Diffusion-weighted MRI (DW-MRI) is showing particular promise in aiding the identification of lymph node metastases, according to several recently published studies.
In a review paper published in the journal Radiology earlier this year, specialists summarized data on DW-MRI in the head and neck. This included a detailed section on nodal metastases, noting that “the general consensus appears to be that ADCs [apparent diffusion coefficients] of malignant nodes are significantly lower than those of benign nodes”.
In one study there was a clear lack of any overlap between the higher ADCs of benign lesions and the lower ADCs of malignant lesions. However, the variety of head and neck lesions that can occur means it is often impractical to establish a single ADC threshold for distinguishing between benign and malignant lesions.
The specialists wrote: “Although these results show the potential of DW imaging for characterization of head and neck lesions, given the heterogenous group of benign and malignant lesions that arise in the head and neck, there will clearly be exceptions and overlap in ADC results.” Future research should include the establishment of ADC thresholds for specific sites and for specific pathologic processes , they argued.1
Meta-analysis: squamous cell carcinoma
Meanwhile, the diagnostic accuracy of standard and DW-MRI in detecting lymph node metastases in patients with head and neck squamous cell carcinoma (HNSCC) was the subject of a meta-analysis recently published in the journal Academic Radiology.
Using data from 16 studies, the researchers in Shanghai, China, calculated that the sensitivity and specificity of standard MRI for determining cervical lymph node status were 76% and 86% respectively. MRI was similar to other diagnostic tools such as PET, CT, and ultrasound, in terms of performance, they added.
A subgroup analysis, however, showed that DW-MRI had a significantly higher sensitivity (86%) than standard MRI. The researchers noted that more data are needed, concluding: “A limited number of small studies suggest DW imaging is superior to conventional imaging for nodal staging of HNSCC”.2
Prospective study in breast cancer
Finally, in the October issue of the Journal of Magnetic Resonance Imaging, specialists reported the findings of a prospective study of the accuracy of DW-MRI in distinguishing between metastatic and benign axillary lymph nodes in patients with breast cancer.
The researchers compared two groups, divided according to histology findings: 19 lymph nodes with a metastasis at least 5 mm in diameter and 24 lymph nodes with no malignant cells (nodes with metastases smaller than 5 mm were excluded from the study).
Overall, the ADC values were significantly lower for the lymph nodes with metastases, compared with the benign lymph nodes (p < 0.001). The researchers identified a threshold for ADC values that resulted in a high sensitivity, specificity, and accuracy (94.7%, 91.7%, and 93%, respectively) for this series of patients.
They concluded: “From these preliminary data, DW imaging seems a promising method in the differential diagnosis between metastatic and benign axillary lymph nodes in patients with breast cancer.”3
1. Thoeny HC, et al. Radiology. 2012;263:19-32.
2. Wu LM, et al. Acad Radiol. 2012;19:331-40.
3. Fornasa F, et al. J Magn Reson Imaging. 2012;36:858-64.