To investigate the incidence and anatomic localization of retropharyngeal (RP) nodal involvement in patients with squamous cell carcinoma of the oropharynx.

The CT studies of 208 patients presenting with oropharyngeal carcinoma were retrospectively analyzed. The location of the nodal neck disease was registered according to recent consensus guidelines for target volume delineation, and special attention was given to the RP nodes. To obtain statistically significant predictors for RP nodal involvement, univariate and multivariate analyses were performed.

RP adenopathies were present in 16% of all patients and in 23% of those patients with nodal disease in other neck sites. Ipsilateral involvement of Level II and contralateral involvement of Level III predicted for involvement of the ipsilateral RP nodes on multivariate analysis (p < 0.05). A solitary ipsilateral RP node was present in 3 (9%) of 34 patients with RP nodes; 2 of these 3 patients had a primary posterior pharyngeal wall tumor. No patients presented with a solitary contralateral RP node.

Given the high incidence of RP nodal involvement in oropharyngeal cancer-16% of all patients and 23% of patients with pathologic nodal disease in other neck sites-RP nodes should be included in the target volume, especially in node-positive necks. In node-negative necks, inclusion of RP nodes into the target volume is advised in posterior pharyngeal wall tumors.