DW-MRI (diffusion-weighted magnetic resonance imaging) is an effective non-invasive imaging technique for tissue characterization. DWI has been considered as a cancer biomarker and could distinguish benign from malignant tumors [13]. Our research aimed to establish the diagnostic validity of the diffusion-weighted magnetic resonance imaging for the distinction between benign and malignant lymph nodes via comparing the ADC values, as solving out this diagnostic problem is mandatory for the management of the patients.
Our study revealed that the prevalence of tumors in the head and neck was higher in males (55%) than females (45%) without significant differences, in agreement with Lambert et al. [14] who reported that males are highly affected than females, but with a significant difference, with a ratio ranging from 2 to 4 folds. Our study results showed that Hodgkin disease incidence is higher in young age groups, although the prevalence of non-Hodgkin disease among the elderly population was higher, with no significant difference. Our study findings are in line with previous studies which reported that Hodgkin lymphoma is higher in younger age groups [15,16,17].
Our analysis included 9 nodes less than 1 cm in their shortest axis diameter; 3/9 were metastatic and showed a pattern of restriction on DWIs and opposing low ADC value. On the other hand, these 9 nodes displayed no definite morphological characteristics of malignancy, such as necrosis and ill-defined margins in the conventional MRI sequences, and classification of metastatic nodes would have been very unlikely, in agreement with ElSaid et al. [18] who reported that all metastatic lymph nodes less than 1 cm were missed due to anatomical MR imaging criteria based on size.
In the present study, on the contralateral side of the primary tumor, 1/3 metastatic differentiated squamous cell carcinoma lymph nodes (< 1 cm) were found, in agreement with Vandecaveye et al. [19] and ElSaid et al. [18] who reported the degree to which DWI changes nodal differentiation efficacy via depicting subcentimetric nodal metastases may affect the clinical management. Our study showed that the pathologically proven malignant lymph nodes (29 out of 30 cases) showed increased signal in b 1000, and low signal in the corresponding ADC maps, the inflammatory diseases (5 out of 6 cases), and reactive lymphoid hyperplasia (4 out of 4 cases) showed signal intensity reduction for increased b values (b = 1000) and intermediate signal intensity on ADC maps representing facilitated diffusion. Our study findings agreeing with Youssef et al. [20] and Abou khadrah and Imam [12] that the DWI with ADC mapping were useful as non-invasive tools for distinguishing between the benign and malignant solid head and neck lesions by using b values 800 and 1000. The malignant lymph nodes in our sample had significantly lower ADCs than benign lymph nodes. The ADC measurements of benign and malignant lymph nodes varied considerably with a P < 0.001, these results agree with Youssef et al. [20]. In our research, the mean ADC value of the 30 malignant lymph nodes was 0.971 ± 0.305 × 10−3 mm2/s, while on the other hand, the mean ADC value of the 10 benign lymph nodes was 1.98 ± 0.33 ± 3 mm2/s with the threshold ADC value for separating malignant from benign nodes obtained from the receiver characteristic analysis being 1.30 × 10−3 mm2/s with 94% sensitivity and 100% specificity. In agreement with Abou khadrah and Imam [12] who recorded 94% accuracy in characterizing the metastatic lymph nodes using a threshold of 1.0210−3 mm2/s. The mean ADC values recorded for benign and metastatic lymph nodes were 1. 24 ± 0.1610−3 mm2/s and 0.78 ± 0.0910−3 mm2/s respectively.
In our research, malignant lymph nodes had been subdivided into subgroups of metastatic carcinoma and lymphoma based upon the histopathology. An attempt was made to distinguish between them according to their ADC values. The mean ADC value for metastatic carcinoma (1.079 × 10−3 mm2/s) was a little higher than that of the lymphoma (0.781 × 10−3 mm2/s). The ADC threshold value for metastatic differentiation from lymphomatous lymph nodes obtained from receiver operating characteristic (ROC) analysis was 0.9 × 10−3 mm2/s with 90% sensitivity and 75% specificity,
Thirty-four true-positives and 6 false-positives were shown via statistical data, providing a sensitivity of 100%, and specificity of 85%; these results agree with Usama and Ahmed [21] who reported the same results of the present study.
Limitations of this study
First, our analysis has some drawbacks, such as being a small cohort study. Also, our statistical tests were carried out on the number of nodes involved, not the number of patients. Second, for several reasons, we did not provide standardized ADCs: (1) As far as we know, the value of using standardized, rather than absolute, ADCs in head and neck imaging at DW was never reported. Unlike the brain, the region of the head and neck is distinguished by an extremely heterogeneous diffusivity of the tissues due to the presence of tissues of distinctly different histological origins. The spine is also the most appropriate reference tissue for normalization. However, echo-planar imaging of the spinal cord is hampered by strong susceptibility influences caused mainly by the osseous elements of the spinal column, which induce additional variability in ADC calculations. (2) The promising results of the current study, obtained using absolute ADCs, may suggest that normalization is not necessary, thus facilitating the implementation of DW imaging into routine clinical practice.