Is Unenhanced 18F-FDG–PET/CT Better than Enhanced CT in the Detection of Retropharyngeal Lymph node Metastasis in Nasopharyngeal Carcinoma?

Abstract

Positron-emission tomography/computed tomography (PET/CT) has been proposed as a means to enhance the pretreatment evaluation of cervical lymph node status in patients with nasopharyngeal carcinoma (NPC). We conducted a prospective study to compare PET/CT and enhanced CT for the detection of retropharyngeal lymph node (RLN) metastasis in NPC, and to ascertain the factors that affect its diagnostic performance. Our study population was made up of 33 patients—24 men and 9 women, aged 30 to 81 years (mean: 52)—with newly diagnosed NPC who had been treated over a 2-year period. All patients underwent enhanced CT first, followed by unenhanced 18F-fluorodeoxyglucose (FDG) PET/CT. The detection rate of RLN metastasis on PET/CT was significantly lower than that on enhanced CT (36.4 vs. 75.8%; p < 0.001). A total of 25 of 26 nodes with a discordant finding were negative on PET/CT; they included 13 metastatic lymph nodes with low FDG uptake, 9 that were located close to the primary tumor, 2 that were confluent RLNs, and 1 that was adjacent to the physiologic FDG-avid prevertebral muscle. The maximum standardized uptake value (SUVmax) of RLNs was positively correlated with the minimum axial diameter (r = 0.803, p < 0.001). The PET/CT detection rate was 0% for lymph nodes smaller than 5 mm, 9% for those 5 to 10 mm, and 73% for those 1 cm or larger. The detection rate of PET/ CT at level C1 was significantly lower than that at C2 (22 vs. 67%; p = 0.035). We conclude that unenhanced PET/CT is markedly inferior to enhanced CT for detecting RLN metastasis in NPC, especially in lymph nodes with a minimum axial diameter of less than 1 cm and those in proximity to the primary tumor. Using enhanced CT in PET/CT is justified to improve the recognition of RLN metastasis in patients with NPC.

Verification of the Efficacy of New Diagnostic Criteria for Retropharyngeal Nodes in a Cohort of Nasopharyngeal Carcinoma Patients

“…Most authors agreed the criterion of LRPNs selected the MIAD ranging from ≥ 5 to ≥ 6 mm in the past two more decades [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. As a single parameter, MIAD was proved to be more useful than the maximal axial diameter by Zhang's study [13].…”

“…Based on control subject analysis, Lam and King used minimal axial diameter (MIAD) of 4 and 5 mm as the upper limit of normal LRPNs [2,3]. A diameter of 5 mm or higher as a criterion of malignancy was widely indicated by previous studies [4][5][6][7][8][9][10][11][12]. However, Zhang et al reported that ≥6 mm diameter might be a better cutoff point for malignancy [13].…”

Different Primary Sites of Hypopharyngeal Cancer Have Different Lymph Node Metastasis Patterns: A Retrospective Analysis From Multi-Center Data

“…Various imaging technologies, such as CT, MRI, and 18 F-FDG, have been widely used in the evaluation of head neck cancer ( 6 , 7 ). MRI has a higher ability in the presentation of soft tissue than CT or PET, especially in the evaluation of primary tumors, since the tumor may extend to the mucous membrane alone.…”

Retropharyngeal Lymph Node Metastasis Diagnosed by Magnetic Resonance Imaging in Hypopharyngeal Carcinoma: A Retrospective Analysis From Chinese Multi-Center Data

“…To date, there have been few published data on prevalence of RPLN involvement in patients with nonnasopharyngeal head and neck cancer and the frequency of positive retropharyngeal nodes reported in HPC varies hugely, ranging from 10% to 62% (10-12). These highly discrepant findings across different reports were mainly ascribed to two reasons, one being that most studies included other head and neck carcinomas and had small sample sizes, and were not limited to HPC; another reason being that various imaging technologies, such as CT, MRI and (18)F-FDG PET had been used (5,13). Actually, MRI has been shown to be superior to CT images for detecting metastatic RPLNs; MRI is considered the preferred method for assessing metastatic RPLNs, as a guide to physicians prescribing appropriate treatment (14).…”