An ultrasound is a noninvasive procedure that can measure the size and shape of the kidneys. Many different conditions can cause an enlarged kidney and ultrasound is a useful procedure for finding these changes. Some of these conditions may involve only one kidney, while others may cause bilateral changes. In order to differentiate which condition may be causing the kidney issues, the physician will need the patient's history and other tests like blood and urine along with the ultrasound results.
Acute Pyelonephritis
Pyelonephritis is an infection of the kidneys, which can be caused by a urinary tract infection or by an infection in the bloodstream, according to the Merck Manual. Women are more likely to develop pyelonephritis due to the anatomy of the urinary tract; women can also develop this infection during pregnancy. Any type of obstruction, like kidney stones or an enlarged prostate, to the flow of urine can make it easier for pyelonephritis to develop. On ultrasound, one or both kidneys may be enlarged, according to John P. McGahan and Barry B. Goldberg in the 2008 book, "Diagnostic Ultrasound, Volume 1."
Renal Vein Thrombosis
Another cause of an enlarged kidney on ultrasound examination is a renal vein thrombosis. A renal vein thrombosis occurs when a blood clot forms or lodges in the vein that takes blood away from the kidney. This condition can be caused by blood clotting disorders, kidney cancer or diabetes. The kidney may appear enlarged on ultrasound, but the best way to diagnose this condition is by using a doppler, as noted by John P. McGahan and Barry B. Goldberg in the 2008 book, "Diagnostic Ultrasound, Volume 1."
Hydronephrosis
In hydronephrosis, a back flow of urine causes the kidney to enlarge. This can be caused by an obstruction like a structural abnormality or stones at the place where the kidney meets the ureter, which is the tube that carries urine to the bladder. An obstruction can also occur lower in the urinary tract system like at the bladder, as well, according to the Merck Manual. Hydronephrosis can be seen in fetuses during pregnancy and may also be seen in pregnant women. This condition can lead to pyelonephritis in some patients. On ultrasound, the kidney appears enlarged and the cause of the obstruction may also be obvious, as noted by John P. McGahan and colleagues in the 2008 book, "Diagnostic Ultrasound, Volume 1."
Polycystic Kidneys
Polycystic kidney disease is a hereditary condition in which the kidneys develop multiple cysts; this increases the size of the kidneys according to the U.S. National Library of Medicine. These cysts destroy healthy kidney tissue and can lead to kidney failure and high blood pressure. This condition affects both kidneys. On ultrasound, the radiologist will be able to see the multiple cysts on the kidneys.
Tumor in the Kidney
Cancer that begins in the kidneys can make the kidney appear enlarged on ultrasound. This condition usually only affects one kidney. The patient may have blood in the urine and back pain. On ultrasound, the cause of the enlargement--the tumor--in the kidney will be obvious, as noted by John P. McGahan and Barry B. Goldberg in the 2008 book, "Diagnostic Ultrasound, Volume 1." Further evaluation will be needed to determine the type of tumor and further treatment.
References
- Diagnostic Ultrasound, Volume 1; John P. McGahan, Barry B. Goldberg; 2008.
- Merck Manual: Kidney Infection
- Merck Manual: Renal Vein Thrombosis
- Merck Manual: Hydronephrosis
- U.S. National Library of Medicine: Polycystic Kidney Disease
