Cystic Renal Masses: characterization with Diffusion- Weighted Imaging versus ContrastEnhanced Magnetic Resonance Imaging
Authors: Hanafi Hanan Mohammed , Botros Samer Malak , Nagi Mona Ali Mohamed Ali , Shaikhli Nameer Hashim Abduljabbar Al 
Published: August 2023

Purpose
To compare the diagnostic performance of magnetic resonance imaging (MRI), and MRI with diffusion-weighted imaging (DWI) in the characterization of cystic renal lesions.

Materials and Methods
Thirty-six adult patients underwent MRI (at 1.5 T), and DWI (at b-values of 0, 400 and 800 s/mm2) for characterization of 63 cystic renal lesions. There were 16 malignant renal cystic lesions (9 cystic clear cell RCC, 4 cystic papillary RCC, 3 massively necrotic RCC) opposite to 37 benign renal cystic lesions, 6 renal abscesses and 4 renal hemorrhagic cysts. A composite reference standards including histology, typical imaging criteria, and follow-up imaging was employed. To determine the diagnostic performance of imaging modalities, area-under-curve (AUC) was calculated by receiver-operating-characteristic analysis and compared. Fisher's exact test was used to compare the diagnostic accuracies and confidence levels with MRI, and MRI + DWI. Furthermore, DWI-ADC cutoff point to detect malignant cystic renal lesions, had been estimated and its diagnostic performance had been tested in term of sensitivity and specificity, PPD and NPV as compared to that of CE-MRI

Results
AUC for CE-MRI (0.915) and DW-MRI (0.834) in the differentiation between benign and malignant lesions (among all study cases) were within corresponding 95% confidence interval (CI) (P &gt; 0.5), furthermore A cutoff ADC point of ≤ 2.26 x10 − 3 mm2/s can be considered as diagnostic threshold for malignant cystic renal lesion lesions (among all study cases) with 87.5% sensitivity, 87.2% specificity, 70.0% PPV, 95.3% NPV, opposite to 100% sensitivity, 82.9% specificity, 66.7% PPV, 100% NPV for the CE-MRI. AUC for CE-MRI (0.976) and DW-MRI (0.917) in the differentiation between benign and malignant lesions (after exclusion of renal abscess and renal hemorrhagic cysts from study cases) were within corresponding 95% confidence interval (CI) (P = &gt;0.5), A cutoff ADC point of ≤ 2.84 x10 − 3 mm2/s could be considered as diagnostic threshold for malignant cystic renal lesion lesions (after exclusion of renal abscess and renal hemorrhagic cysts from study cases) with 93.7% sensitivity, 91.9% specificity, 83.3 PPV, 97.1 NPV, opposite to 100% sensitivity, 95.12% specificity, 88.9% PPV, 100% NPV for the CE-MRI.

Conclusions
Our study showed that malignant cystic renal masses had tendency toward restricted diffusivity and significant lower ADCs in comparison to benign ones, and diagnostic performance of DWI-ADC at b-value of 0-400-800 s/mm2 appeared as efficient as that of CE-MRI in differential between benign and malignant cystic lesions, especially when usage of contrast medium is contraindicated, however there is noticeable ADC overlapping among some malignant and benign lesions, specifically for renal carcinomas versus renal abscesses as well as for renal cell carcinoma versus renal hemorrhagic cysts, For such situation we need to consider clinical data, follow up notes, and correlates with findings of conventional MRI to optimize the characterization of cystic renal lesion before establishment of proper management plan.