Tehran University of Medical Sciences Current Journal of Neurology 2717-011X 14 1 2015 03 15 29 34 Mousa Reza Anbarloui Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Seyed Mohammad Ghodsi Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Alireza Khoshnevisan Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Masoud Khadivi Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Sina Abdollahzadeh Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Ahmad Aoude Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Soheil Naderi Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Zeynab Najafi Department of Pediatrics, School of Medicine AND Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran. Morteza Faghih-Jouibari Department of Neurosurgery, School of Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 14 Background: Distinction between radiation necrosis and recurrence of intraparenchymal tumors is necessary to select the appropriate treatment, but it is often difficult based on imaging features alone. We developed an algorithm for analyzing magnetic resonance spectroscopy (MRS) findings and studied its accuracy in differentiation between radiation necrosis and tumor recurrence. Methods:   Thirty-three   patients   with   a   history   of intraparenchymal brain tumor resection and radiotherapy, which had developed new enhancing lesion were evaluated by MRS and subsequently underwent reoperation. Lesions with Choline (Cho)/N- acetyl aspartate (NAA) > 1.8 or Cho/Lipid > 1 were considered as tumor recurrence and the remaining as radiation necrosis. Finally, pre-perative MRS diagnoses were compared with histopathological report. Results: The histological diagnosis was recurrence in 25 patients and necrosis in 8 patients. Mean Cho/NAA in  recurrent  tumors  was  2.72,  but  it  was  1.46  in radiation necrosis (P < 0.01). Furthermore, Cho/Lipid was significantly higher in recurrent tumors (P < 0.01) with the mean of 2.78 in recurrent tumors and 0.6 in radiation     necrosis.    Sensitivity,    specificity,    and diagnostic accuracy of the algorithm for detecting tumor recurrence were 84%, 75% and 81%, respectively. Conclusion: MRS is a safe and informative tool for differentiating    between   tumor   recurrence   and radiation necrosis. https://ijnl.tums.ac.ir/index.php/ijnl/article/view/576 https://ijnl.tums.ac.ir/index.php/ijnl/article/download/576/226