Sensitivity and Specificity of Perfusion Scintigraphy Combined with Chest Radiography for Acute Pulmonary Embolism in PIOPED II

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FIGURE 1.
Selection of patients from those enrolled in PIOPED II was based on presence of defined diagnostic reference standard and availability of interpretable scintigraphic images. Of 1,090 patients enrolled in PIOPED II, 180 were not eligible for inclusion in our analysis: 28 did not undergo CTA, 37 did not undergo V/Q scanning, 74 of those who did not have a DSA diagnosis either did not have a CTA diagnosis or did not have a Wells' score, and in another 41 of those who did not have a DSA diagnosis, CTA diagnosis and Wells' score were discordant. Discordance between CTA and Wells' score was defined according to PIOPED II (14) criteria: low clinical probability (Wells' score < 2) with CTA positive for PE, or high clinical probability (Wells' score > 6) with CTA negative for PE. Finally, in 21 cases that met selection criteria, films could not be located for rereading. In this flow chart, both CTA and DSA were of pulmonary arteries.

TABLE 1

Modified PIOPED II and PISAPED Scintigraphic Criteria

	Criteria
Finding	Modified PIOPED II	PISAPED
PE present	High probability (2 or more segments of perfusion–chest radiograph mismatch)	One or more wedge-shaped perfusion defects
PE absent	Normal perfusion	Normal perfusion
	Very low probability
	Nonsegmental lesion, for example, prominent hilum, cardiomegaly, elevated diaphragm, linear atelectasis, or costophrenic angle effusion with no other perfusion defect in either lung radiographic lesion	Near normal
	Perfusion defect smaller than radiographic lesion	Contour defect caused by enlarged heart, mediastinum, or diaphragm
	1–3 small segmental defects	Perfusion defect, not wedge-shaped
	Solitary chest radiograph–perfusion matched defect in mid or upper lung zone confined to single segment
	Stripe sign around perfusion defect (best tangential view)
	Pleural effusion in at least one third of pleural cavity, with no other perfusion defect in either lung
Not diagnostic	All other findings	Cannot classify as PE-positive or PE-negative

TABLE 2

Diagnostic Results

TABLE 3

V/Q Scan Results Compared with Perfusion Scan Results

TABLE 4

Predictive Values of Perfusion Scan Compared with CTA

Test	PPV	NPV	Not diagnostic
Modified PIOPED perfusion scan^*	72.4% (220/304)	96.5% (1,069/1,108)	20.6% (366/1,778)
PISAPED perfusion scan^*	84.7% (272/321)	95.5% (1,391/1,457)	0.0% (0/1,778)
CTA^†	85.7% (150/175)	94.8% (567/598)	6.2% (51/824)

TABLE 5

Perfusion Scan Results According to Patient Age^*