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PIOPED II, PISAPED and CTPA Criteria for Diagnosis of Pulmonary Embolus

Efficacy and continued technical improvements in CT pulmonary angiography (CTPA) have produced a significant rise in its use for the diagnosis of acute pulmonary embolism (PE). The growth of CTPA has produced a corresponding reduction in the utilization of pulmonary scintigraphy to the extent that some publications have suggested that lung scanning has become a second-line test. Lung ventilation/perfusion (V/Q) scintigraphy along with modified prospective investigation of pulmonary embolism diagnosis (PIOPED) interpretation criteria has been utilized to diagnose acute PE. More recently, a simplified algorithm comprising pulmonary perfusion scan along with prospective investigative study of pulmonary embolism diagnosis (PISAPED) interpretation criteria has shown a reduction of intermediate probability as one of the lung scan readings generated by the modified PIOPED criteria and has improved the sensitivity and specificity of the lung scintigraphy along with the modified PIOPED criteria to detect acute PE.

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

 

PISAPED scintigraphic criteria

Pulmonary embolism present

  • Presence of single or multiple wedge‑shaped perfusion defects, the size of which corresponds to that of lobar, segmental, or subsegmental regions of the lung

Pulmonary embolism absent

  • Normal scan: No perfusion defects
  • Near normal: Presence of impressions caused by enlarged heart, hila, or mediastinum on an otherwise normal scan
  • Abnormal, not suggestive of PE: Presence of single or multiple other than wedge‑shaped perfusion defects

Modified PISAPED scintigraphic criteria

PE present

  • Abnormal (with normal ventilation): Presence of single or multiple wedge‑shaped perfusion defects the size of which corresponds to that of lobar, segmental, or subsegmental regions of the lung and the perfusion defects being filled up with ventilation
  • Abnormal (with normal ventilation): Presence of single or multiple other than wedge‑shaped perfusion defects and the perfusion defects being filled up with ventilation

PE absent

  • Normal: No perfusion defects and no abnormality of ventilation
  • Near normal: Presence of impressions caused by enlarged heart, hila, or mediastinum on an otherwise normal scan and ventilation defect
  • Abnormal (without normal ventilation): Presence of single or multiple other than wedge‑shaped perfusion defects and the perfusion defects not being filled up with ventilation
  • Abnormal (without normal ventilation): Presence of single or multiple wedge‑shaped perfusion defects the size of which corresponds to that of lobar, segmental, or subsegmental regions of the lung and the perfusion defects not being filled up with ventilation

Nondiagnostic: All other findings or poor image quality

 

CTPA criteria

PE present (As acute PE):

  • Complete arterial occlusion with failure to opacify vessel lumen. Artery may be enlarged as compared to others of the same order
  • Central filling defect surrounded by contrast Peripehral intraluminar filling defect that makes an acute angle with the arterial wall

PE absent (Normal):

  • No perfusion defects by contrast
  • As chronic PE,
  • Complete occlusion of vessel that is smaller than others of same order of branching
  • Peripheral filling defect that makes obtuse angles with the vessel wall
  • Contrast flowing through vessels that appear thick‑walled due to recanalization

Nondiagnostic: Poor image quality

 

 

References:

  1. Cronin P, Dwamena BA. A Clinically Meaningful Interpretation of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) Scintigraphic Data. Acad Radiol. 2017 May;24(5):550-562. [Medline]
  2. Sostman HD, Stein PD, Gottschalk A, Matta F, Hull R, Goodman L. Acute pulmonary embolism: sensitivity and specificity of ventilation-perfusion scintigraphy in PIOPED II study. Radiology. 2008 Mar;246(3):941-6. [Medline]
  3. Tak T, Karturi S, Sharma U, Eckstein L, Poterucha JT, Sandoval Y. Acute Pulmonary Embolism: Contemporary Approach to Diagnosis, Risk-Stratification, and Management. Int J Angiol. 2019 Jun;28(2):100-111. [Medline]
  4. Watanabe N, Fettich J, Küçük NÖ, Kraft O, Mut F, Choudhury P, Sharma SK, Endo K, Dondi M. Modified PISAPED Criteria in Combination with Ventilation Scintigraphic Finding for Predicting Acute Pulmonary Embolism. World J Nucl Med. 2015 Sep-Dec;14(3):178-83. [Medline]

 

Created Jun 30, 2021.

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