Sonographic appearance in edematous form
The mild (interstitial edematous) form of acute pancreatitis occurs in 70–80% of cases. Pathophysiologically, the process is caused by proteolytic enzymes damaging acinar cells, triggering local edema and organ enlargement. At the same time, the inflammatory response is insufficient for tissue destruction.
On ultrasound, the parenchymal appearance may remain completely normal. However, B-mode ultrasound most commonly reveals the following signs:
- Generalized (much less frequently focal) enlargement of the pancreas.
- Heterogeneous or diffusely decreased echogenicity (reduced reflectivity).
- Difficulty in delineating the organ's contours.
- Visualization of a small rim of peripancreatic fluid.
When using contrast-enhanced ultrasound (CEUS), edematous pancreatitis is characterized by homogeneous parenchymal hyperenhancement that persists for about two minutes after contrast injection.
Limitations of ultrasound and transition to CT
A strong inflammatory response triggers cell apoptosis and fat necrosis, which rapidly spreads to the peripancreatic adipose tissue. The development of necrotic changes is the primary factor determining morbidity and mortality.
The main limitation of the ultrasound method is that it fails to reliably detect necrosis. When a severe course is suspected or confirmed, contrast-enhanced CT (Contrast-enhanced CT) becomes the primary imaging method of choice.
CT Features:
- Timing: The method may underestimate the extent of necrosis if performed too early (within the first 24 hours), as 2–3 days are required for the zone of tissue destruction to form. Early CT rarely alters management in the first 24 hours.
- Dynamic monitoring: Repeat computed tomography is indicated for persistent or worsening organ failure, as well as the appearance of signs of sepsis.
- Protocol: Unlike cancer staging, staging pancreatitis requires only a single venous phase CT study (single venous phase CT study) with a contrast dose of 1.5–2 ml/kg. Mandatory intravenous contrast enhancement makes CT the most reliable method for assessing the extent of inflammation and fluid collections.
Severity assessment and prognosis
Detection of parenchymal necrosis strictly correlates with the risk of local and systemic complications. Organ failure develops in 6% of patients with mild pancreatitis, 9% with moderately severe, and 50% with severe. The severe form is associated with extremely high mortality (29.5%) due to respiratory or hemodynamic failure, as well as infectious complications.
To stage the process on CT taking into account fluid volume and necrosis, the Modified CT Severity Index (Modified CT Severity Index) is used. It correlates better with clinical outcomes.
Scoring system:
- Inflammation: normal pancreas — 0; intrinsic changes with/without peripancreatic inflammation — 2; fluid collection or peripancreatic necrosis — 4.
- Parenchymal necrosis: absent — 0; $\le$30% of volume — 2; >30% of volume — 4.
- Extrapancreatic complications: presence of at least one feature (pleural effusion, ascites, gastrointestinal involvement, vascular complications) — 2 points.
Classification by total score:
- Mild (Mild): 0–2 points.
- Moderate (Moderate): 4–6 points.
- Severe (Severe): 8–10 points.
Important to remember: imaging indices do not replace classic clinical severity scores (Ranson, APACHE-II, BISAP) and laboratory markers (e.g., C-reactive protein / C-reactive protein), although the use of the latter may be limited by insufficient specificity.
To remember CT severity assessment, recall the acronym VIE: Inflammation, Necrosis, Extrapancreatic complications — the three pillars of the modified index.
Class and exam questions
Can the diagnosis of pancreatic necrosis be established based solely on ultrasound data?
No, ultrasound does not allow reliable visualization of parenchymal necrosis. Contrast-enhanced CT is necessary to confirm and assess the volume of necrotic tissue.
Why is contrast-enhanced CT not recommended in the first 24 hours of the disease?
In the first 24 hours from clinical onset, CT may underestimate the true extent of parenchymal damage. Complete formation of the necrotic zone takes 2 to 3 days.
How does the parenchyma appear in edematous pancreatitis on contrast-enhanced ultrasound (CEUS)?
Homogeneous hyperenhancement of the pancreatic tissue is observed, which remains stable for approximately 2 minutes after contrast administration.
What else to study on this topic
- Clinical severity scoring systems for acute pancreatitis: Ranson, APACHE-II, BISAP
- Serum inflammatory markers: role and limitations of C-reactive protein
- Pathophysiology of organ failure development in severe pancreatitis
- Differential diagnosis of imaging protocols: acute pancreatitis vs. pancreatic cancer
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