Post-therapy imaging of adult brain tumours: patterns, pitfalls, and practical framework.

Post-therapy imaging of adult brain tumours is among the most challenging tasks in neuroradiology. Distinguishing true tumour progression from treatment-related changes-including pseudoprogression, radiation necrosis, and atypical immunotherapy responses-requires integration of imaging timing, morphology, and clinical context. This review synthesises current literature into a practical, treatment-based framework, addressing gliomas and metastases separately and, within each, organising findings by treatment modality-surgical resection, chemoradiotherapy, stereotactic radiosurgery, systemic therapy (targeted and anti-angiogenic agents, and immunotherapy), and locoregional techniques. For each treatment context, we outline expected imaging evolution, characteristic patterns of treatment effect, key features differentiating these from tumour progression, and the role of MRI and nuclear medicine techniques. The review concludes with a practical reporting framework built around treatment received and time since treatment, integrating clinical context, imaging pattern, and interval change to support radiology reporting across diverse therapeutic combinations. CRITICAL RELEVANCE STATEMENT: Recognising treatment-specific imaging pitfalls-pseudoprogression, pseudoresponse, radiation injury, and immune-related changes-is essential for accurate response assessment and prevents misdirected management in neuro-oncology. KEY POINTS: Distinguishing true tumour progression from treatment-related change on post-therapy brain MRI is a frequent diagnostic challenge, because findings vary with treatment type and timing. Pseudoprogression is context-dependent-its definition, timing, and morphology differ across chemoradiotherapy, IDH-mutant glioma, stereotactic radiosurgery, and immunotherapy, so no single rule fits all settings.