Defined as inflammation of the kidney and renal pelvis, although diagnosis is largely clinical.
Risk factors similar for UTIs
- VUR, upper tract instrumentation increase risk.
Imperative to identify complicated cases of pyelonephritis (i.e. associated with obstruction, requiring surgical intervention, pregnancy) as opposed to uncomplicated cases.
Aetiology is usually ascending urinary tract infection from urethra and bladder, although haematogenous seeding can occur.
Clinical presentation
- Fever and chills
- Flank pain and flank tenderness
- Nausea and vomiting
- Often associated with lower tract symptoms and more classic cystitis symptoms (frequency, urgency, dysuria, suprapubic pain)
- Leukocytosis on bloods and raised CRP
- Positive leukocyte esterase and nitrites on urinalysis
- Raised creatinine (think obstruction)
- Blood cultures positive in 25 %
Imaging
- EAU guidelines suggest imaging should be used in patients with history of stones, impaired renal function, alkaline urine pH, sepsis, or failing to respond with fevers persisting for 2 – 3 days.
- My preference is to perform imaging in all patients presenting to hospital with a diagnosis of pyelonephritis – ultrasound or CT depending on patients age and risk
Ultrasound
- Unilateral renal enlargement
- Abnormal echogenicity
- Most patients will have normal ultrasound of the kidneys
- May show elevated post void residual volumes
- Main role is to exclude abscess and hydronephrosis
CT
- Patchy regions or wedge shaped areas of heterogenous enhancement
- Striated nephrogram in excretory phase
- Exclude renal abscess, stones, hydronephrosis
Management of pyelonephritis
Be confident in excluding obstruction and complicated features.
- Treat any obstruction expeditiously concurrently with antibiotics
Many patients with uncomplicated pyelonephritis who are systemically well, with normal immune systems and able to maintain oral intake can be managed as an outpatient with a 2 week course of oral antibiotics.
In an unwell patient:
- Resuscitation in conjunction with ED +/- ICU
- IV fluids
- Broad spectrum IV antibiotics – ampicillin and gentamicin
- Urine and blood cultures preferably prior to antibiotics
- Imaging to exclude obstruction
- Consider catheter if elevated PVR or patient unwell enough to strictly monitor fluid balance
Follow up the patient to ensure they improve, and consider treatment of any underlying predisposing factors.
Acute lobar nephronia (bacterial nephritis, focal pyelonephritis)
Bacterial infection involving the renal cortex, causing an inflammatory mass.
Patients may be slightly more unwell cf. uncomplicated pyelonephritis – and more likely to have immunosuppression, diabetes.
Probably represents a midpoint on the spectrum between pyelonephritis and renal abscess.
On ultrasound:
- Poorly marginated lesion, generally hypoechoic, with occasional low level echoes and disruption of corticomedullary junction
On CT:
- Difficult to appreciate on non contrast scans
- Wedge shaped areas of reduced enhancement
- No definite wall or liquefication cf. abscess
Treat similarly to pyelonephritis with low threshold for follow up imaging if failure to improve to exclude interval abscess development.