Pulmonary thromboembolism on V-Q scan is suggested by:
**Core Concept**
Pulmonary thromboembolism (PTE) occurs when a blood clot (thrombus) breaks loose and travels to the lungs, obstructing blood flow. The ventilation-perfusion (V-Q) scan is a diagnostic tool used to detect PTE by identifying areas of the lung that are ventilated but not perfused, indicating a possible embolism.
**Why the Correct Answer is Right**
In a V-Q scan, the perfusion scan (usually with Technetium-99m macroaggregated albumin) shows the distribution of blood flow to the lungs, while the ventilation scan (usually with Xenon-133 or Krypton-81m) shows the airflow to the lungs. A mismatch between ventilation and perfusion indicates a possible PTE. This is because the embolism blocks blood flow to a specific area of the lung, but air can still reach that area through collateral pathways, resulting in a perfusion defect (cold spot) without a corresponding ventilation defect (hot spot).
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not specify a characteristic of PTE on a V-Q scan. While PTE can cause a variety of symptoms, the V-Q scan is specifically used to detect the mismatch between ventilation and perfusion.
**Option B:** This choice is incorrect because it describes a characteristic of pulmonary edema, not PTE. Pulmonary edema can cause a match between ventilation and perfusion (hot and cold spots together) due to increased fluid in the lungs.
**Option C:** This choice is incorrect because it is a characteristic of a normal V-Q scan, not PTE. In a normal scan, there should be a match between ventilation and perfusion.
**Option D:** This choice is incorrect because it does not describe a characteristic of PTE on a V-Q scan. While PTE can cause a variety of symptoms, the V-Q scan is specifically used to detect the mismatch between ventilation and perfusion.
**Clinical Pearl / High-Yield Fact**
When interpreting a V-Q scan, remember that a mismatch between ventilation and perfusion is a key indicator of PTE. A classic mnemonic to remember this is "MATCH": Mismatch between ventilation and perfusion indicates a possible Thromboembolism.
**Correct Answer: C. A match between ventilation and perfusion indicates a normal scan (or pulmonary edema), while a mismatch suggests a possible pulmonary thromboembolism.**