bubble_chart Overview

Urinary tract obstruction or urinary tract abnormalities such as vesicoureteral reflux can lead to renal cortical medullary abscesses. Renal cortical abscesses are usually caused by Staphylococcus aureus. In contrast, renal cortical medullary abscesses are often caused by infections with Escherichia coli, Klebsiella, or Proteus species.

bubble_chart Etiology

Acute focal bacterial nephritis is a severe acute infection of the kidney parenchyma, but the infection focus has not yet liquefied (suppurated). It can invade one or more renal lobules. The infection is believed to be confined only to the renal lobules with intrarenal reflux. If this inflammatory mass is not treated promptly and effectively, it will liquefy and form a renal corticomedullary abscess. Xanthogranulomatous pyelonephritis is often associated with intrarenal corticomedullary abscesses complicated by chronic urinary tract infections, renal calculi, and urinary tract obstruction.

Most corticomedullary abscesses in adults are associated with renal calculi, urinary tract obstruction, or damaged kidneys. In children, they are only associated with vesicoureteral reflux. Diabetes is also an important predisposing factor, especially for adult patients. In all age groups, the common pathogens are aerobic gram-negative bacteria. The mechanism of disease is as follows: bacteria first invade the medulla, causing medullary infection, which then liquefies and invades the renal cortex. A possible complication is the rupture of the abscess through the renal capsule, leading to a perinephric abscess.

bubble_chart Clinical Manifestations

Both males and females can develop this disease, with an equal ratio between genders, but the incidence increases with age. The clinical features include shivering, fever, lumbago or abdominal pain, as well as urinary symptoms. Common gastrointestinal symptoms such as nausea and vomiting may also occur. Chronic cases may present with general malaise, fatigue, and weight loss. Physical examination often reveals no specific findings, though tenderness may be noted in the costovertebral angle, lumbar region, or abdomen. Palpable masses are rarely detected.

bubble_chart Auxiliary Examination

Laboratory tests: Apart from positive urinalysis and urine culture, other test results are similar to those of renal cortical abscess, which is due to the communication between the renal corticomedullary abscess and the renal calyces and pelvis. Compared to renal cortical abscess, this condition has a higher rate of positive blood cultures.

Imaging studies: Ultrasound and CT are the most fundamental and effective diagnostic methods for renal corticomedullary abscess. For acute focal bacterial nephritis, renal ultrasound often fails to detect abnormalities but may show a solid hypoechoic mass with no clear boundary from the surrounding normal renal parenchyma, renal contour deformation, and indistinguishable cortex and medulla. Non-contrast CT usually cannot confirm the symptoms of acute focal bacterial nephritis. However, with contrast enhancement, CT may reveal poorly defined, wedge-shaped, non-liquefied low-density areas that can involve one or more renal lobules.

Renal abscesses, whether cortical or corticomedullary, exhibit variable ultrasound findings. The lesions may lack internal ultrasound reflections, resembling renal cysts or calyceal diverticula, or show strong echoic masses similar to tumors. The ideal imaging modality is CT, with characteristic findings including a decrease in CT values of the renal parenchymal lesions to 0–20 Hounsfield units and no enhancement after intravenous contrast administration.

bubble_chart Treatment Measures

Similar to renal cortical abscesses caused by staphylococci, renal corticomedullary abscesses caused by large intestine bacillus infections sometimes only require antibiotic treatment without drainage. Acute focal bacterial nephritis with grade I liquefaction and small abscesses confined to the kidney excess tissue generally also does not require drainage. However, for severe cases, nephrectomy may be necessary.

For antibiotic treatment, initial options may include ampicillin (1g, intravenous injection, every 4-6 hours) or cefazolin (1g, intravenous injection, every 8 hours), which can be combined with aminoglycosides such as gentamicin or tobramycin (1mg/kg) intravenously every 8 hours, with dose adjustments if renal function is impaired. During treatment, the regimen can be modified based on clinical efficacy or drug sensitivity test results. Once symptoms improve, fever subsides for 48 hours, or imaging confirms improvement, the treatment can be switched to oral or intramuscular administration.