Lateral Retropharyngeal Lymph Research Articles

Can Parameters Other than Minimal Axial Diameter in MRI and PET/CT Further Improve Diagnostic Accuracy for Equivocal Retropharyngeal Lymph Nodes in Nasopharyngeal Carcinoma?

PurposeMinimal axial diameter (MIAD) in magnetic resonance imaging (MRI) was recognized as the most useful parameter in diagnosing lateral retropharyngeal lymph (LRPL) nodes in nasopharyngeal carcinoma (NPC). This study aims to explore the additional nodal parameters in MRI and positron emission tomography–computed tomography for increasing the prediction accuracy.Materials and MethodsA total of 663 LRPL nodes were retrospectively collected from 335 patients with NPC. The LRPL nodes ascertained on follow-up MRI were considered positive for metastases. First, the optimal cutoff value of each parameter was derived for each parameter. In addition, neural network (NN) nodal evaluation was tested for all combinations of three parameters, namely MIAD, maximal axial diameter (MAAD), and maximal coronal diameter (MACD). The optimal approach was determined through brute force attack, and the results of two methods were compared using a bootstrap sampling method. Second, the mean standard uptake value (NSUVmean) was added as the fourth parameter and tested in the same manner for 410 nodes in 219 patients.ResultsIn first and second analysis, the accuracy rate (percentage) for the MIAD was 89.0% (590/663) and 89.0% (365/410), with the optimal cutoff values being 6.1 mm and 6.0 mm, respectively. With the combination of all three and four parameters, the accuracy rate of the NN was 89% (288/332) and 88.8% (182/205), respectively. In prediction, the optimal combinations of the three and four parameters resulted in correct identification of three (accuracy: 593/663, 89.4%) and six additional nodes (371/410, 90.5%), representing 4% (3/73) and 13.3% (6/45) decreases in incorrect prediction, respectively.ConclusionNPC LRPL nodes with an MIAD ≥ 6.1 mm are positive. Among nodes with an MIAD < 6.1 mm, if the NSUVmean ≥ 2.6 or MACD ≥ 25 mm and MAAD ≥ 8 mm, the nodes are positive; otherwise, they are negative.

Partial Volume Correction for Equivocal Retropharyngeal Nodal Metastases of Nasopharyngeal Carcinoma with Fluorodeoxyglucose Positron Emission Tomography–Computed Tomography

The objective of this study is to determine the size range where the recovery coefficient (RC) method of fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET–CT) is helpful in detecting lateral retropharyngeal lymph (LRPL) nodal metastases of nasopharyngeal carcinoma (NPC) patients previously treated with radiation therapy. A total of 142 LRPL nodes assessed by magnetic resonance imaging (MRI) in 71 NPC patients were chosen for investigation. LRPL nodes with central necrosis, extracapsular invasion, or asymmetric grouping or those ascertained on follow-up MRI scans were considered positive for metastases. The criterion for positive diagnosis of nodal metastasis on FDG PET–CT scans was defined as maximal standard uptake value (SUVmax) ≥ 2.5. Nodes not separated from main tumors were excluded. An established RC method, the sphere-to-background ratio, was employed. Nodes were further categorized into three groups of minimal axial diameters: below 6, 6–7 mm, and above 7 mm. A total of 88 nodes were examined by FDG PET. Thirty-five nodes were positive and 53 nodes were negative. The RC method significantly improved sensitivity (from 20 to 100 %) and accuracy (from 14 to 71 %) for nodes sized 6–7 mm. In LRPL nodes above 7 mm, the RC method also provided slight improvement, with sensitivity and accuracy both increasing from 92 to 96 %. However, the nodal sizes below 6 mm were too small for valid comparisons. In conclusion, partial volume correction in FDG PET–CT enhances the accuracy of detecting nodes in the equivocal size range of 6–7 mm for LRPL nodal metastases of NPC.