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1.The possible cause could be
lymph nodal enlargement.
2.This enlargement will be seen in presence of any infection / inflammation ( it can be localised or generalised ) so if you are aware of any issue, please treat the cause.
3.The other possible cause could be lymph nodal pathology itself - for which you need to get an FNAC - fine needle aspiration cytology (sample of cells) to confirm.
4.In this case i would recommend an
ultrasound neck, which will help to evaluate the sours of the swelling, its nature ( cystic, solid, mixed) and where all and what all its extending to.
5.After that you can treat the possible cause - as many glands, congenital causes involved in this - so evaluate ant treat. Good luck.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.