2. Pyelonephritis/UTI. Infection and inflammation of the renal parenchyma can also lead to swelling and distension of the renal capsule.
3. Renal masses. This can be in the form of cysts (i.e. polycystic kidney disease) or tumors such as renal cell carcinoma or angiomyolipomas, either of which may distend the renal capsule and cause pain.
4. Renal hemorrhage (intraparenchymal bleeding due to injury or trauma).
6. Renal infarction. A rare cause of kidney pain, this can be due to a thromboembolic event or an in situ thrombosis of the renal artery or its branches. It typically presents with sudden onset, acute flank pain or abdominal discomfort, usually associated with nausea and vomiting. Fever can sometimes be seen as well.
7. Renal vein thrombosis. Can be more insidious or present acutely like renal infarction with sudden onset flank pain.
It is interesting that many of these syndromes/diseases can cause intense pain while others cause absolutely no pain at all. I saw a patient a few months back that had a large ureteral stone causing significant hydronephrosis with complete obliteration of the renal parenchyma. His history only revealed a remote history of stones 30 years ago. This is why renal imaging in invaluable. However, intervention at this point did not result in any improvement in renal function.
Additions: Loin Pain Hematuria Syndrome and Nut Cracker Syndrome.