TKV and ADPKD:- worth knowing

Autosomal Dominant Polycystic Kidney Disease: what is role of Imaging? Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and is the fourth leading cause of end stage renal disease (ESRD).1 • The disease causes development of numerous cysts that cause significant increases in total kidney volume (TKV) during an affected patient’s lifetime and may ultimately lead to ESRD requiring dialysis or kidney transplant.2 • In the majority of patients, this genetic disease is caused by mutations in either of two genes, known as Pkd1 and Pkd2. Patients with a mutation in Pkd1 reach ESRD at 50 years of age on average, whereas patients with a mutation in Pkd2 reach ESRD at 70 years of age on average.3 Significance of Imaging • Measurement of TKV by radiological imaging is the best way to measure disease progression in these patients as other factors like renal function remain relatively stable for many years before a drastic decrease in function is observed. Therefore, measurement of TKV is critical for disease staging, and classification systems have been developed based on age and TKV which can differentiate slowly from rapidly progressing patients.4,5 • Diagnosis is often made by ultrasound and follow-up (to assess disease progression) is most commonly performed by MRI.6 • Methods for measuring TKV include ellipsoid-based (where kidney length, width, and depth are measured and the kidney volume is then approximated as an ellipse), stereology-based (where a grid overlay is placed over the images and a user highlights those grid points which are positioned over the kidneys), and planimetry-based (where a user traces the kidneys in each slice of the acquired 3D volumetric image). These methods all have trade-offs in terms of efficiency and accuracy, with ellipsoid-based methods being the easiest and fastest, whereas planimetry takes the longest amount of time but is the most accurate. • Measurement of TKV needs to be as accurate as possible as there is a wide range of phenotypic variability in disease progression, even for patients with the same mutation from the same family. • Determination of rapid progressors requires measurement of TKV and is important for treatment decisions, as well as for stratification in clinical trials.7 • Radiological imaging and the practicing radiologists play a critical role in the management of patients affected by ADPKD. The partnership between the radiologist and nephrologist is critical for diagnosis, prognosis, and clinical decision making.