HNSCC is one of the major medical causes of mortality and morbidity worldwide [15]. The incidence of HNSCC varies among different geographical regions according to the prevalence of risk factors [16]. The response to the surgical and radio-chemotherapy treatment is an important prognostic and predictive factor in patient survival [17, 18]. The distorted anatomy and soft tissue fibrosis occurring after HNSCC treatment complicating the scanned image finding and may mimic tumor recurrence which represents a challenge for precise and clear reporting, confusing the clinician, especially when it misses the recommended further surveillance.
The American College of Radiology has developed and updated a structured reporting algorism named Reporting and Data system which was first applied to breast, later on, several systems were developed for different body region as liver, thyroid, prostate, coronary artery, ovarian, colon, and recently head and neck. Each system is formed of imaging lexicon and features with reporting template and algorithm for further management [8, 13, 19, 20].
The NI-RADS scoring system was designed based upon the available literature evidence, best available practices and experience, multidisciplinary consensus, and the biopsy result of the suspicious lesion. This scoring system provided a standardized nomenclature for reporting patients with treated HNSCC and guiding their further management [6, 7, 9], it was originally developed for reporting the CECT and positron emission tomography (PET) in treated HNSCC patients, the CEMRI was easily adapted to the NI-RADS.
To our knowledge, two previous studies have evaluated the reliability of the NI-RADS, and they revealed an almost perfect interobserver agreement for assigning NI-RADS categories [7, 12], on the other hand, few studies have evaluated either the negative or the positive predictive value of the NI-RADS categories in either the first or the follow-up surveillance imaging [11, 12, 21], yet in the current study, we evaluated the NPV of the NI-RADS 1 and 2 lesions and the PPV of the NI-RADS 3 lesion. The predictive value was calculated in two of the laryngeal and oral cavity SCC subsites separately and in combination including the first, the follow-up, and the overall scans, also, we analyzed the primary NI-RADS 3 lesion lexicon using a logistics regression module for the morphological and enhancement features.
In the current study, the surveillance program of the treated laryngeal and oral cavity SCC was performed with CECT and CEMRI, the choice of either imaging modality was tailored according to the primary tumor site, the specific clinical question to be answered and the patients’ clinical status, considering the lengthy CEMRI examination.
In this study, the post-treatment surveillance scans were assessed according to the NI-RADS, a significant trend for tumor recurrence was noted with increased NI-RADS category.
For both first and follow-up scan, the overall recurrent rate of NI-RADS 1 and 2 primary lesions was 9.4% and 25.9% respectively with the NPV of 90.6% and 74.1%. Krieger et al. [12] reported a slightly lower recurrence rate for primary NI-RADS 1 and 2 lesions with higher NPV of 96.5% and 81.6% respectively. The PPV of the NI-RADS 3 primary lesion in our study was 80% which was higher than the reported value (59.4%) seen in the Krieger et al. [12]. This difference is explained in part by the different imaging modality as the surveillance imaging modalities in the Krieger et al. [12] study were PET/CT and CECT, yet in the current study, the surveillance imaging was based solely in the cross-sectional examination. Furthermore, Krieger et al. [12] reported much higher PPV for combined primary and nodal NIRADS 3 diagnosed with CECT only, with a recurrence rate measuring 91.7%, near similar result was seen in the current study which revealed primary and nodal lesion recurrence in 88.8% of patients assigned as NI-RADS 3 category. These data suggest that the CECT and CEMRI are more specific and the metabolic and functional data gained with the PET examination shows an impact on the predictive value of NI-RADS score.
In this work, the recurrence rate of the overall first and follow-up NI-RADS 1 nodal lesion was 3.6% which was similar to Krieger et al. [12] result. The NPV of nodal NI-RADS 2 was 75% which was lower than the value seen in the Krieger et al. [12] study who revealed NPV of 85%. On the other hand, the PPV of nodal NI-RADS 3 was 81.8% which was higher than the value seen in Krieger et al. [12] study (70%). Different studies will vary at their PPV and NPV according to variable time points of the included studies. In the current study, the PET/CT was not used as a surveillance imaging and the nodal NI-RADS 3 lesions diagnosed solely according to the abnormal morphological features.
As regards the post-treatment first scan, the NPV of NI-RADS 1 and 2 primary lesions were 100% and 73.3% respectively. Hsu et al. [11] reported a slightly lower recurrence rate for the post-treatment primary NI-RADS 1 lesion with NPV of 93.6%, yet the NPV of primary NI-RADS 2 lesions was higher than our value (88.9%). The PPV of the first post-treatment primary NI-RADS 3 lesions in our study was 55.6%; a lower value was seen in Hsu et al. [11] who reported PPV of 38.5%.
Although no significant difference among the first and the follow-up recurrence rate, yet the PPV of NI-RADS 3 lesion was higher in the follow-up scan, a similar result was reported by Krieger et al. [12]. The first post-treatment surveillance scan represents a challenge for its interpretation due to the distorted and complex anatomy, in addition to the early post-treatment changes that usually regress in the further follow-up scans.
The PPV of the oral cavity NI-RADS 3 primary lesions was higher than that of laryngeal lesions. Further studies may reveal a difference in the NI-RADS predictive value among different HNSCC subsites. The previous study revealed an almost perfect interobserver agreement in the discrimination of the treated laryngeal and oral cavity primary target lesion [7].
The odd of tumor recurrence for NI-RADS 3 primary lesion was 19.6 times that for NI-RADS 1 and 2 primary lesions. The odd ratio was similar if either the morphological lexicon of new/enlarging discrete nodule/mass or the enhancement lexicon of discrete nodular enhancement was detected. Future studies may highlight the contribution of a single NI-RADS lexicon in the recurrence rate. Abdelaziz et al. [7] revealed significant interobserver agreement for detection of discrete nodule/mass and for excluding tissue enhancement.
The accuracy of NI-RADS 3 for lesion recurrence was 80.8%, yet there was still 19.2% lesions in which biopsy recommendation was not balanced by the positive recurrence, further evaluation of the enhancement pattern of the NI-RADS lesion with the dynamic contrast-enhanced MRI, MRI perfusion, and diffusion which was not involved in the NI-RADS lexicon may provide a precise characterization of NI-RADS 2 and 3 lesions, and differentiating between tumor recurrence and post-treatment soft tissue injury which mimics residual tumor.
Finally, the NI-RADS provide a relevant skeleton for further management recommendation based on the evidence-based recurrence rate of each NI-RADS category, assuring patient with NI-RADS 1 and 2 categories, and provide a reasonable reason for biopsy in NI-RADS 3 lesion.
Limitation
Some limitations were encompassed in our study. First, the NI-RADS 3 lesions represented a small percentage of overall NI-RADS lesions in this limited number study and the major NI-RADS lesions were categorized as NI-RADS 1 (17.6% (26/148) versus 58.8% (87/148) respectively), yet our percentage was greater than previously published figures where NI-RADS 3 lesions represented only 4.8% and 5.2% [11, 12]. Second, we did not scrutinize all HNSCC subsites collectively. The investigation of two different subsites separately highlights the difference in the NI-RADS categories and recurrence rate among them. Further study may provide data for each subsite. Third, in this study, we did not correlate the NI-RADS categories to the tumor staging, prevalence of human papillomavirus infection, and the type of management either surgical, radiotherapy, chemotherapy, or combination management. Finally, the combination of CEMRI and CECT scans in our study, instead of investigating each modality separately, yet the previous study also involved the PECT/CT and CECT collectively [11].