Pulmonary embolism other imaging findings

Associate Editors-in-Chief: Ujjwal Rastogi, MBBS [mailto:urastogi@perfuse.org]

Overview
The gold standard for diagnosing pulmonary embolism (PE) is pulmonary angiography (PA). The Pulmonary angiogram has a sensitivity and specificity of >95% in diagnosing PE. The estimated false-negative rate is 0.5% – 1.7%. Pulmonary angiography is used less often because of wider acceptance of CT scans, which are non-invasive. CT pulmonary angiography is the recommended first line diagnostic imaging test in most people. A negative PA excludes clinically important Pulmonary embolism.

Angiography
PA is a definitive diagnostic test, which is generally safe and well tolerated in hemodynamic stable patients. However; in patients with acute, severe pulmonary hypertension, it should be undertaken with caution. Patients who have long-standing pulmonary arterial hypertension and right ventricular failure are considered high-risk patients.

Small emboli cannot be seen angiographically, but are common on postmortem examination following a negative angiogram. Small emboli can produce pleuritic chest pain and can have small sterile effusion in-spite of having a normal V/Q scan and a normal pulmonary angiogram. In most patients, large and small emboli are already present by the time the diagnosis is made or is suspected. Under these conditions, the V/Q scan and the angiogram are likely to detect at least some of the emboli.

This procedure causes variable radiation exposure depending upon the procedure's length and complexity. However the exposure is greater than CT pulmonary angiography. According to the International Commission on Radiological Protection (ICRP), the radiation exposure, from a lung scan with 100 MBq of Tc-99 m macroaggregate of albumi (MAA) is 1.1 mSv. While from spiral CT is 2–6 mSv, and from plain chest X-ray is approximately 0.05 mSv.

Morbidity occurs in less than 5 percent of patients, and is related to:
 * 1) Catheter insertion
 * 2) Contrast reactions
 * 3) Cardiac arrhythmia
 * 4) Respiratory insufficiency.

Pulmonary angiography is more invasive and is harder to perform than MultiDetector-row Computed Tomography Angiography (MDCTA), and for these reasons, it is rapidly being replaced. It should only be done if MDCTA is unavailable or contraindicated.