1. Occasionally, acute pancreatitis
may be mistaken for acute appendicitis
, and the patient goes for appendicectomy. This happens because acute appendicitis is one the many differential diagnoses for acute pain in abdomen which is actually caused by acute pancreatitis. Even I have a personal experience of one such case of acute pancreatitis who presented like acute appendicitis and went for appendicectomy. During this patient's subsequent attacks of pain, the diagnosis of acute pancreatitis was established. This is not always the case, but is possible. Anyway.
2. Considering that appendicectomy was performed for acute appendicitis truly, the subsequent problem of pancreatitis has no relation with the previous appendicectomy. In other words, don't think that pancreatitis is a complication of appendicectomy.
3. Since you haven't mentioned blood investigation reports, I will not be able to define the pathology in your brother's case - whether recurrent acute pancreatitis or chronic relapsing pancreatitis. Anyway. In ~ 40% of cases the exact cause of pancreatitis cannot be ascertained. That is called 'idiopathic' pancreatitis. Nevertheless, keep in mind that eventually, gallstone
may turn out to be responsible later although it is not detected in the present imaging investigations.
4. Consider MRCP (Magnetic Resonance CholangioPancreatography) since US and CT scans have failed to detect the cause.