Diagnostic Challenges in Choroid Plexus Tumours.

Choroid plexus tumours are rare epithelial neoplasms arising from the choroid plexus, accounting for approximately 0.2% of all central nervous system tumours but up to 20% of brain tumours diagnosed during the first year of life. CPTs exhibit marked clinical and biological heterogeneity and are classified into three entities according to the World Health Organization (WHO): choroid plexus papilloma (CPP, WHO grade 1), atypical choroid plexus papilloma (aCPP, WHO grade 2) and choroid plexus carcinoma (CPC, WHO grade 3). Although CPP is a benign tumour with excellent prognosis following complete surgical resection, aCPP is defined by increased mitotic activity and carries a higher risk of recurrence in children older than 3 years and in adults. In addition, a subset of adult (a)CPPs harbours TERT promoter mutations, which have been associated with an increased risk of tumour recurrence. CPC is a highly malignant tumour characterised by frank signs of malignancy and aggressive clinical behaviour, with particularly poor outcomes in TP53-mutant cases, frequently associated with Li-Fraumeni syndrome. Accurate grading and distinction from histological mimics may be difficult, especially in small biopsy specimens or tumours with atypical features. In addition, the integration of molecular findings, including DNA methylation analysis and copy-number assessment, has become an important adjunct in the diagnostic evaluation of CPTs by improving diagnostic accuracy and providing additional prognostic information. In this review, we outline the histological and molecular characteristics of CPTs and highlight common diagnostic pitfalls and relevant differential diagnoses across different age groups.