QOS-58: IMPACT OF CRANIAL RADIATION THERAPY ON HIPPOCAMPAL SUBFIELD VOLUMES AND DECLARATIVE MEMORY IN PEDIATRIC BRAIN TUMOR SURVIVORS

BACKGROUND: Cranial radiation therapy (CRT) is associated with declarative memory impairment and hippocampal volume loss in pediatric brain tumor survivors (PBTS). Animal studies suggest that this may reflect arrested neurogenesis in the dentate gyrus, the neurogenic region of the hippocampus. However, little is known about the distribution of CRT-induced volume loss across hippocampal subfields in humans and how this relates to memory. The goal of the present study was to characterize hippocampal subfield volume loss and relations to memory performance in PBTS. METHODS: MRI scans were obtained for 19 PBTS treated with CRT and 19 age- and sex-matched controls. An automated segmentation algorithm was used to segment hippocampi in each hemisphere into CA1, CA2/3, dentate gyrus (DG)/CA4, stratum radiatum/lacunosum/moleculare (SR/SL/SM) and subiculum. A subset of patients completed a paired associate verbal memory test from the Children's or Wechsler's Memory Scale (n = 11). RESULTS: Global hippocampal volumes were reduced bilaterally in PBTS (p = 0.002), but not all subfields differed significantly between groups. Bilateral DG/CA4 (p = 0.049) and SR/SL/SM (p = 0.019) were significantly smaller in patients. Diagnosis age in patients correlated with DG/CA4 (r = 0.57) and SR/SL/SM (r = 0.77) volumes, with younger diagnosis age predicting smaller volumes. Left DG/CA4 volume correlated with memory performance (r = 0.72), with smaller volume predicting poorer performance. CONCLUSION: Hippocampal subfields are differentially vulnerable to CRT, with DG/CA4 and SR/SL/SM displaying particular compromise. Patients diagnosed at younger ages may be at the greatest risk for volume loss. The brain-behavior relationship that we observed suggests that DG/CA4 compromise may contribute to impaired memory in PBTS.