Classification

Classification

• UTI is classified as uncomplicated when it occurs in an immunocompetent host with an anatomically normal and - functional urinary tract. UTIs may also be classified on their site of origin as pyelonephritis (kidney), cystitis (bladder), urethritis or prostatitis. While acute pyelonephritis indicates an acute infection of the kidney , chronic pyelonephritis is only a morphological description of previous infection-related or nuclear imaging. Acute pyelonephritis This commonly occurs as a result of ascending infection from organisms in the lower tract, usually caused by Gram-negative bacteria. Haematogenous spread may be seen in patients with diabetes and in immunocompromised hosts, people who inject drugs and patients with bacterial endocarditis. It is more common in females, especially during childhood, at puberty , after intercourse and during pregnancy . Acute pyelonephritis usually presents with fever, chills, flank pain, nausea and vomit ing. Loin tenderness may be present. Symptoms may vary from mild to severe illness with septic shock and renal failure. Pyuria is almost always present and its absence in a patient with pyelonephritis may point towar ds an obstructed urinary tract. Urine and blood should be collected for culture. Escherichia coli and other Gram-negative organisms are commonly responsi ble. Imaging is necessary when the patient is not responding to antibiotics to rule out pyonephrosis, renal abscess and obstruction. Renal US is often the first imaging modality used. Contrast-enhanced CT (CECT) typically sho ws decreased patchy opacification of the a ff ected parenchyma. Pyelonephritis complicating pregnancy The relaxing e ff ect of progesterone during pregnancy causes ureteral smooth muscle relaxation and dilatation, presumably predisposing pregnant women to ascending upper tract infec tions. It is associated with fetal growth retardation and preterm delivery . Therefore, all pregnant women must be screened in the first trimester for ABU because, untreated, a third of these patients will develop UTI. Lower tract UTI typically occurs in the first trimester whereas pyelonephritis most often presents in the second or third trimester with acute abdominal pain or premature labour. Pyelonephritis is more common in pregnant women with an underlying urological abnormality or diabetes. A renal US is indicated if response to treatment is poor. Anti biotic use during pregnancy is tailored to avoid fetal harm and typically includes fosfomycin, penicillins or cephalosporins. Renal and perirenal abscess A renal abscess results from an ascending UTI in associa tion with an underlying urinary tract abnormality such as obstructive uropathy or VUR. It is usually caused by common uropathogens such as E. coli and other Gram-negative bacilli. Renal abscesses may extend and perforate the renal capsule to form a perirenal abscess. Multiple renal abscesses may conglomerate into a solitary suppurative lesion called a renal carbuncle. This is usually caused by Staphylococcus aureus reaches the kidney by haematogenous spread. The clinical presentation may be insidious and non-specific but patients usually present with persistent fever, back pain, abdominal pain and costovertebral tenderness. Urine exam ination may be normal if the abscess does not communicate with the collecting system. CECT scan is the investigation of choice to establish the diagnosis. Treatment with antibiotics without drainage may be e ff ec tive in carefully selected patients when the abscess is small (<3 /uni00A0 cm) or in a stab le patient (up to 5 /uni00A0 cm). Empiric antibiotic and other uropathogens causing complicated UTI. Culture- directed antibiotics may be needed for 2 weeks or longer depending on response. Percutaneous aspiration or drainage of pus is indicated in abscesses >5 /uni00A0 cm and in patients not responding to antibiotics. Open surgical drainage is indicated when percutaneous drain - age is inadequate. Emphysematous pyelonephritis This is an acute-onset, rapidly progressive, possibly lethal form - of pyelonephritis characterised by parenchymal necrosis and gas formation, caused by organisms including E. coli , Klebsiella pneumoniae , Pseudomonas aeruginosa and Proteus mirabilis . Most patients have diabetes (up to 90%) and they may have obstruc - tion secondary to calculi or papillary necrosis. Increased glucose levels in those with diabetes may provide a substrate - for carbon dioxide production from fermentation. Symptoms are suggestive of p yelonephritis and an abdominal mass may be palpable. CECT of the abdomen is diagnostic and shows gas in the renal parenchyma, collecting system or both, along with other features of infection such as abscess, obstruction and perinephric stranding. Early diagnosis, intravenous broad-spectrum antibiotics and percutaneous drainage of the abscess and obstructed kidneys have improved outcomes in these patients. Emergency nephrectomy is rarely required and is reserved for patients who do not respond to the described - measures. Xanthogranulomatous pyelonephritis Xanthogranulomatous pyelonephritis (XGP) occurs with severe renal infection in an obstructed kidney and is usually associated with calculi, causing loss of function and paren - chymal destruction. Pathological examination typically shows accumulation of lipid-laden foamy macrophages. Patients may present with flank pain, fever with chills, persistent bacteriuria - and a flank mass. A history of stone disease may be present. It is usually unilateral. CECT of the abdomen is diagnostic and shows a non-functioning enlarged hydronephrotic kidney around a shrunken pelvis with a calculus, also known as the bear’s paw sign ( Figure 82.7 ). Nephrectomy is the defin - - itive treatment. , which - -

Figure 82.7 Xanthogranulomatous pyelonephritis with the ‘bear’s paw sign’.

the pelviureteric junction to be hiked up Putty kidney: extensive dystrophic calci /f_i cation involving all or most of the kidney, seen as calci /f_i ed non-functioning renal tissue Pipe-stem ureter: straightening of the ureter as a result of /f_i brosis of the wall of the ureter Corkscrew ureter: multiple annular strictures along the length of the ureter Golf hole ureteric ori /f_i ce: ureteric ori /f_i ces may become patulous and may be pulled up; tubercles are infrequent in the bladder Figure 82.8 Schematic illustration showing the sequelae of urinary tuberculosis (courtesy of Nivedita Kekre and Dr Madhuri Sadanala).