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Epidemiology

• Most common benign lung tumor
• Found in 0.2% of routine autopsies/0.75% of 47,000 miners
• 5-10% of solitary pulmonary nodules are hamartomas
• Sex Predominance: M:F ratio is 2:1
• Age: usual onset in late 30’s with peak in late 50’s
• Associated with:
  • Other benign tumors
  • Congenital anomalies

Physiology

• Benign neoplasm (typically slow growing)
• Malignant transformation is extremely rare
• May occur endobronchially (10-20% of cases)

Pathology

• Central cartilaginous area (in most cases) with calcification (in some cases)/ myxomatous or fibroblastic tissue/ muscular or adipose tissue/ bronchial glands/ inflammatory cells/ slit-like spaces or clefts lined with epithelium (seen near periphery of tumor)
• Mesenchymal Cystic Hamartoma: rare variant with malignant potential

Diagnosis

• FNA: may be diagnostic
• FOB: TBB diagnostic in some cases
  • Endobronchial Hamartoma (10-20% of cases): usually polypoid/cartilage present in 82% of cases, but often scanty/epithelial clefts are often missing)/EBB usually (but not always) diagnostic

CXR/Chest CT Pattern: usually well-circumscribed nodule <3 cm with sharp margins, lobulation (occasionally, multiple)
-Appearance: heterogeneous
-Location: no lobar predilection
-Growth: usually slow growing over years
-Calcification: occurs in minority of cases (but “Popcorn” calcification is a diagnostic pattern seen in 10-15% of cases on CXR)
–CT is more sensitive for calcification
-Cavitation: none
-Density: Chest CT Hounsfield Unit measurement can determine if there are low density fatty components

HRCT: diagnostic in 50% of cases
-Presence of high attenuation cartilage (with/without calcification) with low attenuation fat

Clinical Manifestations

Treatment

• Surgical excision: curative
• Indications for surgery: symptoms/ growth over time by CXR/ large size/ impingement on a vital structure/ endobronchial location

References

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