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2. CLINICAL APPROACH TO INVESTIGATION AND MANAGEMENT OF UTI
Optimal management of UTI in children is important because of risk of permanent renal damage which is greatest in children aged under 2, but diagnosis can be difficult in young children because symptoms such as fever, vomiting, screaming, anorexia, and irratibility that may indicate UTI are common in other childhood illnesses such as gastroenteritis and viral infection . Once urinary tract infection has been confirmed by urine culture, a decision must be made about upper tract involvement. But no one test or combination of tests has adequate sensitivity or specificity to be applied to the individual. As a result, clinicians have turned to diagnostic imaging for more reliable information(2).
In 1991, an expert multidisciplinary working group of the Royal College of Physicians proposed guidelines for the investigation and management of children with UTI. The group emphasized the importance of making a bacteriological diagnosis, of instituting treatment without delay after urine sample is taken, and of checking for eradication of infection by means of a follow up urine specimen. The group also recommended that all children, regardless of gender, should have renal tract imaging after a first episode of confirmed urinary tract infection and gave recommendations on the type of imaging for each age group.Before any child undergoes imaging there must be bacteriological evidence of a UTI, i.e. more than 10'' organisms of a pure growth in urine . Until the introduction of isotope scintigraphy and ultrasound, the intravenous urography (IVU) was the main nvestigation of the upper urinary tract and the contrast cystography was the standard screening in order to determine the presence or absence of vesicoureteral reflux in children .
It is important to distinguish the group of children with acute pyelonephritis from the one with lower UTI. If renal involvement is present, therapy in these children may be more prolonged in an attempt to prevent long-term renal damage. Nowadays, ultrasonography (USN) should be the initial screening examination of the upper urinary tract in patients with UTI. A child with acute pyelonephritis should have an ultrasound examination on the day of admission and, in absence of hydronephrosis, a 99mTc-DMSA scan within 1-3 days. All patients with abnormal 99mTc-DMSA scans require a follow-up scan 3-6 months later to assess if the defect has progressed to a renal scar. A cystogram is required if an abnormal kidney is found, but this will be 4-6 weeks after the original infection. In girls under 3 years of age DRC (direct isotope cystogram) can be performed, while in those over 3 years IRC (indirect radioisotope cystogram) may be carried out. Boys require MCU (micturating cystourethrogram) to assess the posterior urethra and it is promoted as a means to exclude anatomic abnormalities of the urinary tract, such as posterior urethral valves in boys .
Every child with the first proven UTI, but not acute pyelonephritis, requires a full ultrasound examination as well. If this is normal and the girl is over 5 years of age no further imaging is required. A cystogram (MCU) is required in all boys of any age. If the ultrasound is normal and the child is less than 5 years of age, all children require a 99mTc-DMSA scan to exclude scarring. All girl under 1 year of age require DRC to exclude reflux, since the immature kidney is susceptible to damage in the presence of both reflux and infection. If the 99mTc-DMSA scan is abnormal, girls aged between 1 and 3 years require DRC, while those aged 3-5 years require IRC. If the ultrasound and 99mTc DMSA scans are normal in girls aged 1-5 years, then no further imaging is required unless another UTI occurs. If the ultrasound is abnormal, but no hydronephrosis is detected then in girls under 3 years of age a 99mTc-DMSA scan and DRC are required, while in those over 3 years of age a 99mTcMAG3 scan and IRC are required. If hydronephrosis is found then a dynamic 99mTc-MAG3 scan and cystogram are required to exclude an obstruction or reflux.A clear practical view of the investigation of child with the first proven UTI is shown at the diagram proposed by I.Gordon (click here to see diagram).
As above mentioned, nuclear medicine studies (dynamic, and static renography, direct and indirect cystography as well as GFR estimation) have an important role to play in the localization of infection to the lower or upper urinary tract. Renal cortical scintigraphy (RCS) and radionuclide cystography (RNC) studies can be performed on an outpatient basis in any clinical nuclear medicine department with gamma camera. Sophisticated computer equipment is not needed, and these studies can be achieved within 4 hours during one visit. If stasis or hydronephrosis is present in the kidneys, a diuretic can be given to determine evidence of obstruction. In addition the radiounuclide studies are very sensitive for recognizing congenital malformations such as ectopic location of kidney, or regional functional abnormalities such as duplication and obstruction kidney with significant ureterocele .
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