The cervical segment of the esophagus begins at the upper esophageal sphincter, which is 15 cm from the incisors and is 6 mm long (Fig. 1). The thoracic segment of the esophagus is approximately 19 cm long. Its lumen is open during inspiration and closed during expiration. The imprint of the arch of the aorta is sometimes apparent at 25 cm from the incisors on the left. How to describe where a lesion is in terms of anterior, posterior, right, left, is very important and is shown in Figure 2. The transition between the esophagus and gastric epithelium (Z line) is identified by the change in color of the mucosa from pale-pink to reddish-pink.

Figure 1 Main anatomical features of the esophagus.

Figure 2 Orientation in the esophagus. It is very important to understand your orientation in the esophagus so that you can describe where a lesion is. This figure demonstrates the orientation of the esophagus when the patient is in the left lateral decubitus position, water naturally stays in the left side of the esophagus.

1.2 The stomach

The stomach extends from the cardia to the pylorus (Fig. 3). The fundus is the portion of the stomach above the horizontal line that passes through the cardia and that is visible in a retroflexed endoscopic view. The body is the remainder of the upper part of the stomach and is delimited at its lower edge by the line that passes through the angular notch. Endoscopically, the transition from the body to the antrum is seen as a transition from rugae to flat mucosa (Fig. 4). The pylorus is a circular orifice, which leads to the first part of the duodenum.

Figure 3 Gastric anatomy.

Figure 4 Orientation in the stomach. When the patient is in the lateral left decubitus position, the greater curvature is at the bottom, the lesser curvature at the top, the posterior stomach wall on the right, and the anterior stomach wall on the left.

Clinical Tip

Always consider linitis plastica if the stomach fails to distend normally.

When the patient is in the lateral left decubitus position, the greater curvature is at the bottom, the lesser curvature at the top, the posterior stomach wall on the right, and the anterior stomach wall is on the left (Fig. 4). The anterior wall can be visualized with transillumination, a technique used for PEG insertion (see Ch. 4). A normal stomach distends fully with insufflation, with the rugae flattening out (Fig. 5).

Figure 5 Insufflation of the stomach. (A) Normal insufflations of the stomach. (B) Non-distention of the stomach in a patient with linitis plastica.

1.3 The duodenum

The duodenum extends from the pylorus to the duodeno-jejunal angle. The duodenal bulb extends from the pylorus to the genu superius. The second portion (D2) extends from the genu superius to the genu inferius. The ampulla of Vater is usually found in a horizontal fold in the middle of the second portion of the duodenum (Fig. 6). The accessory papilla is a small protuberance, which is usually found just superior and proximal to the ampulla of Vater.

Figure 6 (A) Normal ampulla of Vater. (B) Biopsies should be taken AWAY from the pancreatic orifice to avoid pancreatitis. A safe area to biopsy is the upper left quadrant in the area within the box.

1.4 Postoperative endoscopy of the stomach and duodenum

Common post-surgical anatomy includes a Billroth I (Fig. 7), where only one lumen is present. In a Polya or Billroth II (Fig. 7), two gastrojejunal orifices are visible. The afferent limb leads to the duodenum, while the efferent limb leads to the colon.