Solitary Pulmonary Nodules

Solitary Pulmonary Nodules

Todd M. Blodgett, MD

Alex Ryan, MD

Carl Fuhrman, MD

Coronal PET (A) shows increased FDG activity in a right lower lobe pulmonary nodule image with areas of fat image and calcification image on axial CT (B, C), compatible with a hamartoma.

Axial CECT (B) shows an 8 mm spiculated adenocarcinoma image, which demonstrates only mildly increased FDG activity on coronal PET (A) and axial fused PET/CT (C).


Abbreviations and Synonyms

  • Solitary pulmonary nodule (SPN)

  • Bronchioloalveolar carcinoma (BAC)


  • Opacity in the lung parenchyma measuring up to 3 cm

    • Usually no associated mediastinal adenopathy or atelectasis


General Features

  • Best diagnostic clue

    • High suspicion for malignancy

      • Any detectable FDG activity higher than background (> mediastinal blood pool) for SPN < 1.5 cm

      • SUV > 2.5 in any nodule

      • Spiculated morphology, particularly with a history of smoking

    • Low suspicion for malignancy

      • Round nodule with dense calcification and uniform morphology

      • FDG uptake equal to background activity

  • Location

    • No regional pattern for benign nodules

    • 2/3 of primary lung tumors arise in upper lobes

    • SPN from extrapulmonary primary most often located in outer 1/3 of lower lobes

  • Size

    • Definition: Nodule < 3.0 cm < mass

    • Larger SPN more likely malignant

      • Over 85% are cancer when larger than 2.0 cm

    • Growth rate

      • 26% increase in diameter corresponds to a doubling of the nodule’s volume

      • Time to 26% increase in diameter = one doubling time

      • Most cancer doubling times: ˜ 30-200 day range

      • Nodule dimension stability: > 2 years highly suggestive that nodule is benign

      • Increase in size seen within 30 days suggestive of infection, infarction, lymphoma, fast-growing metastases

  • Morphology

    • Benign characteristics

      • Margin: Well-circumscribed with smooth borders

      • Density: Fat or water density

      • Calcification: Common

      • Cavitation: Wall thickness < 5 mm

      • Enhancement: Usually minimal

      • Ground-glass opacity (suggests inflammation)

      • Air-fluid level (abscess)

      • Satellite nodules: Common in granulomatous lesions

    • Malignant characteristics

      • Margin: Irregular, lobulated, ill-defined with spiculated borders

      • Density: Soft tissue density

      • Calcification: 10% demonstrate calcification that is usually peripheral and stippled

      • Cavitation: Present in 80% of cavitary lung cancers (e.g., squamous cell carcinoma)

      • BAC may appear entirely as ground-glass opacity

      • Enhancement: More prominent

      • Spiculation highly specific for malignancy

      • Up to 20% of smooth nodules with sharp margins are malignant (e.g., carcinoid)

      • Air bronchogram: Present in 25-65% of cancers

      • Pseudocavitation: Common to malignancies such as BAC

      • Wall thickness > 1.5 cm strongly suggestive of malignancy

Imaging Recommendations

  • Best imaging tool: PET/CT demonstrates superior accuracy to CT or PET alone

  • Protocol advice

    • Dual-time point imaging may be helpful in differentiating benign from malignant pulmonary nodules

      • Malignant nodules gain intensity between hour 1 and hour 2

      • Benign nodules decrease in intensity

Radiographic Findings

  • Chest X-rays (CXR) helpful for determining time course of nodule development

    • Little change over 2 years or longer is strongly suggestive of a benign process

  • 1-2 SPN detected per 1,000 CXR, routine screening radiographs

    • CXR has low sensitivity for detection of subcentimeter noncalcified nodules

CT Findings

  • Indications

    • Accurate localization of nodule (intra-/extrapulmonary)

    • Detection of additional unsuspected nodules

    • Characterization of margin, density, and calcification patterns

    • Assessment of extrapulmonary involvement (lymph nodes, pleura, chest wall, liver, adrenals, etc.)

  • Malignant morphology

    • CT may misclassify 25-40% of nodules as benign based on morphologic characteristics

      • BAC and lymphoma, for example, often appear benign

    • Coarse spiculation and bronchovascular bundle thickening around tumor

      • More common in presence of vessel invasion &/or lymph node metastasis

    • Heterogeneous internal composition

    • Hazy or indistinct margins

    • Peripheral spiculation with halo

    • Pleural retraction adjacent to tumor

    • Necrosis

    • Extension to bronchi or pulmonary veins

  • SPN calcification characteristics

    • Malignant

      • Generally not calcified

      • Nodules with eccentric calcification cannot be classified as benign

      • Bone cancer, soft tissue sarcoma, and mucinous adenocarcinoma metastases may calcify

      • 1/3 of carcinoid tumors calcify

      • Colon and ovarian metastases may show psammomatous calcification

      • Internal hemorrhage may simulate calcification (melanoma and choriocarcinoma)

    • Benign

      • Central, laminated, popcorn, diffuse

      • Diffuse calcifications > 300 HU through nodule

      • > 1/2 granulomas are calcified

      • 1/3 of hamartomas have popcorn calcification

  • Ground-glass opacity (GGO)

    • GGO nodules are lower density than solid nodules and do not obscure lung parenchyma

    • 20% of lung nodules demonstrate this density

      • 34% of these are malignant

    • More difficult to distinguish malignant from benign disease based on morphology

      • Much higher incidence of malignancy among ground-glass and mixed opacity nodules

    • Bronchoalveolar carcinoma often demonstrates this density

      • Also adenocarcinoma with BAC features

    • Adenocarcinoma > 2 cm with > 50% GGO has low risk of lymph node metastasis and vessel invasion

  • Enhancement

    • Malignant nodules often hypervascular and highly enhancing

    • Generally, > 25 HU = malignant, and < 15 HU = benign

    • Insensitive for subcentimeter, cavitary, or necrotic nodules

  • Fat

    • Malignant: Liposarcoma, renal cell carcinoma metastases (uncommon)

    • Benign: Hamartoma, lipoid pneumonia

  • Air bronchograms

    • Caused by small airway distortion

    • More typical of malignant than benign nodules

      • Seen in 30% of malignant nodules and 6% of benign nodules

    • As much as 55% of BAC shows bubble-like lucencies = pseudocavitation

Nuclear Medicine Findings

  • PET

    • Significant overlap in FDG activity between benign and malignant nodules

    • SUV > 2.5 has sensitivity/specificity 90-100%, 69-95% for detection of malignancy

    • Detection depends largely on size

      • Lower resolution limit 6-8 mm

      • Partial volume averaging of small nodules can produce falsely low SUV

    • Bronchioloalveolar carcinoma has multifocal form that is often detected with FDG PET

      • Overall, BAC tends to have lower FDG uptake than other pulmonary malignancies

    • False positives

      • Focal hypermetabolic uptake unrelated to malignancy

      • Most common include infection, inflammatory reaction, granulomata, hamartoma

    • False negatives

      • Malignant subcentimeter nodules may not be detected on FDG PET

      • Hypometabolic tumors: BAC, carcinoid

      • Temporary decrease in FDG uptake of active lesions post-therapy (“stunned tumor”)

      • Ground-glass nodules often false negative due to size and association with BAC

    • PET provides prognostic information for malignant nodules

Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Solitary Pulmonary Nodules

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