European Radiology: MRI in the differentiation of benign and metastatic retropharyngeal lymph nodes

Nasopharyngeal carcinoma (NPC) is one of the squamous cell carcinomas of the head and neck and is very common
in East and Southeast Asia.
Retropharyngeal lymph nodes (RLNs) are located in the retropharyngeal space, bounded by the middle layer of the deep cervical fascia in front, prevertebral fascia in the back, and carotid sheath on the side, and are considered sentinel lymph nodes
in patients with nasopharyngeal carcinoma.
As mentioned earlier, nasopharyngeal carcinoma is the most common malignancy that metastasizes to RLNs, and the presence of metastatic RLNs is associated with
a poor prognosis.
Therefore, accurate detection of RLN metastasis in nasopharyngeal carcinoma is important
for further treatment planning.
However, due to the relatively deep anatomical location and complex surgical incision, RLN metastases are clinically difficult to biopsy and surgical resection
.
Therefore, imaging methods play a crucial role
in the diagnosis of RLN lesions.

Traditional MRI (cMRI) has been widely used to measure the size of lymph nodes due to its good characterization of soft tissue components, which is the most commonly used criterion
in the differential diagnosis of benign and malignant lymph nodes.
However, some large lymph nodes may be reactive rather than metastatic, and small lymph nodes may also contain metastases, so false-positive or false-negative results are frequent
.

Functional MR imaging, such as diffusion-weighted imaging (DWI), can provide quantitative information on water diffusion properties, describe the complex physiological state of tissues, and aid in the distinction
between benign and malignant lymph nodes.

Synthetic MRI (syMRI), also known as magnetic resonance image preparation (MAGiC), is a relatively new quantitative MRI technique
.
By using multi-echo and multi-delay acquisition methods, a complete set of relaxation measurement maps such as longitudinal relaxation time (T1), lateral relaxation time (T2), and proton density (PD) can be obtained in one measurement to reflect the microstructural differences
within the lesion at the cellular level.

Recently, a study published in the journal European Radiology explored the clinical feasibility of syMRI to distinguish benign and metastatic RLNs features under two different ROI scribing methods, and compared
the corresponding diagnostic performance of syMRI with syMRI, DWI and morphological features.

A total of 58 patients with a total of 63 RLNs (21 benign and 42 metastatic) were enrolled in this review
.
syMRI-derived relaxation measurement parameters (T1, T2, PD; T1_SD, T2 SD_, PD_SD).

Compare parameters
from benign and metastatic RLNs using Student's t or chi-square tests.
Logistic regression analysis was used to construct multiparametric models of syMRI, syMRI+DWI, syMRI+DWI+morphological features
.
Use the DeLong test to compare the area under the curve (AUC) to determine the best diagnostic method
.

Benign RLNs had significantly higher T1, T2, PD, and T1_SD values (0.
05 for all p <) in the ROI of some lesions and whole lesions compared with metastatic RLNs
.
T1SD obtained from whole-lesion ROI showed optimal diagnostic performance
across all syMRI-derived single parameters.
The AUC of multiple parameters (T1, T2, PD, T1_SD) of combined syMRI is higher than the AUC
of any single parameter in syMRI.
Regardless of ROI depiction, the combination of synthetic MRI and DWI can improve AUC
.
In addition, the combination of synthetic MRI, DWI-derived quantitative parameters and morphological features can significantly improve the overall diagnostic performance
.

Fig.
49-year-old female with throat cancer with metastatic retropharyngeal lymph nodes (RLN) (arrow).

ROI delineation methods include the largest rectangle (partial lesion, P) and the maximum area of the largest section (whole lesion, F).

On conventional MRI, lymph nodes show uniform isosignaling (A, B) on T2WI, clear boundaries (C), and significantly enhanced on T1WI (D).

On ADC plot (E), the lymph nodes also show a low ADC value
of 0.
74 × 10−3 mm2/s.
Compared with benign RLN, it showed partial lesion ROI (T1: 1141 ms; T1_SD：59 ms； T2：88 ms； PD: 81.
9 pu) and panlesion ROI (T1:1129) in axial T1 mapping (F), T2 mapping (G), and PDmapping (H) significantly reduced syMRI-derived quantitative parameters (T1_SD: 51 ms; T2：80 ms； and PD: 81.
0 pu).

This study shows that synthetic MRI and DWI-derived quantitative parameters (T1, T2, PD, T1 SD, and ADC) have clinically important clinical value in distinguishing benign and metastatic RLN_, and T1_SD values have the highest diagnostic accuracy
in distinguishing between the two entities.
In addition, the combination of syMRI and DWI-derived quantitative parameters (T1_SD, PD, AD) and morphological characteristics (size) can significantly improve diagnostic performance
.
This finding has important implications
for the identification of preoperative radiotherapy and the reduction of the number of unnecessary or inadequate radiotherapy.

Original source:

Peng Wang,Shudong Hu,Xiuyu Wang,et al.
Synthetic MRI in differentiating benign from metastatic retropharyngeal lymph node: combination with diffusion-weighted imaging.
DOI:10.
1007/s00330-022-09027-4