A 26-year-old man presented with dysuria and colicky pain in the right loin radiating to groin.

General clinical examination was unremarkable. There was mild tenderness in the right renal angle. The hemogram was normal. The urine examination showed a few pus cells, red blood cells with proteinuria. The renal chemistry was normal.

An ultrasound of the abdomen was obtained.

Fig 1

The sonogram reveals a lesion of mixed echogenicity but predominantly hypoechoic in the upper pole of the right kidney.

An intravenous urogram was then obtained.

Fig 2

The 10 minute film of this study merely shows downward displacement and blunting of the upper group of calices. There is no destruction of the papilla.

A plain and contrast enhanced CT scans of the abdomen was then performed.

CT reveals a mixed attenuation, minimally enhancing lesion with multiple small, cystic components in the upper pole of the right kidney. The visualised renal vessels are normal. There is no calcification seen.

Diagnosis : Renal abscess

Fig 3

Fig 4

Discussion :

Renal abscesses normally begin multiple microabscesses which coalasce to eventually from a larger abscess. The route of infection may be hematogenous, lymphatic, direct contamination or retrograde spread from the lower urinary tract (VUR). The most common causative organism is Staphylococcus aureus or E. coli.

Clinically, the patients may present with sepsis ( i.e. fever with chills) or as is the case in this patient, present with flank pain and dysuria. Rupture of the abscess into the pelvis may produce pyuria.

A plain radiograph may reveal focal or generalised enlargement of the kidney. In case of infection with gas producing organism, air may also be seen.

An excretory urogram usually reveals only a mass effect with displacement, stretching and distention of calices. The excretion of contrast in the affected kidney may be poor or, in case the entire kidney is involved, there may be no excretion at all. Calculi are not as consistent a feature of this disease as they are in xanthogranulomatous pyelonephritis.

Ultrasonographically, an abscess may be demonstrated as a predominantly fluid-filled but complex mass, with fairly good through transmission. Internal echoes that shift with changes in patient's position may be noted, producing a fluid-debris interface.

On CT, an abscess is usually well delineated, has a lower density than the normal parenchyma and has an irregular thickened wall. The central part of the abscess does not enhance with IV contrast medium, though there may be intense wall enhancement.

There are no specific features that point towards the diagnosis on an angiographic study.

Gallium or Indium labelled leukocytes are - picked up by renal abscesses producing an intense hot spot on scinti scanning.