الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Multi-phasic contrast enhanced multi detector computed tomography (MDCT) is the golden standard for imaging and characterization of renal masses; however, some lesions remain of equivocal nature. When contrast media administration is prohibited, non contrast study is of little help. Recently magnetic resonance imaging (MRI) thanks to its new advances has improved as a problem solving technique in characterization of renal masses.
The aim of this work was to evaluate the additive value of the MRI with diffusion weighted imaging (DWI) in the characterization of the renal masses comparable with the multi-phasic contrast enhanced CT.
This study was conducted on 58 patients with 72 indeterminate renal lesion varying from solid renal tumors and complex renal cysts as well as 10 simple cysts. These data was collected in 26 months duration starting from September 2010.
All patients were subjected to full history taking, thorough clinical examination and laboratory investigations. Radiological investigations which included Plain X ray, US, MDCT and MRI using 1.5 tesla machines. Contrast administration in CT and MRI studies was performed as possible.
The final diagnosis was reached by histopathological examination in 58 lesions. In the remaining 24 lesions the diagnoses was based on the consensus of clinical and imaging modalities with follow up and monitoring therapeutic response was done for lesions diagnosed as renal abscesses.
The current study found significantly higher pre-contrast attenuation in papillary renal cell carcinoma (PRCC) than other RCC subtypes, High pre-contrast attenuation was also noted in lipid poor AML and transitional cell carcinoma (TCC).
Through multi-phasic MDCT study; solid renal masses can be classified according to their enhancement pattern into two groups with significant difference in the degree of enhancement between them at corticomedullary and nephrographic phases; the first group (61.9%) showed early enhancement with wash out pattern and includes clear cell renal cell carcinomas (CCRCC), oncocytomas, lipid rich angiomyolipomas (AML) and chromophobe renal cell carcinoma (CHRCC). The second group (38.1%) included the rest of the solid renal lesions which showed less degree of enhancement with no wash out pattern (gradual or prolonged enhancement pattern).
Heterogeneous enhancement was noted in solid malignant lesions with 100% specificity while internal scar was noted in oncocytomas and CHRCC, this central scar show delayed enhancement in three out of five lesions.
In non contrast conventional MRI sequences, T2-weighted sequence was a good method in assessment of tumor homogeneity; however, contrast enhanced studies was superior to it as it could not differentiate the internal scar from the central degeneration. Hypo-intensity in T2- weighted sequence was noted in PRCC, lipid poor AML and TCC. Conventional non contrast sequences were also able to differentiate solid from cystic lesions with the ability to assess the cystic lesions regarding their mural thickening, internal septa and the nature of their fluid content.
Dynamic contrast enhanced MRI (DCEMRI) confirmed the enhancement in solid lesions with mild CT enhancement, however, these lesions showed similar intensity and pattern of enhancement in both techniques, in renal cysts DCEMRI excluded enhancement in CT hyper-dense renal cysts that have been categorized by multi-phasic CT as Bosniak II and II f cysts.
Using diffusion weighted MRI (DWI), the current study found that restricted diffusion was noted in most of malignant lesions (47 out of 48 malignant lesion) and two benign processes including; renal abscess (n=2) where the restriction occurred in the central portion and in sub-acute hemorrhage (n=2) which showed hyper-intense signal in T1 weighted sequence. All the other renal lesions (n=31) showed no restricted diffusion. The current study found that the solid portion of lipid- rich AML showed mild restriction with overlapping ADC values with CCRCC; however, it can be predicted by the presence of fat.
By excluding renal abscesses, sub acute hematomas and lipid rich AML assuming that these lesions can be diagnosed by conventional MRI sequences, the current study found for differentiation malignant from benign renal lesions, a cut-off-point for ADC value of 1.45x10-3 m2/sec and for lesion to parenchymal ADC ratio of 0.72, both with sensitivity and specificity of 100%.
The current study compared the accuracy in differentiating benign from malignant renal lesions between MDCT and MRI; this was done using radiological indicators that gave specificity of 100% (the presence of fat as an indicator of benignity and the heterogeneous enhancement as an indicator of malignancy) as well as diffusion restriction in the soft tissue component of the lesion.
The current study found that in cases with renal insufficiency (23 lesions) the accuracy of non contrast MDCT was 39.1% while that of conventional MRI including DWI was 91.3%.
In cases that performed contrast enhanced CT (59 lesions included), the accuracy of multi-phasic contrast enhanced CT was 66.1% versus 98.3% for non contrast MRI with DWI.
In cases who performed contrast-enhanced CT and DCEMRI (39 lesions), the accuracy of multi-phasic contrast enhanced CT was 74.4%, DCEMRI without DWI was 79.4%, non contrast MRI with DWI was 97.4% and the MRI accuracy improved to 100% when both DWI and contrast administration were applied.