What initial imaging study would be indicated for a child after a first episode of pyelonephritis?

The appropriate initial imaging study for a child after a first episode of pyelonephritis is a renal and bladder ultrasound. This choice is particularly important because it helps evaluate the urinary tract for any anatomical abnormalities, which could predispose the child to recurrent urinary tract infections (UTIs) or complications stemming from the pyelonephritis.

An ultrasound is non-invasive, does not involve radiation, and provides valuable information about kidney size, structure, and the presence of any structural abnormalities (like hydronephrosis) or any obstructions. Identifying these issues early can guide further management and provide insight into preventing future infections.

Other imaging modalities, such as computed tomography scans, while providing detailed images, are generally not first-line due to radiation exposure, especially in children. Similarly, abdominal X-rays and chest X-rays do not provide relevant information about the kidneys and urinary tract in the context of pyelonephritis, making them unsuitable choices in this scenario.