Stranding around kidneys means that the normally dark fat surrounding kidneys becomes brighter and patchy in appearance. This is a common finding which can be around one or both kidneys. Stranding around the kidneys may or may not be associated with symptoms or other abnormalities of the kidneys.
Stranding around both kidneys
Stranding around both kidneys is very common on CT scans done and is often asymptomatic and benign. This is especially true in older patients. Stranding around both kidneys can be barely noticeable to extensive with pockets of fluid.
In most cases, this is not associated with other abnormalities of kidneys or lab abnormalities in my experience. It may be described in the report to alert the clinical doctor to a potential abnormality of the kidneys. This is done so that the clinical doctor can order appropriate testing or to consider the kidneys as a potential cause of the presentation.
Stranding around one kidney
Stranding of the fat around one of the kidneys is more concerning. This often indicates that there is an abnormality of the kidney. Most commonly, I see this when a patient is passing a stone and there is a blockage of the kidney. In these cases, we will see the stone in the ureter and a dilated kidney collecting system on CT. Stranding is a reaction to the stone passage and blockage of the kidney. Stranding is not the only finding in this case.
Stranding around one of the kidneys can also be seen with infection of the kidney or pyelonephritis. In these cases, the patients will have pain in the flank and fever. On a CT without contrast given through the vein, we may only see stranding around the kidney. Abnormalities of the kidney may not be seen.
When we give contrast, we may see abnormalities of the kidney itself. There may be darker patchy areas in the kidney extending to the periphery. The collecting system of the kidney may also be slightly dilated related to the infection. There will also often be stranding around the kidney.
Less common causes of stranding about a kidney
Stranding around a kidney can also be seen with less common abnormalities. Infarcts of the kidney happen when there is a blockage of the artery feeding the kidney. A renal vein thrombus can also result in some stranding around the kidney. Stranding around the kidney can be seen after procedures like biopsies or surgery.
Stranding of the kidneys on CT is a common finding. Stranding around both kidneys is often a benign incidental finding. It is often mentioned so that the clinical doctor can be made aware of a potential abnormality of the kidneys and do appropriate lab testing and clinical evaluation.
Stranding around one kidney is more concerning for a blockage or infection. Often the CT will show additional abnormalities which will give us the reason for the stranding. The clinical evaluation is important because it also give us clues to the most likely diagnosis.