Bilateral Hilar Foci on ¹⁸F-FDG PET Scan in Patients Without Lung Cancer: Variables Associated with Benign and Malignant Etiology

Abstract

Bilateral hilar 18 F-FDG-avid foci are often noted on PET studies of patients without lung cancer. This finding may lead to diagnostic uncertainty about the presence of metastatic disease. Our objective was to evaluate features of these foci associated with benign or malignant etiology. Methods: We performed a retrospective study of patients with cancer with bilateral hilar foci on 1 or 2 sequential 18 F-FDG PET studies between 2002 and 2006. Patients with lung cancer, sarcoidosis, or anthracosis/ silicosis were excluded. Variables evaluated were maximum standard uptake values (SUV max), purity (absence of 18 F-FDGavid foci in nonhilar mediastinal nodes), symmetry (difference between left and right side SUV max), the primary tumor, node size determined by CT, and, in those who participated in 2 studies, stability of uptake over time. The gold standard was histologic diagnosis or long-term clinical follow-up (range, 19-41 mo; mean, 25 mo). Results: Fifty-one patients with the finding of bilateral hilar 18 F-FDG-avid foci underwent a staging-only PET study; 52 scans from an additional set of patients demonstrated this abnormality on at least 1 of 2 sequential studies, the first of which was performed for staging. On univariate analysis, variables associated with malignancy were SUV max (6.6 6 4.1 vs. 3.5 6 1.0 for benign, P , 0.001; t test); impurity (P , 0.001; x 2 test), with 79% of impure scans versus 18% of pure scans being malignant; node size determined by CT (P 5 0.027); and change in uptake between scans 1 and 2 (change in SUV 5 2.7 6 2.1 vs. 0.73 6 1.1 for benign, P , 0.01; t test). Variables associated with benign etiology were: symmetry (difference between left and right sides 5 0.57 6 0.54 for benign vs. 1.8 6 1.7 for malignant, P , 0.01), purity, and colorectal primary (75% of colorectal were benign vs. 34% of breast, 49% of lymphoma, and 37% of other, P 5 0.030; x 2 test). After multivariate analysis, SUV max and purity were found to be independent predictors, with the odds of malignancy increasing by 1.54 (95% confidence interval, 1.16-2.05) for each unit increase in SUV and decreasing by 0.08 (95% confidence interval, 0.03-0.22) if pure. Conclusion: In patients with nonlung cancer, in particular colorectal, foci of symmetric and mild uptake limited to the hilar regions that are stable on 2 sequential PET studies despite intervening anticancer therapy are likely related to a benign etiology.

Observer Variation in Interpreting 18F-FDG PET/CT Findings for Lymphoma Staging

“…There was also lower agreement about hilar nodes than about other nodal stations. Hilar 18 F-FDG uptake is not uncommon, because of inflammatory changes secondary to a reactive or granulomatous process (12). In staging lung carcinoma with PET/CT, we have previously described lower agreement in the hilar region than in mediastinal nodal stations (13).…”

Sarcoidlike Reaction of Neoplasia Causing Hypermetabolic Thoracic Adenopathy in Setting of Extrathoracic Malignancy: Report of Two Cases and a Review of the Differential Diagnostic Considerations

“…Usually, a diffuse reticular, nodular, or reticulonodular pattern of pulmonary parenchymal disease is identified on chest radiographs or CT. The enlarged hilar and mediastinal nodes can demonstrate eggshell calcification and are often indistinguishable from those seen in sarcoid, including their ability to accumulate 18 F-FDG (6,8). The patient may be asymptomatic initially, although respiratory symptoms usually progress in correlation with radiographic changes (6).…”

“…A variety of infectious etiologies, most commonly granulomatous infections such as histoplasmosis and tuberculosis, can cause mediastinal lymph node enlargement with increased 18 F-FDG uptake (7,8). These granulomatous lesions are characterized by cellular infiltrates, granuloma formation, and macrophage proliferation (9).…”

Restaging: Should We PERCIST Without Pattern Recognition?

“…Many potential pitfalls in the interpretation of PET/CT can be avoided by learning patterns associated with benign processes. Symmetric uptake in hilar nodes is a well-known pattern for differentiating inflammatory from malignant lymphadenopathy (6). The typical distribution of brown fat (7,8), the pattern of intense 18 F-FDG uptake in the bowel of patients treated with metformin (9), or elastofibroma dorsi (10) are surprisingly easy to recognize.…”