Hamartoma (Lung and Mediastinum)
A hamartoma involving the lung or mediastinum is a benign (non-cancerous) growth made of normal tissue components that are mixed together in an unusual arrangement. Pulmonary hamartomas most often appear within the lung tissue itself, while mediastinal hamartomas are much less common and arise in the central chest area. These growths are usually slow-growing, well-defined, and frequently discovered incidentally on imaging performed for unrelated reasons.
What is it?
A hamartoma is a benign mass made of various tissues that naturally exist in the lung or mediastinum—such as fat, cartilage, connective tissue, or small airway elements—but arranged in a disorganized or “mixed” way. In the lungs, hamartomas typically appear as round, well-circumscribed nodules, often measuring 1–4 centimeters. Mediastinal hamartomas behave similarly, though they are less common and may involve more fatty or cystic components.
These growths arise from normal tissue rather than from cancer cells, and they do not spread to other parts of the body. Many individuals are unaware of their presence until the mass is found on imaging obtained for unrelated symptoms or routine screening.
Important to Know
On CT imaging, hamartomas may display distinctive features such as visible fat or “popcorn” calcifications in the lungs, which help radiologists differentiate them from malignant tumors. Mediastinal hamartomas may appear as fatty or mixed-density masses but often maintain a smooth, rounded shape that supports their benign nature.
Additional evaluation may be recommended if the mass grows, appears atypical, or occurs in someone with elevated cancer risk. A biopsy or MRI may help clarify the diagnosis. Concerning symptoms—such as worsening cough, new chest pain, difficulty breathing, or coughing up blood—should prompt timely medical review. When confidently diagnosed, hamartomas have an excellent prognosis and often require no treatment beyond routine monitoring.