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
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)
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
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%
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
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]