**Question:** In Renal cell carcinoma investigation of choice to evaluate inferior vena cava & renal vein for thrombus

**Core Concept:**
The correct investigation for assessing thrombus in renal vein and inferior vena cava in cases of renal cell carcinoma is crucial for determining the extent of the disease and guiding treatment decisions. Renal cell carcinoma (RCC) is the most common type of kidney cancer, accounting for around 80-85% of all cases.

**Why the Correct Answer is Right:**
In the case of renal cell carcinoma, computed tomography (CT) angiography is the investigation of choice for evaluating the inferior vena cava (IVC) and renal vein for thrombus presence. This is because:

1. **CT angiography:** It provides detailed images of the venous system, including the IVC, renal veins, and the tumor itself. This allows for accurate assessment of thrombus presence and extent.
2. **Comparison with MR angiography:** CT angiography is generally faster and more accessible than magnetic resonance angiography (MRA). However, MRA has become more common due to its non-ionizing radiation exposure, making it a safer option for patients.

**Why Each Wrong Option is Incorrect:**

1. **Option A (USG):** Ultrasonography (USG) is a non-invasive imaging modality but lacks the resolution to accurately assess the IVC and renal veins. Additionally, USG is less effective in detecting thrombus in the central venous system compared to CT or MR angiography.
2. **Option B (CT venography):** While CT venography provides detailed images of the venous system, it involves contrast media injection, which may have complications for patients with renal dysfunction or allergy to contrast agents.
3. **Option C (MRV):** Magnetic resonance venography (MRV) is another imaging technique that assesses the venous system, but it shares the same reasons as option B (CT venography) for being less suitable for certain patient populations.
4. **Option D (Angiography):** Angiography is an invasive technique involving injection of contrast media into the blood vessels, which carries risks for patients, especially those with renal dysfunction or allergy to contrast agents.

**Clinical Pearl:**
The use of contrast media in CT and MR imaging techniques is essential for accurate detection of renal vein and IVC thrombus in patients with renal cell carcinoma. However, alternative imaging modalities, such as ultrasound or non-contrast CT, can be considered for patients with contraindications to contrast agents. In such cases, these techniques may be useful for detecting renal vein and IVC thrombus, but their accuracy may be compromised due to limited resolution and sensitivity.