Here is a pathologically proven case of neck bronchogenic cyst (NBC) that is a rare neck cystic lesion. 

Although NBCs generally present liquid density on CT scans, in some cases, they can present densities greater than 30HU, due to the high protein content, as in the current case. No enhancement is observed after contrast administration. Ultrasound evaluation reveals a rounded mass, with well-defined edges, inner echogenic particles, and posterior acoustic enhancement.

This possibility should be considered in the differential diagnosis of asymptomatic neck mass in adults together with branchial cleft and thyroglossal duct cysts. However, the definitive diagnosis is obtained by histopathology.