Indications
Diagnosis/Staging of Langerhans Cell Histiocytosis (LCH) (see Langerhans Cell Histiocytosis, [[Langerhans Cell Histiocytosis]])
- May demonstrate increased uptake (especially early in the course of disease)
- PET-Positive Scan in LCH: more likely to occur with nodular disease, suggesting earlier-stage disease
- PET-Negative Scan in LCH: more likely to occur with cystic disease and fewer nodules, suggesting more advanced disease
Diagnosis/Staging of Neuroendocrine Tumors
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Diagnosis/Staging of Non-Small Cell and Small Cell Lung Cancer (see Lung Cancer, [[Lung Cancer]])
- General Comments: routine PET use may prove cost-effective by sparing patients surgery who are found later to have unresectable disease
- Evaluation of Solitary Pulmonary Nodule
- Localization of Mediastinal and Distant Metastases (Bone/Liver/Adrenals) Which are Not Detected by CT: PET is especially useful
- PET Sensitivity/Specificity for Staging Mediastinum: 85%/88%
- CT Sensitivity/Specificity for Staging Mediastinum: 60%/81%
- Differentiation of Central Tumor or Inflammatory Disease from Mediastinal Involvement: may not be possible with PET -> consequently, PET-positive tumors should still have histologic confirmation of unresectability
- PET Lacks the Spacial Resolution of CT and MRI
- Lower Limit of Spatial Resolution of Modern PET Scanners: 4 mm -> allows accurate characterization of lesions >8 mm in diameter
- PET Lacks the Spacial Resolution of CT and MRI
- Staging for Contiguity of Malignancy in Mediastinum or Chest Wall/Direct Invasion of Mediastinum by Tumor: PET is not useful
- Diagnosis of Brain Metastases: since 18-FDG normally accumulates in brain, PET is less reliable than CT in the detection of brain metastases
- Combined PET-CT is Superior to PET Alone
Diagnosis/Staging of Pleural Mesothelioma (see Pleural Mesothelioma, [[Pleural Mesothelioma]])
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Technique
Positron Emission Tomography (PET) Uses 18F-Fluorodeoxyglucose (FDG) as a Tracer
- Tumor demonstrates increased uptake
- Radiation Exposure with PET Scan: 5-7 mSv (considered a moderate dose)
- Radiation Exposure with Conventional Diagnostic Chest CT: 7-7.5 mSv
- Radiation Exposure with PET-CT: 10-25 mSv
Spatial Resolution of Positron Emission Tomography (PET)
- Lower Limit of Spacial Resolution of Modern PET Scanners: 4 mm -> this allows accurate characterization of lesions >8 mm in diameter
Clinical Efficacy of Positron Emission Tomography (PET)
Positron Emission Tomography (PET) Determination of the T Factor in Lung Cancer Staging (Tumor Size)
- Reported Sensitivity/Specificity of PET Scan (Data from a Meta-Analysis of Cross-Sectional Imaging Techniques in the Diagnosis of Solitary Pulmonary Nodules; Radiology, 2008) [MEDLINE]
- Sensitivity: 95%
- Specificity: 82%
- Positive Predictive Value: 91%
- Negative Predictive Value: 90%
- Range of Sensitivities of PET Scan from Various Studies (Chest, 2013) [MEDLINE]
- Sensitivity: 72-94%
Positron Emission Tomography (PET) Determination of the N Factor in Lung Cancer Staging (Staging of Mediastinal Lymph Nodes)
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Positron Emission Tomography (PET) For Determination of the M Factor in Lung Cancer Staging (Staging of Metastatic Disease)
- Bone Metastases
- PET is More Accurate than Technetium Methylene Diphosphate Bone Scan for Diagnosis of Bone Metastases (see Bone Scan, [[Bone Scan]]): although PET display images only from the head to just below the pelvis and it may not detected osteoblastic bone lesions
- Sensitivity: 90% (comparable to bone scan)
- Specificity: 95% (far better than bone scan)
- PET is More Accurate than Technetium Methylene Diphosphate Bone Scan for Diagnosis of Bone Metastases (see Bone Scan, [[Bone Scan]]): although PET display images only from the head to just below the pelvis and it may not detected osteoblastic bone lesions
- Adrenal Metastases: PET has high sensitivity
- Other Sites: PET is useful to detect liver metastases, soft tissue metastases, retroperitoneal lymph nodes, and supraclavicular lymph nodes
Clinical Efficacy of Integrated Positron Emission Tomography-Computed Tomography (PET-CT) (in a Single Gantry)
PET-CT For Determination of the T Factor in Lung Cancer Staging (Tumor Size)
- PET-CT May Identify Margins of the Tumor and/or Chest Wall, Detect Mediastinal Infiltration, and Differentiate Tumor from Adjacent Inflammation or Atelectasis
PET-CT For Determination of the N Factor in Lung Cancer Staging (Staging of Mediastinal Lymph Nodes)
- PET-CT is More Accurate for Lymph Node Staging than CT Alone
- Sensitivity for Pathologic Lymph Nodes: 80-90%
- Specificity for Pathologic Lymph Nodes: 85-95%
- PET-CT Has a High Negative Predictive Value for the Evaluation of the Mediastinum: with a negative mediastinum by PET-CT, invasive staging can be eliminated
- However, Certain Conditions Should Lead to Less Confidence in a Negative Mediastinal Result by PET-CT
- Primary Tumor >3 cm in Size
- Insufficient FDG Uptake by the Primary Tumor
- Centrally-Located Tumor
- Concurrent Hilar Nodal Disease Which May Obscure Existing N2 Disease on PET
- However, Certain Conditions Should Lead to Less Confidence in a Negative Mediastinal Result by PET-CT
- Positive Mediastinal Nodes on PET-CT Should Usually Be Pathologically Confirmed: due to potential for a false-positive result
PET-CT For Determination of the M Factor in Lung Cancer Staging (Staging of Metastatic Disease)
- General Comments
- PET-CT is Almost Uniformly Superior to CT Alone, Except for Brain Imaging (Since Brain Uptakes FDG)
- Sensitivity for Extrathoracic Mets: 77%
- Specificity for Extrathoracic Mets: 95%
- PET-CT is Almost Uniformly Superior to CT Alone, Except for Brain Imaging (Since Brain Uptakes FDG)
- Pleural Involvement: PET-CT may be useful in some cases
Etiology of False-Negative Positron Emission Tomography (PET) Scan
Lesion-Dependent
- Bronchial Carcinoid Tumors (see Bronchial Carcinoid, [[Bronchial Carcinoid]]): due to low metabolic activity
- Ground Glass Opacity Neoplasms
- Lepidic-Predominant Adenocarcinoma (Minimally-Invasive or In Situ): due to low metabolic activity
- Mucinous Adenocarcinoma
- Small Tumor Size: <0.8-1.0 cm
- Small Tumors are Often Not Detected Because of the Limits of Resolution of the Test and Respiratory Motion
Technique-Dependent
- Excessive Time Between Injection and Scanning
- Hyperglycemia (see Hyperglycemia, [[Hyperglycemia]])
- Poorly-Controlled Diabetes Mellitus (see Diabetes Mellitus, [[Diabetes Mellitus]]): elevated glucose and insulin reduce FDG uptake in malignant cells
- Paravenous FDG Injection
Etiology of False-Positive Positron Emission Tomography (PET) Scan
Infectious/Inflammatory Lesions
- Anthrasiliocosis (see Silicosis, [[Silicosis]])
- Bronchiectasis (see Bronchiectasis, [[Bronchiectasis]])
- Chronic Non-Specific Lymphadenitis
- Granulomatous Disease
- Wegener’s Granulomatosis (Granulomatosis with Polyangiitis) (see Wegener’s Granulomatosis, [[Wegeners Granulomatosis]])
- Sarcoidosis (see Sarcoidosis, [[Sarcoidosis]])
- Lung Abscess (see Lung Abscess, [[Lung Abscess]])
- Organizing Pneumonia (see Cryptogenic Organizing Pneumonia, [[Cryptogenic Organizing Pneumonia]])
- Post-Obstructive Pneumonia
- Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]])
- Reflux Esophagitis (see Gastroesophageal Reflux Disease, [[Gastroesophageal Reflux Disease]])
- Solitary Pulmonary Nodule Due to Fungal Infection
- Histoplasmosis (see Histoplasmosis, [[Histoplasmosis]])
- Coccidioidomycosis (see Coccidioidomycosis, [[Coccidioidomycosis]])
- Solitary Pulmonary Nodule Due to Mycobacterial Infection
- Tuberculosis (see Tuberculosis, [[Tuberculosis]])
Iatrogenic Etiologies
- Bone Marrow Expansion After Chemotherapy
- Administration of Colony Stimulating Factors
- Granulocyte Colony Stimulating Factor (GCSF) (see Granulocyte Colony Stimulating Factor, [[Granulocyte Colony Stimulating Factor]])
- FDG Embolus
- Invasive Procedures
- Biopsy
- Puncture
- Radiation Esophagitis (see Radiation Esophagitis, [[Radiation Esophagitis]])
- Radiation Pneumonitis (see Radiation Pneumonitis and Fibrosis, [[Radiation Pneumonitis and Fibrosis]])
- Talc Pleurodesis
- Thymic Hyperplasia After Chemotherapy
Benign Mass Lesions
- Active Goiters (see Goiter, [[Goiter]]): can give false positives in the mediastinum
- Adrenal Adenoma
- Colorectal Dysplastic Polyp
- Residual Thymic Structures: can give false positives in the mediastinum
- Salivary Gland Adenoma (Warthin)
- Thyroid Adenoma
Focal Physiologic FDG Uptake
- Atherosclerotic Plaque
- Brown Fat
- Gastrointestinal Tract
- Muscle
- Unilateral Vocal Cord Acivity
References
- Solitary pulmonary nodules: meta-analytic comparison of cross-sectional imaging modalities for diagnosis of malignancy. Radiology. 2008;246(3):772-782 [MEDLINE]
- Evaluation of individuals with pulmonary nodules: when is it lung cancer? Diagnosis and management of lung cancer, 3rd ed: American College of Chest Physicians evidence-based clinical practice guidelines. Chest. 2013 May;143(5 Suppl):e93S-120S. doi: 10.1378/chest.12-2351 [MEDLINE]