Letters

Further studies of value of spiral computed tomography are needed

EDITORAn editorial by Hansell and Flower dealt with the challenge of adequately diagnosing pulmonary embolism with spiral computed tomography.¹ Although I am in favour of changing one's diagnostic algorithm in line with improvements in diagnostic modalities, I would like to take a closer look at the proof in support of this new technique.

As the editorial states, there is some evidence that large central emboli are easily visualised. The subsegmental vessels, however, remain a problem. Oser et al studied the anatomical distribution of pulmonary emboli by angiography and concluded that spiral computed tomography would miss up to 30% of patients with angiographically proved pulmonary emboli.² This proportion corresponds well with findings of a study in patients with non-diagnostic results of lung scanning: pulmonary angiography showed emboli in subsegmental or smaller vessels in 15% of patients.³

In the first management study that used spiral computed tomography 164 patients with non-diagnostic results of lung scanning and a normal ultrasound scan of the deep leg veins remained untreated and were followed up for three months.⁴ Spiral computed tomography gave normal results in 112 patients, and anticoagulant treatment was withheld. During follow up three patients developed deep vein thrombosis, two had non-fatal pulmonary embolism, and one died of proved pulmonary embolism (event rate 5.4% (95% confidence interval 1.9% to 11%) and mortality related to embolism 0.9% (95% confidence interval 0.02% to 5.0%)). These figures compare unfavourably with a management study that used lung scintigraphy in combination with repeat ultrasonography of the leg or pulmonary angiography.⁵

We would be ill advised to include spiral computed tomography in the routine clinical management of patients before further studies have been performed.