Dermatofibroma are common benign skin tumours that cause lumps in the skin and frequently cause concern upon discovery. The causes of dermatofibroma may include a reaction to trauma such as insect bites but the precise cause is often unclear.
Causes. It's not clear what causes simple kidney cysts. One theory suggests that kidney cysts develop when the surface layer of the kidney weakens and forms a pouch (diverticulum). The pouch then fills with fluid, detaches and develops into a cyst. 1  Symptoms. 2  Risk factors.
People with simple kidney cysts have sacs that are filled with fluid within their kidneys. It is possible to have one or more cysts in one or both kidneys. The exact cause of simple kidney cysts is not known but they tend to be more common as people age.