Renal Structure and Function&

Urinary Tract Infections

Angus RitchieBPT Lecture Series 2012

Content• Anatomy/Radiology/Function

– Structure and function of the renal system and male and female genital tract

– Applies basic science knowledge to appreciate the significance of, and appropriately act, on reports of imaging (renal tract ultrasound, functional renal scans, renal angiograms, urograms), renal biopsies, urine composition

• Urosepsis / UTI– epidemiology, pathophysiology, clinical presentation, differential

diagnosis,– investigations, detailed initial management, principles of ongoing

management, potential complications of the disease and its management,– preventive strategies

Lets start at the very beginning

…

Urinary tract anomalies• Affects 10% newborns • Kidney

– Agenesis, hypoplasia/dysplasia – Fusion (horseshoe), pelvic location– PUJ obstruction

• Ureters– Bifid, ectopic (duplex)– Megaureter

• Bladder - reflux• Urethra - posterior urethral valves

Normal adult renal anatomy

• Kidneys– Size

• Men 12.4 ±0.9cm, 202 ±36mL• Women 11.6 ±1.1cm, 154 ±33mL

– Right kidney lies lower than left– Retroperitoneal

• Age related change– 10% loss of mass per decade after 40y– 10-30% glomeruli sclerosed by 80y– Approx 1mL/min/y decline in GFR after 40y

Renal anatomy

Common normal variants

• Accessory renal vessels in 25%• Horseshoe kidney 1 in 600

Renal physiology (on 1 page)

• Autoregulation of RBF, GFR

• Glomerular filtration, selectivity• Tubular transport• Tubuloglomerular feedback• Countercurrent system• Oxygen sensing• Pressure sensing• Renal sympathetic

outflow

• Electrolyte homeostasis

• Water homeostasis• BP regulation• Erythropoiesis

regulation• Vit D activation

Renal physiology

• Renal blood flow– 1L/min (Approx 20% CO)– Autoregulation (80-180mmHg)– Afferent (PGE2, PGI2)– Efferent (ATII, ET1)

• Normal GFR 120mL/min/1.73m2 (wide range)

Renal histopathology

Renal investigations• Dipstick UA• Urine microscopy, culture

– Cells, casts, crystals• Plasma and urine electrolytes• Plasma and urine osmolality• GFR measurement• Urine protein assessment• Acid-base measurement• Renal imaging• Renal biopsy

Casts

Lupus nephritis

Renal imaging• Plain xray• Xray KUB• IVP• Ultrasound• CT KUB (multiple phases)• MRI• DTPA/MAG3• DMSA• PET

Plain imaging

• Xray-KUB• IVP• MCUG

Ultrasound

• Good tissue definition– cortex, medulla, pyramids, pelvis

• Sensitive for obstruction, cysts• Good for antenatal imaging• Poor imaging of

– Ureters– Obese patients– Renal vasculature (except transplant)

Renal CT• Better for obese patients• Less sensitive than US for obstruction• Issues with contrast nephropathy• CT-KUB

– Stones– Fine calcification

• Multiphase CT (non-contrast, arterial, venous, delayed)– Vasculature, vascular lesions, complex cysts– Delayed phase has essentially replaced IVP

• CT-angiography for renovascular disease screening

Renal MRI

• Excellent for:– Complex masses (necrosis v haemorrhage v fat)– Renal vasculature (with or without contrast)

• Best test for renal vein thrombosis • Gadolinium & nephrogenic systemic fibrosis

– Only an issue if GFR<30 and multiple studies– Gd can be removed efficiently by haemodialysis

• Not rebatable

Renal angiography

• Formal angiography the gold standard for RAS – CT insensitive for fibromuscular dysplasia

• Allows angioplasty• PCI for atherosclerotic RAS not of proven

benefit cf medical therapy• Preoperative embolisation of renal tumours• ?Expanding role for renal artery denervation.

Nuclear renal imaging• Technetium-99m

– Used in essentially all nuclear renal imaging– Emits gamma rays, half-life 6h

• Nuclear GFR– 99mTc-DTPA or 51Cr-EDTA (5% difference)

• DTPA, MAG3– Renal perfusion, uptake, excretion, drainage– MAG3 better if impaired renal function, obstruction– Lasix optional

• DMSA (to look at the ‘meat’)– Acute pyelonephritis– Cortical scarring

Cystoscopy

• Good for investigation of haematuria– Especially macroscopic haematuria

• Allows retrograde imaging– Defines location of obstruction

• Diagnosis of radiolucent stones (eg indinivir)

Urinary tract infections

• Common• Wide spectrum of disease

– Mild, community treated– Fatal septic shock

Common UTI organisms

• E. coli • Proteus mirabilis• Klebsiella spp. • Enterococci• Group B Strep. • Other gram –ves

UTI is a clinical diagnosisCYSTITIS PYELONEPHRITISDysuria Irritative Sx may be absentUrine frequency Back/flank painNocturia Fever, rigors chillsNo features of pyelo Renal angle tenderness

UTI Confirmation• UA

– Positive leucocytes (false –ve VitC, protein, glucose, AB)– Positive nitrites (most Gram –ves)– Small blood, protein common

• Urine microscopy– Pyuria WC 10-100– Organisms– No epithelial cells

• Culture– Pure growth >10^7 CFU

• Bacteraemia = pyelonephritis

Role of imaging in UTI• NOT REQUIRED FOR DIAGNOSIS• Rule out obstruction

– Old men– Associated with ARF– History of stones

• Failure to respond to Rx– ?Abscess or lobar nephronia

• Recurrent infections– ?Renal scarring or bladder dysfunction

• Stranding on CT is ENTIRELY NON-SPECIFIC

Childhood UTIs

• Common – 8% of girls, 2% of boys <7y– 10-30% have recurrent infection

• Similar organisms to adults• DMSA sensitive test for pyelonephritis• May indicate VUR

– Screening with US, MCUG highly recommended for febrile UTI <2y.

• ?Role of circumcision (NNT 111)

Cystitis

• Often urine culture not required• Treatment

– Trimethoprim, cephalexin, amoxy+clav– Women: 3-5 days – Men: 14 days. Look for anatomical abnormality

Pyelonephritis• Blood and urine cultures before treatment• Antibiotics

– IV AB until afebrile, then orals. Complete 10-14d– Empirical AB depends on local epidemiology

• Cephazolin + gentamicin– Repeat urine culture 48h after Rx

• If not improving look for abscess– Areas of lobar nephronia are considered antecedent of

abscess and require extended treatment.• Oral quinolones excellent penetration of renal tissue

but overuse associated with resistance

Pyelonephritis in Pregnancy

• Must be treated seriously - can cause ARF• Mild hydronephrosis (esp R sided) is common

and not indicative of obstruction• Repeat urine culture 48h post treatment

Ok Avoid

Penicillins Tetracyclines

Cephalosporins Gentamicin

Nitrofurantoin Quinolones

Trimethoprim

Pyelonephritis in Transplant

• Mimics acute rejection– Fever– Graft tenderness– ARF

• Look for suggestive UA, urine micro• Imaging mandatory to rule out obstruction• Treat aggressively, prone to shock

Catheter-associated UTI

• Bacterial colonisation inevitable• Only symptomatic infections require Rx

– Use broad-spectrum AB– May respond to Rx even if organism is resistant

• Lower rate of infection with SPC• Catheter change with symptomatic infections

– With antibiotic cover• Routine catheter changes

UTI prophylaxis

• Recurrent UTI (2 or more in a year)• Evidence of benefit in non-pregnant women if

taken for 6-12 months (Cochrane Review)– Intermittent self-treatment– Intermittent prophylaxis (eg post-coital)– Continuous

• Options– Cephalexin 250mg nocte– Trimethoprim 150mg daily

UTI prevention• Good urine volume• Urinary acidification

– Sodium citrate (Ural)– Cranberry tabs (in women)*

• Topical estrogens (postmenopausal women)*• Hexamine hippurate*• Double-voiding (men with prostatism)

– Or intermittent self-catheterisation

* Evidence based benefit on Cochrane review

Prostatitis

• Disease of older men• Presentation:

– Lower urinary tract symptoms– Perineal pain– Fever– Prostatic tenderness

• 2-4 weeks Rx. Quinolones a good choice. • Check for Chlamydia in young men

Asymptomatic findings

• Asymptomatic bacteriuria– In general no Rx required– Exceptions: pregnant women, before procedures

• Asymptomatic Candiduria– Remove catheters, stents– Treat only high risk patients

• Asymptomatic pyuria

Random tips

• Stones and UTI - associated with Proteus spp. • Old men - always look for urine retention• Emphysematous pyelonephritis associated

with diabetes.• Increasing community prevalence of ESBL