Answer
Unlike CT scanning, PET scanning does not rely on the anatomic assessment of nodes. It is primarily a metabolic imaging technique that relies on a biochemical difference between normal and neoplastic cells. Mediastinal nodes containing tumor have an increased uptake of FDG, a glucose analogue labeled with a positron emitter (fluorine-18 [18 F]).
The combined PET/CT is more accurate in the tumor and node staging than that of conventional visual correlation of PET and CT scanning. [26] PET scanning is superior to CT scanning in the assessment of mediastinal and hilar nodal metastases. A large number of studies have validated the higher sensitivity and accuracy of FDG PET/CT compared with conventional CT in detecting metastatic nodal involvement. A meta-analysis compared the diagnostic performance of PET demonstration of mediastinal nodal metastases in patients with non–small cell lung cancer with that of CT (based on 14 studies of the first modalities and 29 the studies of the second). [27] In this study, the mean sensitivity and specificity were 79% and 91%, respectively, for PET and 60% and 77%, respectively, for CT.
False-negative PET CT can be seen with microscopic metastatic nodal involvement and false-positive PET/CT is commonly present with inflammatory reactive nodes. PET/CT can provide valuable information for the assessment of nodal stations that are inaccessible by mediastinoscopy. FDG-PET enables accurate staging of regional lymph node disease in patients with stage I non–small cell lung cancer. A negative PET scan in these patients suggests that mediastinoscopy is unnecessary and that thoracotomy may be performed. FDG-PET is justified as a supporting staging measure in cases presenting unclear differentiation between N2 and N3 after conventional staging.
-
A chart summarizing the tumor, node, metastasis (TNM) staging system of lung tumors. The information is separated into 2 boxes based on the presence or absence of metastases. In cases with no distant metastases, the different stage groupings can be identified by intersecting appropriately matched horizontal (regional lymph node involvement) and vertical (tumor characteristics) columns. Unique stages such as stage 0 are defined separately. Reproduced with permission from the American College of Chest Physicians (Lababede O, Meziane M and Rice T, Seventh Edition of the Cancer Staging Manual and Stage Grouping of Lung Cancer: Quick Reference Chart and Diagrams. CHEST. January 2011;139(1):183-189).
-
Two illustrations summarizing the tumor, node, metastasis (TNM) staging system of lung tumors. The T classification can be defined by evaluating the size first (upper left), then upgrading the classification (if necessary) based on the presence of the other criteria of primary tumor invasion/extent (A, B, and C). The criteria of extent should not be used to assign a lower classification. The lower diagram can be used to define the N and M classification and to determine the corresponding stage. Note that N1, N2, N3, and the separate tumor nodule of M1a were depicted in the lower illustration based on a right-sided tumor (T). For left lung tumors, a mirror image of these descriptors should be used. Additionally, the endobronchial extension and local invasion (A and B of the criteria of extent) were shown in the upper illustration based on a left-sided tumor to simplify the drawing. Reproduced with permission from the American College of Chest Physicians (Lababede O, Meziane M and Rice T, Seventh Edition of the Cancer Staging Manual and Stage Grouping of Lung Cancer: Quick Reference Chart and Diagrams. CHEST. January 2011;139(1):183-189).
-
A 56-year-old man with an incidental 1.5-cm subpleural nodule in the right upper lobe. Following wedge resection, histopathologic evaluation revealed adenocarcinoma with acinar, micropapillary, and bronchioloalveolar cell carcinoma components and evidence of invasion into the visceral pleura. Contrast-enhanced CT scanning in lung window settings (A) demonstrates that the contact between the nodule and the pleura is more than 50% of the nodule diameter. Obtuse angle and pleural thickening are present at the margins of the contact (blue arrow). On the same section displayed in soft tissue window (B) and on oblique coronal reconstruction (C), the extrapleural fat plain is preserved (yellow arrow).
-
Stage IA lung neoplasm (T1N0M0) in 72-year-old man with history of severe chronic obstructive pulmonary disease (COPD)–emphysema and smoking. An incidental left lung nodule was suspected on chest radiograph and confirmed by CT scanning (not shown). Follow-up contrast-enhanced CT scanning demonstrates a slightly enlarging spiculated 8 X 10-mm left upper lung nodule (blue arrow). Fine-needle aspiration was positive for malignant cells (squamous cell carcinoma).
-
The previous case (stage IA lung neoplasm [T1N0M0] in 72-year-old man), continued: Further workup included positron emission tomograph (PET) scanning, which showed that the left upper lobe nodule is hypermetabolic (increased fluorodeoxyglucose (FDG) activity: maximum standardized uptake value of 3.2) with no evidence for hypermetabolic metastatic disease. (Top: Three axial PET images without and with CT fusion at the level of the nodule [blue arrow].) (Bottom: Two coronal PET/CT images demonstrating the hypermetabolic nodule [blue arrow].)
-
Stage IIB lung neoplasm (T2bN1M0) in 61-year-old man and exsmoker with an intermittent cough over a month period. Posteroanterior and lateral chest radiographs (A and B, respectively) demonstrate masslike opacity in the medial right lower lobe.
-
The previous case (stage IIB lung neoplasm [T2bN1M0] in 61-year-old), continued: Contrast-enhanced CT scanning confirmed the presence of 6.5 X 5-cm right lower lobe mass (blue arrow) with central necrosis (*) and mildly enlarged peribronchial lymph nodes (yellow arrow).
-
The previous case (stage IIB lung neoplasm [T2bN1M0] in 61-year-old), continued: Positron emission tomography (PET) scan showed that the lesion is fluorodeoxyglucose (FDG)–avid (maximum standardized uptake value = 19.7). Biopsy and postresection histopathologic evaluation confirmed the diagnosis of adenosquamous carcinoma with metastatic involvement of hilar and lobar lymph nodes.
-
A 66-year-old female with a significant history of tobacco use presented with epigastric pain. A liver lesion was suspected on Ultrasound. A follow-up abdomen CT scan showed a hypodense lesion in the left hepatic lobe (yellow arrow). Liver biopsy was positive for small cell carcinoma. The carcinoma is positive for synaptophysin and chromogranin, confirming neuroendocrine differentiation.
-
The previous case (liver lesion in a 66-year-old), continued: Further workup included chest CT, which showed a lobulated lesion in the right lower lobe (blue arrow). The liver lesion is presumed to be metastatic from this primary neoplasm. The neoplasm is considered stage IV due to the presence of distant metastasis (M1)
-
The previous case (stage IV lung neoplasm in 66-year-old), continued: The chest CT also demonstrated right hilar adenopathy, likely metastatic (yellow arrow).
-
The previous case (stage IV lung neoplasm in 66-year-old), continued: brain MRI showed a 2.1 x 2.9 x 2.1 cm nodular, mixed cystic and solid soft tissue mass in the subcortical white matter underlying superior aspect of the right precentral gyrus (yellow arrows). On the fluid-attenuated inversion recovery (FLAIR) sequence (A), this rim is slightly hyperintense. The central aspect of the solid component is hypointense. The anterior fluid component has a signal characteristic of a proteinaceous nature. A thin irregular rim of enhancement is noted along the margins following gadolinium administration (B). There is only minimal surrounding vasogenic edema and only mild localized mass effect. This is most likely metastatic.
