Abstract
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.
Highlights
The hemangio blastomais common primary cerebellar neoplasm in the adult population.(2,3)Accurate preoperative diagnosis is an important goal in pediatric patients with cerebellar neoplasms, because the most common tumors in this location and age group, juvenile pilocytic astrocytoma (JPA) and medulloblastoma, may dictate the need for different surgical approaches and have significantly different natural histories and outcomes.( 4)Diffusion -weighted MR imaging exploits the phenomenon of diffusion, which is related to Brownian motion at the molecular level
Cerebellar neoplasms, between JPAs and medulloblastomas, indicate that these lesions could potentially be distinguished by their ADC values.( 12.21) The purpose of this study is To assess the value of diffusion weighted imaging and apparent diffusion coefficient in making distinction between the different histological types of posterior fossa tumors
Patients: This is a Prospective study conducted at MRI unit at AL-Imammain AL-Kadhimain medical city From December2014 through August 2015.the study was approved by the Ethics Committee of the Faculty of Medicine- Al Nahrain University and informed consent was obtained .the study included 19 Patients with newly diagnosed posterior fossa tumor for whom conventional & Diffusion-weighted imaging (DWI) MRI was performed &the type of the lesion was ascertained by histopathology postoperatively
Summary
Patients: This is a Prospective study conducted at MRI unit at AL-Imammain AL-Kadhimain medical city From December2014 through August 2015.the study was approved by the Ethics Committee of the Faculty of Medicine- Al Nahrain University and informed consent was obtained .the study included 19 Patients with newly diagnosed posterior fossa tumor for whom conventional & DWI MRI was performed &the type of the lesion was ascertained by histopathology postoperatively. Diffusion weighted MR imaging (DWI) : before the contrast enhanced imaging , routine diffusion - weighted MR imaging were obtained using single - shot multislice spin -echo EPI sequence (TR 5327, TE 162 ),and (TR 3700,TE141) with diffusion sensitivities of b values =1000s/mm . Image analysis : DW images visually inspected and classified as hyper intense , isointense ,or hypointense compared with normal white matter; The ADC map as obtained automatically for b-value (1000s/mm2) with a pixel -by pixel analysis, by using advanced work station software after DWI data acquisition. Avoiding the cystic and necrotic areas and for the contralateral white matter normal area by drawing the circular region of interest (ROIs) manually on all axial ADC map using the manufacturers software , the ROIs measurements varied from 40-80 mm[2] for tumor. Statistical study: T-test was conducted calculating the difference in the mean ADC value and the mean ADC ratio between different posterior fosse tumors P
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