Criteria for the Diagnosis of Extranodal Extension Detected on Radiological Imaging in Head and Neck Cancer: HNCIG International Consensus Recommendations

Purpose/Objective(s)
Pathological evidence of extranodal extension (pENE) is known to be a negative prognostic factor in head and neck cancer (HNC). The available evidence suggests that radiologically or imaging-detected extranodal extension (iENE) is also associated with worse clinical outcomes. Although the reliable detection of iENE before initiation of treatment may help guide treatment selection, the diagnostic criteria and terminology used to report iENE are not widely agreed upon. The Head and Neck Cancer International Group (HNCIG) conducted a Delphi survey with the aim of developing a framework for decision-making on the most important areas of iENE diagnostic criteria and terminology requiring consensus.

Materials/Methods
All 21 international member groups of the HNCIG were invited to nominate a practicing radiologist with HNC expertise to join the global consensus panel. A three-round modified Delphi process with 18 international radiology experts representing 14 national clinical research groups was completed. Online questionnaires via a survey platform included four main sections pertaining to iENE: diagnostic criteria, inter-observer agreement, the impact of core biopsy, and classification systems.

Results
We generated consensus recommendations on the terminology and criteria for iENE to harmonize clinical practice and research. Overall, we achieved consensus on 47 items. The experts strongly agreed that there is no difference in iENE features between HPV-positive and HPV-negative HNC. Regarding iENE features, the experts strongly agreed that indistinct nodal margin, extension into perinodal fat, extension into adjacent structures, and conglomerate/matted/coalescent nodes should all be used as criteria by which to identify iENE, while nodal necrosis and capsular thickening should not be used as criteria for identifying iENE. The experts also agreed that “conglomerate”, “matted”, and “coalescent” do not describe different things. Importantly, we also proposed a new 5-tier classification system to aid diagnosis, which was supported by the majority of respondents over existing systems but which will require clinical validation. The experts strongly agreed in support of using a standardized classification system and synoptic reporting for iENE. The recommendations have been endorsed by 19 national organisations, representing 34 countries.

Conclusion
These guidelines will serve to standardize definitions and classifications to aid reporting in both clinical practice and research. We have also proposed a new classification system for the diagnosis of iENE that requires validation before wider clinical implementation.