Pediatrics

Pediatric Intracranial Infection: Find the Drainable Collection

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

Watch · concise explainerRestricted diffusion is pus

Core clinical idea

On a sick child, the unmissable call is a drainable, rapidly-lethal pyogenic collection (epidural/subdural empyema or abscess). The single unifying finding across every compartment is markedly restricted diffusion inside an organized collection — DWI is the read. Work out-to-in and, when you see it, say infection/surgical and report the complications, because children decompensate faster than the imaging comfort suggests.

Bottom line

Restricted diffusion in a collection is pus — work out-to-in, call it 'extra-axial,' and report the complication that drives surgery.

Core workstation questions

Is there an organized collection, and does its center restrict diffusion?
Which compartment(s) are involved — and have I called it 'extra-axial infection' rather than betting epidural vs subdural?
Is the meningeal disease basal-predominant, raising TB?
Parenchymal: is this cerebritis (medical) or a capsular rim-enhancing abscess (drain)?
Is there intraventricular layering debris with ependymal enhancement (ventriculitis)?
Are there complications to report now — venous thrombosis, arterial stroke, hydrocephalus?
Is there cortical restricted diffusion in a seizing infant — HSV until excluded?
What is the calcification distribution, and is there an associated migrational anomaly (CMV) or hydrocephalus/microcephaly (toxoplasmosis)?

What changes reporting / management

Epidural/subdural empyema and parenchymal abscess with central restricted diffusion are often surgical emergencies — state the collection, mass effect, and recommend urgent neurosurgical evaluation.
In children call it 'extra-axial infection/collection' because epidural and subdural spaces communicate and infection usually coexists in both.
Imaging does not rule out uncomplicated meningitis (normal in roughly half of proven cases) — it is for complications; LP is the diagnosis.
Basal-predominant enhancing meningitis (± basal hyperdensity) should prompt 'consider TB,' with posterior fossa tuberculomas/abscess favored in children.
Stage parenchymal infection (cerebritis vs capsular abscess) because the stage is the medical-vs-surgical decision; flag infection-related hydrocephalus and possible shunt need.
Put HSV in the impression and recommend urgent treatment/CSF PCR when a seizing infant shows cortical restricted diffusion, even if the rest of the scan looks mild.
Describe both calcification distribution and the associated malformation/head-size pattern, since timing of in-utero insult drives severity and the malformation points to the organism (CMV migrational anomalies).
Use neonatal ultrasound through an open fontanelle to confirm periventricular calcifications and spare CT radiation.
Call the abscess diffusion pattern; absent enhancement in an immunocompromised neonate raises rather than lowers suspicion, and note Aspergillus angioinvasion and Mucor sinus origin.
Stage neurocysticercosis (viable / degenerating with rim enhancement and edema / calcified) because it separates active treatable disease from burnt-out calcification.

Practical traps

Letting a normal CT/MRI 'rule out meningitis' — it cannot; the study is normal about half the time in proven disease.
Reading treated-meningitis residual leptomeningeal enhancement (which can persist for months) as active or relapsed infection.
Committing to epidural vs subdural in a child and missing coexisting infection in the other communicating compartment.
Under-calling infant HSV because the scan looks only mildly abnormal while the brain is being destroyed — cortical restricted diffusion is the sensitive early sign.
Treating TORCH calcifications as specific; they are a shared signature, and the discriminator is the associated malformation and timing.
Trusting a clean conventional gradient-echo in suspected malaria or angioinvasive fungus — microhemorrhages may only show on SWI.

Teaching pearls

DWI is the read — restricted diffusion in an organized collection is pyogenic infection until proven otherwise.
In kids, call it 'extra-axial infection' — epidural and subdural communicate, so don't bet on one.
You can't rule out meningitis with imaging — it's an LP diagnosis and the scan is normal half the time.
Treated meningitis can enhance for months — residual is not relapse.
Basal-predominant meningitis -> think TB; posterior fossa in kids.
Cerebritis can be medical; a capsular abscess gets drained — MRI stages it.
Cortical restricted diffusion in a seizing infant = HSV until proven otherwise — call it, don't wait.
Infant HSV imaging undersells the damage; brainstem can look spared while the cortex is gone.
TORCH calcifications aren't specific — the associated malformation and timing tell you which.
Migrational anomaly with periventricular calcification points to CMV.

Source lectures

Pediatric Intracranial Infection. Part 1 (bacterial)
Pediatric Intracranial Infection. Part 2 (TORCH, viral, fungal, parasitic)

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.