Collection of purulent material confined to the renal parenchyma.
The majority (about 80 %) are caused by gram -ve organisms and associated with stones, recurrent UTIs and PCKD.
A minority are caused by gram positive organisms, usually staph aureus, and are usually seeded haematogenously associated with IVDU, skin infections and infected prostheses.
Risk factors also including diabetes, immunosuppression, steroid use and HIV.
TB may be a cause.
Clinical presentation
- Often presents with systemic symptoms – fevers and chills, lethargy, malaise, weight loss.
- Nausea and vomiting common.
- Flank pain, or often non specific abdominal or back pain.
- May have urinary symptoms.
Investigations
Often marked leukocytosis.
Often positive blood cultures, but urine cultures can often be negative.
Ultrasound:
- Hypoechoic or anechoic space occupying lesion with increased transmission
CT:
- Enlarged kidney with focal hypodense lesion
- Thick fibrotic wall after a few days, often hyperenhancing
- Standing and inflammatory change around the kidney
- Often well rounded cf. nephronia
Management
Initial management is resuscitation with IV fluids, cultures before broad spectrum IV antibiotics and appropriate imaging.
Multidisciplinary management with ID, +/- ICU and renal physicians, radiology etc.
May need underlying source treated and further investigation if staph bacteraemia (TOE etc).
Management of the abscess itself is dictated by size, and haemodynamic stability of the patient:
- < 3 cm – can be managed conservatively generally with IV ABx (5 days minimum + long oral tail)
- 3 – 5 cm – may be managed conservatively with ABx if stable and responding, or alternatively with percutaneous drainage
- > 5 cm – usually percutaneous drainage +/- open exploration and drainage +/- nephrectomy.
Things to consider in management – coagulopathy or anticoagulants precluding perc drainage, presence of normal contralateral kidney, fitness for anaesthetic
May require multiple drains with multiple manipulations.
I generally defer duration of antibiotics to ID specialists, usually 14 – 28 days.
Repeat imaging may be omitted for < 3 cm abscesses with good clinical response. I generally repeat ultrasound at least for large abscesses managed without drains.
Perinephric abscess
- Extending beyond renal capsule but contained with Gerota’s
- Usually resulting from rupture of an acute cortical abscess, extravasated urine, haematogenous seeding, or infection of a perinephric haematoma
- Diabetics and stone formers seem prone (think XGP)
- Breach of Gerota’s can result in paranephric abscess – paranephric or psoas abscesses can be from haematogenous seeding but also from bowel issues, pleural infections or spinal osteomyelitis.
- Psoas extension may cause hip irritability and pain on hip flexion
- Consider management of underlying causes (eg bowel disease)