Background: Conventional MR imaging is essential for diagnosis and evaluation of the posterior fossa tumors Objectives: To assess the value of diffusion weighted imaging and apparent diffusion coefficient in making distinction between different histological types of posterior fossa tumors.
Type of the study: Cross-sectional study.
Methods: Brain MRI and DWI assessed 19 patients (12 female and 7 male) with MRI diagnosis of posterior fossa tumors. absolute ADC values of contrast -enhancing solid tumor region and ADC ratio of solid tumor to ADC of normal -appearing deep White matter were compared with histological diagnosis postoperatively .The mean ADC value and ratio were determined by using a 2-tailed T test. Results: In eight of medulloblastoma ,The mean ADC value was 0.67±0.14x 10-3 mm 2/s and ratio 0.86±0.19 , ependymoma (n=3), ADC value 1.09 ±0.14 x10 -3 mm 2 /s and ratio 1,43±0.13 , pilocytic astrocytoma (n=4) ADC value 1,72 ±0.27x10 -3 mm2/s and ratio 2.19±0.4, brainstem glioma (n=2) with ADC value1.18±0.06 x10-3mm2/s and ratio 1.64±0.08 , haemangioblastoma (n=1) with ADC value1.46x10-1mm2/s and ratio 1.87 , and meningioma with ADC value 0.72x10-3mm2/s and ratio 0.85. ADC values were higher in JPA than in ependymomas and medulloblastoma (P value <o,o5).ADC ratio were also statistically significant difference among these three tumors type .
Conclusion: calculation of apparent diffusion coefficient value in the solid enhancing portion of tumor seems to be reliable for differentiate between medulloblastoma at one end and , juvenile pilocytic astrocytoma (JPA) and ependymoma at other end as the former has ADC of < 1 while other tumors have ADC value of >1.
