Hi welcome to HCM.... Here you have left side swelling and you are saying its cyst ...... So it might be benign cystic lesion or if solid it can be lymph node ....And so it can be metastatic lymph node also .... So consult ENT surgeon for examination... Because examination of swelling must in your case. ... Then to decide its nature FNAC taken from lesion to rule out whether it is inflammatory , benign or malignant lesion ... According to diagnosis treatment given ..... If needed for confirmation of diagnosis biopsy done and send for Histopatho examination ... If it comes benign than no need for much worry ... But if it is malignant one than search for primary done .... Take care. ....