Combined PET and X-ray Computed Tomography Imaging in Pulmonary Infections and Inflammation

Jamshed Bomanji; Ahmad Almuhaideb; Alimuddin Zumla

Disclosures

Curr Opin Pulm Med. 2011;17(3):197-205. 

In This Article

Inflammatory, Noninfectious Conditions

Inflammatory, noninfectious conditions may include sarcoidosis, pneumoconiosis and other conditions.

Sarcoidosis

Sarcoidosis is a multisystem noncaseating granulomatous disease. The aggregation of inflammatory cells in sarcoidosis results in accumulation of 18F-FDG,[27] and it has been suggested that intensity of 18F-FDG uptake may reflect disease activity.[28]

The initial manifestation of thoracic sarcoidosis appears as mediastinal and hilar lymphadenopathy, followed by the parenchymal involvement; both manifestations can show increased 18F-FDG activity (Fig. 3). Rarely myocardial infiltration may be observed (Fig. 4). Extrathoracic sites also show 18F-FDG uptake.[29–31] Nishiyama et al.[29] compared 67Ga-citrate with 18F-FDG PET in patients with sarcoidosis and showed that 18F-FDG PET had a sensitivity of 90–100% and was good at detecting extrathoracic involvement. In a large cohort study of 137 patients,[31] 18F-FDG PET identified occult sites of disease that were not detected clinically or by conventional imaging and CT in 15% of patients.

Figure 3.

Patient with histology-proven sarcoidosis
18F-FDG PET/CT scan in a patient who presented with shortness of breath and fever. Upper left (MIP), upper right (axial fused PET/CT in lung window), lower left (axial CT in mediastinal window) and lower right (axial CT in lung window) panels show 18F-FDG avid parenchymal disease (yellow arrow) with a nonavid calcified mediastinal and hilar nodes (red arrow). FDG, fluorodeoxyglucose; MIP, maximum intensity projection.

Figure 4.

Patient with histology-proven sarcoidosis
18F-FDG PET/CT scan in a patient who presented with shortness of breath, arrhythmia and fever of insidious onset along with a palpable right supraclavicular node. MIP PET image shows abnormal increased 18F-FDG uptake in the myocardium (yellow arrow) with multiple FDG avid lymphadenopathy at both supraclavicular (red arrow), right hilum (green arrow), mediastinum (blue arrow), retroperitonum (white arrow) and right external iliac (black arrow) regions. Histology of the supraclavicular node showed noncaseating granuloma compatible with sarcoidosis. FDG, fluorodeoxyglucose; MIP, maximum intensity projection.

It should be noted that 18F-FDG PET cannot distinguish sarcoidosis lymphadenopathy from other common causes such as lymphoma and tuberculosis and that histopathologicl confirmation is needed in most of the cases.[32] However, 18F-FDG PET is useful in assessing the extent and degree of the disease, delineating a site for biopsy, as well as the response to treatment after establishing the diagnosis.[18]

Apart from 18F-FDG, 111In-octreotide has been used for imaging of sarcoidosis[33] and it may be inferred that 68Ga-DOTATATE could also be used. At present there is no literature on the use of 68Ga-citrate PET imaging in sarcoidosis, but if it were to be applied, the sensitivity would be far superior to that of the conventional 67Ga-citrate.

Pneumoconiosis

Pneumoconiosis is a tissue reaction to the accumulation of dust in the lungs. One clinicopathologic form of this reaction is fibrosis, whereas the other form consists in aggregates of particle-laden macrophages with minimal or no accompanying fibrosis, a reaction that is typically seen with inert dusts such as iron, tin, and barium.[34]

Coal workers' pneumoconiosis (CWP) is characterized by small (<1 cm) nodules with an upper lobe predominance. Coalescence or conglomeration of these small nodules to form larger nodules sometimes raises the concern for malignancy and can present a diagnostic dilemma. 18F-FDG PET studies have revealed increased uptake in pneumoconiosis and progressive massive fibrosis. Some of this uptake is perhaps related to the presence of inflammatory cells such as macrophages, as well as fibroblasts.[8,35]

Reichert and Bensadoun[36] showed that 18F-FDG PET imaging is often positive in patients with CWP, and owing to the high rate of false positive results, PET imaging seems to be of limited utility in diagnosing malignancy in patients with underlying CWP. Careful follow-up with serial CT imaging may be the most appropriate approach in many of these patients, with invasive procedures being reserved for those who show nodule growth.

Other Conditions

In a small series of patients with thoracic trauma, diffuse lung uptake of 18F-FDG was detected by PET imaging 1–3 days prior to clinically determined ARDS.[37]

18F-FDG PET has also been used to determine the inflammatory burden of disease in patients with cystic fibrosis.[2,38•] Chen et al.[2] were able to show a positive correlation between the rate of 18F-FDG uptake in the lung field and the amount of neutrophils present in bronchoalveolar lavage fluid in patients with cystic fibrosis, suggesting that 18F-FDG PET may be a useful adjunct to monitor the inflammatory burden.

18F-FDG PET is also a useful tool for monitoring pulmonary toxicity and disease activity in bleomycin-induced pneumonitis following ABVD chemotherapy for Hodgkin's disease, in that it can distinguish between active inflammation and residual scarring.[39]

In patients with lung transplants, 18F-FDG PET is useful in differentiating pulmonary infection from acute rejection as the latter does not elicit as high a neutrophilic response as infection.[40]

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