7.13: Approach to acute abdomen

Annirudh Kohli

The acute abdomen is a common presentation to the emergency services of a medical facility. The imaging specialist is now well armed with a full complement of diagnostic and interventional modalities to evaluate the acute abdomen as well as utilize them as a guide for therapeutic procedures.

A plain X-ray of the abdomen is usually the first investigation ordered, both erect and supine. These are very useful to detect bowel perforation, seen as free air in the abdominal cavity especially under the domes of diaphragm on the erect X-ray. Supine and erect films are also useful to detect bowel obstruction by demonstrating fluid levels on the erect film and dilated loops on the supine film. Additionally, presence of calculi, foreign bodies, location and placement of tubes in the abdomen are demonstrated on plain X-rays.

A chest X-ray is also mandatory as this is the most sensitive means to demonstrate free air under the domes of the diaphragm. A number of chest pathologies may present clinically as an acute abdomen, such as pneumonia, CCF, dissecting aneurysm, pulmonary infarction, pleural effusions and pericarditis. Secondary effects of an acute abdomen such as pleural effusions, atelectasis, aspiration pneumonia, acute lung injury may be also visualized on the chest X-ray. Finally, a chest X-ray on admission forms as a good baseline study for postoperative complications such subphrenic abscess which may be evident only after comparing with the previous X-rays.

Sonography is an indispensable tool in the evaluation of the acute abdomen as it is portable and can be done at the bedside. It is quick and the modality of choice for evaluating the gallbladder, genitourinary system, detecting free fluid and compares as well as CT in evaluation of the liver. It is also very useful for evaluating the lower chest for presence of effusions which may not have been visible on a chest X-ray or to clarify an opacity on the chest X-ray whether parenchymal or pleural. Unfortunately, sonography has its share of limitations, it is operator dependent, bowel gas, obesity, wound dressings may interfere with sonographic evaluation.

CT scan is the modality of choice as it is not limited by factors which interfere with sonographic evaluation. The only disadvantage is the need to transport the patient to the CT scan suite. However, the information gained outweighs the risk of transportation of the patient.

CT studies may be done with or without contrast.

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