Fluorodeoxyglucose-Positron Emission Tomography (FDG-PET)

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

  • xx

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]])

  • xxx

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)

  • xxxx

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

Infectious/Inflammatory Lesions

Iatrogenic Etiologies

  • Bone Marrow Expansion After Chemotherapy
  • Administration of Colony Stimulating Factors
  • 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]