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.
The cause of simple kidney cysts is not fully understood, but they do not appear to be inherited. Being male is a risk factor, however, as is age: Almost half of all people age 50 or older have one or more simple cysts in the kidneys. The size of these cysts may also increase with age and may double over 10 years.