Teaching Case

The patient was admitted in the emergency department after blunt trauma in the left renal region. The patient complained about pain in this region. Apart from skin bruises, the rest of the clinical examination was unremarkable.

On admission, the patient underwent contrast enhanced CT of the abdomen which revealed a small rupture of the left renal cortex, situated in the posterior surface of the kidney. This rupture had caused a large retroperitoneal haematoma (mainly in the left posterior pararenal space) and perirenal haematoma which in turn pushed the kidney anteriorly. There was also a small extravasation of the contrast medium in the left perirenal space. The excretion of the contrast medium was normal in both kidneys. (Fig. 1, 2)
The day after admission (15 hours later), the patient underwent a second abdominal CT where no remarkable change was observed. Of note was the fact that the gallbladder was opacified by a dense material which did not exist in the previous day’s scan. (Fig. 3)

The term “vicarious excretion” of a contrast medium (VECM) refers to the excretion of the contrast medium from a route other than the normally expected. In general, intravenous contrast media are mainly excreted by the renal glomeruli. However, 1.5%-2% of dose can be excreted by alternative routes including biliary tract, gastrointestinal tract and glandular epithelium. [1]
One common example is that of an intravenously administered contrast medium being excreted by the gallbladder. This type of excretion can occur with normal renal function and large doses of contrast agents or with impaired renal function or obstruction. For example, there are reports about iodinated contrast media being excreted by the small and large intestine in trauma patients with low blood pressure due to renal vascular pedicle injury. Other reports involve trauma patients with retroperitoneal haematomas where the i.v. contrast medium was excreted by the gallbladder. [1, 2, 3]
One possible mechanism that could account for this phenomenon is the sustained decrease in blood pressure which in turn decreases renal function and hinders the excretion of contrast medium. Consequently, the contrast medium is excreted by different organs like the gallbladder. [4]
In a published case series, such a type of vicarious excretion occurred both in patients with unilateral renal pathology and in patients with normally functioning kidneys. The time for the visualization of the contrast medium in the gallbladder varied from 20 minutes to 72 hours. It is possible that newer contrast agents are less excreted by the biliary tract because they bind less to proteins. [5] Another case series of patients with unilateral ureteral obstruction who underwent intravenous urography showed that vicarious contrast media excretion in the gallbladder may happen in 42% of patients. [6]
Another kind of VECM involves the excretion of per rectum administered gastrografin by the kidneys. As this phenomenon is only rarely expected, it can be falsely considered to represent recto-vesical fistula, thus delaying the patient’s management. This phenomenon is caused by the fact that roughly 3% of the orally ingested ionic agents is absorbed by the gastrointestinal tract into the portal vein through both a paracellular and a transcellular route. After its absorption, the contrast medium will be normally excreted by the kidneys but can sometimes cause adverse reactions. Increased absorption of oral contrast medium by the gastrointestinal tract may also occur in patients with diseases like enteric ischaemia, inflammatory bowel disease, gastroenteritis, diverticulitis or bowel obstruction. [7, 8]