Renal Structure and Function
&
Urinary Tract Infections
Angus Ritchie
BPT 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
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Countercurrent system
Oxygen sensing
Pressure sensing
Renal sympathetic outflow
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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
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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
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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
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E. coli
Proteus mirabilis
Klebsiella spp.
Enterococci
Group B Strep.
Other gram –ves
UTI is a clinical diagnosis
CYSTITIS
Dysuria
Urine frequency
Nocturia
No features of pyelo
PYELONEPHRITIS
Irritative Sx may be absent
Back/flank pain
Fever, rigors chills
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