What type of investigation is best for diagnosing necrotizing enterocolitis?

In diagnosing necrotizing enterocolitis (NEC), an abdominal plain film is the most suitable investigation. This technique allows for rapid assessment of the infant's abdomen and is particularly useful for identifying signs of intestinal obstruction or perforation, such as free air under the diaphragm, which could indicate perforation. In addition, plain abdominal films can help visualize bowel dilatation and identify other characteristic changes associated with NEC, such as abnormal air patterns in the bowel wall.

Plain films are also advantageous in the pediatric population, especially in neonates, because they are quick, non-invasive, and can often be performed at the bedside. The results can be assessed almost immediately, allowing prompt decision-making for further management or intervention.

Other modalities like CT scans and magnetic resonance imaging are generally not first-line investigations in this scenario due to factors such as radiation exposure, contrast risk, and longer processing times, which can delay critical treatment in a potentially unstable patient. Ultrasound can be useful in some cases but may not provide the same level of detail about air fluid levels or perforation, making it less reliable than plain films in establishing a diagnosis of NEC decisively.