Urinary Tract Infection on CT

Urinary tract infections can involve the bladder, ureters and kidneys.   Urinary tract infections occur when bacteria infect the urinary tract, although other organisms like fungus and tuberculosis can also be involved.   Patients with urinary tract infection present with painful urination, frequent urination, flank pain, cloudy or bloody urine, and systemic symptoms like fever and chills.

Uncomplicated versus complicated urinary tract infections

Urinary tract infections are divided into uncomplicated and complicated types of infections.  Uncomplicated infections occur in healthy patients who have a normal urinary tract.  Complicated urinary tract infections make therapy less likely to be effective.  This can be because of structural abnormalities of the urinary tract.  Certain patient factors like being immunocompromised, elderly or pregnant.

When should a urinary tract infection be imaged?

Uncomplicated types of infections are treated with antibiotics.   Imaging is often not suggested but still often done to exclude other possibilities, complicating factors or when symptoms and lab testing is not conclusive.    Complicated urinary tract infections will be imaged to look for abscess (pocket of pus) or structural abnormalities of the urinary tract.

Bladder infection

Infection of the bladder will demonstrate wall thickening on CT.  There may be haziness of the fat surrounding the bladder.  Not all bladder infections will show up on CT.  A bladder which is not completely filled may look like it has a thick wall and mimic a bladder infection.   Bladder infections can be complicated with gas formation in the wall or bleeding.

Kidney infections

Kidney infections are called pyelonephritis.   They are more common in women.  They present with fevers, flank pain and tenderness.   Bacteria gain access to the bladder and then extend up the ureters to the kidneys.  Imaging is often reserved for patients who may have an obstructed infected kidney, structural abnormalities or those who are at risk like the immunocompromised.

CT for pyelonephritis is best done with contrast given through the vein.  Often there will be areas of low density abnormality involving the kidney.  There may fluid or haziness of the fat surrounding the kidney.  The renal pelvis and ureters which pass urine to the bladder may look thickened.  Complicated cases may show an abscess in the kidney.  An obstructed infected kidney is an emergency and needs to be treated by relieving the obstruction.

Urinary tract infections which occur in healthy patients without known structural abnormalities are often not imaged and responds well to antibiotics.  Those which are complicated or occur in sick or immunocompromised patients will often be imaged.  Urinary tract infections are often evident based on clinical symptoms and lab abnormalities.  Imaging will often confirm the suspicion of a urinary tract infection.  Imaging may also show structural abnormalities of the urinary tract which may make treatment less effective.