Hippocampal Atrophy Following Therapeutic Irradiation of Intracranial and Nasopharyngeal Tumors

The review aims to summarize and evaluate existing data on macroscopic changes in hippocampal volume following therapeutic brain irradiation, with a focus on the patterns, dynamics, and modulating factors of this structural damage. This narrative review is based on a structured search of the PubMed/Medical Literature Analysis and Retrieval System Online (MEDLINE) database and relevant bibliographies (2000-2025), selecting studies that applied MRI volumetry to assess hippocampal changes after radiotherapy. We summarized the results of studies using MRI volumetry in patients undergoing radiation therapy for central nervous system tumors and nasopharyngeal cancer. The analysis covered various irradiation methods, including local and whole-brain techniques, with a focus on dose-volume relationships, temporal dynamics, and differential vulnerability of subfields. The data indicate a marked, dose-dependent reduction in hippocampal volume following irradiation. The degree of atrophy, often reaching 5-9% in the early years, significantly exceeds normal age-related decline and may rival that seen in neurodegenerative pathologies. Certain subregions, particularly the dentate gyrus and CA1, show particular sensitivity. The temporal development of atrophy varies, showing both rapid initial loss followed by stabilization and progressive patterns. The pediatric population may show partial recovery of the growth trajectory, albeit with a reduced baseline. Critical factors influencing the degree of atrophy include patient age and, potentially, neoadjuvant chemotherapy, while concurrent chemotherapy is often not a determining factor. Quantitative assessment of hippocampal volume change is a reliable and objective biomarker of radiation-induced neurotoxicity. This parameter is an important tool for refining hippocampal radiation dose constraints in radiation therapy planning and for functional assessment after treatment, highlighting the need to incorporate hippocampal protection strategies into modern neuro-oncology practice.