Cervical cyst. Coloured 3-D ultrasound scan of a mucous cyst (pale oval, lower right) on a patient's cervix. The cervix is the neck of the uterus (top), where it connects to the vagina (bottom). Mucous glands can become blocked leading to the development of mucous cysts (also called nabothian cysts). They are mostly between two and ten millimetres in diameter and are filled with yellow mucous. In most cases cervical cysts are considered normal and are not treated. Ultrasound is a diagnostic technique that sends high frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure.