Objective Brain biopsy has a diagnostic yield of >95% in neoplastic conditions. There is limited knowledge about the usefulness of brain biopsy in children with undiagnosed neurological conditions and the aim of this audit is to address this issue; therefore we undertook an audit of these patients.

Methods This was a retrospective, five-year case-note review of brain biopsies requested by neurologists in a tertiary children’s hospital (2008–2013). Information was collected on clinical features, neuroimaging, investigationsand histology reports.

Results Twelve (eight male) patients were identified. Median (range) age was 9.5 (2–16) years.

The considered clinico-radiological diagnosis pre-biopsy included: non-neoplastic space occupying lesion (n = 5), central nervous system (CNS) vasculitis (n = 3), encephalitis (n = 2), neurosarcoidosis (n = 1) and pachymenigitis (n = 1). Presenting features included: signs of raised intracranial pressure (n = 4); cerebellar signs [(n = 3, one with growth failure and diabetes insipidus and another with a progressive paraparesis]; encephalitis with seizures and a movement disorder (n = 1); steroid dependent encephalitis (n = 1); transient ischaemic attacks (n = 2) and neurological regression with a movement disorder and epilepsy (n = 1).

Twelve biopsies were from the identified lesion and two were from non-lesional from the frontal lobe (suspected CNS vasculitis). Two children (suspected neurosarcoidosis and pachymeningitis) had repeat lesional biopsies before immunosuppressant treatment was started.

A definite diagnosis was identified in eight: demyelination (n = 3); grade II astrocytomas (n = 2); HSV co-infection in a case of known NMDAR encephalitis; granulomatous meningitis (consistent with neurosarcoidosis) and Rosenthal fibres (consistent with atypical Alexander’s with negative glial fibrillary acidic protein (GFAP) stain. Biopsy in one showed non-specific features of encephalitis and three biopsies were unremarkable. Histological results gave useful information in call cases and altered the management in 10 cases.

Complications included: subdural effusion [n = 1 (spontaneous resolution)], suspected meningitis (no LP undertaken) n = 1, late superficial wound infection n = 1. All recovered fully.

Conclusion Brain biopsy appears to have a useful role in some children with undiagnosed neurological disorders. The procedure should be considered if the findings are likely to alter management or to establish a specific diagnosis of a degenerative condition, or both. One quarter had an acute complication with no long term sequalae. The long term effects are unknown.