**1.1 Natural history of pancreatic fluid collections**

*Pancreatitis*

**Figure 1.**

**Figure 2.**

*echogenic debris in the cyst cavity.*

*solid component within the fluid collection.*

**8**

**Figure 3.**

*necrotic debris in the cyst cavity.*

*Endosonographic image in a case with walled off necrosis. Not the well-defined boundaries with echogenic* 

*Endosonographic image in a case with pancreatic pseudocyst. Not the well-defined boundaries without any* 

*Endosonographic image of acute necrotic pancreatic fluid collections. Note the ill-defined boundaries and the* 

APFCs develop in about 20–40% of patients after acute interstitial pancreatitis [2–4]. Majority (~90%) of APFCs resolve and do not transform into pseudocyst. Moreover, majority of the pseudocysts resolve or reduce in size with time and therefore, do not require an intervention [4]. On the other hand, majority (90–100%) of the patients with acute necrotizing pancreatitis develop ANPFCs. Nearly half of the patients with ANPFCs develop walled off necrosis (WON) [2, 3]. The natural history of WON is not well known and appears to be more unpredictable than pseudocysts. An intervention may be required in one quarter to more than half of the patients with WON [2, 3].
