**Core Concept:** Hydrocephalus is a condition characterized by an abnormal increase in the volume of the cerebral spinal fluid (CSF) in the brain ventricles, leading to increased intracranial pressure and potential brain damage or dysfunction. In neonates, it is often due to obstructive mechanisms, and seizures can be a presenting symptom due to increased pressure on the brainstem.

**Why the Correct Answer is Right:** The most probable diagnosis in this case is **D:** Obstructive Hydrocephalus. Obstructive hydrocephalus in neonates is usually caused by an obstruction in the CSF pathways, such as in the aqueduct of Sylvius or fourth ventricle. The high-output cardiac failure and dilated lateral ventricles seen on CT imaging are suggestive of increased intracranial pressure and ventricular dilation, respectively. Seizures in this context can be attributed to raised intracranial pressure affecting brainstem function.

**Why Each Wrong Option is Incorrect:**

A. Hydrocephalus can present with various symptoms, but high-output cardiac failure is not a common manifestation. This option is incorrect because the clinical presentation does not align with typical hydrocephalus symptoms.

B. Hydrocephalus can present with seizures, but the combination of high-output cardiac failure and dilated lateral ventricles is not commonly seen. This option is incorrect as the specific combination of symptoms and CT findings does not match typical hydrocephalus presentations.

C. Obstructive hydrocephalus can cause seizures, but it is less likely to cause high-output cardiac failure. This option is incorrect as the specific combination of symptoms and CT findings does not align with typical hydrocephalus presentations.

**Clinical Pearl:** Hydrocephalus should be considered in neonates presenting with seizures, especially when accompanied by high-output cardiac failure and dilated ventricles. Early diagnosis and intervention are crucial to prevent neurologic impairment or regression.