Renal cortical abscesses, also referred to as cortical abscesses of the kidney, include multiple small abscesses in the renal cortex, which are termed renal carbuncles. When these small abscesses coalesce into a larger abscess, it is known as a renal abscess. The primary pathogens are most commonly Staphylococcus aureus, but Escherichia coli and Proteus species are also implicated. Most cases originate from distant inflammatory foci, such as skin boils, carbuncles, dental caries, tonsillitis, pulmonary infections, or osteomyelitis, which spread hematogenously. With the advent and widespread use of effective antibiotics, abscesses caused by Gram-positive bacteria have been decreasing, while those caused by E. coli and Proteus species have become more frequently observed. Pathologically, this condition differs from classic acute pyelonephritis, as the lesions may rupture outward from the renal cortex, forming a perinephric abscess.
The clinical manifestations primarily include chills, fever, flank pain, muscle tension, and tenderness at the costovertebral angle, without symptoms of bladder irritation. The disease course typically lasts one to two weeks. If the renal abscess ruptures into the perirenal space, systemic and local symptoms may become significantly more severe. Laboratory findings commonly show an elevated white blood cell count with neutrophilia. Urinary microscopy may show an absence of pyuria or bacteriuria. However, if the abscess communicates with the collecting system, pyuria and bacteriuria may subsequently develop. Gram staining of urine smears may reveal the causative pathogens, and urine cultures are often positive. Blood cultures may also demonstrate bacterial growth. Imaging studies such as ultrasound and CT scanning are beneficial for diagnosing abscesses. Definitive diagnosis can be established by aspiration and analysis of pus obtained under ultrasonographic guidance.
Early-stage renal cortical abscesses are managed with timely antibiotic therapy. Broad-spectrum antibiotics, such as ampicillin, vancomycin combined with aminoglycosides, or third-generation cephalosporins, are commonly recommended. In cases where a renal abscess has formed or is complicated by a perinephric abscess, percutaneous aspiration or surgical incision and drainage under ultrasonographic guidance is required. If there is significant renal destruction, nephrectomy may be performed when necessary.