Angular incisure

The angular incisure, also known as the incisura angularis, is a distinct notch or sharp angular depression located along the lesser curvature of the stomach, near its pyloric end, that demarcates the junction between the gastric body and the pyloric antrum.^[1][2] Its position may vary slightly depending on the degree of stomach distension, and it is externally visible as a landmark on the organ's contour.^[2] Anatomically, the angular incisure divides the stomach into its proximal body region, responsible for initial digestion and mixing of food with gastric secretions, and the distal pyloric part, which regulates chyme passage into the duodenum.^[1][3] In veterinary anatomy, a similar structure exists in domestic animals, aiding in the identification of gastric boundaries during dissection or imaging.^[4] Clinically, the angular incisure holds significant diagnostic value, as it is a predilection site for Helicobacter pylori colonization, glandular atrophy, intestinal metaplasia, and dysplasia, which are precursors to gastric adenocarcinoma.^[5] Routine biopsies from this region during gastroscopy are recommended to improve the accuracy of gastritis staging according to the OLGA (Operative Link on Gastritis Assessment) system, enhancing detection of advanced mucosal changes that may be missed elsewhere in the stomach.^[6][5] In patients with chronic gastritis, antralization—replacement of fundic-type mucosa with antral-type epithelium—occurs more frequently at the incisura, correlating with increased risk of neoplastic progression.^[7]

Anatomy

Location and boundaries

The angular incisure, also known as the incisura angularis, is a sharp angular notch located on the lesser curvature of the stomach.^[8] It marks the transition point where the vertical portion of the lesser curvature meets its more horizontal distal segment.^[8] This notch forms an imaginary boundary separating the gastric body from the pyloric antrum, dividing the stomach into its proximal and distal functional regions.^[8][1] Positioned along the lesser curvature, the angular incisure is situated beneath the medial segments of the liver and corresponds to the junction of the stomach's body and antrum.^[8] It is superior to the pyloric sphincter and inferior to the cardiac notch (incisura cardiaca) near the esophagogastric junction.^[1] The structure aligns with the attachment of the lesser omentum (hepatogastric ligament), which runs along the lesser curvature and contains the right and left gastric vessels.^[8] Internally, it corresponds to a fold of mucous membrane creating a small recess, while externally it relates to the vascular arcade of the lesser curvature.^[1] Anatomical variations in the angular incisure include differences in its prominence and angulation, which can be influenced by body position; it appears more evident in the supine posture compared to the erect position.^[9] These variations are typically more pronounced in adults than in fetal stages, reflecting maturational changes in stomach shape, such as from cylindrical to J-shaped forms.^[9]

Gross and microscopic structure

The angular incisure presents as a sharp indentation or notch along the lesser curvature of the stomach, typically located near the junction between the gastric body and pyloric antrum, and is readily visible during endoscopic examination or gross anatomical dissection.^[1] This feature becomes more pronounced and angular in appearance when the stomach is contracted, formed by converging gastric rugal folds that create a distinct recess on the mucosal surface.^{[3] [10]} At the mucosal level, the angular incisure marks a transitional zone between the fundic-type mucosa of the proximal stomach body and the pyloric-type mucosa of the distal antrum, characterized by an admixture of both tissue types often referred to as intermediate mucosa.^[7] The rugal folds from the body converge toward this site, gradually flattening as they transition into the smoother antral mucosa, with the overall epithelial lining consisting of simple columnar cells that secrete mucus to protect against gastric acid.^[11] Microscopically, the epithelium proximal to the incisure features oxyntic glands containing parietal cells responsible for hydrochloric acid and intrinsic factor secretion, alongside chief cells that produce pepsinogen, while the distal side shifts to glands dominated by mucous neck cells and endocrine cells with minimal parietal or chief cell presence.^[11] The underlying submucosa forms a continuous layer of loose connective tissue supporting vascular and neural elements, while the muscularis externa maintains the typical three-layered smooth muscle arrangement of the stomach, ensuring coordinated peristalsis across the transition.^[11] The vascular supply to the angular incisure arises primarily from anastomosing branches of the right gastric artery, originating from the proper hepatic artery, and the left gastric artery, a direct branch of the celiac trunk, forming an arcade along the lesser curvature that provides robust perfusion to this junctional area.^[12] Neural innervation at the site is provided by the vagus nerve, with parasympathetic fibers from the anterior vagal trunk forming the anterior nerve of the lesser curvature, which densely supplies the region to regulate glandular secretion and motility, complemented by sympathetic input from the celiac plexus for vasomotor control.^{[13] [14]}

Physiological role

Relation to gastric regions

The angular incisure serves as a critical anatomical landmark on the lesser curvature of the stomach, delineating the boundary between the proximal stomach—comprising the fundus and body (corpus)—and the distal stomach, which includes the antrum and pylorus. This division is essential for the stomach's functional specialization, as the proximal region primarily handles storage and initial processing of ingested material, while the distal region focuses on further mechanical breakdown and preparation for intestinal transit. The incisure's position helps define these zones, with an imaginary line extending from the notch across the stomach marking the transition.^[3][15] Physiologically, the body region proximal to the angular incisure is dominated by oxyntic glands containing parietal cells that secrete hydrochloric acid and intrinsic factor, facilitating protein digestion through pepsin activation and initial mixing of chyme. In contrast, the antral region distal to the incisure features pyloric glands rich in G cells that release gastrin, a hormone that stimulates acid production in the proximal stomach while promoting antral contractions for grinding and propulsion of food particles. These regional differences ensure coordinated gastric function, with the proximal area emphasizing secretory and accommodative roles and the distal area prioritizing mechanical processing.^[16][17][16] The angular incisure also influences gastric accommodation, marking the shift from the proximal stomach's receptive, low-pressure storage capacity—allowing relaxation to accommodate meal volumes with minimal intragastric pressure rise—to the distal stomach's propulsive zone, where peristaltic waves initiate emptying. This boundary supports the stomach's ability to adapt volume through vagally mediated receptive relaxation in the fundus and body, contrasting with the tonic contractions in the antrum. Embryologically, the angular incisure arises from the foregut's fusiform dilation around the fourth week of gestation, followed by a 90-degree clockwise rotation around the longitudinal axis that repositions the stomach and establishes regional specializations. This rotation, occurring between Carnegie stages 13 and 18, contributes to the formation of the incisure by the end of stage 18, influencing the differential growth that separates the proximal and distal domains and their distinct physiological roles.^[18][19]

Contribution to stomach motility

The boundary at the angular incisure separates the regions of the stomach with distinct motility patterns: propagating slow waves in the gastric body contribute to mixing motions, while more forceful contractions in the antrum are responsible for grinding and propulsion of chyme.^[20] These peristaltic waves typically originate along the greater curvature in the proximal corpus and travel distally, differentiating the functions of the proximal and distal stomach to optimize content distribution during digestion. This regional specialization enhances the efficiency of mechanical breakdown by directing partially digested material toward the distal stomach. In coordination with the pyloric sphincter, the distinct motility of the gastric regions facilitates the generation of pressure gradients essential for controlled gastric emptying. The proximal stomach serves as a reservoir, while antral contractions generate the force to propel small boluses of chyme through the pylorus, preventing reflux.^[21] This separation supports rhythmic emptying based on antral tone and sphincteric resistance. Neural and hormonal mechanisms regulate these motility patterns across the gastric regions. Vagal efferents primarily mediate receptive relaxation in the proximal stomach, promoting distal propulsion via favorable pressure gradients, while intrinsic enteric neurons coordinate wave propagation.^[22] Hormonally, gastrin released from G cells in the antrum—beginning just distal to the incisure—stimulates antral smooth muscle contraction, enhancing motility and aiding the transition to pyloric ejection without directly affecting the proximal region. During digestion, the angular incisure exhibits adaptive changes in position and angulation to accommodate gastric filling and emptying, thereby improving mixing efficiency. As the stomach fills, the incisure may straighten or shift inferiorly, facilitating broader content distribution, while emptying phases involve accentuated angulation to direct chyme distally and support peristaltic progression.^[23] These morphological adjustments, driven by local muscular tone, underscore the incisure's position in relation to coordinated motility across varying luminal volumes.

Clinical significance

Diagnostic procedures

Routine gastroscopy, also known as esophagogastroduodenoscopy (EGD), is the primary method for visualizing the angular incisure and obtaining tissue samples to assess for conditions such as Helicobacter pylori infection and gastritis.^[5] During the procedure, a flexible endoscope is inserted through the mouth to examine the stomach's lesser curvature, where the angular incisure is located, allowing direct identification of mucosal abnormalities like erosions or irregularities at this site.^[24] Biopsies taken from the incisure during EGD are crucial for detecting H. pylori, as this region often exhibits higher bacterial density and early pathological changes compared to other gastric areas.^[25] The updated Sydney system provides a standardized biopsy protocol for accurate staging of gastritis, recommending one biopsy from the angular incisure in addition to two each from the antrum and corpus (updated Sydney system core protocol), with optional cardia sampling in extended protocols.^[26] This protocol, involving a minimum of five sites including the incisure, enhances diagnostic precision by capturing the transitional zone where preneoplastic changes like intestinal metaplasia frequently originate.^[27] Biopsy from the incisura angularis, as a key transitional site, provides representative tissue for histopathological evaluation, particularly in high-risk patients for gastric cancer.^[28] Recent studies, including the RE.GA.IN. initiative (2024), have questioned the mandatory inclusion of incisura biopsies in all cases, proposing it as optional in low-risk scenarios, though it remains recommended for comprehensive staging (as of 2025).^[29][30] Imaging techniques such as double-contrast barium meal studies can delineate the angular incisure as a characteristic notch on the lesser curvature, aiding in the detection of morphological alterations like filling defects or irregular contours indicative of underlying pathology.^[31] Computed tomography (CT) scans of the abdomen, often with oral contrast, visualize the incisure region for assessing wall thickening or masses, with hyperattenuating changes near this site signaling potential inflammatory or neoplastic processes.^[32] Histological processing of angular incisure biopsies involves fixation in 10% neutral buffered formalin, followed by paraffin embedding, sectioning at 4-5 μm, and staining with hematoxylin and eosin (H&E) to evaluate metaplasia, characterized by the presence of goblet cells and intestinal-type epithelium.^[33] For H. pylori detection, Giemsa or Diff-Quik stains are applied to highlight bacterial organisms on the mucosal surface, while periodic acid-Schiff (PAS) or Alcian blue stains distinguish complete from incomplete metaplasia subtypes in incisure samples, where such changes are often more pronounced.^[34] These methods allow for OLGA/OLGIM staging, emphasizing the incisure's role in identifying advanced atrophy.^[35]

Associated conditions and pathologies

The angular incisure, as a transitional zone in the stomach, exhibits a high rate of Helicobacter pylori colonization, often leading to chronic active gastritis that is more severe in this region compared to other gastric areas.^[36] Biopsies from the incisura angularis provide critical insights into the extent of inflammation and activity in H. pylori-associated gastritis, highlighting its role as a key site for bacterial persistence and mucosal damage.^[35] Intestinal metaplasia and gastric atrophy frequently develop at the angular incisure due to its vulnerability in chronic H. pylori infection, positioning it as a sentinel location for precancerous lesions.^[37] In the Operative Link for Gastritis Assessment (OLGA) staging system, biopsies from the incisura are essential for evaluating the topographic extent of atrophy, with advanced stages (III or IV) indicating higher risk for progression to dysplasia when metaplasia is present at this site.^[38] The Operative Link on Gastric Intestinal Metaplasia (OLGIM) system similarly uses incisura samples to stage metaplasia, underscoring its prognostic value in identifying patients at elevated risk for gastric neoplasia.^[39] The angular incisure shows a predilection for gastric ulcers, particularly recurring benign ulcers, owing to the hemodynamic stress and mucosal transition at this notch.^[40] This site also harbors early gastric adenocarcinoma more frequently than other regions, facilitated by the progression from metaplasia and atrophy, with endoscopic detection often revealing superficial lesions amenable to curative resection.^[41] Antralization, characterized by the replacement of oxyntic mucosa with antral-type epithelium at the incisura, is strongly associated with H. pylori-induced gastritis and contributes to hypergastrinemia through altered gastrin expression.^[7] Mucosal hypertrophy in this area may occur as a reactive change in chronic inflammation, though less commonly documented. Risk factors such as advanced age and cigarette smoking exacerbate these pathological changes, promoting metaplasia progression and increasing the likelihood of neoplastic transformation at the incisura.^[27][42]