BM-31STUDY OF INCIDENCE AND ESTIMATION OF RISK FACTORS ASSOCIATED WITH HIPPOCAMPAL METASTASIS.

BACKGROUND: Modern radiation techniques are being used to attempt hippocampal-sparing whole brain RT in brain metastasis in order to minimize neurocognitive decline. However this technique is accompanied by potential risk of hippocampal recurrence. AIMS: To evaluate the incidence of metastasis in the hippocampal region and identify factors which can predict the occurrence of metastasis in this region. METHOD: Pre-treatment MRIs of 40 cases(median age 55)with single or multiple brain metastases between Jan 2010-Dec 2013 were analysed. The hippocampus was contoured on 1mm thick planning-MRI on T1 image as per RTOG guidelines. All gross lesions were contoured, volume and minimum distance from hippocampus measured. Hippocampus was expanded by 5mm to represent peri-hippocampus. All lesions within this volume were considered as "hippocampal region metastases". Various clinical parameters were analysed by Pearson's test for correlation with presence of hippocampal disease. RESULTS: A total of 120 lesions were found in 40 patients.Incidence of metastasis in the hippocampal region was 20%(7.5% intra-hippocampal, 12.5% peri-hippocampal) of which 50% had breast primary, 27.5% lung,12.5% endometrium. Primary was controlled in 62.5%, 62.5% had received chemotherapy before diagnosis of brain metastasis. 87.5% of patients with hippocampal disease also had lung metastasis. Median aggregate volume and number of brain metastasis was 5.5cc and 2,while in those with hippocampal disease it was 23.81cc and 6. Among the parameters tested for correlation with presence of hippocampal metastasis, median aggregate volume(p = 0.001) and number of metastasis (p = 0.0001) had significant correlation, while presence of lung metastasis had a trend towards significance (p = 0.09). CONCLUSION: Metastasis in the hippocampal region are more likely to be present in patients who have larger number, larger aggregate volume of brain metastases and advanced systemic disease(lung-metastasis).