The aim of this study is to determine whether the distribution pattern of intratumoral susceptibility sign (ITSS) derived from susceptibility-weighted imaging (SWI) could differentiate glioblastoma multiforme (GBM) and single brain metastasis.Nineteen intracranial brain neoplasm patients (19 male, age 69.4 ± 7.1 years (mean ± SD), 7 with non small cell lung cancer (NSCLC) metastases, 5 with small cell lung cancer (SCLC) metastases, 2 with renal cell cancer (RCC) metastases, and 5 with glioblastomas WHO IV), underwent examinations that included SWI in addition to conventional magnetic resonance (MR) sequences on a 3T, were enrolled in this study. Two radiologists investigated the distribution patterns of ITSS of the tumors and applied an ITSS grading system based on the degree of the ITSS. Then, we compared the grade of the visibility of ITSS in the central portion of tumors (CITSS) and in the tumor capsular area (PITSS) on SWI in consensus. Magnetic ITSS were defined as either linear or dot like foci of low signal intensity on SWI, which are not obvious on conventional MR imaging. The frequency of ITSS was assessed and graded on a scale of 1-4. Grade 1 was defined as no ITSS, grade 2 as 1-5, grade 3 as 6-10, and grade 4 as more than 10 of either linear or focal foci of low signal intensity on SWI. For statistical assessment of the comparison of each sequences ratings of the visibility of tumor margin and the visibility of internal architecture of tumors, Student t-test (p < 0.05) was used.The mean visibility scores of the CITSS in GBM and SCLC brain metastases were significantly higher than NSCLC and RCC brain metastases. The mean visibility scores of the PITSS in GBM and SCLC brain metastases were significantly lower than NSCLC and RCC brain metastases (p < 0.05, Student t-test) (Figure 1). Graphical illustration of the ratio of score of the visibility of the ITSS in the central portion of the tumor versus tumor capsular area of the different tumor histological groups is presented in Figure 2. Figure 3, 4 show examples of different distribution pattern of the CITSS, PITSS in GBM and NSCLC metastasis. MRI is currently the main imaging modality in the detection and diagnosis of brain tumors. Gross anatomical features of tumors in the brain can be assessed by conventional MRI sequences. Further characterization is commonly performed with postcontrast T1 to depict areas with impairment of the blood-brain barrier caused by tumor growth. To increase the specificity and sensitivity of conventional MRI, more functional approaches such as proton MR spectroscopy, perfusion-weighted imaging, and diffusion-weighted imaging, are increasingly added to clinical examinations of patients with tumors. But it is frequently necessary to perform histopathological diagnosis on a biopsy. As shown by the previous report, SWI was much more sensitive for showing blood products, calcifications, and venous vasculature, which usually appeared as low-signal intensity structures on SWI. These low-signal intensity structures detected on SWI may not be obvious on conventional MR imaging but could be useful in tumor characterization, tumor grading, or diagnosis of specific tumor type. The findings of our study show that although the SWI was unable to differentiate between GBM and SCLC brain metastasis, differentiation was achieved between GBM and the other brain metastases using the ITSS distribution pattern of the brain tumors. The distribution pattern of ITSS derived from SWI could be helpful to differentiate GBM and single brain metastasis.