A 54-year-old construction worker has smoked two packs of cigarettes daily for the past 25 years. He notes swelling in his upper extremity and face, along with dilated veins in this region. A computerized tomography (CT) scan and venogram of the neck are performed. What is the most likely cause of the obstruction?

**Core Concept**
The patient's symptoms and history are indicative of superior vena cava (SVC) syndrome, a clinical condition characterized by obstruction of the SVC, leading to venous congestion and dilation of veins in the upper body. SVC syndrome is often caused by external compression or invasion of the SVC by adjacent structures, such as tumors or lymph nodes.

**Why the Correct Answer is Right**
The correct answer involves a thoracic mass that has grown large enough to compress the SVC. The patient's history of smoking is a significant risk factor for the development of lung cancer, which is the most common cause of SVC syndrome. The mass may be a bronchogenic carcinoma, typically originating from the right upper lobe of the lung. The tumor's growth can lead to compression and eventual obstruction of the SVC, resulting in the patient's symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Aortic aneurysm is unlikely to cause SVC syndrome, as it would more likely lead to aortic dissection or rupture. While an aortic aneurysm can compress the SVC, it is not the most common or likely cause in this scenario.
**Option B:** Aortic dissection can cause SVC syndrome by compressing the SVC, but it is a less common cause compared to thoracic masses or lymphadenopathy.
**Option C:** Lymphadenopathy can cause SVC syndrome by compressing the SVC, but it is typically associated with infections, such as tuberculosis, or malignancies, such as lymphoma. In this scenario, the patient's history of smoking and symptoms are more suggestive of a thoracic mass.

**Clinical Pearl / High-Yield Fact**
SVC syndrome is often associated with lung cancer, and patients with a history of smoking are at increased risk. A high index of suspicion and prompt imaging studies, such as CT scans and venograms, are essential for diagnosing SVC syndrome.

**Correct Answer:** C.

✓ Correct Answer: C. Bronchogenic carcinoma