الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
DWI is non invasive technique that added to value of magnetic resonance imaging in differentiating between begin and malignant non traumatic orbital lesions. Most of malignant lesions have restricted diffusion while most of benign lesions have free diffusion. Malignant lesions have lower apparent diffusion coefficient (ADC) values than benign ones. The present study aimed at evaluation of the role of Diffusion- Weighted MRI in the characterization of the non traumatic orbital lesions and differentiation between benign and malignant ones. This prospective study was conducted on 30 patients with nontraumatic orbital lesions referred to radio-diagnosis and medical imaging department at Tanta University Hospitals throughout period extending from July 2018 to August 2020. 16 (53.3%) cases were females and 14 (46.7%) cases were males, their ages ranged from 2 - 60 years with a mean age of 37.70 ± 19.78 years. By histopathology; 14 were benign orbital lesions and 16 were malignant orbital lesions. All patients submitted to the following: 1.Clinical assessment by ophthalmologist. 2.Laboratory investigations including total and differential leucocytic counts, erythrocytic sedimentation rate and thyroid function tests. 3. Radiological assessment including: Conventional MRI, MRI with contrast for selected patients, Diffusion weighted MRI and ADC . Facilitated diffusion (low signal intensity at DWI and high at ADC maps) was found in 16 cases with ranged ADC value from 1.2 - 1.9 x 10-3 mm2/sec. Restricted diffusion (high signal intensity at DWI and low at ADC maps) was found in 14 cases with ranged ADC value from 0.5- 0.90 x 10-3 mm2/sec. We reported the mean ADC values of benign and malignant orbital lesions were 1.58 ± 0.21 mm2/s and 0.73 ± 0.15 mm2/s respectively. The mean ADC values of benign lesions were significantly higher than that of malignant orbital lesions. We noticed no restricted diffusion detected within benign orbital lesions (14 cases). Also 14 cases with pathologically proved malignant lesions showed restricted diffusion, however 2 malignant cases; one with optic glioma and other with orbital metastasis showed free diffusion with ADC values measured (1.8 x 10-3 mm2/sec and 1.2 x 10-3 mm2/sec) respectively (false negative result), so the presence of free diffusion not exclude malignancy. The cut off value of ADC of ≤ 1.0 x 10-3 had sensitivity 87.5 %, specificity 100%, and positive predictive value 100 % and negative predictive value 94.92 % to distinguish between benign and malignant orbital mass lesions. The outcomes of the current study showed clear differences between malignant and benign lesions. The absolute ADC value of lesions was significantly different between benign and malignant orbital lesions(p<0.001). Hence, the ADC value can be considered a biomarker to differentiate malignant and benign orbital lesions.