Brain imaging is at the heart of diagnosing and monitoring hydrocephalus. The two main tools are the CT scan and the MRI, and you'll likely encounter both over the course of care. Understanding what each one shows — and what to expect — can make these tests less intimidating.
What imaging shows in hydrocephalus Both CT and MRI can reveal the hallmark of hydrocephalus: enlarged ventricles (the brain's fluid chambers). Imaging can also show:
- The pattern of enlargement — which ventricles are affected, helping distinguish obstructive from communicating hydrocephalus.
- The cause, in many cases — such as a blockage, tumor, bleed, or malformation.
- Signs of raised pressure — like fluid pushed into the surrounding brain tissue.
- A baseline to compare against future scans, which is essential for monitoring.
CT scans A computed tomography (CT) scan uses X-rays to create cross-sectional images of the brain. Its strengths:
- Fast — often just minutes, useful in emergencies.
- Widely available, including in most emergency departments.
- Good at quickly showing ventricle size, bleeding, and major problems.
Its trade-offs: it uses a small amount of radiation (a consideration especially with repeated scans in children), and it shows less soft-tissue detail than MRI. CT is often the go-to when speed matters — for example, when a shunt malfunction is suspected and a quick look at ventricle size is needed.
MRI scans Magnetic resonance imaging (MRI) uses powerful magnets and radio waves (no radiation) to create highly detailed images. Its strengths:
- Exquisite detail of brain structures and the ventricular system.
- Excellent for identifying causes — blockages, tumors, malformations.
- Specialized sequences can assess CSF flow and other details.
- No ionizing radiation.
Its trade-offs: MRI takes longer, is noisier, requires lying still in an enclosed scanner, and is more affected by movement (young children sometimes need sedation). MRI is often used for detailed diagnosis and planning, and for monitoring when avoiding radiation is desirable.
What to expect during the scans.
- CT: You lie on a table that moves through a ring-shaped scanner. It's quick and painless. Sometimes a contrast dye is used.
- MRI: You lie on a table that moves into a tube-shaped scanner. It's loud (you'll usually get earplugs or headphones), takes longer, and requires staying still. Tell the team if you're claustrophobic — options can help. Crucially, if you have a shunt with a programmable (adjustable) valve, tell the MRI team beforehand, because the strong magnet can affect some valve settings, which then need to be checked and reset after the scan (covered in its own article).
A note on "rapid" MRI for children Many pediatric centers use fast MRI protocols specifically to monitor children with shunts — providing the detail of MRI while avoiding radiation and often without sedation. This is increasingly common for routine follow-up.
The bottom line CT and MRI are complementary. CT is fast and ideal for emergencies and quick checks; MRI offers superior detail for diagnosis, planning, and radiation-free monitoring. Your team chooses based on the situation — and over time, you'll likely become familiar with both as part of living with hydrocephalus.