**Core Concept**
A pancreatic pseudocyst is a fluid collection that forms in the abdomen due to pancreatic juice leakage, often as a complication of pancreatitis. These pseudocysts can cause various symptoms and may require drainage or surgical intervention.

**Why the Correct Answer is Right**
The commonest complication of pancreatic pseudocysts is rupture. Rupture can lead to leakage of pancreatic juice into the peritoneal cavity, causing chemical peritonitis and potentially life-threatening infection. This can occur when the pseudocyst wall is weakened, allowing the fluid to escape into surrounding tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** Infection is a potential complication of pancreatic pseudocysts, but it is not the most common complication. Infection typically occurs when the pseudocyst becomes contaminated with bacteria.
**Option B:** Hemorrhage can occur in the setting of pancreatic pseudocysts, particularly if the pseudocyst erodes into a nearby blood vessel. However, it is not the most common complication.
**Option C:** Obstruction is a potential complication of pancreatic pseudocysts, particularly if the pseudocyst compresses or obstructs the nearby duodenum or bile duct. However, it is not the most common complication.

**Clinical Pearl / High-Yield Fact**
Pancreatic pseudocysts are more common in patients with chronic pancreatitis, and their formation is often preceded by an episode of acute pancreatitis.

**Correct Answer: B. Hemorrhage is a rare complication of pancreatic pseudocysts, but it is not the most common complication.