Hello,
Thank you for writing at HCM.
There are two most common causes of the "cysts" behind the ear.
1. One is called sebaceous cyst- which is a cyst filled with "fatty material". These are very common and are not dangerous at all and we remove them just to not let them be too big and cause us esthetic problems and on the other hand a big lump removed will leave a bigger scar also.
2. Another cause might be a lymphnode. These are oval shaped structures that react to infection and is a normal finding many times. You might need to check your
scalp for any wounds that might be the cause. Sometimes we do not find a cause and this is OK but a doctor needs to see the lump to make the difference between a sebaceous cyst and a lymphnode. In the case of a lymphnode it not important to remove it, they generally do not tend to grow with time, the most important thing with a lymphnode is to check if it is a reactive one (benign- they are soft, oval, regular borders and smaller than 2 cm) or not.
If the doctor thinks it is a sebaceous cyst will use local injection on the skin over the cyst to numb it and try to remove the cyst with the capsule and put sutures to close the skin.
If the doctor thinks it is a lymphnode he/she will have to evaluate if it is benign or not and if he/she thinks it is benign very likely you will not be recommend removal but review of the lump in a few months or earlier if it grows. In case the doctor is not sure he/she might ask for further tests than just watchful approach.
Hope this answers to your question