Our study describes the time course of necrotic damage to the rat brain resulting from Leksell Gamma Knife (LGK) irradiation at a dose that was previously considered to be subnecrotic. A lesion induced in the rat hippocampus by 35 Gy irradiation was monitored by MRI, MRS, and DW-MRI for 16 months. T2-weighted images revealed a large hyperintense area with an increased apparent diffusion coefficient of water (ADCw), which occurred 8 months after irradiation, accompanied by metabolic changes (increase of lactate (Lac) and choline (Cho), and decrease of creatine (Cr) and N-acetyl aspartate (NAA), as determined by MRS) that indicated an edema. In two animals, the hyperintensity persisted and a postnecrotic cavity connected to enlarged lateral ventricles developed. In the rest of the animals, the hyperintensity started to decrease 9 months post-irradiation (PI), revealing hypointense areas with a decreased ADCw. Histology confirmed the MRI data, showing either scar formation or the development of a postnecrotic cavity.