What embryological process disruption is most likely causing the patient's imaging findings of pancreas divisum?

Failure of Fusion of Ventral and Dorsal Pancreatic Ducts Causes Pancreas Divisum

The patient's imaging findings of a dorsal pancreatic duct draining into the minor papilla and a separate smaller duct draining into the major papilla, along with abnormal splenic positioning, are diagnostic of pancreas divisum resulting from failure of fusion of the ventral and dorsal pancreatic ducts during embryological development.

Embryological Basis of Pancreas Divisum

Pancreas divisum is the most common congenital anomaly of the pancreatic duct anatomy, occurring in approximately 6-10% of the general population 1. This condition develops during the second month of gestation when:

1. The ventral pancreatic bud (which forms the inferior head of the pancreas) and the dorsal pancreatic bud (which forms the body, tail, and superior head of the pancreas) fail to fuse properly
2. This results in two separate, non-communicating pancreatic duct systems:
   • The dorsal duct (Santorini's duct) becomes the main pancreatic drainage system, emptying through the minor papilla
   • The ventral duct (Wirsung's duct) remains small and drains only a small portion of the pancreatic head through the major papilla

Diagnostic Imaging Features

The MRCP findings in this patient are classic for pancreas divisum 1, 2:

• Dorsal pancreatic duct draining into the minor papilla
• Separate smaller ventral duct draining into the major papilla
• Non-communication between the two ductal systems

The abnormal splenic position (anterior to the left kidney rather than posterior) represents an associated embryological anomaly that can occur with pancreas divisum, as both develop during similar embryological timeframes.

Clinical Significance

While most individuals with pancreas divisum remain asymptomatic, approximately 5% develop symptoms 3. The patient's presentation with acute abdominal pain, nausea, and vomiting is consistent with acute pancreatitis, which can occur in pancreas divisum due to:

• Relative obstruction to pancreatic exocrine flow through the minor papilla
• Inadequate drainage of pancreatic secretions through the small minor papilla orifice
• Increased intraductal pressure in the dorsal pancreatic duct system

Management Considerations

For symptomatic patients with recurrent episodes of pancreatitis and objective signs of outflow obstruction:

1. Initial evaluation should include ruling out common causes of pancreatitis with serum tests (amylase, lipase, liver function tests, triglycerides, calcium) 2

2. Endoscopic therapy may be considered:

   • Minor papilla sphincterotomy
   • Temporary stent placement
   • Balloon dilation

3. Surgical options may be considered in cases where endoscopic management fails 3

Potential Complications

Patients with symptomatic pancreas divisum are at risk for:

• Recurrent acute pancreatitis
• Development of chronic pancreatitis
• Pseudocyst formation
• Pancreaticopleural fistula in severe cases 4

The risk of post-ERCP pancreatitis is 10-15% in patients undergoing endoscopic therapy for pancreas divisum 2.

In summary, the patient's imaging findings are diagnostic of pancreas divisum resulting from failure of fusion of the ventral and dorsal pancreatic ducts during embryological development, with associated abnormal splenic positioning.