<unk> 's<unk>  is usually acquired but may also be congenital (inborn) or iatrogenic <unk>  by medical treatment). Although most<unk>  are relatively benign,<unk> 's<unk>  may reflect serious pathology in the neck or chest (such as a Pancoast tumor or thyrocervical venous dilatation) and hence requires workup.
Horner's syndrome causes
Pott's disease causes
Schwannoma causes
Cowden syndrome causes
Dermoid cyst causes
Malignant peripheral nerve sheath tumor causes
Noonan syndrome causes
Acoustic neuroma causes