Solitary Pulmonary Nodule
Eric J. Stern, MD
DIFFERENTIAL DIAGNOSIS
Common
Granuloma
Lung Cancer
Intrapulmonary Lymph Node
Less Common
Carcinoid
Solitary Metastasis
Nodule Mimics (Pseudonodules)
Nipple
Skeletal Lesions
Infectious/Inflammatory Process
Rare but Important
Hamartoma
Pulmonary Arteriovenous Malformation
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Solitary pulmonary nodule (SPN): Single, focal-rounded, or ovoid opacity ≤ 3 cm
SPN detection
Radiography
SPN found in up to 2% of chest radiographs
SPNs measuring < 9 mm are likely calcified granulomas
Dual energy or tomosynthesis are promising techniques to increase sensitivity for detecting SPNs
CT: Superior detection/characterization
Multiplanar reconstructions, maximum intensity projections (MIPs) increase confidence
Risk factors for malignancy in SPN
Exposure to cigarette smoke or other carcinogens
History of malignancy (pulmonary or extrapulmonary)
History of pulmonary fibrosis
Age > 40 years
SPN imaging assessment
Characterization
Benign SPN: No follow-up required
Indeterminate SPN: Imaging follow-up to document growth or stability
Possibly malignant SPN: Further imaging assessment ± biopsy
Helpful Clues for Common Diagnoses
Granuloma
Solid, rounded SPN, stable in size
Satellite nodules
Benign patterns of calcification include solid, laminar, or concentric
Complete or diffuse (pitfall, metastatic osteosarcoma)
Central, > 10% of SPN cross section (pitfall, calcified carcinoid tumor)
Most common: Histoplasmosis, tuberculosis, coccidioidomycosis
Lung Cancer
Upper lobes most common, but peripheral and basilar in patients with preexisting pulmonary fibrosis
Increased risk of cancer in nodules > 1 cm
Doubling times typically between 1-18 months; average: 100 days
Irregular, spiculated, or lobular borders
Calcification in 13%, usually eccentric, stippled
Intrapulmonary Lymph Node
Common normal finding on multidetector CT
Elongate morphology, fissural location; typically located within 20 mm of pleura
Helpful Clues for Less Common Diagnoses
Carcinoid
Well-defined lobular borders
Contrast enhancement, vascularity
Multifocal or coarse calcification
Calcification more common with lesions adjacent to central airways
Solitary Metastasis
Typically from sarcomas, melanomas, testicular cancers
Peripheral location
Nodule Mimics (Pseudonodules)
Nipple
Bilaterally symmetric rounded opacities, mid to inferior hemithorax, midaxillary line
Skeletal Lesions
1st costochondral junction: Contiguity with anterior 1st rib; often asymmetric
Rib fracture callus, bone island: CT, tomosynthesis, or shallow oblique radiography to determine location
Infectious/Inflammatory Process
Helpful Clues for Rare Diagnoses
Hamartoma
Slow growing with well-defined lobular or notched borders
Fat (33%) or popcorn calcification (25%) in 50% (pitfall, metastatic chondrosarcoma)
If multiple, consider Carney triad or Cowden syndrome
Pulmonary Arteriovenous Malformation
Peripheral lower lobe location
Typically 1-5 cm in diameter, with feeding and draining vessel(s)
Vascular enhancement
Single in 2/3; when multiple, usually 2-8
Alternative Differential Approaches
SPN features
Size: 90% of nodules < 2 cm are benign
Growth pattern
2-year stability implies benignity, but rare indolent lung cancers occur, especially in screening studies
Doubling time < 30 days or > 465 days favors benignity
Morphology and border characteristics
Spiculation: Highly suggestive of malignancy
Pleural tags in 60-80% of peripheral lung cancers
Lobulation (histologic heterogeneity) seen in 40% of malignant nodules
Round, more characteristic of benign lesions
Attenuation
Solid (soft tissue): Most lung cancers but less likely malignant than part-solid or nonsolid SPNs
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