Neck imaging reporting and data system (NI-RADS)

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NI-RADS (Neck Imaging and Reporting and Data System) is a lexicon and risk classification proposed by the American College of Radiology for reporting surveillance imaging of treated head and neck cancer. The terminology and categories may be applied to any head and neck malignancy (e.g. squamous cell carcinoma, mucoepidermoid carcinoma), and are intended to direct clinical management.

This article reflects revisions published in the 2018 ACR white paper .

Background

Standardized reporting systems (e.g. BI-RADS, LI-RADS) are designed to improve communication between radiologists, referring clinicians, and/or patients, in areas of high clinical impact. In head and neck oncology, imaging is primarily used to monitor for disease recurrence following initial treatment. Thus, NI-RADS was developed to address whether or not imaging demonstrates evidence of tumor recurrence .

The primary purpose of NI-RADS is to provide a framework for consistent reporting across readers and institutions. The framework consists of a standardized terminology and 4-tier classification, used to support direct management recommendations.

NI-RADS is intended for contrast-enhanced cross-sectional imaging (i.e. CT or MRI), with or without FDG-PET/CT. While protocols for the timing of post-treatment imaging vary by institution, surveillance may begin as early as 8-12 weeks post-treatment .

Imaging frequency

As there is no universal algorithm to direct timing/frequency of post-treatment imaging, NI-RADS advocates following institution-defined protocols in order to maintain consistency.

NI-RADS suggests timing for surveillance imaging in head and neck squamous cell carcinomas:

first post-treatment (baseline)
- 8-12 weeks after treatment, CT neck and PET/CT
- if negative...
second post-treatment
- 6 month after last imaging, CT neck and chest or (CT and PET/CT)
- if PET/CT negative... no need for further surveillance
- if CT negative...
third post-treatment
- 6 months after last imaging, CT neck
- if CT negative...
four post-treatment
- 12 months after last imaging, CT neck and chest

If the primary tumor is near or involving the skull base, MRI should be used instead of CT neck for evaluation of soft tissue/perineural involvement.

Category descriptors

The primary tumor site and neck lymph nodes are scored separately based on imaging suspicion of recurrence. Primary designator "X" can be used for an unknown primary.

NI-RADS 0: incomplete (prior imaging unavailable, but will be obtained)
NI-RADS 1: no evidence of recurrence
NI-RADS 2: low suspicion of recurrence
- 2a: superficial mucosal
- 2b: deep
NI-RADS 3: high suspicion of recurrence ("can and should be biopsied")
NI-RADS 4: known recurrence

NI-RADS 0 refers to a new baseline study in which prior comparison imaging is unavailable at the time of interpretation and will be procured in the future. If prior imaging cannot be obtained, the NI-RADS category and management decisions should be assigned based on available information.

NI-RADS 4 refers to recurrence that is either proven pathologically or considered definite by imaging or clinical criteria.

Imaging findings

CT

NI-RADS 1
- primary site
  - expected post-treatment changes with non-mass-like distortion of soft tissues
  - low-density submucosal/mucosal edema (post-radiation edema)
  - diffuse curvilinear mucosal enhancement (especially after radiation, i.e. radiation mucositis)
- neck
  - no nodal enlargement or new suspicious morphology (necrosis, extra-nodal extension)
NI-RADS 2
- primary site
  - 2a: non-mass-like, focal, mucosal enhancement
  - 2b: non-mass-like, ill-defined, deep soft tissue with only mild differential enhancement
- neck
  - residual abnormal, new, or enlarging node(s), without new suspicious morphology (necrosis, extra-nodal extension)
NI-RADS 3
- primary site
  - new or enlarging discrete soft tissue with intense differential enhancement (± osseous erosion )
- neck
  - enlarging node(s), with new necrosis or gross extranodal extension

PET

NI-RADS 1
- primary site
  - no abnormal FDG uptake
  - diffuse curvilinear mucosal FDG uptake after radiation (benign radiation mucositis)
- neck
  - no FDG avidity of residual nodes
NI-RADS 2
- primary site
  - 2a: mild focal mucosal FDG uptake
  - 2b: mild FDG uptake to ill-defined deep soft tissue
- neck
  - mild FDG uptake to residual nodes
NI-RADS 3
- primary site
  - intense focal FDG uptake to discrete nodule/mass
- neck
  - intense FDG uptake to residual, new, or enlarging nodes

When there is discordance between CT and PET, the NI-RADS category should be assigned to the lower of the adjacent scores. For example, when there is ill-defined deep soft tissue without any FDG uptake, the NI-RADS category is 1. When there is focal intense FDG uptake without discrete mass, the NI-RADS category is 2. When there is a discrete enhancing mass with at most moderate FDG uptake, the NI-RADS category is 2. Only when CT and PET are concordant for highly suspicious features is the NI-RADS category 3 assigned.

Management recommendations

Each NI-RADS category carries a management recommendation. Considering the most prudent next step in management is helpful when deciding on a NI-RADS category for borderline findings. These recommendations are as follows:

NI-RADS 0: obtain prior imaging examinations, after which a score can be assigned in an addendum
NI-RADS 1: continue routine surveillance
NI-RADS 2a: direct visual inspection of area of concern
NI-RADS 2b: additional PET or short-interval (3 month) follow-up with CT
NI-RADS 3: biopsy (image-guided or clinical) area of concern
NI-RADS 4: treatment of disease (with or without biopsy)

Performance

NI-RADS demonstrates good risk stratification. Rates of persistent or recurrent head and neck squamous cell carcinoma (as demonstrated on biopsy, subsequent imaging, or physical examination) have been reported by NI-RADS category :

NI-RADS 1: 4%
NI-RADS 2: 15-17%
NI-RADS 3: 59%