Spot Diagnosis

Pyonephrosis

When the infection involves a dilated PC system, there is pyonephrosis, as in this patient with a calculus in the lower third with hydronephrosis. There is reduced function with enhancement of the walls of the pelvis and calyces (Fig. 1). A focal parenchymal lesion is also noted (Fig. 2).

Emphysematous pyelonephritis

Sometimes, patients with acute focal bacterial nephritis, progress to frank abscess formation and on occasion, especially with diabetics, the infection involves gas-forming organisms, leading to the entity emphysematous pyelonephritis.

The diagnosis on CT is relatively easy, with the presence of a focal area of necrosis and altered density with air, which may extend into the peri-renal space (Figs. 1-3)

Multifocal acute bacterial nephritis - incipient abscess formation

When the acute pyelonephritis /multifocal acute bacterial nephritis progresses, the lesions undergo liquefaction and start getting walled-off, starting to form abscesses.

This is one such patient, where the lesions are now well-defined, unlike last week's example, see bilaterally, with areas of necrosis.

Acute focal bacterial nephritis with incipient abscess formation

This 42-years old man had pain and tenderness in the left lumbar region with pus cells in the urine. Ultrasound showed a focal hypodense lesion in the left kidney. The CT showed a lesion with a wedge-shaped appearance (Figs. 1, 2), showing significant hypodensity and an almost well-defined well (Fig. 3), suggesting the development of an abscess.

Acute focal bacterial nephritis can progress to abscess formation in severe or untreated cases.

Renal biopsies in the adult

Renal biopsies have always been a bit controversial and in the adult patient, have rarely been required in the presence of an enhancing renal mass, which is always assumed to be a renal cell carcinoma, unless proved otherwise. The only time we have gone ahead with biopsies, has been when there is a high possibility of infection, especially in younger individuals.

A new article by Silverman SG et al in the July issue of Radiology talks about this issue in detail. It divides the indications for renal biopsy into established and emerging.

Established

1. When there is an extra-renal primary and a renal mass
2. When the mass seems non-operable
3. When there are significant co-morbid conditions preventing surgery (Fig. 3)
4. When there is a high risk of infection

Emerging

1. Small lesions less than or equal to 3cms, homogeneous and hyperattenuating. The chance that such lesions may be benign increases with reducing size, being almost 44% in those less than 1cm.
2. Before RF ablation
3. In Bosniak type III indeterminate cystic renal masses (Figs. 1, 2)

Acute pyelnephritis with a tiny calculus

This was a 45-years old lady who presented with fever and renal tenderness. Her urine showed pus cells.
The CT scan showed a calculus in the upper pole of the right kidney without obstruction (Figs. 1-3 - red arrow). More importantly, the right kidney showed heterogeneous enhancement with wedge-shaped areas of altered enhancement - this pattern is highly suggestive of multifocal acute bacterial nephritis / acute pyelonephritis.

PU junction injury - post-operative

The patient shown last week with a PU junction injury was operated. The urinoma was drained and a inferior calyceal-ureteric anastomosis was performed. A drainage tube was placed near the anastomosis, which kept draining significant urine for almost two weeks.

A repeat CT scan showed a leak at the calyco-ureteric junction (Figs. 1-4). Subsequently, this healed on its own and the patient is now fine.

PU junction injury

This was a 5-years old boy who had trauma. The ultrasound showed a peri-renal collection. The CT urogram showed a contusion in the right upper pole (Fig. 1), with extravasation of contrast at the PU junction level (Fig. 2), into a peri-renal urinoma (Fig. 3). This was well appreciated on the MIP urogram images (Figs. 4, 5).

A post-operative repeat study was also performed.

Renal fracture

This seven-years old girl was hit by a car. She had hematuria and abdominal pain. The ultrasound showed left renal injury. The CT urogram showed clearly the lower pole fracture in the arterial phase (Fig. 1), with intact upper and lower polar arteries on the angiogram (Fig. 2). The venous phase image (Fig. 3) also showed the fracture well. The CT urogram image showed the injury to the lower pole calyx (Fig. 4) and mild extravasation.

Renal trauma can be very well assessed with CT and these two articles (1) and (2), provide comprehensive summaries.

Absent left kidney

This 30-years old indivdual had non-specific abdominal pain. Ultrasound suggested an absent left kidney and the patient came for a CT urogram. The CT (Fig. 1) clearly showed complete absence of the left kidney, which is extremely well appreciated on the CT urogram (Fig. 2).