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The normal main pulmonary artery diameter

I read with interest the short communication regarding idiopathic dilatation of the pulmonary artery by Drs Ring and Marshall [1]. This diagnosis of exclusion requires a definition of the normal diameter of the main pulmonary artery. In Case 1 of their article they refer to the upper limit of normal as being 2.1 cm, demonstrated by echocardiography, and in Case 2 the upper limit being 2.8 cm, demonstrated by MRI. Unless there is a calibration error the upper limits of normal of the main pulmonary artery demonstrated by ultrasound, CT or MRI should be the same. However, normal main pulmonary artery measurements are likely to vary between patients as a result of patient size; this may account for the differences.

In a study by Edwards et al [2], the upper limit of normal of the main pulmonary artery was calculated as 3.3 cm (mean +2 standard deviations). This was derived from 100 normal subjects, none of whom had pulmonary artery pressure measurements. In the only study that confirmed normal pulmonary artery pressures, Haimovici et al [3] defined the normal mean pulmonary artery pressures as less than or equal to 18 mm Hg. The investigators measured the main pulmonary artery diameters on CT. They calculated that if the values were less than or equal to 2.1 cm there was a 95% certainty of normal mean pulmonary artery pressures, and if greater than or equal to 3.5 cm in diameter there was a 95% certainty of high mean pulmonary artery pressures. 17 of 55 patients had normal mean pulmonary artery pressures from right-sided heart catheterization. The patients analyzed were all pre-heart or heart-lung transplant candidates. All of these patients had, or were suspected of having, chronic lung disease or pulmonary vascular disease. Clearly, there is a need for a study of normal subjects with normal hearts and lungs. The confirmation of normal pulmonary artery pressures could be performed non-invasively with echocardiography and correlated with main pulmonary artery diameters derived from ultrasound, CT or MRI measurements. The normal values should be tabulated against the variables of age, sex, height and body surface area, and the best linear relationship calculated. As radiologists we all know when something looks too large. One gets the impression that having accurate tables or graphs will make the main pulmonary artery diameter measurement a useful diagnostic tool.

Yours etc.,

C Wittram

Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston MA 02114, USA

Received for publication August 22, 2002. Accepted for publication September 10, 2002.

References

1. Ring NJ, Marshall AJ. Idiopathic dilatation of the pulmonary artery. Br J Radiol 2002;75:532–5.[Abstract/Free Full Text]
2. Edwards PD, Bull RK, Coulden R. CT measurement of main pulmonary artery diameter. Br J Radiol 1998;71:1018–20.[Abstract]
3. Haimovici JBA, Trotman-Dickenson B, Halpern EF, et al. Relationship between pulmonary artery diameter at computed tomography and pulmonary artery pressures at right-sided heart catheterization. Acad Radiol 1997;4:327–34.[CrossRef][Medline]

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Author's reply

N J Ring and A J Marshall
BJR 2003 76: 79. [Full Text]  

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