Dermoid and branchial cysts are common in this location but generally occur in childhood.Sebaceous cyst is likely. In tropical countries a tubercular cold abscess is thought of too. A fine needle aspiration study(FNAC) will help in getting a clearer picture.
For such a lump, three possibilities are there to be ruled out. These include:
1) It can be a swollen lymph node like a submandibular lymph node which has swollen in response to nasal and sinus infections.
2) Second possibility is of parotid gland infection which can be due to mumps or parotitis due to bacterial or viral causes.
3) Third possibility is of any stone in the salivary gland.
I suggest you to get an examination and a FNAC (fine needle aspiration cytology) done from your physician to confirm the diagnosis.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Thank you everyone for your responses! Your answers were of great help.
Wanted to give you all an update....
I went to see a dermatologist which ended up referring me to an ENT due to what she thought was possible parotid/salivary gland involvement.
The ENT doctor removed it in the office under local anesthetic. Before the ENT doctor started the excision, she said it felt like a lipoma although it was an unusual location, however she planned on sending it to pathology for a definite diagnoisis. During the excision, she said that it was obvious that it was just a large cyst and it ruptured so there was nothing to send to pathology.
I still do not know what caused it as it just "showed up out of nowhere" and was essentially asymptomatic and only doubled in size over a 3 month period.
Thankfully, it was nothing concerning! Thank you all again.