Zenker diverticulum

Large mottled soft tissue density in the retropharyngeal and retroesophageal soft tissues from C5 to at least T1 level, measuring approximately 2.9 cm AP and
5 cm craniocaudal diameter. Smooth radiolucent stripe consistent with adjacent gas at its superior and posterior aspects. Superiorly, there is a well
demarcated line separating it from the hypopharynx, which is moderately dilated.
The cervical esophagus is displaced anteriorly and appears compressed. Neck soft tissues are otherwise unremarkable. Incidental note is made of anterolisthesis at C3-4, C4-5 and C5-6, likely due to facet joint OA. Multilevel lower cervical degenerative disc disease, most prominent at C5-6.
IMPRESSION:
Large soft tissue density with adjacent gas in the retropharyngeal and retroesophageal soft tissues.  Impacted food within a large Zenker's diverticulum is favored. Retropharyngeal abscess is considered unlikely in the absence of supporting clinical features. Further evaluation via barium swallow is recommended.

The tonsillar beds bilaterally appear irregular with calcified nodules identified on both sides suggesting prior or chronic inflammation.
There is a gas containing structure immediately posterior to the origin of the esophagus in the midline. There is an air-fluid level and some apparent food debris within this. Appearance is typical of Zenker's diverticulum.
Otherwise, multinodular goiter is noted. 
Visualized portion of the cranial structures shows no apparent intracranial
abnormality.
Small 3.3 mm osteoma suspected left ethmoid sinus.
Severe degenerative spondylosis is seen throughout the cervical spine with multilevel disc space narrowing most obvious at C5-6 and C6-7.
Bony defects in the occipital bone near the midline appear to relate to Pacchionian granulation as a normal variant.

Erect swallow was done.  There is immediate filling of a moderate-sized Zenkers
diverticulum.  There are filling defects within this suggesting food residue. Barium periodically refluxes from the Zenker's diverticulum back into the pharynx.
 The rest of the esophagus appeared normal.