IMAGING OF ACUTE ABDOMEN

Objectives

To know the imaging modalities used in the assessment of the acute abdomen

To understand the choice of imaging methods in different conditions causing acute abdomen and limitations of each modality

To identify the imaging appearances of common conditions causing acute abdomen

Acute abdomen

A clinical condition characterized by sudden onset of severe abdominal pain developing over a period of hours requiring early surgical or medical treatment.

Causes of acute abdomen (except trauma)

Role of Imaging

• Aid rapid & accurate diagnosis.

• Aid in therapy using interventional radiological techniques.

Imaging Methods in acute abdomen

• Plain Film Radiography• Contrast Studies• Ultra Sound• Computerized Tomography• Nuclear Medicine• Magnetic resonance imaging

Choice of Imaging depends on the clinical diagnosis and the imaging facilities available in the institution.

Plain Film Radiography in acute abdomen

Remains the current first line radiological test in suspected bowel obstruction and detection of free air.Detects calcifications related to acute abdomen.Detects soft tissue masses and gas.

Ultrasonography

No ionizing radiation ( Important in younger patients and pregnant women)The spatial resolution of a high-frequency US image is higher than that of a CT image if the target organ can be approached closely. The dynamic, real-time qualities -can observe fetal movements, peristalsis etc. Directly visualize blood flow and pulsations.

CT

Multi-slice CT is increasingly replacing ultrasonography for the evaluation of patients with acute abdominal pain.

MRI

Useful to evaluate acute abdomen in pregnancy

Isotope studies

Useful in GI bleeding

Plain Radiography

Standard Radiographs Supine – AP abdomen Erect PA Chest

Additional Radiographs Erect- AP abdomen Left lateral decubitus abdomen

Normal supine AP Abdomen/Erect AP abdomen

Plain Radiograph helps to detect

Bowel obstructionPneumoperitoneum Pneumonia mimicking abdominal painEmphysematous pyelonephritis or cholecystitis

Three Cardinal Radiological signs of a bowel obstruction are,1. Absence of distal gas.2. Differential distension3. Long / differential air fluid levels

Small bowel obstruction

Supine AP abdomen Erect AP abdomen

Large bowel obstruction

Distended colon proximal to obstruction (peripheral location)Small bowel also distended if ileo-caecal valve is incompetent

Sigmoid Volvulus

Paralytic ileus

Supine AP abdomen - Distension of small bowel and colonErect AP abdomen- Fluid levels may be seen in colon but not in small bowel

Pneumoperitoneum- Supine AP abdomen

Rigler’s signFalciform ligament outlined by air

Perforation of GIT -Pneumoperitoneum

Erect PA chestFree air seen under the diaphragm

Pneumoperitoneum- Left lateral decubitus

Free air seen between liver and lateral abdominal wall

Ischaemic colitis

Pneumobilia

Calcifications related acute abdomen

Aortic and arterialUrinary tract calculi (85% calcify)Gallstones(10-15% calcify)Pancreatic secondary to chronic pancreatitisappendicoliths

GB calculi

Appendicolith

Pancreatic calcification

Ureteric calculi

Gallstone ileus

Contrast studies

Barium or water soluble GI contrast study

Small bowel obstruction

Identify its cause and locationAdhesions account for 60-80% of all casesThe 'Small Bowel Feces Sign' (SBFS) is a very useful sign as it is seen at the zone of transition thus facilitating identification of the cause of the obstruction.

Choice of imaging modalities in different common conditions and its appearances

US / contrast studies / CT / Isotope / MRI

1. Acute appendicitis

Most common abdominal surgical emergency. US confirms appendicitis by visualizing the inflamed appendix (successful in 90 %) or to exclude appendicitis, either by visualization of the normal appendix (successful in 50%) or by demonstrating an alternative condition (possible in 20 %).If US result is equivocal /if most of the above patients in the latter group are obese, - >CT. An inflamed appendix has a diameter >6 mm, and is usually surrounded by inflamed fat. The presence of a faecolith or hypervascularity on power Doppler strongly supports inflammation.

Appendicitis with appendicolith - MRI

2. Cholecystitis Signs of cholecystitis

Gall bladder wall thickening Hydropic gall bladder Positive Murphy sign

Imaging Modalities-US, CT, MRI

3. Pancreatitis

Imaging Modalities-US, CT, MRI

4. Intussusception

Imaging Modalities-US, CT, MRI

5. Diverticulitis

6. Ureteric calculi

7. Ruptured aneurysm

Sonography is a quick and convenient modality, but it is much less sensitive and specific for the diagnosis of aneurysmal rupture than CT.The absence of sonographic evidence of rupture does not rule out this entity if clinical suspicion is high.

Acute GI BleedingMinimum of 0.5ml/min is detectedOptimum sensitivity with 1ml/min

8. Salphingitis

9. Ectopic pregnancy

Interventional radiological techniques used in acute abdomen

1. Selective angiographic infusion of vasoconstrictive agents2. Embolic occlusion of bleeding vessels

Embolisation