Objectives: SPECT V/Q scintigraphy is more sensitive and specific than planar imaging in the diagnosis of Pulmonary Embolism (PE). In practice, the tomographic presentation of data allows greater perception of single segmental and sub-segmental mismatched defects. However, the significance of these isolated defects remains unknown

Methods: A retrospective review was performed of cases presenting to RNSH between 2005 and 2008 for suspected PE. Patients with isolated segmental or sub-segmental mismatched defects were identified from a database of reports. Scans were reviewed by an experienced nuclear medicine physician to confirm the scan report. Cases with previous PE or those on therapeutic anticoagulation at the time of presentation were excluded. Medical records were reviewed to determine pre-test clinical probability (Wells Criteria), pre-existing respiratory or cardiac disease, and whether patients were subsequently treated for PE. Finally, patients in whom PE was not treated were contacted to determine if there had been any further symptoms or diagnosis of PE.

Results: Of the 2255 patients who underwent V/Q scintigraphy, interim analysis reveals 39 patients had SPECT scans demonstrating isolated segmental or subsegmental mismatched defects (19 low, 17 intermediate, and 3 high clinical probability). Of these, 24 patients (63%) were considered not to have suffered pulmonary embolism clinically and anticoagulation was withheld. There was no difference in the rate of treatment between clinical populations (X2 =3.12, p = 0.21).

Conclusion: Isolated segmental or subsegmental defects on V/Q scans are relatively uncommon. A significant number of patients with such defects are not treated for PE.