Peptic ulcer disease (PUD) affects about 4 million Americans each year, and is a common cause of gastrointestinal bleeding and abdominal pain requiring hospital admission.
The most common causes of PUD are NSAID overuse and H. pylori infection (for the remarkable story of how we know H. pylori causes stomach ulcers, go here), and the best way to diagnose it is via endoscopy. This involves anesthesia or sedation, and a 4-12 hour fast, which are uncomfortable, inconvenient, and potentially harmful. Ideally, ulcers could be ruled out with a simple bedside ultrasound protocol, and limit the need for this invasive procedure.
Anatomy
The stomach is a crescent-shaped organ that sits on the left, lateral side of the upper abdomen. The stomach can be separated into its three portions for imaging: Antrum, Body, and Fundus, and each portion can be imaged in the short-axis (cross section) and long-axis view (longitudinally).
Antrum
The most medial portion of the stomach is the antrum. It stretches from the body of the stomach to the pyloris. The cross-section can be best viewed with the patient supine or in the left lateral decubitus position, with the probe marker facing the head in the head-to-toe axis.
The antrum is located just inferior and lateral to the left lobe of the liver. When empty, it is a flattened oval with hyperechoic inner wall and hypoechoic exterior. Just deep and posterior is the head of the pancreas, followed by the superior mesenteric artery (SMA), the aorta, and then the spine.
When the stomach is empty, it is collapsed and oval-shaped.
As the stomach fills, the antrum becomes more circular, and gastric contents can be seen:
Antrum in longitudinal view
With the probe in the horizontal, left-to-right axis, the longitudinal view of the antrum can be appreciated. When empty, it looks like a finger with its rounded end in the center-right of the image below:
Body
The body of the stomach is larger and sits more lateral. The cross-section can be appreciated by angling the transducer toward the left subcostal area.
Gastric Body Cross section on ultrasound:
Gastric Body Longitudinal on ultrasound:
Fundus
The fundus is the most cranial portion of the stomach and sits deep to the spleen and anterior and superior to the left kidney.
It is the most difficult portion to visualize due to its location and partial obstruction by the ribs and may need probe angle adjustment to see between the ribs. Both an intercostal trans-splenic approach (figure below) and a mid-axillary longitudinal (head-to-toe axis) have been described:
Stomach layers
As seen in the figure below, the stomach is divided into multiple layers: the serosa (1), the muscularis propriae (2), the submucosa (3), and the muscularis mucosa (4). To qualify as an ulcer, it must penetrate below the stomach lining (serosa) into the underlying mucosa.
PUD distribution
Since the fundus of the stomach is obscured by the spleen and ribcage, it is a sonographically convenient fact that the majority of ulcers occur on the anterior wall of the stomach, in the antrum and lesser curvature of the body.
Therefore, by just visualizing these two portions of the stomach, one should be able to rule in or out most PUD.
Abdominal contents
Just as ultrasound waves travel differently through air-filled or fluid-filled structures, the composition of the gastric contents alters the appearance of the stomach. Empty, fluid-filled, early solid, and late-stage solids all look very different. It is important to understand this to be able to interpret what you are seeing.
Fluid-filled stomach
When fluid is ingested, the stomach distends. Air bubbles are initially visible but dissipate within a few minutes.
Once the air bubbles dissipate, the fluid works to improve the ultrasound transmission and makes the posterior gastric walls more visible.
Early solid phase
Since food is filled with air and solid particles, ultrasound waves cannot penetrate well through it. Because of this, you have a hyperechoic appearance of the superficial portion of the antrum and posterior acoustic shadowing behind it, obscuring the rest of the stomach and vessels posterior to it. This is similar to how a rib and rib shadow appear on ultrasound, called the frosted glass appearance:
Late solid phase
About 1-2 hours after ingestion, the air has dissipated and the food has been compacted, improving the ultrasound wave transmission and the entire stomach and posterior structures can again be visualized.
Can these facts be used to diagnose gastric and
duodenal ulcers?
In 1990, physicians in Saudi Arabia attempted to diagnose PUD in 65 patients with ultrasound, and then compare the results to endoscopy. The subjects fasted overnight and then drank 500 cc of tap water before the exam, to enhance visibility. It turns out water is almost equally as effective as oral contrast for viewing the stomach.
After allowing the bubbles to dissipate, they scanned the stomach and duodenum, and the results are shown below in Table 2:
In all patients with duodenal ulcers, the ultrasound noted significant duodenal wall abnormalities. In 28 of the normal endoscopies, 25 were normal with ultrasound and 3 were thought to have mild abnormalities. For gastritis or duodenitis, ultrasound was less effective. They concluded that ultrasound "of the stomach and duodenum is sensitive (91%) and specific (89%) in detecting or excluding wall abnormalities that are indicative of inflammation associated with peptic ulcer disease. [Ultrasound] may be a suitable nonstressful procedure in the evaluation of patients who cannot tolerate endoscopy."
Quite impressive results, even with their low-resolution, 1990 Hitachi AUB-40 ultrasound machine.
In another study from China in 2017, doctors evaluated the ability of transabdominal ultrasound augmented with an oral cellulose-based contrast agent to detect gastric ulcers. Over 4 years they scanned over 120 people with confirmed gastric ulcers (the sonographer was blinded to the results) and performed biweekly follow-up ultrasound exams to monitor for treatment response. After ingesting 500 mL of the oral contrast agent the ultrasound exam was performed with the following protocol:
Each portion of the stomach visualized:
Gastric ulcer examples
Gastric ulcers were noted if there was a localized hypoechoic wall thickening with uneven or depressed mucosal surface (reflecting gastric wall damage) and a hyperechoic line covering the mucosal surface. Wall thickness and size were used to monitor for improvement.
A typical benign gastric ulcer. (a) Endoscopic view showing a gastric ulcer (0.4 cm, long arrow) with surrounding edema (short arrow). (b) Ultrasound view showing a localized hypoechoic wall thickening (reflecting edema, short arrow) with a depressed mucosal surface (reflecting gastric wall damage, long arrow; 0.4 cm). Few gas echoes trapped at the base of the ulcer. (c) Endoscopic view showing a red ulcer scar (long arrow), indicating that the ulcer was almost healed. (d) Ultrasound view showing localized hyperechoic submucosal layer was replaced by a hypoechoic line (0.4 cm, long arrow), corresponding with an ulcer scar.
Malignant ulcer example:
A typical malignant gastric ulcer. (a) Endoscopic view showing a gastric ulcer (1.5 cm, thick arrow) with surrounding edema (thin arrows). The gastric ulcer was covered by white fur (a benign indicator) and the initial biopsy result was also benign. (b) Ultrasound view showing a localized hypoechoic wall thickening (1.0∼1.4 cm, thin arrow) with an uneven mucosal surface (thick arrow). This ultrasonic characteristic indicates that this ulcerative lesion may not be benign, and repeat gastroscopy with biopsy was performed, finally identifying the lesion as a gastric cancer.
Another malignant ulcer:
Transabdominal ultrasound with oral cellulose-based contrast agent (TUS-OCCA) in the surveillance of a gastric ulcer. (a) The lesion was detected by gastroscopy and the initial biopsy result was benign. (b) Two weeks later, the follow-up TUS-OCCA examination shows hypoechoic thickening (5 mm) of the gastric wall with uneven mucosa. (c) Three months later, TUS-OCCA shows hypoechoic thickening (12 mm) of the gastric wall with mucosal depression. This ultrasonic finding indicates that the lesion may be a malignant. (d) Repeat gastroscopy and biopsy finally confirmed that the lesion was a gastric cancer. The arrow points to the ulcerative gastric lesion.
Overall, their ability to detect gastric lesions greater than 5 mm was very good. They further separated their analysis into patients with "suitable body habitus" (Group S), who were thin, and "Unsuitable body habitus" (Group U) who were obese.
In the thin patients, they detected 100% of gastric ulcers larger than 5 mm (5 mm or more is the criteria for an ulcer), and in obese patients detected most of them. The majority of lesions in the antrum, angle, and body were detected, while those in the cardia and fundus were more difficult to visualize.
A GIGANTIC study out of China found similar results with oral contrast-enhanced ultrasound. Over the course of 8 years they enrolled a whopping 383,945 patients who underwent endoscopy for suspected gastric lesions. The results were compared to conventional ultrasound exam (without water or contrast), and contrast-enhanced gastric ultrasound.
This enormous sample included 103,568 cases with benign lesions including over 45,000 gastric ulcers, as well as over 46,000 malignant lesions. As seen below, conventional ultrasound (without water or contrast enhancement) did pretty terribly at detecting gastric lesions while contrast-enhanced ultrasound was on par with endoscopy:
Researchers noted that "oral contrast-enhanced ultrasonography was more accurate than conventional ultrasound in detecting the sites, sizes, numbers, and extensions of gastric lesions, and provided almost similar results as upper endoscopy in detecting small gastric lesions."
Does this translate to POCUS?
Contrast-enhanced ultrasound ventures out of the realm of POCUS and into the formal ultrasound study. But since water can act as a contrast medium with similar improvement in gastric wall visualization, asking a patient to drink some water before evaluating their stomach could offer a good alternative.
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