In many centers, multi-detector CTA has replaced V/Q scanning for the initial evaluation of pulmonary embolism. High risk patients for PE with a non-diagnostic CTA require additional testing. The PIOPED study showed that standard V/Q scans are indeterminate in up to two thirds of patients. Therefore, we compared the efficacy of spect V/Q scans to CTA in patients with a high clinical suspicion of PE.
From January 2007 to December 2008, we identified 100 patients at Lenox Hill Hospital with a moderate to high clinical probability for pulmonary embolism that underwent both SPECT V/Q scan and CTA within a 3 day period. The diagnostic utility of CTA was compared to spect V/Q scan.
23 patients were clinically diagnosed with pulmonary embolism. 14 patients had CTA positive for PE, and 55 had negative CTA for PE. 31 out of 100 CTAs were non-diagnostic due to either technical issues (17) or non-diagnostic abnormalities (14). Of non-diagnostic CTAs, 5 patients (21.7%) were diagnosed with pulmonary embolism. The sensitivity and specificity of the two diagnostic modalities were similar, sensitivity for CTA and spect V/Q scan were 67% and 72%, respectively. Specificity of CTA and spect V/Q were 96% and 94%, respectively. Interestingly, only 9 patients had an indeterminate spect V/Q scans, of which only 1 was diagnosed with PE. CTA showed a lower false positive rate (2.6%) compared to V/Q scans (5.2 %). Among false positive V/Q spect scan 2 patients had “chronic/old” PE and 2 had malignancy.
In patients with a moderate to high pre-test probability for PE, CTA remains a rapid and effective method in the evaluation of PE. However, in patients with technically limited or inconclusive CTA, V/Q scan reliably confirms or excludes the diagnosis of PE.
Spect V/Q is comparable to CTA with less indeterminant scans than previously reported with standard V/Q imaging.
Ramyar Mahdavi, No Financial Disclosure Information; No Product/Research Disclosure Information