Modified PIOPED II criteria for diagnosis of pulmonary embolus

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The modified PIOPED II criteria for the diagnosis of pulmonary embolus indicate the presence or absence of pulmonary emboli based on findings on V/Q scan (ventilation-perfusion scintigraphy). The following article reflects the modified interpretation criteria promulgated in 2008  based on recategorized readings from the Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II), a trial in which patients underwent some combination of CT pulmonary angiography, V/Q scanning, and pulmonary digital subtraction angiography . These criteria supersede the revised PIOPED criteria and replace the multiple probabilistic categories with fewer categories of definitive interpretations , which may be more understandable for referring clinicians.

Ventilation/perfusion modified PIOPED II criteria

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.

Pulmonary embolism present (high probability)
  • two or more large mismatched segmental perfusion defects or the arithmetic equivalent of moderate and/or large defects
Nondiagnostic (low or intermediate probability)
  • all other findings not falling into the pulmonary embolism present or absent categories
Pulmonary embolism absent (normal or very low probability)
  • no perfusion defects
  • nonsegmental perfusion defects (e.g. pleural effusion at the costophrenic angle, cardiomegaly, elevated hemidiaphragm, hilar enlargement, linear atelectasis), without other perfusion defects in either lung
  • perfusion defects smaller than corresponding chest radiographic opacity
  • one to three small subsegmental perfusion defects
  • two or more matched ventilation and perfusion defects with a regionally normal chest radiograph and some areas of normal perfusion elsewhere
  • solitary triple matched defect (matched ventilation and perfusion defect with corresponding chest radiographic opacity) in a single segment in the middle or upper lung zone
  • stripe sign (a stripe of perfusion peripheral to a defect, best seen on tangential view)
  • large pleural effusion (occupying one-third or more of the pleural cavity), without other perfusion defects in either lung

Perfusion-only modified PIOPED II criteria

The modified PIOPED II criteria have been adapted for perfusion scintigraphy (i.e. no ventilation scan) . In this scheme, the presence of a match or mismatch is determined by comparing the perfusion scan with the chest radiograph rather than a ventilation scan. A perfusion defect without a corresponding radiographic opacity is considered mismatched. In addition, the criterion of multiple matched ventilation and perfusion defects with normal radiograph has been removed from the category of pulmonary embolism absent.

Perfusion-only interpretation reduces both the specificity and the proportion of nondiagnostic readings compared to ventilation and perfusion using modified PIOPED II criteria .

Pulmonary embolism present (high probability)
  • two or more large mismatched segmental perfusion defects or the arithmetic equivalent of moderate and/or large defects
Nondiagnostic (low or intermediate probability)
  • all other findings not falling into the pulmonary embolism present or absent categories
Pulmonary embolism absent (normal or very low probability)
  • no perfusion defects
  • nonsegmental perfusion defects (e.g. pleural effusion at the costophrenic angle, cardiomegaly, elevated hemidiaphragm, hilar enlargement, linear atelectasis), without other perfusion defects in either lung
  • perfusion defects smaller than corresponding chest radiographic opacity
  • one to three small subsegmental perfusion defects
  • solitary matched defect in a single segment in the middle or upper lung zone
  • stripe sign (a stripe of perfusion peripheral to a defect, best seen on tangential view)
  • large pleural effusion (occupying one-third or more of the pleural cavity), without other perfusion defects in either lung