**Question:** A patient develops pulmonary thromboembolism due to?

**Core Concept:** Pulmonary thromboembolism is a clinical condition characterized by the blockage of one or more pulmonary arteries by a blood clot that originated from the deep veins of the lower limbs, pelvis, or heart.

**Why the Correct Answer is Right:** Pulmonary thromboembolism results from the formation of a blood clot in a deep vein, which then breaks off and travels to the pulmonary circulation, causing blockage in the pulmonary arteries and leading to reduced blood flow and oxygen supply to the lungs. In this case, the correct answer is **Option D:**

**Correct Answer: Deep Vein Thrombosis (DVT)**

**Why Each Wrong Option is Incorrect:**

A. **Option A (Deep Vein Thrombosis)**: Deep vein thrombosis (DVT) is the formation of a blood clot in a deep vein, typically in the legs or pelvis. While DVT can lead to pulmonary embolism, the correct answer is not DVT itself but the subsequent pulmonary thromboembolism that occurs due to the broken-off clot.

B. **Option B (Atrial Fibrillation)**: Atrial fibrillation is an irregular heart rhythm that increases the risk of clot formation in the atria, but it does not directly cause pulmonary thromboembolism by itself. The correct answer is DVT resulting from atrial fibrillation.

C. **Option C (Venous stasis)**: Venous stasis occurs when blood flow in the veins is slow or stopped due to immobility or compression. While venous stasis can contribute to DVT formation, it is not the direct cause of pulmonary thromboembolism.

D. **Option D (Deep Vein Thrombosis)**: As mentioned earlier, DVT is the formation of a blood clot in a deep vein, which can lead to pulmonary thromboembolism. In this case, DVT is the initial event causing the formation of the blood clot that travels to the lungs and results in pulmonary thromboembolism.

**Core Concept:** Pulmonary thromboembolism occurs when a blood clot from a deep vein in a limb or pelvis travels to the lungs, blocking pulmonary arteries and impairing blood flow and oxygen delivery to the lungs.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Atrial Fibrillation)**: Atrial fibrillation increases the risk of clot formation, but it does not directly cause pulmonary thromboembolism. The clot formation occurs in the deep veins (DVT) before it can travel to the lungs and cause pulmonary thromboembolism.

B. **Option B (Lower Limb Injury)**: An injury to the lower limb does not directly cause pulmonary thromboembolism; it is the formation of a DVT that leads to pulmonary thromboembolism.

C. **Option C (Hematoma)**: A hematoma is a collection of blood outside the blood vessels, not a direct cause of pulmonary thromboembolism.