Post-operative paediatric cerebellar mutism syndrome (pCMS) is a well-recognised complication of resective surgery for brain tumours of the cerebellum and fourth ventricle in children. Occurring in around 25% of infratentorial craniotomies, it is characterised by a delayed onset of mutism and emotional lability, and may comprise motoric and cognitive cerebellar deficits. Transient mutism gives way to prolonged, and often incomplete, recovery. Neuroimaging studies are beginning to reveal anatomical and functional aberrancies in the brain of children with pCMS. The cerebellar efferent pathways are likely to be implicated as a neuroanatomical substrate in the development of pCMS, as shown by a handful of diffusion tractography studies to date. However, the pathophysiology of this condition still remains unclear. Hypoperfusion of supratentorial cortical and subcortical structures may mediate the speech and behavioural deficits seen in pCMS, and is a candidate for a causal pathophysiological mechanism.

This study aims to prospectively image children with pCMS using advanced MRI techniques including diffusion tractography and arterial spin labelling, and to correlate this with clinical descriptions of the syndrome.

All children referred to Great Ormond Street Hospital for Children with a posterior fossa brain tumour will be imaged pre-operatively, post-operatively and at delayed follow-up. In tandem with this, clinical assessments will be made of children post-operatively to ascertain which patients develop pCMS. In addition, anonymised advanced MRI data on healthy controls will be used as a comparator group.

Inclusion Criteria:

Age <18 Referred and operated upon within study period Brain tumour of cerebellum, IVth ventricle, brainstem undergoing craniotomy for resection (including re-do surgery) No restrictions as to tumour histology or grade (embryonal tumour / glioma / ependymoma) Informed consent given by parents

Exclusion Criteria:

Non-neoplastic infratentorial lesions Claustrophobia Contraindication to MRI Pregnant female Scans missing at >2 timepoints Tumour resection surgery at another hospital if no pre- or post-operative scans available

All children referred to our institution with a brain tumour of the posterior fossa