False positive and false negative FDG-PET scans in various thoracic diseases

Abstract

Fluorodeoxyglucose (FDG)-positron emission tomography (PET) is being used more and more to differentiate benign from malignant focal lesions and it has been shown to be more efficacious than conventional chest computed tomography (CT). However, FDG is not a cancer-specific agent, and false positive findings in benign diseases have been reported. Infectious diseases (mycobacterial, fungal, bacterial infection), sarcoidosis, radiation pneumonitis and post-operative surgical conditions have shown intense uptake on PET scan. On the other hand, tumors with low glycolytic activity such as adenomas, bronchioloalveolar carcinomas, carcinoid tumors, low grade lymphomas and small sized tumors have revealed false negative findings on PET scan. Furthermore, in diseases located near the physiologic uptake sites (heart, bladder, kidney, and liver), FDG-PET should be complemented with other imaging modalities to confirm results and to minimize false negative findings. Familiarity with these false positive and negative findings will help radiologists interpret PET scans more accurately and also will help to determine the significance of the findings. In this review, we illustrate false positive and negative findings of PET scan in a variety of diseases.

Fig. 1

Normal distribution of FDG. Coronal FDG-PET image shows physiologic uptake in the liver, kidneys, intestine, and urinary bladder. Also note the minimal uptake in the mediastinum, and bone marrow.

Fig. 2

Normal increased FDG uptake in the shoulder area which represents brown fat.

Fig. 3

Tuberculoma in a 53-year-old female. A. Contrast-enhanced CT scan shows a round mass in the left lower lobe. B. Axial FDG-PET image shows intense uptake (arrow) in the left upper lobe suggesting a malignant condition with a maximum standardized uptake value of 4.3. The pathologic examination reveals tuberculoma. Another lesion showing high FDG uptake (arrowhead) is a pulmonary artery.

Fig. 4

Tuberculous lymphadenitis in a 56-year-old male. A. Axial contrast-enhanced CT scan shows right hilar lymph node enlargement (arrow). B. Coronal FDG-PET scan shows high uptake in the same area (arrow).

Fig. 5

Sarcoidosis in a 32-year-old male. A. Axial PET-CT scans show bilateral paratracheal and hilar lymph node enlargement with high FDG uptake. B. Coronal section of PET shows high FDG uptake with rhamda shape (arrowheads) which is highly suggestive of sarcoidosis. A mediastinoscopic biopsy confirms sarcoidosis.

Fig. 6

Cryptococcosis in a 68-year-old female. A. Contrast-enhanced CT scan shows a cavitary nodule (arrow) in the left lower lobe. B. Transverse section of a whole body PET image shows increased uptake (arrow) in the left lower lobe and a standardized uptake value of 2.6. The lesion is a round mass-like lesion unlike the CT findings due to respiration artifact.

Fig. 7

Paragonimiasis in a 68-year-old male. A. In the lung window setting, axial transverse CT scan shows linear, wedge shaped consolidation and small centrilobular nodules. Radiologic diagnosis is atypical tuberculosis. B. Coronal section of FDG-PET image shows intense uptake in the right lower lung zone. Bronchoscopic washing and sputum cytology reveals many parasitic eggs of paragonimus species.

Fig. 8

Lung abscess in a 72-year-old male. A. Axial contrast enhanced CT scans show a consolidation with air density in the right upper lobe (black arrow). Multiple conglomerated mediastinal lymph node enlargements are also noted (white arrow). B. Coronal FDG-PET image shows high uptake (arrows) in the right upper lobe. High uptake in the left hilar lymph node (arrowhead) is also noted. Malignancy is suspected in PET scan. Percutaneous needle biopsy reveals a lung abscess.

Fig. 9

Pneumocystis carinii infection in a 61-year-old female. A. In the lung window setting of chest CT, multifocal ground-glass opacities are noted. The patient had been diagnosed with systemic lupus erythematosus, and cytoxan and steroid pulse therapy was performed. B. PET-CT shows multifocal hypermetabolic lesions with an standardized uptake value of between 4.0-5.8 in both lung parenchymas.

Fig. 10

Radiation fibrosis in a 61-year-old male by radiation therapy due to lung cancer. A. Axial CT scan shows consolidation in the left lower lobe, suggesting lung cancer recurrence. B. Axial PET image shows increased uptake in the left lower lobe (arrow) which was mistaken for lung cancer recurrence. C. Microscopic image reveals severe fibrosis with inflammatory cell accumulation.

Fig. 11

Progressive massive fibrosis in a 58-year-old male. Coronal FDG-PET image shows increased uptake in right upper lobe (arrow) and a mean standardized uptake value of 6.4.

Fig. 12

Sclerosing hemangioma in a 43-year-old female. A. Axial contrast-enhanced CT shows a round well demarcated, highly enhancing mass in the right lateral side of the superior vena cava in the right upper lobe. B. FDG-PET fusion CT image shows increased uptake in the lesion with a maximum standardized uptake value of 3.4.

Fig. 13

Bronchioloalveolar carcinoma in a 75-year-old male. A. Contrast-enhanced CT shows a cavitary lesion in the left lower lobe (arrow). B. Transverse FDG-PET image of the transverse scan shows subtle uptake (arrow) in the left lower lobe with a maximum standardized uptake value of 1.7.

Fig. 14

Mucinous bronchioloalveolar carcinoma in a 61-year-old female. A, B. Axial chest CT images show a low attenuating mass in the left upper lobe. C. FDG-PET also shows a hypermetabolic lesion with a maximum standardized uptake value of 3.8 in the left upper lobe. D. Another area of ground-glass opacity is noted in the right lower lobe. E. FDG-PET shows no abnormal uptake in this area. Both the left upper and right lower lobe lesions were bronchioloalveolar carcinomas, mucinous type. In the same patient, FDG uptake for each of the lung lesions was different, and the amount mucin in mass may have been the major cause of this difference.

Fig. 15

Small malignant mediastinal lymph node in a 56-year-old male. A. Axial contrast-enhanced CT shows a nodular lesion in the right upper lobe with a lymph node of less than 1 cm in the right paratracheal area (arrow). B. FDG-PET fusion CT shows no increased uptake due to the small size of the lesion (arrow). C. Pathology reveals a 0.6 cm lymph node with metastatic tumor cells.

Fig. 16

Metastatic lung nodule from mucinous carcinoma of the left breast. A. Gadolinium-enhanded MR shows a well enhancing lobulating mass. B. FDG-PET fusion CT shows a nodular lesion in the right lower lung without increased FDG uptake (arrow).

Fig. 17

Metastasis from renal cell carcinoma in an 83-year-old male. A. Axial contrast-enhanced CT scans shows a mass lesion in the right kidney suggesting renal cell carcinoma. B. Axial CT scan of lung window setting shows a lung nodule in the right middle lobe (arrow). C. A selected transverse section of whole body-PET image shows no demonstrable uptake in the right lung.

Fig. 18

Post-chemotherapy related decreased lymph node uptake in a 57-year-old male lung cancer patient. A. Pre-chemotherapy FDG-PET fusion CT shows increased FDG uptake in the subcarinal lymph node with a maximum standardized uptake value of 9.4. B. After two months of chemotherapy, the residual lesion in the subcarinal area is noted. C. FDG-PET fusion CT shows no abnormal FDG uptake.