RADIOLOGY: NECK: Case# 33113: BENIGN CONGENITAL CYST- HYGROMA VS. BRANCHIAL CLEFT CYST. The patient is an 18 year old female with a 3 month history of left sided neck swelling. The patient reports that this swelling began after a mouth injury with subsequent infection. 1. Left neck fluid collection as above. The differential diagnosis would include cystic hygroma/lymphangioma, ranula, or atypical presentation of branchial cleft cyst. The associated swelling and pain could be related to an infection in this structure, although no evidence of infection is seen on todays examination. Abscess is not present. 2. Paranasal sinus mucosal thickening is consistent with mild sinusitis.