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Background
This study aims to estimate the total renal volume of patients with autosomal dominant polycystic kidney disease using simple MRI measurements.

Educational Goals / Teaching Points
Polycystic kidney disease is an autosomal dominant inherited genetic multisystemic disease (ADPKD) characterized by the presence of multiple cysts that progressively replace both renal parenchyma. It is the fourth leading cause of end-stage renal disease. Total renal volume (TRV) is a parameter used to stage and monitor patients with typical ADPKD. Besides being a good prognostic marker, it allows stratification of patients into slow or fast progressors. MRI is preferred for the measurement of TRV because it is radiation-free and avoids the use of iodinated contrast. In addition, it provides high-resolution images with tissue contrast that allows easy differentiation between complex and simple cysts.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Sagittal, coronal, and axial T1- and T2-weighted sequences of the totality of the kidneys, including liver and pancreas, were used. The Mayo Clinic (Rochester, MN) has developed a classification system that predicts the risk of renal function deterioration and classifies patients with typical ADPKD into five groups according to the risk of renal function deterioration. Measurements to obtain TRV are as follows. For each kidney separately, the length (sagittal and coronal plane), width, and depth (axial plane) are measured. Then the kidney volume calculator is used. This model has been developed by the Mayo clinic and published in 2015, which uses the ellipsoid formula to calculate renal volume and, in addition other patient characteristics such as age, height, and weight, is able to classify the patient into five categories according to their risk of progression to end-stage renal disease. Class 1A is an end-stage renal disease is not likely to be reached, low-risk. Class 1B is a slowly progressive disease, intermediate risk. Class 1C, 1D, and 1E is a rapidly progressive disease, high risk.

Conclusion
TRV has become an important prognostic biomarker in the context of ADPKD because it provides information on the severity and progression of the disease. Regardless of the measurement method used, the important thing is that it can determine small changes in renal volume throughout follow-up and during assessment of response to treatment; therefore, it is necessary and indispensable for our role as radiologists to know and master these tools to provide as much information as possible to the treating specialist.