Micturition ultrasonography is a special ultrasound diagnosis of the urinary tract and kidney using contrast media. Its main goal is to detect any backflow of urine from the bladder into the kidneys. Most often, this examination is performed in children who have had a urinary tract infection in which renal involvement was suspected because of accompanying fever.
What is micturition urosonography?
Micturition urosonography is a special ultrasound diagnosis of the urinary tract and kidney using contrast media. The term micturition urosonography (MUS) incorporates micturition (the emptying of the bladder), urology (medical specialty that deals with the organs that drain urine), and sonography (ultrasound examination of organs). The purpose of this examination, which is often performed on children, is to diagnose vesico-uretero-renal reflux (VUR), i.e. the backflow of urine from the bladder via the ureters to the kidney, with the help of contrast medium. It complements classical examinations such as normal ultrasound diagnostics as well as laboratory diagnostics, for example the examination of urine for germs as well as special blood tests. In order to record the physiological processes in the patient’s urinary tract not only as a snapshot, but also with regard to functional activity, the examination is also performed during urination or subsequent refilling of the urinary bladder. Frequently, color-coded Doppler sonography is used to visualize a possible VUR
because here the course of the contrast medium can be shown particularly accurately and in this way a very precise diagnosis can be made.
Function, effect, and goals
When children suffer a urinary tract infection that is accompanied by fever, it is suspected that the kidney is involved in the disease process. This is caused by germs entering the kidney via nonphysiologic reflux of urine from the urinary bladder. On the one hand, this reflux can occur due to congenital anatomical disorders (primary VUR), but it can also be caused by acquired defects such as surgical sequelae, inflammations or urinary outflow disorders (secondary VUR). To prevent kidney damage from common disorders of this type, any reflux must be detected promptly. Since classical sonography alone cannot do this, the accuracy of the diagnosis is considerably improved by micturition urosonography. At the start of the examination, a thin catheter is inserted into the bladder of the usually lightly sedated patient and a conventional ultrasound of the condition of the kidney and urinary organs is performed. The urinary bladder is then filled with a body-warm physiological saline solution and the contrast medium required for imaging is added. Already at this point, micturition urosonography can possibly provide the first important indications: If a reflux of the contrast-enriched fluid can already be seen here, low-pressure reflux, i.e. reflux already occurring when the bladder is full, can be assumed. In the further course of the examination, the movement of the contrast medium during micturition is observed sonographically. If urine flows back to the kidneys, this is referred to as high-pressure reflux, since the pressure inside the bladder increases during urination. Sometimes it is important to check the process of filling and emptying the bladder several times in micturition urosonography to reliably confirm the diagnosis. In the same examination, it is also possible to fill the bladder with air to see if air bubbles rise up into the kidney region. The examination can not only confirm beyond doubt if reflux is present. By showing the function of the ureter and kidneys laterally, the area responsible for the reflux can often already be identified – in contrast to laboratory examinations. The informative value of micturition urosonography with regard to VUR is very high – especially when several micturitions are observed and a color Doppler is used. However, if the examination is inconclusive, it is advisable to consistently examine the urine for bacterial load if further urinary tract infections with fever occur and possibly to perform micturition urosonography again with the question of reflux. The benefit of preventing possible kidney damage is usually greater than the inconvenience associated with this examination.
Risks, side effects and dangers
The risks of micturition ultrasonography are low – especially compared with otherwise possibly overlooked renal hazards due to possible reflux. Compared with the alternative diagnostic procedure, micturition cystourethrography (MCU), MUS even offers a distinct advantage: unlike MCU, which also sends X-rays into the area of the reproductive organs of mostly young patients, the sonographic variant of urologic diagnostics does not require any radiation at all. The ultrasound waves used are absolutely harmless and can be used as often as desired. The contrast medium is usually well tolerated. In order to relieve the fear or discomfort of the somewhat unpleasant examination, especially for children, a light sedation is possible, which is also usually well tolerated. Until the sedative drug has worn off from the body, the child must be closely monitored so that he or she does not fall, for example, due to a slight impairment of coordination. Sedation also has the advantage of avoiding injury when the catheter is inserted by a restless patient. A possible but rare side effect of micturition urosonography may be the introduction of germs and a resulting urinary tract infection despite careful disinfection as prescribed. For this reason, it is important to pay attention to typical symptoms, especially fever, in the days following the examination. If an infection is suspected, a urinalysis should be performed quickly and, if germs are present in the urine, the necessary antibiotics should be administered.
