I have swelling and pain in my armpit, neck, and collarbone on the left side. ultrasound showed a mass in my neck but a follow-up ct scan showed nothing. ultrasound also showed none of my lymph nodes are swollen. what else could the swelling be?

Was the neck swelling documented by a physician's examination and, if so, was it also noted when the CT scan was done? In a case like yours I'd recommend consulting an ENT specialist and would also review the ultrasound and the CT scan with the radiologist and the ENT to determine whether any other studies, such as a chest CT scan or an MRI or needle biopsy.of any lump would be helpful.