Lung adenocarcinoma and squamous carcinoma are the most common types of non-small cell lung cancer, and their proper treatment requires accurate clinical staging. Mediastinoscopy is still considered the gold standard for determining the status of mediastinal lymph nodes, but it is not routinely performed in many developing countries. Among the non-invasive methods, CT examination is not accurate because it is mainly based on the size of the lymph nodes. 18F-FDG
PET/CT may be of interest for evaluating lymph nodes <15 mm in diameter. < p="">In response to this situation, Dr. Yu et al. of the Thoracic Surgery Department, Henan Cancer Hospital, China, conducted a retrospective study and found that 18F-FDG
PET/CT has limited usefulness in the evaluation of lymph nodes <15 mm in diameter in adenosquamous/squamous carcinoma and has a high false positive rate in squamous carcinoma, and considering the attenuation of CT helps to improve the accuracy. The article was published in the May 2014 issue of Lung
Cancer. The retrospective study included patients who underwent preoperative 18F-FDG between October 2005 and October 2012
PET/CT with mediastinal lymph nodes <15 mm in diameter in 116 patients with adenocarcinoma and 234 patients with squamous carcinoma, all of whom subsequently underwent pathological examination to confirm the diagnosis and compare the differences between PET/CT and pathological findings. The results of the study showed that the specificity and accuracy of PET/CT was higher in the adenocarcinoma group than in the squamous cancer group. Compared with PET, PET/CT had higher specificity and accuracy in the squamous carcinoma group and higher specificity, accuracy and positive predictive value in the adenocarcinoma group. Figure 1. 18F-FDG in a 73-year-old male with adenocarcinoma
PET/CT examination showed false positive mediastinal lymph node metastasis. A 30 mm mass (arrow) with obstructive pneumonia (arrow) is seen in the right lower lung, (a) lung window (b) 18F-FDG
PET (c) 18F-FDG
PET/CT integration. Mediastinal window (d) shows a lymph node with a short axis diameter of 8 mm and 10 mm below the bulge (arrow). 18F-FDG
PET (e) and 18F-FDG
PET/CT integration (f) showed elevated 18F-FDG uptake in the same area (SUVmax=3.8,4.2) (arrows). Figure 2. Correction of 18F-FDG by integrating 18F-FDG uptake and CT high attenuation in a 72-year-old female patient with adenocarcinoma
PET/CT images. The lung window (a) shows a burr-like nodule of 21 mm in diameter in the right upper lobe (arrow). Mediastinal window (b) shows a high attenuation lymph node (112HU) of 8 mm in diameter under the ramus (arrow). PET scan (c) and 18F-FDG at the same level
PET/CT (d) shows elevated 18F-FDG uptake (SUVmax=10.2) (arrow). This nodule was interpreted as benign, and histological testing confirmed the nodule as benign. The study showed that 18F-FDG
PET/CT has limited usefulness in evaluating the status of mediastinal lymph node metastasis in adenosquamous/squamous carcinomas <15 mm in diameter, with a higher rate of false positives in squamous carcinomas, and consideration of the attenuation properties of CT can help improve the specificity and accuracy of the test.