Gallstone ileus

Mechanism of development (pathogenesis)

The development of gallstone ileus is directly related to severe, long-standing inflammation of the gallbladder wall. Against the background of a chronic inflammatory process, a pressure ulcer forms through which a large calculus migrates directly into the duodenum. Thus, the stone enters the gastrointestinal tract, completely bypassing the common bile duct system.

Moving through the digestive tract, the calculus sooner or later becomes trapped in the narrowest segment. As a rule, this is the terminal ileum (loops located in the pelvic cavity). Occlusion of the lumen leads to mechanical small bowel obstruction (SBO).

Radiographic and CT findings

A specific radiographic triad or other classic features are present in only 38% of cases. In the majority of patients (>50%), plain abdominal radiographs show only non-specific signs of intestinal obstruction.

Imaging features of the gallstone itself:

• On a plain radiograph, the calculus can be identified in approximately one-third of patients.
• On computed tomography (CT), detecting the stone is more difficult than it seems: less than 15% of gallstones have a sufficient degree of calcification. Consequently, on tomograms, the X-ray density of the stone often blends with normal bowel contents.
• The CT scout image (scout image) may demonstrate only a few gas-distended loops, since in pronounced obstruction most loops are filled with fluid, and natural gas contrast is absent.

Pneumobilia: differential diagnosis

In approximately 33% of patients with gallstone ileus, radiographs reveal gas within the biliary tree — pneumobilia. The sensitivity of CT in detecting this sign reaches 95–100%.

It is critical to differentiate pneumobilia from hepatic portal venous gas:

1. Pneumobilia is characterized by a branching pattern, with gas being more prominent and concentrated in the central regions (closer to the porta hepatis).
2. Hepatic portal venous gas typically distributes peripherally, accumulating in small venous branches along the edge of the hepatic parenchyma.

In addition to gallstone ileus, pneumobilia can be caused by other factors:

• Prior sphincterotomy or other biliary interventions (the most frequent cause).
• Peptic ulcer perforation with fistulization into the common bile duct.
• Formation of a malignant fistula.
• Age-related laxity of the sphincter of Oddi in elderly patients.
• Prior asymptomatic, spontaneous passage of a gallstone.

Intestinal intussusception in adults

Another important cause of SBO is intussusception (intussusception). Unlike in pediatric practice, this condition in adults is almost always secondary and develops in the setting of neoplasms. Tumors such as submucosal lipomas, lymphomas, or melanoma metastases act as the so-called "lead point", which pulls the bowel wall along with it.

• On a plain radiograph: the intussusceptum may appear as a soft-tissue mass partially outlined by gas. In the axial projection (end-on), the target sign (target sign) is revealed — two concentric fat-density rings alternating with soft-tissue structures.
• On 3D-reconstruction CT: it is clearly visible how the intussusceptum (intussusceptum) draws mesenteric fat into the lumen of the intussuscipiens (intussuscipiens). CT often allows accurate identification of the underlying tumor.

Tactics and imaging modality selection in SBO

Although ultrasonography (US) can demonstrate fluid-filled, dilated small bowel loops, it generally fails to reliably establish the level and cause of obstruction (hernia, adhesions, gallstone, or tumor). For this reason, routine ultrasound in suspected SBO is not recommended.

If the clinical presentation indicates complete obstruction and the patient clearly has an emergency surgical indication, an extended radiological workup is not strictly mandatory. Nonetheless, the absolute majority of surgeons consider preoperative CT extremely useful for precise topographic diagnosis and surgical planning (e.g., to identify an incarcerated inguinal hernia).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Radiographic signs of classic small bowel obstruction (SBO)
• CT diagnosis of incarcerated hernias (using inguinal hernia as an example)
• The "target sign" in neoplastic intussusceptions
• Sphincter of Oddi laxity as a cause of spontaneous pneumobilia
• Differential imaging diagnosis of hepatic portal venous gas

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.