## **Core Concept**
The patient in this scenario has undergone a significant surgical procedure, a right hemicolectomy, for carcinoma of the caecum. Post-operative complications such as fever and leg pain could be indicative of a serious condition, particularly one that is directly related to the surgery or the patient's immobility post-surgery.

## **Why the Correct Answer is Right**
The correct answer, **D. Deep Vein Thrombosis (DVT)**, is a well-known complication following major surgeries, especially in cancer patients. Cancer itself is a hypercoagulable state, and surgery further increases this risk. DVT can present with leg pain and swelling but can also be asymptomatic. The development of fever could be due to a pulmonary embolism (PE) if the clot dislodges and travels to the lungs, causing a blockage. The clinical suspicion for DVT or PE should be high in post-operative patients, especially with risk factors like cancer and immobility.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While infections can cause fever post-operatively, the specific mention of leg pain points more towards a thromboembolic event rather than a localized infection.
- **Option B:** This option does not provide a specific enough condition to directly relate to both fever and leg pain in the post-operative context described.
- **Option C:** Similar to option A, wound infection could cause fever but does not directly explain leg pain unless the infection has spread, which would be less common and not the first consideration given the scenario.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Virchow's triad** (venous stasis, hypercoagulability, and endothelial injury) is crucial in understanding the risk factors for DVT. In post-operative patients, especially those with cancer, assessing for DVT and taking prophylactic measures (like anticoagulation) is critical to prevent potentially fatal pulmonary embolism.

## **Correct Answer:** **D. Deep Vein Thrombosis**