The revised PIOPED criteria for the diagnosis of pulmonary embolus indicate the probability of pulmonary emboli based on findings on V/Q scan (ventilation-perfusion scintigraphy).

Usage

This article reflects the revised interpretation criteria promulgated in 1993 ¹ based on retrospective analysis of data from the original Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), which compared V/Q scans against catheter pulmonary angiography ². The revised criteria were prospectively validated as more accurate than the original PIOPED criteria, although the modified PIOPED II criteria superseded them in 2012 ^3,4.

Classification

The interpretation of V/Q scans is based on detecting the presence of perfusion defects, identifying any matched ventilation defects, determining whether the perfusion defects are segmental or nonsegmental, and then evaluating the size of the segmental defect. The finding should be correlated with a chest radiograph.

A large segmental defect covers >75% of a pulmonary segment. A moderate, subsegmental defect covers 25-75% of a pulmonary segment and is considered in the interpretative criteria equivalent to one-half of a large defect. A small, subsegmental defect covers <25% of a pulmonary segment.

High probability (≥80%)

• more than two large mismatched segmental perfusion defects, or the arithmetic equivalent of moderate and/or large defects

Borderline high probability

• two large mismatched segmental perfusion defects or the arithmetic equivalent of moderate and/or large defects

  • individual readers may correctly interpret this pattern as high probability but it should generally be considered intermediate probability

Intermediate probability (20-79%)

• One moderate to two large mismatched segmental perfusion defects or the arithmetic equivalent of moderate and/or large defects

• any other pattern difficult to characterize as high probability or low probability

Borderline low probability

• single matched ventilation-perfusion defect with clear chest radiograph

  • individual readers may correctly interpret this pattern as low probability but it should generally be considered intermediate probability

Low probability (≤19%)

• nonsegmental perfusion defects (e.g. pleural effusion, cardiomegaly, elevated diaphragm, ectatic aorta, enlarged hila)

• any perfusion defect with a substantially larger chest radiographic abnormality

• extensive matched ventilation and perfusion defects with a normal chest radiograph and some areas of normal perfusion elsewhere

• any number of small perfusion defects with a normal chest radiograph

Normal

• no perfusion defects; perfusion scan exactly outlines the shape of the lungs on chest radiograph