A normal AP supine abdominal X-ray should have several key visual characteristics:

1. Bowel Gas Pattern:

   • Stomach: There may be some gas in the stomach, usually in the left upper quadrant.

   • Small Intestine: Minimal gas is seen in the small intestine. Normal small bowel gas appears as a few scattered, central air pockets.

   • Large Intestine: The large intestine often contains more gas, and the haustra (folds) may be visible, especially in the ascending and transverse colon. These haustra appear as incomplete, widely spaced indentations along the colon.

2. No Abnormal Air-Fluid Levels:

   • In a normal image, air-fluid levels may be visible in the stomach but should not be present throughout the small or large intestine. Multiple air-fluid levels in loops of bowel may suggest obstruction.

3. Absence of Free Air:

   • Free air, which would appear as a sharp radiolucency (dark area) beneath the diaphragm, is not present in a normal abdomen. The presence of free air often indicates a perforation and requires immediate attention.

4. Soft Tissue and Organ Shadows:

   • The liver is typically seen in the right upper quadrant and appears as a soft tissue density without any clear air inclusions.

   • The kidney outlines may also be faintly visible, along with the psoas muscles on both sides of the spine, which appear as slightly denser, symmetrical structures running parallel to the spine.

   • The bladder may show a faint outline, particularly if partially filled, in the lower pelvis.

5. Bony Structures:

   • The lumbar spine, lower ribs, pelvis, and iliac crests are visible. The bones should appear intact without any abnormal lesions or fractures.

   • The vertebrae should align properly, and the sacroiliac joints should appear symmetrical.

A normal AP supine abdomen has a balanced and organized appearance, with no signs of abnormal gas distribution, fluid levels, free air, or unusual soft tissue masses

An abnormal AP supine abdominal x-ray should appear as :

1. Non-specific Bowel Gas Patterns:

   • Mildly Distended Loops of Small or Large Bowel: Gastroenteritis can sometimes cause mild, diffuse gas throughout the bowel, leading to slight distension in both small and large intestines.

   • Fluid Levels: Occasionally, in more severe cases, air-fluid levels may be present, particularly in the small intestine, indicating irritation and slowed transit through the gut.

2. Absence of Free Air:

   • In typical gastroenteritis, there is no free air under the diaphragm. Free air would suggest a different, more severe underlying issue like perforation, which is not a characteristic of simple gastroenteritis.

3. Thickened Bowel Wall (if visible):

   • In severe cases or cases with complications, bowel wall thickening might be observed, indicating inflammation or edema. However, this finding is more often seen on a CT scan than an X-ray.

4. Localized Gas Distension:

   • Some patients may show segmental gas distension in the colon, indicating localized irritation of the large intestine. This might be more visible in cases where the large bowel is more affected (such as with colitis).

5. Normal Soft Tissue Outlines:

   • The liver, spleen, kidneys, and psoas muscle shadows should appear normal in uncomplicated gastroenteritis.