**Core Concept**
Calculous cholecystitis, also known as acute gallbladder inflammation, is often caused by gallstones obstructing the cystic duct and leading to ischemia and necrosis of the gallbladder wall. This condition is a common cause of acute abdomen and can be complicated by gangrene or perforation of the gallbladder.

**Why the Correct Answer is Right**
The pathophysiology of calculous cholecystitis involves the obstruction of the cystic duct by gallstones, leading to stasis of bile and subsequent ischemia of the gallbladder wall. The gangrenous and perforated forms of cholecystitis are complications of this process. The inflammation and ischemia can lead to the release of pro-inflammatory cytokines and mediators, which exacerbate the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be incorrect if it is a condition not typically associated with calculous cholecystitis, such as a congenital anomaly of the biliary system.
**Option B:** This option might be incorrect if it is a condition not typically associated with calculous cholecystitis, such as a viral infection of the gallbladder.
**Option C:** This option is likely a condition associated with calculous cholecystitis, such as a gallstone impacted in the cystic duct or a stone in the common bile duct.

**Clinical Pearl / High-Yield Fact**
A key clinical consideration in the management of calculous cholecystitis is early surgical intervention to prevent complications such as gangrene or perforation of the gallbladder.

**Correct Answer: C.**