A benign lung lesion discovered incidentally commonly contains cartilage, cellular fibrous tissue, and fat. What is this lesion?

• A. Adenocarcinoma
• B. Hamartoma
• C. Fibroma
• D. Lipoma

Answer: (B)

The main idea here is that a benign lung lesion made up of cartilage, fibrous tissue, and fat is classic for a hamartoma. Pulmonary hamartomas are disorganized but mature mixtures of normal lung tissues, with cartilage being the hallmark component, often accompanied by fat and fibrous stroma. This combination reflects a benign mesenchymal origin and explains why the lesion is typically incidental and presents as a solitary pulmonary nodule.

In contrast, an adenocarcinoma would show malignant epithelial gland-forming cells rather than a mixture of cartilage and fat. A fibroma would be mainly fibrous tissue without cartilage or fat. A lipoma would be predominantly adipose tissue with little to no cartilage or fibrous stroma.