Teaching Case

A 67-year-old male patient presented to the emergency department with right lateral abdominal pain of acute onset. On clinical examination, there was tenderness of the right lateral abdomen. His past medical history included atrial fibrillation.

The patient was referred for abdominal contrast-enhanced CT which demonstrated a low-attenuation area of the right kidney, showing no enhancement (Fig. 1). A lack of contrast filling at the right renal artery was noted, suggesting thrombosis. On closer observation of angiography, a normally opacified supernumerary renal artery was seen originating at a higher level of the aorta. The part of the kidney vascularized by the supernumerary artery showed normal enhancement (Fig. 1). A couple of days later, the patient was referred for follow-up examination with US. On colour Doppler technique, there were less blood flow signals noted on the upper half of the kidney. On CEUS, the infarcted part of the cortex showed no enhancement while the lower half of the cortex showed normal enhancement (Fig. 2).

Renal infarction can be caused by either compromise of arterial or venous renal circulation. Potential causes include embolism from left cardiac cavities, possibly occurring in the setting of atrial fibrillation, arterial atherosclerosis, dissection, vasculitis and renal vein thrombosis. Patients with renal infarction usually present with acute abdominal pain and are urgently referred for imaging [1, 2]. Ultrasound (US) may occasionally detect renal infarcts as hypoechoic areas of the renal cortex showing decreased or absent colour flow signals on colour Doppler technique [1].
Contrast-enhanced ultrasound (CEUS) has been recently introduced in the evaluation of renal pathology gaining wide acceptance. CEUS is characterized by increased sensitivity and confidence in identifying infarcts compared to the unenhanced technique. It is estimated that CEUS diagnostic performance for the diagnosis of ischemia is similar to that of computed tomography. Infarcts appear on CEUS as wedge-shaped areas showing no enhancement while they can be readily differentiated from cortical necrosis thanks to the technique’s increased spatial resolution. US contrast agents have an excellent safety profile, are not contraindicated in renal failure and remain strictly within the blood vessels, accounting for the technique’s increased sensitivity in differentiating viable from necrotic tissue [3, 4, 5].
Contrast-enhanced multi-detector computed tomography (MDCT) represents a valuable modality for diagnosis of renal infarction, which appears as a single or multiple wedge-shaped areas of low-attenuation within an otherwise normal appearing kidney. The infarcted area may occasionally appear enlarged due to inflammation and oedema. MDCT is also valuable in identifying potential causes of renal infarcts such as thrombosis, dissection and atherosclerosis of the renal vasculature. It should be kept in mind that pyelonephritis may also be complicated by segmental infarction and wedge shaped changes, which may be of venous aetiology if there is normal arterial opacification [2, 6]. Collateral capsular perfusion may sometimes give rise to the cortical rim sign which refers to the presence of a thin rim of enhancement in the renal cortex, noted several days after the occurrence of ischemia. Other findings of renal ischemia include perirenal fat stranding, subcapsular fluid collections and thickening of the perirenal fascia [7-10].