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MCUG MCUG Document Transcript

  • /home/pptfactory/temp/20101027133047/mcug3871.doc Imaging (Scans and X-rays) after Urinary Tract Infections in Children Information for Parents Thomas B. Newman, MD, MPH Attending Pediatrician, UCSF Medical Center Professor of Epidemiology & Biostatistics and Pediatrics Chief, Division of Clinical Epidemiology University of California, San Francisco Isky Gordon, FRCR, FRCP, FRCP&CH Professor of Paediatric Imaging Great Ormond Street Hospital for Children London, UK Introduction If your child has had a urinary tract infection (UTI), your doctor may recommend imaging to get a picture of the urinary tract. We have written this handout to help you make decisions about imaging for your child, because we believe you or your doctor may want to do less imaging than has been traditionally recommended. The handout explains what problems the doctors are looking for with imaging, what can be done if they are found, and what the different imaging tests are like for your child. If you and your doctor do decide on imaging, this leaflet can help prepare your older child by telling him or her a bit about what to expect. The urinary tract The urinary tract includes the kidneys, (organs that filter the blood to make the urine), the ureters (the tubes that connect the kidneys to the bladder), the bladder (the balloon-like muscle that stores the urine) and the urethra (the tube that leads from the bladder to the outside, through the penis in boys, and through an opening just above the vagina in girls). What problems are the doctors looking for? Although any time one does imaging there is a possibility of The urinary tract finding something unexpected, the main things doctors are looking for when they do imaging are obstruction, reflux, and scarring. Each of these is explained below. Obstruction The most important problem that can be detected by imaging is obstruction – a blockage to the flow of urine. Obstruction is usually due to an abnormality in the formation of the kidney or bladder that occurred before birth. Obstructions are important because if the urine can't easily get out of the body it can back up and damage the kidneys. Also, if the urine stays in the body a long time and can't get out it is more likely to get infected again. An important type of obstruction, which occurs mostly in boys, is called posterior urethral valves. These valves cause blockage to the flow of urine out of the bladder.
  • /home/pptfactory/temp/20101027133047/mcug3871.doc The reason to look for obstruction after a UTI is that sometimes a UTI is the first sign that there is an obstruction. Often, especially in boys, obstruction can be suspected because parents notice that the urine dribbles out, rather than squirting out in a nice stream. Also, nowadays many cases of obstruction of the urinary tract are diagnosed by ultrasound scans during pregnancy, especially if the scans are done late in pregnancy (after 28 weeks). If a careful ultrasound scan was normal late in pregnancy, the chance of obstruction is very low, and some doctors may not do another ultrasound scan unless there is a second UTI or some other sign of a problem. If there was not a late prenatal ultrasound, (or there was only a quick scan to estimate dates) many doctors recommend an ultrasound scan to rule out obstruction, especially in children less than 6 months old and those who were very sick with their first UTI. Sometimes obstruction causes damage to the kidneys, particularly if there are several UTIs. Obstruction is usually treated by an operation. Reflux Reflux is a term that means something is flowing in the wrong direction. Doctors use Latin words to describe where it is happening. The Latin prefix for bladder is vesico-, so vesicoureteral reflux (VUR) means that urine is going backwards from the bladder up the ureters towards the kidneys (on either or both sides). Unlike the case with obstruction, doctors disagree about whether it is important to diagnose reflux, because it usually goes away by itself and compared with obstruction it is much less likely to damage the kidneys. In fact, the whole area of VUR is controversial, because it is not clear how it should be treated. Twenty or thirthy years ago, most infants and children diagnosed with VUR had one or more operations to "repair" the reflux, but we now know that most of these operations were unnecessary, because children treated with daily antibiotics to prevent infection did just as well. More recently, studies suggest that even this daily treatment with antibiotics may not be necessary and that just giving antibiotics promptly when they are needed for UTI works as well or better than giving them daily to try to prevent UTI. Many doctors and families prefer this as-needed approach, because of concerns about overuse of antibiotics and because this treatment is the X-ray showing VUR same whether or not the child has reflux, thus making the imaging for reflux unnecessary. Diagnosis of VUR requires a micturating cystourethrogram, or MCUG, (also called a voiding cystourethrogram (VCUG); discussed in detail below). After a first UTI, about 35% of children can be found to have mild or moderate VUR (which usually goes away by itself) if a VCUG is done. Severe VUR can be found in about 1-2% of children after a first UTI. (Some, but not all of these cases can be found by ultrasound.) Children with severe reflux are more likely to have current or future kidney problems. Scarring Scarring is a term used to describe areas of the kidney that appear not to be working any longer. If scars are found, doctors worry more about the risk of kidney problems later, including high blood pressure (especially during pregnancy) and kidney failure. However, newer imaging techniques allow us to see scars much smaller than those that were linked to kidney problems in the past. How often these small scars cause problems is not known.
  • /home/pptfactory/temp/20101027133047/mcug3871.doc There isn't any treatment for scarring itself. Rather, the health care professional will wish to watch out for the subsequent suspected problems such as high blood pressure and kidney failure. For this reason, instead of doing tests for scarring, another approach is simply to recommend that all children who have had a urinary tract infection get their blood pressure measured regularly (once a year). Scarring is best detected using a nuclear medicine kidney scan (DMSA scan). (The old test for scarring, an "IVP" (intravenous pyelogram) generally should not be used.) About 4-20 % of children will have an abnormal DMSA scan after a first urinary tract infection. We don't know how many of these children will develop high blood pressure or other problems. Using the old fashioned IVP, about 20% of children with damage of the kidneys on the IVP developed high blood pressure after 20 years. However, because the DMSA scan can find little scars that would be missed by the IVP and may be of no importance at all, the frequency of high blood pressure in the 20 years following an abnormal DMSA scan is probably much lower. What are the imaging studies like? Most children find preparation helpful, so they will know what to expect and be less likely to be frightened. Ultrasound: This is like the examination most women have during pregnancy. Your child will need to lie still on a special padded table. The technician will put jelly on the tummy and then sweep the ultrasound probe up and down the tummy including over the bladder to get the picture. The examination does not hurt and will take about 15 – 30 minutes. Other than drinking plenty of fluids to fill the bladder, no special preparation is required and it can take place at any time of the day. There is no radiation involved and there are no known side effects or ill effects. MCUG/VCUG The MCUG or VCUG (Micturating- or Voiding CystoUrethroGram) is an X-ray examination of the bladder. (Micturating and Voiding both mean peeing; Cysto means bladder, Urethro refers to the urethra, and Gram means picture. So VCUG or MCUG mean "Picture of the bladder and urethra when peeing.") No special instructions for eating or drinking are required. In older children especially, telling them what will happen can help them get through this test. The child has to be in a special room with large X-ray equipment both over and under the table. The examination uses X-rays and so all the staff present as well as you the parent will need to use a lead lined apron to reduce your exposure to X-rays. The amount of radiation that your child will have depends on how long the examination takes, but is generally said to be equal to about 100 chest x-rays or one year of natural background radiation. In the room your child will lie on the radiology bed and have his/her lower tummy and bottom exposed. The radiologist will then clean the penis / vaginal area with sterile fluid before placing a sterile cloth over your child’s bottom and tummy. A small plastic tube, with lubricant jelly, will be passed up the urethra into the bladder. Although this is not very painful, children may find it frightening and uncomfortable. The urine will be drained off via the tube and then the bladder will be filled with a liquid that can be seen by the X-ray equipment. Once the bladder is full your child will be asked to pee while on the table into a special bedpan. The radiologist will be looking at the bladder (using X-rays) during both the filling and emptying of the bladder. When the child is finished peeing, the plastic tube will be removed. Many doctors will give the child antibiotics for 3 days after this examination to prevent the possibility of introducing an infection with the catheter. When this is done, the chance of infection is small. All children should be encouraged to drink plenty of fluids after this examination.
  • /home/pptfactory/temp/20101027133047/mcug3871.doc An alternative method to look for VUR uses radioisotope rather than X-rays. A nuclear MCUG (sometimes called a RadioNuclideCystogram, or RNC) is identical to the MCUG / VCUG described above but the advantage is a reduced radiation dose by a factor or 100. However both techniques require a small tube to be inserted through the urethra into the bladder. The object of this examination is to see if any of the liquid placed into the bladder goes back up to the kidney. If it does, the child has VUR. For children who are toilet trained, many institutions now look for VUR without a bladder catheter. This is done at the end of a nuclear medicine renal nuclear scan (see below). This is called an indirect radionuclide cystogram. Nuclear Renal Scan (DMSA Scan) This is a test to look for renal scarring. This requires the injection of a specific "radiotracer" ("DMSA") that goes to the kidney and gets trapped by the cells of the kidney. The radiotracer has a tiny bit of radioactivity. This means that it releases small amounts of energy that can be detected by a very sensitive camera. The image reflects the kidney’s function -- if there is a part of the kidney that is not working, it will show up as a cold spot (place where there is no radioactivity) on the picture. No special instructions for eating or drinking are required. Picture of the kidneys from a DMSA scan Your child may have an anaesthetic cream, called EMLA, applied to the skin over a vein in the hand or elbow. If your child is very fearful of needles this is worth asking and waiting for. EMLA takes 40-60 minutes to have its effect. Your child will then have a small needle inserted into the vein and a tiny amount of the DMSA will be injected. Two to four hours later your child will lie on top of a special camera (a gamma camera) than detects the DMSA radiotracer to obtain pictures of the kidneys. This will take 30 - 40 minutes. Your child will have to lie still for about 10 minutes on 3 occasions. Bringing some favorite books, tapes or toys can help pass this time. Although the DMSA scan involves exposure to radiation, the dose is much lower than the MCUG/VCUG. The dose is equivalent to about 50 chest radiographs or to about 6 months' natural background radiation. Intravenous Pyleogram ("IVP") An IVP should not be done to evaluate children with a UTI unless there are very unusual circumstances, such as a suspicion that the ureters are in the wrong place. If your doctor recommends an IVP for other reasons, you might want to get a second opinion before proceeding.
  • /home/pptfactory/temp/20101027133047/mcug3871.doc Recommendations Different expert groups have proposed different recommendations over the years. As more data becomes available and technology improves the recommendations change. In 2007 the National Institute for Health and Clinical Excellence (NICE) of the United Kingdom produced a guideline based on the latest research that recommended much less imaging than had been traditionally recommended. (If the link does not work, just Google "Nice UTI guideline.") We agree with most of the NICE guideline. You should decide with your doctor what imaging you would like for your child, based on your preferences and your child's particular case. We recommend an ultrasound to make sure there is no obstruction for infants < 6 months old with a UTI and in older infants if there are other worrisome features, (e.g., poor response to treatment, a poor urinary stream or recurrent infections). This will identify almost all cases of obstruction without pain or radiation to the child. If the ultrasound scan is abnormal, other tests may be indicated. This matches recommendations for ultrasound in the NICE guideline. We do not recommend routine DMSA scans to look for scarring, because we don't think the results change the treatment at all. We recommend that all children have future urinary tract infections promptly diagnosed and treated and their blood pressure measured periodically in childhood, whether or not they have scarring. If your child will get this follow-up anyway, identifying scarring is of little value. The NICE guideline suggests DMSA scans only for worrisome or recurrent infections. We recommend against routine VCUG/MCUGs. These tests are more distressing to the child and serve primarily to identify vesicoureteral reflux. Since a reasonable approach to treating reflux is simply identifying and treating future UTIs promptly and following the child's blood pressure, we prefer to treat all children this way, rather than imaging them. NICE recommends VCUG/MCUGs only for infants with abnormal sonograms, poor urine flow, or worrisome or recurrent infections in infants < 6 months old. Finally, the focus on imaging should not lead to neglect of the history and physical examination, which can detect reasons (like constipation or nerve problems) why the bladder might not be emptying properly.