**Question:** A 50-year-old male is evaluated for haemoptysis. His CXR shows a cavitating lesion. All of the following can be the cause for this EXCEPT:

A. Pulmonary tuberculosis
B. Infectious mononucleosis
C. Lung cancer
D. Chronic bronchitis

**Core Concept:** Cavitary lesions on chest X-ray are typically seen in conditions causing granuloma formation or necrosis. These can be caused by infections (like tuberculosis), malignant tumors (like lung cancer), or inflammatory conditions (like chronic bronchitis).

**Why the Correct Answer is Right:** The correct answer, "B. Infectious mononucleosis," is right because this condition does not typically result in cavitary lesions on the chest X-ray. Infectious mononucleosis is an infection caused by the Epstein-Barr virus and is primarily characterized by lymphadenopathy, hepatosplenomegaly, and constitutional symptoms. Unlike the other options, it does not lead to cavitary lung lesions.

**Why Each Wrong Option is Incorrect:**

A. **Pulmonary tuberculosis (TB)** is a common cause of cavitary lesions on chest X-ray, particularly in its advanced stages. TB causes granuloma formation due to Mycobacterium tuberculosis infection.

C. **Lung cancer** can present with cavitary lesions on the chest X-ray. Solid lung tumors can lead to necrosis and cavitation, which is why lung cancer is a possible cause.

D. **Chronic bronchitis** can also lead to cavitary lesions on the chest X-ray. Chronic bronchitis typically occurs secondary to longstanding inflammation and infection, leading to fibrosis and necrosis in the lung parenchyma, which results in cavitation.

**Clinical Pearl:** A cavitary lesion on a chest X-ray is a clinical clue pointing towards the need for further evaluation for potential underlying pulmonary pathology. In the context of a 50-year-old male presenting with haemoptysis, the presence of a cavitary lesion should prompt a thorough clinical examination, including a detailed history and physical examination, to identify the possible cause and initiate appropriate management and treatment.

**Why the Correct Answer is Right:** The correct answer, "Infectious mononucleosis," is right because this condition does not typically lead to cavitary lesions on chest X-ray. Infectious mononucleosis is associated with lymphadenopathy, hepatosplenomegaly, and constitutional symptoms. Chest X-ray findings are typically consistent with the early stages of the disease, such as lymphadenopathy and hepatosplenomegaly.

**Why Each Wrong Option is Incorrect:**

A. **Pulmonary tuberculosis** (TB) is a common cause of cavitary lesions on chest X-ray, especially in its advanced stages. TB results in granuloma formation due to Mycobacterium tuberculosis infection, which can lead to necrosis and cavitation in the lung parenchyma.

C. **Lung cancer** can present with cavitary lesions on a chest X-ray, often secondary to fibrosis and necrosis in the lung parenchyma.

D. **Ch