## **Core Concept**
The question tests knowledge of imaging modalities for diagnosing hydrocephalus, particularly in infants. Hydrocephalus is characterized by an accumulation of cerebrospinal fluid (CSF) within the brain, leading to ventricular enlargement. Imaging plays a crucial role in its diagnosis.

## **Why the Correct Answer is Right**
Ultrasound is considered an ideal imaging method for diagnosing hydrocephalus in infants because it is non-invasive, does not expose the infant to radiation, and can be performed quickly at the bedside. It allows for the assessment of ventricular size and can detect signs of increased intracranial pressure. The anterior fontanelle in infants serves as an acoustic window for ultrasound waves, making it an effective tool for this age group.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While CT scans can diagnose hydrocephalus by showing ventricular enlargement, they involve radiation, which is a concern, especially in infants due to their sensitivity to radiation effects.
- **Option B:** MRI provides detailed images of the brain and is useful for diagnosing hydrocephalus and its causes. However, it may require sedation in infants, is more expensive, and less readily available than ultrasound.
- **Option C:** This option might seem plausible but given the context, it's less commonly used for initial diagnosis of hydrocephalus compared to ultrasound in infants.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in infants, the anterior fontanelle can be used as an ultrasound window, making ultrasound a quick, bedside, and radiation-free method for assessing ventricular size and diagnosing hydrocephalus.

## **Correct Answer:** . Ultrasound