Imaging of the urinary system

Kidney stone disease

Kidney stone disease, also called nephrolithiasis or urolithiasis, refers to the presence of kidney stones in the urinary tract. When stones are present in the ureter it may be called ureterolithiasis, while stones in the bladder are usually simply called bladder stones or bladder calculi. It's a relatively common condition, with a lifetime prevalence of 10 - 20 percent.

Imaging

A low-dose non-contrast CT is usually the first choice as this has little radiation exposure and can detect the majority of stones. Ultrasonography is a reasonable alternative first choice, especially in pregnant and children, but many stones are not visible on ultrasound (70% sensitive and specific). Kidney, ureter, bladder (KUB) radiography was previously widely used, but it is not sensitive and so is rarely used nowadays.

If the stone causes urinary obstruction, one may see hydronephrosis and dilated proximal ureters.

Acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome which is characterised by an acute decrease kidney function (GFR) (over hours or days), as evidenced by elevated creatinine. There may also be accumulation of urinary waste products and oliguria/anuria, but not always. The cause may be prerenal, renal, or postrenal, but the most common causes are prerenal and acute tubular necrosis.

During the evaluation it’s important to determine whether it’s really acute or chronic, and to determine the underlying cause. Management includes treating the cause and correcting severe electrolyte disturbances. In some cases, renal replacement therapy may be required.

The condition is nowadays called acute kidney injury rather than acute renal failure.

Diagnosis and evaluation

In case of AKI, the kidney is usually enlarged, which can be visualised on ultrasonography. Ultrasound may also reveal an underlying cause and is therefore usually the first choice imaging modality for AKI.

Chronic kidney disease

Chronic kidney disease (CKD), previously called chronic renal failure is defined as the presence of either kidney damage or decreased kidney function for more than 3 months. Decreased kidney function is measured by decreased GFR.

Diagnosis and evaluation

Kidneys with CKD have abnormal morphology. On ultrasound the following features are seen:

Decreased size of kidney (< 100 mm)
Thinning of cortex (< 10 mm)
Irregular surface

Renal scintigraphy may be used to precisely determine the kidney function of each kidney.

Glomerulonephritis

Glomerulonephritis refers to a disease affecting the glomeruli, even though inflammation itself (-itis) is not necessarily present. Glomerulonephritis is rare, and it can cause severe symptoms and chronic kidney disease.

Diagnosis and evaluation

On ultrasonography, the kidney is enlarged and has hyperechoic parenchyme.