Superior vena cava syndrome is caused most commonly by –
**Core Concept**
Superior vena cava syndrome (SVCS) is a clinical condition characterized by obstruction of the superior vena cava, leading to impaired venous return from the upper body, resulting in facial swelling, arm edema, and other symptoms. This obstruction can be caused by various factors, including malignancies, thrombosis, and external compression.
**Why the Correct Answer is Right**
The most common cause of SVCS is external compression of the superior vena cava by a mass, typically a lung tumor, such as squamous cell carcinoma. This compression can lead to partial or complete obstruction of the superior vena cava, resulting in the characteristic symptoms of SVCS. The external compression can also lead to thrombosis of the superior vena cava, further exacerbating the obstruction.
**Why Each Wrong Option is Incorrect**
* **Option A:** While lymphoma is a potential cause of SVCS, it is not the most common cause.
* **Option B:** Thrombosis of the superior vena cava is a potential complication of SVCS, but it is not the most common cause.
* **Option D:** Metastatic disease to the superior vena cava can cause SVCS, but it is less common than external compression by a lung tumor.
**Clinical Pearl / High-Yield Fact**
The most common cause of SVCS is external compression by a lung tumor, particularly squamous cell carcinoma. This is a classic exam trap, as many students may incorrectly identify lymphoma or metastatic disease as the most common cause.
**Correct Answer: C. Lung tumor**