Basic instrumental methods and screening
Initial evaluation often begins with echocardiography, which visualizes the sizes of the left heart chambers, detects shunts, and allows the calculation of systolic pulmonary artery pressure from the tricuspid regurgitation velocity. Contrast enhancement is used in cases of weak signals. However, the method is highly operator-dependent and affected by the patient's body habitus (e.g., obesity).
For screening patients with suspected pulmonary arterial hypertension (PAH) and ruling out chronic thromboembolic pulmonary hypertension (CTEPH), European guidelines endorse ventilation-perfusion (V/Q) scintigraphy. If the result is normal, CTEPH is ruled out. Mismatched perfusion defects may indicate pulmonary veno-occlusive disease or PAH itself.
The gold standard for confirming the diagnosis, planning therapy, and performing a vasoreactivity test (in idiopathic and hereditary forms) remains right heart catheterization.
The role of MRI in assessing function and perfusion
Magnetic resonance imaging provides objective data without ionizing radiation, making it ideal for follow-up. The method allows direct assessment of right ventricular (RV) morphology, stroke volume, and cardiac output measurement.
- Phase-contrast MRI: quantitatively assesses blood flow, shunts, and pulmonary artery distensibility.
- Differential diagnosis: CTEPH reveals wedge-shaped defects or delayed perfusion due to stenoses, whereas in PAH, perfusion is simply reduced and heterogeneous.
It is important to remember that although PAH significantly prolongs the mean pulmonary transit time and reduces pulmonary blood flow, these parameters do not correlate with the severity of hypertension. Poor prognostic signs include decreased stroke volume, a drop in left ventricular (LV) diastolic volume, and an increase in RV diastolic volume.
CT angiography: vascular signs
Pulmonary CT angiography (CTPA) is increasingly acting as the first-line test. When signs of hypertension are detected, the radiologist must systematically search for cardiac causes, vascular obstruction, or parenchymal pathology.
Key vascular markers on CT:
- Pulmonary artery trunk dilation: normal is up to 29–33 mm. Important: in interstitial lung disease, the trunk can dilate up to 4 cm even without hypertension.
- Pulmonary artery to ascending aorta diameter ratio (PA:AA): a value greater than 1 has a specificity of about 90% for diagnosing PAH.
- Artery-to-bronchus ratio: if the diameter of a segmental artery exceeds that of the accompanying bronchus (>1) in three or more lobes, it directly indicates hypertension.
- Bronchial artery dilation (>1.5 mm): typical for CTEPH and Eisenmenger syndrome. In CTEPH, developed collaterals are considered a favorable prognostic factor prior to surgery.
Cardiac changes on CT
Increased vascular resistance inevitably affects the heart, which is clearly visible on tomography. The main cardiac signs include right ventricular dilation and interventricular septum changes.
In the early stages of RV overload, septal flattening is noted. As dysfunction progresses, its distinct bulging toward the left ventricle is observed. CT also effectively visualizes intracardiac and vascular shunts, such as a large patent ductus arteriosus leading to severe RV hypertrophy.
Briefly: answers to topical questions
What hemodynamic criteria are used to diagnose precapillary pulmonary hypertension?
To diagnose precapillary pulmonary hypertension, indicators of pulmonary arterial pressure, wedge pressure, pulmonary vascular resistance, and the diastolic gradient are used.
- Mean pulmonary arterial pressure (PAPm) — ≥ 25 mm Hg
- Pulmonary artery wedge pressure (PAWP) — ≤ 15 mm Hg
- Pulmonary vascular resistance (PVR) — > 3 Wood units.
- Diastolic pulmonary gradient (DPG) — > 7 mm Hg
What radiological signs are characteristic of pulmonary veno-occlusive disease on high-resolution CT?
Pulmonary veno-occlusive disease is characterized by pronounced changes in the lung parenchyma and the presence of concomitant extrapulmonary manifestations.
- Lung parenchymal changes — significantly more pronounced than in regular pulmonary arterial hypertension (may resemble hypersensitivity pneumonitis or respiratory bronchiolitis).
- Lymphadenopathy (lymphadenopathy) — often detected as a comorbid condition.
- Pleural effusion (pleural effusion) — also among frequent incidental findings.
What radiological signs of pulmonary hypertension exist on conventional chest radiography?
According to conventional chest radiography, a characteristic sign of pulmonary hypertension is the enlargement of the pulmonary arteries.
- Massive enlargement of the pulmonary arteries — marked dilation of the vascular bed is observed.
- Enlargement of the pulmonary artery trunk (main pulmonary artery) — significant dilation is determined.
To detect PAH on CT, remember the "rule of one": the pulmonary trunk-to-aorta ratio > 1 and the segmental artery-to-bronchus ratio > 1.
Class and exam questions
Does pulmonary artery dilation on CT always mean pulmonary hypertension?
No, not always. In patients with interstitial lung disease, the trunk can dilate up to 40 mm even with normal pulmonary artery pressure.
Which method best rules out chronic thromboembolism (CTEPH)?
The screening method of choice is ventilation-perfusion (V/Q) lung scintigraphy. A normal result almost entirely rules out CTEPH.
What does leftward bulging of the interventricular septum indicate?
This is a direct consequence of pressure overload and right ventricular dysfunction, typical of advanced stages of pulmonary arterial hypertension.
Does the pulmonary artery diameter correlate with exact pressure figures?
No. Neither the pulmonary artery-to-aorta size ratio nor the body mass index-adjusted diameter correlates directly with the mean pulmonary arterial pressure.
What else to study on this topic
- Clinical classification of pulmonary hypertension (breakdown of 5 main groups)
- Hemodynamic criteria: precapillary, postcapillary, and combined PH
- The role of traditional angiography in patient selection for pulmonary endarterectomy
- Differential diagnosis of idiopathic PAH and pulmonary veno-occlusive disease (PVOD)
- Indications and methodology for the vasoreactivity test
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