Small bowel perforation

Small bowel (SB) perforation is an acute pathological condition resulting from a discontinuity of the small bowel wall secondary to different etiologies with subsequent leakage of intestinal gas and contents into the peritoneal cavity.

Clinical presentation

• clinical diagnosis maybe difficult, symptoms are usually vague with diffuse non-specific abdominal pain
• on some occasions, the pain is severe (acute abdomen)

Pathology

Etiology

• trauma: blunt, penetrating
• foreign bodies: ingestion
• iatrogenic e.g. laparoscopy, endoscopy
• inflammation e.g. Crohn disease, small bowel diverticulitis (rare)
• perforated duodenal ulcer
• perforated duodenal diverticulum
• ischemia: arterial or venous
• neoplastic: either primary or secondary
  • especially primary malignant lymphoma under treatment with chemotherapy and steroids

Radiographic features

Plain radiograph

• free gas under the diaphragm is a classic sign of pneumoperitoneum on the erect chest and abdomen radiographs and it is suspicious for bowel perforation
• other signs of pneumoperitoneum, including Rigler sign

Ultrasound

• although not a primary modality for evaluating pneumoperitoneum, free gas may be detected on ultrasound when gas shadowing is present along the peritoneum
• free intraperitoneal fluid collection

CT

CT is the imaging modality of choice in the diagnosis of small bowel perforations especially in the early stages.

Technique

• oral contrast: water-soluble contrast agents are safe if leaked into the peritoneal cavity as they are easily absorbed with no associated peritoneal inflammatory reaction
• intravenous contrast: for assessment of the bowel wall and splanchnic vessels
• multiplanar reconstruction (sagittal and coronal)
• different CT window sittings (abdominal, lung, and bone windows)

CT findings

General:

• pneumoperitoneum: free intraperitoneal gas that is best seen in the lung window. A careful search for extraluminal gas should be done as the amount is occasionally minimal especially in the early disease and small perforations.
• leakage of oral contrast into the peritoneal cavity: it is highly specific for perforation; however, its sensitivity is low. Small perforations are usually not associated with significant oral contrast leakage. Moreover, some perforation sites require a specific patient position to give an evident oral contrast leakage like right lateral decubitus for duodenal perforations.
• intraperitoneal free fluid collection: in the absence of parenchymatous organ injuries or active inflammation
• blurred and smudged mesenteric fat
• precise detection of the perforation site: is usually difficult. Some helpful signs include; localized bowel wall thickening or focal bowel wall interruption with adjacent free gas bubbles and localized dirty mesenteric fat. The presence of pneumoperitoneum on both sides of the falciform ligament favors the possibility of proximal rather than distal bowel perforations

Findings specific for different etiologies

• penetrating small bowel injury: recognition of the injury site is very helpful as the extension of the wound track into the bowel wall is the most sensitive sign in diagnosis. Pneumoperitoneum is not a strong suspicious sign for bowel perforation as it is usually related to gas entry through the wound
• bowel injury secondary to ingestion of foreign bodies: metallic or calcified foreign bodies (fish or chicken bones) are seen in the bone window, fresh woody foreign bodies are also dense while dry woody foreign bodies contain gas and best seen in the lung window. Free pneumoperitoneum is uncommon as the foreign body is usually stuck at the perforation site preventing considerable gas leak. Localized pneumoperitoneum is more commonly seen
• duodenal perforation during ERCP: the perforation is usually retroperitoneal with free gas seen at the anterior pararenal space, rarely extending intraperitoneal. If an injury is suspected during the procedure, non-enhanced CT is recommended after, for detection of the leakage of contrast used during the procedure.
• ileal perforation secondary to Crohn disease: usually the perforation is not free, more commonly leads to localized peritonitis with loops adhesions and formation of an inflammatory mass or abscess similar to the pathology in complicated acute appendicitis
• bowel perforation secondary to ischemia and gangrene: associated with pneumatosis intestinalis, portal venous gas, free intraperitoneal fluid, and pneumoperitoneum. Multiphasic contrast-enhanced CT is usually capable of detection of the culprit diseased vessel.

Differential diagnosis

• other causes of pneumoperitoneum
• other causes of free intraperitoneal fluid