Suboptimal CT angiogram for evaluation of pulmonary embolism: Outcome with VQ scan and clinical follow-up

1666 Objectives Indeterminate CT angiogram (CTA) can occur due to suboptimal opacification of contrast during evaluation pulmonary embolism(PE). In this situation, CTA report typically described no central PE, but peripheral subsegmental PE can not be excluded and recommend VQ scan. The purpose of this study is to evaluate 1.) frequency of this event, in terms of timing of requested VQ scanning, 2.) the outcome of PE based on composite reference control with VQ scan and clinical follow-up for 6 months. Methods Twenty patients who had so-called suboptimal CTA for PE and subsequent VQ scan were retrospectively evaluated for outcomes of VQ scan and clinical follow-up for 6 months.Timing of CT study and VQ scan were evaluated to see when this event occurs most frequently: off-hour vs. on-hour (i.e. 8 AM to 5 PM) interval. Age ranges from 23 to 79 year-old with mean age of 43. Female to male ratio was 16 to 4. 19 patient was from emergency department. Results 1. Outcome of VQ scan and clinical follow-up: None of these patients reported clinical evidence of PE by using composite reference control. 13 CT studies reported no central PE, but recommended VQ scan because of poor bolus, susegmental PE can not be excluded; among these patients, VQ scan was normal in 9, very low probability in 3 and intermediate probability in 1 patient who had a normal follow-up CT and VQ. 7 CT studies reported a questionalble filling defect and recommended VQ scan; it was normal in 5, very low probability in 1, intermediate proabability in 1. Subsequent follow-up on a patient with intermediate probability proved to be a negative for PE. 2. Timing of poor CT bolus: 14 studies were off-hour study-mid night to early in the morning. Conclusions Suboptimal CTA occurs most often during off-hour. There were no clinical and scintigraphical evidence of PE in the patients with indeterminate CTA with concern of subsegmental/peripheral PE. Further investigation of outcome of single isolated subsegmental pulmonary embolism is warranted