Radiological feature of intestinal perforation in enteric fever
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radiological features intestinal perforation enteric fever typhoid pneumoperitoneum X-ray
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https://annals.edu.sg/pdf/41VolNo7Jul2012/V41N7p281.pdf
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Here is a comprehensive answer on the radiological features of intestinal perforation in enteric fever:
Radiological Features of Intestinal Perforation in Enteric Fever
Background
Typhoid (enteric fever) is caused by Salmonella Typhi. The organism colonises the Peyer's patches in the terminal ileum, causing hyperplasia, necrosis, and ulceration. Perforation typically occurs in the 3rd or 4th week of untreated or inadequately treated illness. The bowel may perforate at multiple sites, including the large bowel.
Plain Radiograph (X-ray) - Most Important Initial Investigation
The cornerstone radiological finding is pneumoperitoneum (free gas in the peritoneal cavity):
1. Erect Chest X-ray (First Choice)
- Shows free gas (air) under the diaphragm as a crescentic lucency beneath one or both domes
- The patient must remain upright for 10-20 minutes before the film to allow gas to rise
- As little as 1 ml of free gas can be detected in this way
- This is the most important and classic radiological sign
2. Left Lateral Decubitus Film (for very ill patients who cannot stand)
- Patient lies on their left side; free gas rises and is seen between the right lateral abdominal wall and the liver
- Preferred when the patient is too sick to sit upright
- A lateral chest X-ray has been found to be even more sensitive than an erect chest X-ray for pneumoperitoneum
3. Supine Abdominal X-ray - Additional Signs of Pneumoperitoneum
| Sign | Description |
|---|---|
| Rigler's sign (double wall sign) | Gas visible on both sides of the bowel wall - the outer wall is outlined by free peritoneal air |
| Football sign | Large oval collection of free gas outlining the entire peritoneal cavity (seen in children) |
| Falciform ligament sign | Free gas outlines the falciform ligament as a vertical curvilinear opacity in the right upper quadrant |
| Cupola sign | Free gas collecting under the central tendon of the diaphragm on supine film |
| Obliteration of liver dullness | Percussion sign (not radiological, but correlates with gas overlying the liver) |
Note: Erect plain X-ray shows free gas in approximately 70% of cases of perforation. - S Das, A Manual on Clinical Surgery
CT Scan (Most Sensitive and Specific)
CT is the gold standard for detecting perforation and defining the extent of disease:
CT Findings Specific to Perforation:
- Free intraperitoneal gas (pneumoperitoneum) - pockets of extraluminal air
- Free intraperitoneal fluid - ascites/peritoneal contamination
- Terminal ileal wall thickening - at the site of typhoid ulcers
- Identification of the exact perforation site
CT Findings of Enteric Fever (even without perforation):
| Finding | Frequency |
|---|---|
| Mesenteric lymphadenopathy | 75% |
| Splenomegaly | 75% |
| Bowel wall thickening (circumferential) | 58% |
| Free intraperitoneal fluid | 50% |
| Hepatomegaly | 25% |
| Gallbladder wall thickening | 8% |
(Data from Hennedige et al., Annals Academy of Medicine Singapore, 2012)
CT is particularly useful in:
- Culture-negative suspected enteric fever
- Detecting complications: perforation, bleeding, abscess
- Localizing the perforation site pre-operatively
Ultrasound
- Can demonstrate free fluid in the peritoneal cavity
- May show mesenteric lymphadenopathy, splenomegaly, hepatomegaly
- Less sensitive for pneumoperitoneum than X-ray
- Useful as a bedside tool in resource-limited settings
Summary of Key Radiological Signs
| Modality | Key Finding |
|---|---|
| Erect CXR | Free gas under diaphragm (crescentic lucency) |
| Left lateral decubitus AXR | Free gas between liver and abdominal wall |
| Supine AXR | Rigler's sign, Football sign, Falciform ligament sign |
| CT abdomen | Free gas + free fluid + bowel wall thickening + mesenteric LAD |
| USG | Free fluid, organomegaly, LAD |
Clinical Context for Diagnosis
Per Bailey & Love's Surgery (28th ed.):
"After the second week, signs of peritonitis usually denote perforation, which is confirmed by the presence of free gas seen on a radiograph."
Any patient on treatment for typhoid fever who shows sudden deterioration with abdominal signs should be considered to have a typhoid perforation until proven otherwise.
Key takeaway for exams: The single most important radiological feature is free gas under the diaphragm on an erect chest X-ray (pneumoperitoneum). CT is the most sensitive modality and also shows the characteristic features of enteric fever (mesenteric LAD, splenomegaly, terminal ileal thickening) alongside perforation.
- Bailey and Love's Short Practice of Surgery, 28th Ed.
- S Das, A Manual on Clinical Surgery, 13th Ed.
- Hennedige et al., CT Features in Enteric Fever, Ann Acad Med Singapore, 2012
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