Spot Diagnosis

MDCT for assessing pancreatico-biliary union

This article, by Itoh S et al , in the September issue of the AJR, shows how MDCT (using 4-slice) can depict the pancreatico-biliary ductal anatomy exceptionally well. This allows the diagnosis of the abnormal channel, especially in patients with choledochal cysts.

Because of the superior spatial resolution with multi-slice scanners, it is highly likely that the results with MSCT for this particular purpose, will be better than MRCP.

We have had a similar experience on our 64-slice CT. This is a child with a choledochal cyst (Fig. 1), where the abnormal pancreatico-biliary channel is extremely well seen (Figs. 2, 3).

Severe pancreatitis - abscess drainage

In patients with severe pancreatitis, one of the complications that often occurs is abscess formation. Invariably, it proceeds from infection of an acute fluid collection.

Once there is a frank abscess, an image-guided drainage can be easily performed, as in this case, where the drainage catheter is seen in the anterior abscess.

Pancreatitis - aspiration of fluid collections

In the absence of air, it is not possible to deduce whether a fluid collection in infected or not. If there is a strong clinical suspicion of infection, and if there is no air or air-fluid level, then a CT or USG-guided aspiration of one or more of the collections is suggested, for this purpose.

In this patient, there are multiple acute fluid collections (Figs. 1, 2). Infection was suspected and though frank pus was not aspirated (Fig. 3), the aspirate grew gram negative bacteria and the patient was put on appropriate antibiotics and improved.

Acute severe pancreatitis with infected necrosis

In patients with pancreatitis, CT scan is typically not done only for diagnosis, which is usually made on clinical and biochemical features. A baseline CT is usually performed at around seven days. However, if there is fever, raised white cell count, deterioration of general condition, etc. then a CT is performed earlier to look for complications.

On such complication is infection. Infection is not always easy to diagnose, however, if air is seen within a collection or area of necrosis, then this diagnosis can be confidently made.

Acute severe pancreatitis

In acute severe pancreatitis, there is more than one acute fluid collection and at least 30% or more necrosis, as seen in this case (Fig. 2 - arrow). Extensive peri-pancreatic fluid is seen (Figs. 1, 3). Necrosis is diagnosed as the absence of enhancement after at least 48 hours of onset of the inflammation. In the first 24 hours, the absence of enhancement may be due to ischemia and can lead to erroneous staging.

Acute mild pancreatitis with an acute fluid collection

Though still called acute mild pancreatitis, as compared to last week's example, this case illustrates a slightly more severe situation, without necrosis, but with an acute fluid collection seen in the lesser sac (Fig. 1).

Acute mild pancreatitis

Acute mild pancreatitis can be exquisitely depicted on CT scans. There is usually minimal peri-pancreatic fluid (Fig. 1) with stranding of the peri-pancreatic fat. There may be a small or single acute fluid collection. The pancreatic parenchyma usually enhances homogeneously and rarely is there mild necrosis.

Acute choledocholithiasis

Just as acute cholecystitis can be diagnosed by CT, so can acute choledocholithiasis. Both calcified (Fig. 1) and cholesterol (Fig. 2) calculi can be picked up. Cholesterol calculi may be difficult to see sometimes, especially in a non-dilated system, but subtle changes in density in the CBD should be looked for. MRCP of course in this setting is even more sensitive (Fig. 3) and all calculi can be seen as filling defects.

Acute cholecystitis

This is a 52-years old lady with acute pain in the right hypochondriac region. The CT showed a distended gall-bladder (arrow) with increased density and stranding of the adjacent fat, findings pathognomonic of acute cholecystitis.

Though routinely ultrasound is used for diagnosing or ruling out acute cholecystitis, CT also allows us to make this diagnosis with a good degree of certainty. Cholesterol calculi however are easily missed and the type of cholecystitis may be difficult to discern.

Liver Infarct

This 43-years old lady presented with acute abdominal pain. A CT scan was performed, which showed wedge-shaped hypodense areas in the periphery of the right lobe of the liver (Fig. 1). She also had hypodensities in the spleen (arrowhead) and in the kidney (arrow in Fig. 2). The celiac axis (arrowhead in Fig. 2) showed marked narrowing with soft tissue within.

This patient has a shower of emboli, with liver, spleen and bilateral renal infarction and she succumbed within 24 hours. Peripheral, wedge-shaped hypodensities are typically seen with liver infarction and may be due to hepatic arterial or more commonly portal venous disease.