Okay, let's tackle this question about the next investigation for a 2-year-old with a UTI. First, I need to recall the standard workup for UTI in young children. UTI in toddlers can have various causes, so the next step after confirming the infection would be to check for underlying abnormalities. The core concept here is probably about identifying structural or functional issues in the urinary tract that might predispose the child to recurrent infections.

The correct answer is likely a voiding cystourethrogram (VCUG) or renal ultrasound. Wait, but in a first-time UTI in a young child, especially under 2 years, the guidelines might recommend a renal ultrasound first to check for hydronephrosis or other structural issues, and then a VCUG if there's a suspicion of vesicoureteral reflux (VUR). Alternatively, in some cases, especially with a complicated UTI or if there are other risk factors, they might go straight to VCUG. But I think for a first UTI in a 2-year-old, the initial investigation is usually renal ultrasound. Then, if there's evidence of hydronephrosis or the ultrasound is inconclusive, VCUG is done. So the next step after a first UTI would be renal ultrasound.

Now, looking at the options. Let's say the options are A. Renal scan, B. Ultrasound, C. VCUG, D. Micturating cystogram. Wait, but the correct answer would be B. Renal ultrasound. Because in the initial evaluation of a first UTI in children under 2 years, the American Academy of Pediatrics recommends renal and bladder ultrasound followed by VCUG if the ultrasound is abnormal. If the ultrasound is normal, then no further imaging is needed unless there's a recurrence. So the next investigation after a first UTI would be renal ultrasound. Therefore, the correct answer is B.

The other options: A. Renal scan (DMSA scan) is used for scarring, usually after a febrile UTI in older children. C. VCUG is for diagnosing VUR but is invasive and requires catheterization. D. Micturating cystogram is another term for VCUG. So the wrong options are either more invasive or not first-line. The clinical pearl here is that in first UTI in young children, start with imaging that's non-invasive, like ultrasound. The high-yield fact is that renal ultrasound is the first step in evaluating a first UTI in a child under 2 years to detect structural abnormalities before proceeding to VCUG if needed.

**Core Concept**
In children under 2 years with a first urinary tract infection (UTI), the next investigation aims to detect structural abnormalities like hydronephrosis or vesicoureteral reflux (VUR). **Renal ultrasound** is the initial imaging modality to assess kidney and bladder anatomy.

**Why the Correct Answer is Right**
A **renal ultrasound** is non-invasive and evaluates for hydronephrosis, renal scarring, or bladder abnormalities (e.g., posterior urethral valves in males). If hydronephrosis or other abnormalities are found, **voiding cystourethrogram (VCUG)** is performed to confirm VUR, a common cause of recurrent UTIs in young children. This approach aligns with guidelines to avoid unnecessary radiation or invasive procedures.

✓ Correct Answer: A. Abdominal Ultrasound