P14.09 Incidence of left-right hippocampal metastases:analysis of 473 patients with 4063 brain metastases
Authors: A. Kuklova, T. Kazda, P. Burkon, P. Pospisil, L. Hynkova, A. Dziacky, R. Belanova, R. Lakomy, P. Slampa, R. Jancalek
Journal: Neuro-Oncology (2017)

INTRODUCTION: Strategies for preservation of memory function in patients irradiated for brain metastases (BM) are currently widely investigated. Rare presence of BM within hippocampus (Hipp), where neuronal stem cells involved in memory formation are harbored, led to development of Hipp avoiding (HA) whole brain radiotherapy (WBRT). However, this HA zone may be undertreated with the risk of subsequent BM recurrence. Some reports indicate postWBRT cognitive impairment may be associated particularly with unilateral Hipp radioinjury. The question arises, thus, sparing of only unilateral (left, respective dominant) Hipp may be also superior in terms of decrease of undertreated volume of brain. It would be useful to know, whether there is some difference in incidence of BM within left vs. right Hipp, however, no previous study assessed the sidedness of Hipp BM seeding. The aim of presented retrospective study is to describe spatial distribution of 4063 BM and to evaluate distribution separately in the left and right Hipp. METHODS: Consecutive patients with BM referred to radiotherapy from 2011 till 2014 were analyzed. The first MRI or CT scan revealing BM was retrieved to describe distribution of BM. For those with BM in proximity to Hipp, both Hipp were contoured (RTOG contouring atlas) and expansion of 5mm was performed to create HA zone. All BM in proximity were delineated for recording of contact to Hipp or to HA zone. RESULTS: Mean age 60, most common primary diagnosis lung cancer, 50.3 % mens. Only 45 % had MRI for analysis. In our cohort, solitary BM was in 153 (32%) patients, median number of BM per patient was 3 with interquartile range 1-7, most commonly cerebellum and frontal lobes. BM within left and right temporal lobe were described in 23 and 23.5 % of patients. 114 patients (24%) were considered to have BM in proximity to Hipp. Overall, 8.2 % of patients developed BM within Hipp and 17.5 % within HA zone, representing 1.2 and 3.3 % of all BM, respectively. There was no difference in sidedness of Hipp or HA BM. Left and right Hipp were involved in 4.2 and 5.1 % of patients (HA involvement in 10.6 and 10.1 % of patients). Left and right Hipp BM represented 0.5 and 0.7 % of all BM (HA zone BM 1.6 and 1.7 % of all BM). DISCUSSION: As expected, no significant difference in sidedness of Hipp or HA BM was observed in our cohort. More BM was described within Hipp of HA zone comparing to previously published cohorts. This may be related to higher number of BM diagnosed (median 3, mean 9 BM per patient) in our non-selected consecutive cohort as well as to limited availability of MRI for early diagnosis of solitary BM. CONCLUSION: No difference between involvement of left and right hippocampus was retrospectively observed in large consecutive cohort of 473 patients. Incidence of hippocampal BM in our cohort was higher comparing to previous studies. Superiority of HA WBRT must be confirmed in ongoing phase III clinical trials.