For a 3-month-old presenting with possible urinary tract infection, what imaging is appropriate following initial treatment?

In the case of a 3-month-old infant presenting with a probable urinary tract infection (UTI), it is critical to assess for any underlying anatomical abnormalities that could predispose the child to recurrent infections. A renal and bladder ultrasound is particularly appropriate in this scenario because it provides valuable information about the kidneys and urinary tract, including the size of the kidneys, the presence of hydronephrosis, and any structural abnormalities such as vesicoureteral reflux (VUR).

This imaging is non-invasive, does not involve radiation, and is well-suited for infants, making it the safest option for evaluating potential causes of the infection. The ultrasound can help guide further management by identifying any abnormalities that might require specific treatment or follow-up.

Other imaging options, such as a head ultrasound, would not provide relevant information regarding urinary tract issues. A CT abdomen, while detailed, utilizes radiation and is not standard for pediatric UTIs due to safety concerns and the availability of safer alternatives. An X-ray of the abdomen would be insufficient for assessing the urinary system's integrity and anatomy in relation to a UTI. Therefore, the renal and bladder ultrasound is the most appropriate choice following initial treatment in this situation.