What is the most likely finding on CT imaging of the head in a patient with a history of congenital hydrocephalus and a ventriculoperitoneal (VP) shunt presenting with headache, confusion, lethargy, and nonbilious emesis?

VP Shunt Malfunction: Expected CT Findings

In this 8-year-old with VP shunt malfunction presenting with headache, lethargy, vomiting, and difficult compression of the shunt valve chamber, CT imaging will most likely show dilation of the lateral and third ventricles.

Clinical Presentation Indicates Shunt Obstruction

The clinical picture strongly suggests proximal (ventricular catheter) shunt obstruction:

• Progressive lethargy and confusion indicate rising intracranial pressure 1
• Multiple episodes of nonbilious emesis are classic signs of increased intracranial pressure in children 1
• Difficult compression of the shunt valve chamber is a critical physical finding that suggests the proximal catheter is obstructed, preventing CSF from flowing into the valve chamber 2
• Headache in a shunted patient warrants immediate evaluation for malfunction 1

Expected CT Findings in VP Shunt Malfunction

Ventricular dilation (lateral and third ventricles) is the hallmark finding when a VP shunt fails:

• When the shunt malfunctions, CSF accumulates in the ventricles, causing them to enlarge compared to the patient's baseline imaging 1, 2
• The lateral ventricles and third ventricle dilate because the obstructed shunt cannot drain CSF effectively 1
• CT imaging should be compared to prior studies to assess for increased ventricular size, which has 100% positive predictive value for shunt malfunction when present 2

Why Other Options Are Incorrect

Calcification of the choroid plexus:

• This is an incidental finding unrelated to acute shunt malfunction 1
• Does not explain the acute clinical deterioration

Layering debris in the lateral ventricles:

• This finding suggests intraventricular hemorrhage or infection 1
• Not the primary finding in mechanical shunt obstruction
• The clinical presentation lacks fever or signs of shunt infection

Slit-like ventricles:

• This represents over-drainage of CSF, the opposite of obstruction 2
• Would not cause difficult compression of the shunt valve chamber
• Inconsistent with signs of increased intracranial pressure

Imaging Approach

CT head without contrast is appropriate for emergency evaluation:

• Rapidly identifies ventricular size changes compared to baseline 2
• A limited 4-slice CT protocol can reduce radiation exposure by 87% while maintaining diagnostic accuracy for ventricular size assessment 2
• Key slices should include the fourth ventricle, third ventricle, basal ganglia level, and lateral ventricles 2

Critical Management Considerations

This patient requires urgent neurosurgical consultation:

• Shunt malfunction with increased intracranial pressure is a neurosurgical emergency 1
• The combination of lethargy, vomiting, and difficult valve compression strongly predicts proximal obstruction requiring surgical revision 2
• Delay in treatment can lead to herniation and permanent neurological injury 1