Rare Tumours of the Central Nervous System in Children

Since tumours of the central nervous system (CNS) are rare in children to begin with, there are certain types that are very rare, occurring with a frequency of less than 5 % of all paediatric CNS tumours. These deserve special focus because of some key challenges. For one, the initial descriptive histology gathered from a small series of tumour samples makes it challenging to define unique characteristics for some very rare tumours. Most pathologists and clinicians will encounter examples of these tumours infrequently, adding a challenge to their recognition and the overall awareness of a management strategy. From a clinical perspective, tumours that are ‘very rare’ cannot be studied in a specific randomized trial in order to determine the best course of treatment; therefore the treating physician must rely upon case series and reports, always paying special attention to the exception to the rules. In this chapter, we outline some key examples of very rare paediatric CNS tumours and discuss how to approach some of these challenges.