Pulmonary Hamartoma

Epidemiology and Etiology:

• Most common benign pulmonary neoplasm
• 8% of coin lesions of chest X-ray
• Neoplasm

Common sites:

• Farily uniform distribution throughout the lungs
• Peripheral mostly
• Endobronchial (10%)

Gross features:

• Imaging:
• Well-circumscribed nodule
• Solitary
• Popcorn calcification (infrequent but important radiologic finding)
• Adipose tissue as seen on CT
• Rarely multifocal
• Firm
• Round to multilobulated
• Pale tan
• Well-circumscribed
• < 4 cm mostly
• Uncommonly cavitation or large size

Histologic features:

• Varying amounts of at least 2 mesenchymal elemnts (differentiation from benign monomorphic soft tissue tumours)
• Cartilage
• Fat
• Connective tissue
• Smooth muscle
• Entrapped respiratory epithelium
• Chondroid or chondromyxoid tissue
• Fat
• Connective tissue
• Smooth muscle
• Bone
• Clefts of respiratory epithelial cells
• No atypia (differentiation from primary or metastatic sarcomas)

Immunophenotype:

Marker:	Sensitivity:	Specificity:
Mesenchymal markers
Sex steroid receptors

Molecular features:

• t(3;12)(q27-28;q14-15) (HMGA2-LPP fusion gene) (high frequency in pulmonary hamartomas)
• exons 1-3 of HMGA2
• exons 9-11 of LPP

Other features:

• Benign neoplasm
• Excellent prognosis
• Recurrence and malignant transformation very rare

References:

• Travis et al. eds. WHO Classification of Tumours of the Lung, Pleura, Thymus, and Heart. (2015)