Why does a sigmoid volvulus appear on the right side of an abdominal X-ray (X-ray)

From the Guidelines

A sigmoid volvulus typically appears on the right side of an abdominal X-ray due to the anatomical positioning that occurs during this condition, as the sigmoid colon twists on its mesenteric axis and becomes massively dilated, rising out of the pelvis and displacing toward the right upper quadrant of the abdomen 1. When the sigmoid colon twists, it creates the classic "coffee bean" or "bent inner tube" sign, with the dilated loop of bowel extending from the pelvis upward and to the right. The appearance on the right side occurs because as the sigmoid colon becomes increasingly distended with gas, it expands into available space in the abdomen, which is often toward the right side where there is less anatomical restriction. Additionally, the fixed points of the sigmoid colon at the rectosigmoid junction and descending colon create a pivot point that directs the distended loop rightward. This rightward displacement is a key radiographic finding that helps differentiate sigmoid volvulus from other causes of large bowel obstruction. Some key points to consider in the diagnosis of sigmoid volvulus include:

• The classic "coffee bean" sign on abdominal X-ray, which is a strong indicator of sigmoid volvulus 1
• The importance of clinical evaluation, including history and physical examination, to identify risk factors and symptoms of sigmoid volvulus 1
• The use of CT imaging in cases where the diagnosis is in doubt or if ischemia or perforation is suspected 1
• The potential for sigmoid volvulus to present with non-specific symptoms, making diagnosis challenging 1
• The high recurrence rate of sigmoid volvulus after endoscopic decompression, highlighting the importance of considering surgical intervention to prevent recurrent volvulus 1

From the Research

Sigmoid Volvulus on Abdominal X-ray

• The sigmoid volvulus typically appears on the left side of the abdominal X-ray, not the right side, due to the anatomical location of the sigmoid colon 2.
• However, the studies provided do not specifically address why a sigmoid volvulus would appear on the right side of an abdominal X-ray.
• The plain abdominal X-ray radiographs of sigmoid volvulus typically show a dilated sigmoid colon and multiple small or large intestinal air-fluid levels 2.
• Certain radiological signs, such as the apex of the loop under the left hemi-diaphragm, inferior convergence on the left, and the left flank overlap sign, are highly specific and sensitive for diagnosing sigmoid volvulus 3.
• It is possible that an unusual presentation or anatomical variation could cause a sigmoid volvulus to appear on the right side of an abdominal X-ray, but this is not supported by the provided evidence.
• Computed tomography (CT) scans may be valuable in cases of unusual clinical or plain film presentation, as they can demonstrate a whirl pattern of the dilated sigmoid loop around the mesocolon and vessels 4.