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CT is the modality of choice in the acute setting (assuming any imaging is required). MRI can be useful in the subacute setting to demonstrate diffuse axonal or other parenchymal injury that may not be apparent on CT.
If the onset of headache is sudden, and haemorrhage is a consideration (such as from an arteriovenous malformation), then non contrast CT is indicated acutely, with CT angiogram (CTA) if non-traumatic haemorrhage is identified. Similarly, if there is clinical concern about the possibility of significantly raised intracranial pressure, it may be more appropriate to perform a CT scan on an urgent basis. In both these settings further imaging with MRI may be required in addition to the CT scan. This would depend on the CT findings and the patient's clinical course. In a stable patient with non-benign headaches, particularly a patient with focal neurology, MRI is the gold standard.
Many childhood seizures have typical benign features and do not require imaging. Non-acute MRI is indicated in otherwise well children with clinical or investigative features suggesting an underlying lesion. Acute MRI may be indicated in unusual circumstances, after discussion with a neurologist.
MRI is undoubtedly superior to CT at demonstrating meningeal and parenchymal changes and vascular complications of infection. However, in the acute setting, contrast enhanced CT is effective in exclusion of complications of infection that may require intervention, such as abscess or subdural empyema and in assessing potential sites of origin such as sinusitis or mastoiditis. Contrast enhanced CT is also effective when there is concern of major associated cerebral venous sinus thrombosis. Pre-contrast CT is unnecessary.
MRI is the imaging modality of choice in all cases of sensineural hearing loss (SNHL) but for pragmatic reasons of current lack of availability of MRI under GA, CT is a reasonable alternative for those children who would need sedation. Brainstem and cranial nerves are better shown on MRI than CT.
In a patient with known hydrocephalus, or possible shunt malfunction, CT is generally all that is required. Some institutions have the capacity for "fast" T2 MRI for monitoring patients with already documented or treated hydrocephalus.
All cerebral malformations are shown more elegantly on MRI than CT. Necessity for MRI will depend on the indication and the questions which need answering.
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- Date last published: 01 September 2013
- Document type: Imaging Guideline
- Services responsible: Paediatric Radiology
- Author(s): F Wilson, G Thomson, D Perry
- Editor: Greg Williams
- Review frequency: 2 years
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