculature.
• Sympathetic supply - Preganglionic sympathetic fibers arise from the grey matter in the 5th-12th thoracic spinal cord segments and travel through the greater and lesser thoracic splanchnic nerves to the celiac plexus. These fibers synapse in the celiac and superior mesenteric ganglia. The postganglionic axons then travel to the duodenal wall via peri-arterial plexuses on branches of the celiac trunk and SMA. The sympathetic nerves act as vasoconstrictors to the duodenal blood vessels and inhibit the duodenal muscles. ^[3]

Anatomy on diagnostic imaging

The pharynx and esophagus are evaluated by barium swallow; areas of normal constriction in the esophagus are the pharyngoesophageal junction (at the level of C6), the aortic arch (at the level of T2-T3), the left bronchus (at the level of T4-T5), and the esophageal hiatus in the diaphragm (at the level of T10). Barium meal helps to evaluate the stomach and duodenum. A small bowel follow-through helps to evaluate the small intestine (jejunum and ileum). Enteroclysis involves injection of radiological contrast directly into the proximal jejunum through a nasojejunal tube — this provides better delineation of the small intestine. Computed tomography can also be combined with enteroclysis.

A rigid pharyngoscope helps in visualizing various parts of the pharynx. The esophagus (along with the stomach and duodenum) is evaluated by EGD, also called upper GI endoscopy, which is performed using a flexible fiberoptic endoscope with the patient under sedation. Endoscopic landmarks include the following elements shown in Table 10.

As the esophagus runs from the neck to the stomach, local anatomy of the region affects its diameter.

The esophagus has three main points of physiological narrowing, which are clinically significant as they are common sites where swallowed objects may get lodged or where strictures can form due to conditions like gastroesophageal reflux disease (GERD) or malignancy. These narrowing points include:

1. Cricopharyngeal constriction (upper esophageal sphincter): Located at the level of C6, this narrowing occurs at the junction of the pharynx and esophagus, where the cricopharyngeus muscle forms a sphincter. It serves as a barrier to prevent air from entering the esophagus during breathing.
2. Aortic arch and left bronchus constriction: At approximately the level of T4-T5, the esophagus is compressed by the aortic arch and the left main bronchus as it descends through the thoracic cavity. This is a common site for difficulty in swallowing (dysphagia) due to external compression.
3. Lower esophageal sphincter (LES) or diaphragmatic constriction: This occurs at T10, where the esophagus passes through the esophageal hiatus of the diaphragm before entering the stomach. The LES prevents gastric reflux, but dysfunction here can lead to GERD or hiatal hernia.

These physiological narrowings are important in clinical practice, particularly in endoscopic procedures, barium swallow studies, and the assessment of esophageal pathology.

Table 10. Esophageal Constrictions and Their Distance From the Incisors ^[3] (Open Table in a new window)

For the purpose of endoscopy, the upper GI tract includes the esophagus, stomach, and duodenum (EGD or upper GI endoscopy), and the lower GI tract includes the anus, rectum, colon, and cecum (anoproctosigmoidocolonoscopy or lower GI endoscopy). ^{[5, 6, 7]} The small intestine (jejunum and ileum) is relatively inaccessible to endoscopy. The proximal jejunum can be examined by push enteroscopy using balloon-tipped upper GI endoscopes, whereas the distal ileum can be examined by retrograde ileoscopy at colonoscopy. Capsule endoscopy can examine the entire small intestine.

TCE is an emerging technology that addresses these limitations. Patients swallow an optomechanically engineered pill that captures three-dimensional, microscopic images of the digestive tract after it has been swallowed. The tethered capsule uses optical frequency domain imaging that provides multiple 30 μm (lateral) × 7 μm (axial) resolution cross-sectional images of the gut wall as the capsule moves through the digestive tract, propelled by peristalsis. The capsule is tethered, allowing the operator to control its position and perform circumferential scans. The images obtained offer detailed architectural information, spatially correlated with histopathology. After the procedure, the capsule is retrieved and disinfected for reuse. ^[8]

Various studies with TCE have shown its potential in screening for Barrett's esophagus, particularly in patients who require frequent follow-ups. TCE imaging of the stomach is challenging due to the large lumen preventing circumferential contact (except in the antrum), difficulty accessing the fundus, and positional control issues. However, in the duodenum, TCE enables wide-area villous morphology mapping and inflammation assessment, crucial for celiac disease diagnosis. Its less invasive nature and comprehensive imaging reduces sampling uncertainty, aiding initial diagnosis in seropositive patients and evaluating gluten-free diet resistance. ^[2]

Positron emission tomography and magnetic resonance imaging enterography are hybrid imaging techniques that combine the metabolic information from positron emission tomography scans with the high spatial resolution and soft tissue contrast of magnetic resonance imaging. They are beneficial for assessing and managing inflammatory bowel disease and other GI inflammatory disorders. ^[4]

VCE enables better visualization of mucosal abnormalities and subtle structural changes, aiding in detecting and treating conditions such as Barrett's esophagus, esophageal squamous cell carcinoma, and gastric cancer. ^[1] It relies on a narrowed portion of the available spectral bandwidth and uses a combination of optical and digital (pre- or post-processing of white light endoscopy images) filtering to enhance their contrast. This processing includes a surface enhancement for detecting GI tract abnormalities, tone enhancement for pattern characterization, and optical enhancement for detailed visualization of blood vessels, glandular ducts, and mucosa. ^[1]  

The upper GI tract has the usual four-layer structure characteristic of the rest of the GI tract. The innermost mucosa contains mucous membrane, lamina propria, and muscularis mucosa. The submucosa contains a rich vascular network. The muscular layer includes inner circular and outer longitudinal muscles. The outer surface is covered with serosa. ^[3] (See Table 11.)

Table 11. The Four Layers in the Microstructure of the Wall of the Gastrointestinal Tract ^[3] (Open Table in a new window)

Wall layers on ultrasonography

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

1. Mucosa (hyperechoic)
2. Lamina propria (hypoechoic)
3. Submucosa (hyperechoic)
4. Muscularis propria (hypoechoic)
5. Adventitia (hyperechoic)

Surgical identification of these layers is critical for cancer planning. These techniques include endoscopic ultrasound, endoscopy, and histopathology confirmation. Identification of these layers is related to cancer staging, leading to different planning for surgical treatment.

1. Endoscopic ultrasound (EUS)

• This modality can assess for tumor invasion depth and distinguish between mucosal (T1a) and submucosal (T1b) cancers.
• Hypoechoic layers on EUS correspond to tumor invasion areas.

2. High-resolution endoscopy and narrow-band imaging

• Detects superficial neoplasia and assesses mucosal irregularities.

3. Histopathology (after biopsy or resection)

• This method is most invasive and confirms the exact depth of invasion and determines the presence of lymphovascular invasion, influencing treatment decisions.

Based upon identification of layers, there is significant impact on the final resection strategy.

• T1a tumors (limited to mucosa or lamina propria) → Endoscopic resection is often curative
• T1b tumors (submucosal invasion) → Higher risk for metastasis, requiring esophagectomy and lymph node dissection
• Deep invasion beyond submucosa (T2 or higher) → Often requires neoadjuvant therapy before surgery

Endoscopic ultrasonography is extremely helpful in the diagnosis and staging of early esophageal and gastric cancer. It can be used to visualize periesophageal and perigastric lymph nodes and to guide fine-needle aspiration cytology from them.

Duplication cysts can occur in any part of the GI tract.

Atresia can involve the esophagus, duodenum, and small intestine (jejunum and ileum).

Esophageal atresia results from failure of recanalization of the foregut. In the most common variant, the proximal stump of the esophagus ends blindly, and the distal stump of the esophagus is connected to the trachea (tracheoesophageal fistula). Esophageal atresia may be related to trachea-esophageal fistulae or other associations of vertebral defects, anal atresia, cardiac defects, renal and limb anomalies. ^[3]

Duodenal atresia, a developmental defect occurring in 1 in 5000 live births, is often associated with an annular pancreas or bile duct anomalies. In 40-60% of cases, the atresia is complete, with pancreatic tissue filling the lumen. Diagnosis is made via abdominal x-ray and ultrasound, showing a characteristic double bubble appearance. It frequently co-occurs with other developmental defects such as cardiac and skeletal anomalies and Down's syndrome. ^[3]

Infantile hypertrophic pyloric stenosis, with a prevalence of 2 in 1000 live births, is commonly associated with male sex and family history. The etiology is unclear, but factors such as immature parietal cell function, neutral gastric pH, and slow maturation of gastrin feedback mechanisms may contribute to acid over-secretion, stimulating pyloric sphincter hypertrophy. Risk factors include being first born, cesarean delivery, preterm birth, and formula feeding; exclusive breastfeeding is protective. ^[3]

Zenker’s false diverticulum (so called because it contains mucosa and submucosa only, rather than all four layers as a true diverticulum does) occurs in the neck between the cricopharyngeus and the thyropharyngeus. True esophageal diverticula occur in two locations, either the subdiaphragmatic or parabronchial part of the esophagus. ^[3]

Hypopharyngeal diverticula, or Zenker's diverticula, arise in the lower pharynx through weak areas in the pharyngeal wall, specifically between the cricopharyngeus and thyropharyngeus muscles (dehiscence of Killian). Delayed cricopharyngeus relaxation during swallowing creates elevated pressure, leading to the formation of a pulsion diverticulum. This pouch of prolapsing mucosa breaches the thin muscle wall near the sixth cervical vertebra and expands into the parapharyngeal space, often to the left. It can trap food, causing regurgitation, aspiration pneumonia, halitosis, and weight loss. ^[3]

Malrotation of the gut results in the DJ flexure to lie to the right (instead of the normal left) of the midline and cecum in the epigastrium or right hypochondrium (instead of normal right iliac fossa); a band (of Ladd) runs across the duodenum from right to left and the narrow base of the small bowel mesentery predisposes it to volvulus.

Meckel's diverticulum is the most common anomaly of the GI tract. It is a remnant of the vitelline (omphalomesenteric) duct and is located in terminal ileum about 2 ft from the ileocecal junction.