Emergency: Abdomen

Discussion

65-year-old female was found unconscious at home. Brain and carotid CT excluded acute vascular cerebral pathology. High fever, hypotension, and signs of multiorgan failure indicated sepsis, and abdominal dual-energy CT was performed to determine the origin.

Virtual non-contrast images help demonstrate urinary tract stones obscured by iodine by removing iodine remaining from recent previous studies.

Axial images

Conventional CT scan showed iodine in the urinary tract from previous studies and demonstrated decreased areas of enhancement of left renal parenchyma with perirenal fat infiltration. Mild hydronephrosis was present, but urinary tract stone could not be distinguished from iodine. Virtual non-contrast images demonstrated the stone in left upper ureter as a cause of obstruction. Iodine density and Z effective images showed renal parenchymal areas with lower iodine content compatible with pyelonephritis, and also allowed better demarcation of these areas. The stone was removed by ureteroscopy. Urine and blood culture was positive for E. coli. The patient was treated with nephrostomy and responded well clinically to appropriate antibiotic therapy according to antibiogram results.

Iodine in urinary tract from recent previous studies may obscure urinary stones. Virtual non-contrast images demonstrate the stone by removing iodine from the image. This is particularly important in diagnosis for appropriate treatment. Such patients may develop serious complications like severe pylenephritis and septic shock. Urinary stones might be hidden due to contrast medium excretion in the urinary tract. Spectral CT has the capacity to separate iodine from calcium and demonstrate the presence of a stone.

Conventional CT axial image: proximal ureter stone (white arrow) cannot be distinguished from iodine in the urinary tract (blue arrow) from recent previous imaging with contrast.

Virtual non-contrast axial image: demonstration of proximal ureter stone (arrow) by removal of iodine in urinary tract.

Iodine density axial image: iodine density of the affected areas of left kidney is decreased (2.04 mg/ml, blue arrow) compared to adjacent non-affected parenchyma (5.52 mg/ml, white arrow). Note the removal of the stone on this iodine density image.

Z effective axial image: lower effective atomic number (8.40) and lower iodine content of the affected part of the left kidney is color coded in light blue-green (blue arrow) compared to adjacent non-affected renal parenchyma with higher effective atomic number (9.75) color coded in dark blue (white arrow).

History