Diagnostic imaging of acute pancreatitis

Imaging modalities: from ultrasound to CT

Ultrasound serves as the first-line method, but in interstitial edematous pancreatitis, the findings are often completely normal. At best, the physician will see a diffuse enlargement of the gland, decreased echogenicity, and a small rim of peripancreatic fluid. The main drawback of conventional ultrasound is its inability to reliably confirm the presence of pancreatic necrosis.

The primary diagnostic method is contrast-enhanced computed tomography (CECT). CT allows for an accurate assessment of the volume of parenchymal necrosis and surrounding adipose tissue. It is critical to adhere to the timing: performing the study within the first hours of symptom onset is useless for detecting necrosis, as it requires 2–3 days to develop. If the patient suffers from renal failure and CT is contraindicated, contrast-enhanced ultrasound (CEUS) serves as an alternative, where zones of necrosis clearly stand out as areas without contrast uptake.

Classification of fluid collections

The Revised Atlanta classification strictly categorizes pancreatic collections based on their content (fluid or debris) and the duration of the process (before or after 4 weeks).

• Acute peripancreatic fluid collection occurs in the early phase, lacks a wall, and contains no solid necrotic components.
• Pseudocyst forms from fluid after 4 weeks. It is characterized by a well-defined fibrous capsule and uniformly low density without debris.
• Acute necrotic collection also appears in the early stages, but includes fragments of devitalized tissue. It is important to remember that ultrasound and MRI detect tissue debris in such collections better than CT.
• Walled-off necrosis (WON) is a "mature" necrotic collection formed after a month, enclosed by a thick capsule and containing liquefied and solid non-liquefied material inside.

Modified CT severity index

For objective disease staging and correlation with outcomes, the Modified CT Severity Index is used. This system sums up points across three main criteria:

1. Pancreatic inflammation: from normal (0 points) to the presence of fluid collections or peripancreatic necrosis (4 points).
2. Parenchymal necrosis: absence gives 0 points, involvement of up to 30% of the parenchyma is 2 points, more than 30% is 4 points.
3. Extrapancreatic complications: the presence of ascites, pleural effusion, or vascular issues adds another 2 points to the total.

Depending on the total score, pancreatitis is classified as mild (0–2), moderately severe (4–6), and severe (8–10 points). However, CT indices do not replace clinical severity scores such as APACHE-II.

Biliary pancreatitis: the role of MRCP

In biliary pancreatitis, early removal of bile duct stones is of decisive importance. However, endoscopic retrograde cholangiopancreatography (ERCP) carries significant risks on its own and can provoke complications, up to and including duodenal abscesses.

To avoid unwarranted interventions, magnetic resonance cholangiopancreatography (MRCP) is used. This method has a 100% negative predictive value: if MR cholangiography (especially on T2-weighted images) reveals no stones in the common bile duct, preoperative ERCP is strictly not indicated for the patient.

Complications of acute pancreatitis

The detection of complications on tomograms directly correlates with patient survival.

• Infected necrosis: on CT, it often manifests as characteristic gas bubbles within the collection cavity. This is the most formidable complication.
• Vascular pathologies: enzymatic aggression can lead to splenic vein thrombosis or arterial erosion with the formation of pseudoaneurysms. In case of their rupture and hemorrhage, selective angiography with coil embolization of the vessel becomes the method of choice.
• Gastrointestinal involvement: close contact of intestinal loops with the inflammation zone threatens edema, ischemia, and spontaneous perforation of the stomach or duodenal wall.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Assessment of pancreatitis severity using Ranson, APACHE-II, and BISAP scores.
• Differential diagnosis of infected and sterile pancreatic necrosis.
• Technique of performing MRCP when choledocholithiasis is suspected.
• The role of contrast-enhanced ultrasound in dynamic monitoring.
• Endovascular treatment of vascular complications (pseudoaneurysm embolization).

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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