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Urinary Imaging

E2713. Ultrasound SERVeillance of Acute Kidney Injury: Size, Echogenicity, Renal Hilum, and Vascularity

Kelahan L,  Kamaya A. Stanford University, Stanford, United States

Address correspondence to L. Kelahan (lkelahan2@gmail.com)

Background Information: Ultrasound can be a helpful tool in assessing acute kidney injury and in identifying potentially reversible etiologies. Acute kidney injury (AKI) can be defined as an increase in serum creatinine or decreased urine output occurring over less than a week. AKI is either reversible or persistent. The causes of renal injury are often multifactorial. Having a consistent search pattern and logical differential diagnosis can facilitate appropriate patient management in these time-sensitive renal evaluations.

Educational Goals/Teaching Points: Clinical categories of renal injury include: prerenal, renal, and postrenal etiologies. The imaging manifestations of renal injury can be simplified by evaluating the following characteristics: size, echogenicity, appearance of the renal hilum, and vascularity (SERVeillance). These renal imaging abnormalities can help narrow the clinical differential and guide management to preserve nephrons from further injury. This presentation will guide the learner through this search approach and provide a differential diagnosis for each aberration.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Abnormal renal size has a differential based on whether the kidney is too large or too small, but also whether one or both kidneys are affected. For example, increased renal size, if bilateral, can suggest a differential of HIV-associated nephropathy, lymphoma, multiple myeloma, and amyloidosis. Increased renal echogenicity can be seen in both acute and chronic kidney injury. Chronic kidney disease is recognized by increased parenchymal echogenicity due to underlying fibrosis, cortical thinning, and small size due to atrophy. Normal echogenicity in acute kidney injury can be seen in primary glomerular pathology as glomeruli make up only 8% of renal parenchyma. However, when present acutely, increased parenchymal echogenicity is generally associated with an intrinsic etiology, most commonly, acute tubular necrosis. The differential also includes papillary necrosis, lupus nephritis, amyloidosis, leukemic infiltrate, and HIV-associated nephropathy. Evaluation of the renal hilum, with respect to the sinus fat and collecting system can reveal infiltrative tumor, inflammation, or hydronephrosis. Abnormal perfusion of the kidney can be seen in pyelonephritis, renal artery stenosis, and aortic dissection.

Conclusion: Having an understanding of how renal ultrasound can identify reversible etiologies of acute kidney injury and potentially identify chronic renal disease is critical in helping direct further patient management. Rare renal pathology such as cortical necrosis can have pathognomonic ultrasound findings, rapidly narrowing the differential diagnosis. Reversible etiologies such as obstructive hydronephrosis can be identified and prompt appropriate intervention. Having a systemic search pattern (SERVeillance) and corresponding differential diagnosis facilitates the approach to ultrasound evaluation in the setting of acute renal injury.