Elsevier

Clinical Imaging

Volume 40, Issue 4, July–August 2016, Pages 821-827
Clinical Imaging

Original Article
CT measurement of central pulmonary arteries to diagnose pulmonary hypertension (PHTN): more reliable than valid?

https://doi.org/10.1016/j.clinimag.2016.02.024Get rights and content

Abstract

The association between main pulmonary artery (MPA) size and pulmonary arterial hypertension (PAHTN) is well established; however, the clinical utility of routine measurement of MPA is uncertain due to considerable overlap between normal patients and those with pulmonary hypertension. The lack of diagnostic accuracy could be further degraded by variability among the radiologists. It is unknown whether the addition of right and left pulmonary artery measurements would improve accuracy or further impair it.

The purposes of this study are to verify the accuracy of a proposed cutoff value for the size of MPA in the diagnosis PAHTN, to determine the interrater agreement for this measurement, and to determine whether addition of right pulmonary artery (RPA) and left pulmonary artery (LPA) measurement or simple assessment of patient comorbidities can improve the accuracy.

Materials and methods

Patients undergoing both cardiac catheterization and chest computed tomography (CT) within 3 months of each other at a large university hospital between January 2010 and December 2012 were identified. Patients with prior cardiac surgery or congenital heart disease and critically ill patients were excluded from the study population. Patients with pericardial disease or severe lung disease documented on CT examinations were also excluded. From the remaining patients, 45 patients with normal pulmonary artery pressure and 50 patients with proven pulmonary hypertension were selected. Demographic data and clinical information was collected from medical records of these patients.

Three radiologists with different years of experience in cardiothoracic imaging measured the MPA, RPA, and LPA diameters on axial images using an electronic ruler on 3D work stations independently and were masked to the patient clinical symptoms, diagnosis, and each other's measurement to prevent bias. Association between MPA diameter (MPAD) and patient characteristics assessed by one-way analysis of variance for scalar measures. Each reader's measurements were used to construct a separate receiver operating curve (ROC) to assess optimal MPA threshold. The ability of an MPA measurement threshold to correctly identify PAHTN was assessed using chi-squared. Chi-squared was also used to assess the effect of categorical comorbidities on false positive diagnosis.

Results

None of the demographic data or patients' factors (age, gender, height, weight, body surface area, and body mass index) were related to the size of MPAD.

The distribution of the MPAD was normal in both groups. Based on prior literature, MPAD (≥ 3.15 cm) was selected as the cutoff value to diagnose PAHTN. Review of ROCs did not suggest a superior cutoff value for any reader. Using this threshold per case interrater agreement was good, kappa values > 0.65.

Based on an average measurement for all three readers, MPAD was 82% sensitive and 62% specific for PAHTN. Limiting positive diagnosis to those subjects with both MPAD ≥ 3.15 and either enlarged RPA diameter (RPAD) or LPAD diminished sensitivity but did not improve specificity. Defining positive study as the presence of any dilated artery (MPAD, RPAD, or LPAD) increased sensitivity to 94% but decreased specificity to 27%.

Comorbidities that might cause fluctuating mean pulmonary artery pressures could not be shown to account for false positive studies. The 29 true negative patients and 16 false positive patients did not differ in the prevalence of obstructive sleep apnea/home oxygen use or documented congestive heart failure/low ejection fraction.

Conclusion

Previously proposed threshold of MPAD ≥ 3.15 cm is likely optimal but is not specific for identifying patient with PAHTN. Interobserver differences in MPAD measurement do not account this inaccuracy.

Incorporation or RPA and LPA measurement does not improve diagnostic accuracy of PAHTN, and assessment of comorbidities does not easily identify likely false positive cases. Diagnosis of PAHTN based solely on CT examinations of the chest may not be sufficiently accurate for clinical use.

Introduction

Although main pulmonary artery (MPA) dilatation is associated with pulmonary arterial hypertension (PAHTN), the clinical accuracy of routine measurement of MPA diameter (MPAD) on computed tomography (CT) to identify PAHTN is uncertain. Neither is the impact of interobserver measurement variation on diagnostic accuracy well quantified.

Various size thresholds have been proposed, but currently, MPAD greater than 3 cm on CT is commonly used to suggest the diagnosis of PAHTN [1] of the chest. There is however considerable overlap between patients with normal pulmonary artery pressures and patients with PAHTN based on MPAD alone. Clinical practice suggests that the specificity of this measurement is low and reader variability may be high. It is uncertain if additional measurement of the right pulmonary artery (RPA) and left pulmonary artery (LPA) may increase specificity or decrease reader variability.

The purposes of this study are to verify the accuracy of cutoff values of MPAD in diagnosis PAHTN, to determine the interrater agreement for this measurement, and to determine whether addition of RPA diameter (RPAD) and LPA diameter (LPAD) measurement can improve diagnostic accuracy. We also sought to determine if comorbidities easily identified in medical records could be used to identify patients with increased likelihood of either false positive or false negative diagnoses of PAHTN.

Section snippets

Materials and methods

The study was approved by the Institutional Review Board, and the informed consent was waived.

Results

None of the demographic data or patients' factors were related to the size of MPAD (Table 1). Gender is not associated with the size of MPA (P-value = .14). The size of MPA did not differ between gender in either the PAHTN group (P-value =.33) or in patients with normal MPAP (P-value =.42).

There is no statistical significance of MPAD, RPAD, and LPAD measurement among three radiologists in normal patients and PAHTN groups (P-values .76–.98, .24–.41, and .37–.66, respectively).

As expected, MPAD was

Discussion

Measurement of MPA has been under investigation since the 1960s. The initial effort was to predict PAHTN by measuring right descending pulmonary first on chest radiographs, then on CT scan [4]. Results of these measurements have been compared to a changing definition of pulmonary hypertension. Historically, the initial value to discriminate normal pulmonary artery pressure from PAHTN was 18 mmHg [5], [6]. This value has subsequently been raised to 20 mmHg and most recently to 25 mmHg [7], [8].

In

Conclusion

Measurements of MPAD on routine CT examinations of the chest are reproducible between readers and do not vary sufficiently to affect clinical diagnosis of PAHTN on a case-by-case basis. An MPAD cutoff value of 3.15 may be optimal but yields only good sensitivity and moderate specificity. No clearly superior threshold value can be selected, and the incorporation of RPA and LPA measurement does not improve diagnostic accuracy of PAHTN. Neither does assessment of comorbidities allow for easy

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