Causes and diagnostic challenges
Regardless of etiology, pulmonary hypertension has an extremely unfavorable prognosis. The classification of the disease is based on pathophysiological mechanisms, which directly determines treatment tactics. The most frequent causes are secondary changes associated with chronic lung diseases and left heart pathologies.
A particular challenge is chronic thromboembolic pulmonary hypertension (CTEPH). This form often remains undiagnosed (statistical underdiagnosis). Diagnostic imaging methods are of fundamental importance for establishing this diagnosis. In addition, during differential diagnosis, it is extremely critical to rule out group 2 pulmonary hypertension. To do this, the physician needs to assess pulmonary capillary wedge pressure (PCWP) and carefully study cardiac morphology and function.
CT semiotics of vascular and parenchymal changes
Computed tomography allows visualization of specific signs indicating pulmonary circulation overload:
- Signs of CTEPH: CT clearly shows pronounced right heart chamber dilatation. Contrast medium reflux into the inferior vena cava (IVC) and hepatic veins is characteristic. The parenchyma reveals a "mosaic perfusion" pattern (mosaic perfusion) — an alternation of dark hypoperfused areas and bright areas of normal perfusion. Notably, the caliber of pulmonary arteries in areas of decreased attenuation is markedly reduced compared to healthy areas.
- Changes in Eisenmenger syndrome and PAH: Small tortuous intrapulmonary vessels (neovascularization) may be detected. They originate from centrilobular arterioles, and their anatomy does not correspond to the normal structure of the pulmonary vascular bed.
In severe disease, CT identifies two patterns of parenchymal changes, which are currently viewed as spectra of a single process:
- Pulmonary capillary hemangiomatosis (PCH): manifests with pronounced centrilobular ground-glass nodules and smooth interlobular septal thickening.
- Pulmonary veno-occlusive disease (PVOD): is characterized by widespread ground-glass opacities in the lung parenchyma (with a centrilobular predominance) and moderately prominent septal thickening.
Pulmonary arteriovenous malformations (PAVMs)
Pulmonary arteriovenous malformations (PAVMs) are direct communications between a pulmonary artery and vein.
Etiology and epidemiology: They are most often identified by clinical presentation or during family screening in patients with hereditary hemorrhagic telangiectasia (HHT). Acquired forms can occur in liver cirrhosis, schistosomiasis, and metastatic thyroid cancer. About 10% of cases manifest in the first decade of life, but the majority present in the third or fourth decade. Up to 50% of patients have multiple pulmonary lesions.
Clinical presentation and classification: Direct blood shunting leads to systemic desaturation, causing dyspnea, hypoxia, cyanosis, and heart failure. Vessel rupture carries a risk of massive hemoptysis and hemothorax. There is also a high risk of paradoxical embolism, which causes neurological symptoms in 2/3 of patients with hereditary hemorrhagic telangiectasia.
Based on structure, two types of PAVMs are distinguished:
- Simple (80%): consist of a single feeding artery and one or more draining veins.
- Complex (20%): have more than one feeding artery.
Imaging methods and treatment of PAVMs
On standard radiographs, malformations appear as round, oval, or lobulated opacities with visible tortuous vessels. Their typical location is the lower lobes of the lungs. However, small lesions are often not visualized on plain chest radiographs.
In modern practice, CT angiography (CTA) has become the gold standard. The method uses thin slices and 3D reconstructions of the vascular bed: maximum intensity projection (MIP) and volume rendering technique (VRT). This allows for a highly detailed study of angioarchitecture prior to surgery. The sensitivity of CT angiography approaches 100%, significantly outperforming conventional pulmonary angiography (~60%). Magnetic resonance imaging (MRI) can also be used, but it is inferior to multislice CT in spatial resolution.
The primary and preferred treatment method for PAVMs is non-invasive embolotherapy. Surgical intervention is used only as an alternative.
Briefly: answers to topical questions
What clinical groups of pulmonary hypertension are distinguished according to the WHO classification?
Five main clinical groups of pulmonary hypertension are distinguished based on the pathophysiological mechanism.
- Group 1 (PAH) — pulmonary arterial hypertension, including idiopathic and hereditary forms.
- Group 2 — pulmonary hypertension due to left heart disease.
- Group 3 — pulmonary hypertension due to lung diseases and/or hypoxia.
- Group 4 (CTEPH) — chronic thromboembolic pulmonary hypertension.
- Group 5 — pulmonary hypertension with unclear and/or multifactorial mechanisms.
What radiographic signs of pulmonary hypertension are detected on a plain posteroanterior chest radiograph?
A plain posteroanterior chest radiograph may reveal signs of pulmonary vessel enlargement and right heart changes.
- Enlargement of the pulmonary artery trunk — the upper limit of normal for its diameter varies in literature from 29 to 33 mm.
- Dilatation of segmental vessels — a pulmonary artery-to-bronchus ratio greater than 1 in at least three lobes indicates pulmonary arterial hypertension.
- Right heart changes — right ventricular hypertrophy and dilatation may be visualized.
What hemodynamic parameters must be assessed during catheterization to rule out group 2 pulmonary hypertension?
To rule out group 2 pulmonary hypertension, it is necessary to assess pulmonary capillary wedge pressure (PCWP). An evaluation of cardiac morphology and function is also required to detect left heart pathology.
What ECG criteria indicate right heart strain and hypertrophy in pulmonary hypertension?
Changes in the electrical axis, as well as specific signs in chest and standard leads, indicate right heart strain and hypertrophy.
- Deviation of the electrical axis of the heart — right axis deviation or a vertical heart position is observed.
- Changes in chest leads (V1–V2) — dominant R wave with increased amplitude, decreased S wave amplitude, and inverted negative T wave.
- P pulmonale phenomenon (P-pulmonale) — tall, peaked P waves with an amplitude greater than 2.5 mm in leads II, III, aVF, and V₁, indicating right atrial overload.
Class and exam questions
Which method allows for a definitive diagnosis of pulmonary hypertension?
The diagnosis is confirmed using invasive right heart catheterization. The disease is diagnosed when the mean pulmonary artery pressure is 25 mm Hg and higher.
Why is conventional angiography no longer the primary method for PAVMs?
Thin-section CT angiography with 3D reconstructions has superseded the classical method because its sensitivity reaches 100%, whereas conventional pulmonary angiography has a sensitivity of only about 60%.
How to differentiate pulmonary capillary hemangiomatosis from pulmonary veno-occlusive disease on CT?
In hemangiomatosis, pronounced centrilobular ground-glass nodules predominate, whereas in veno-occlusive disease, a more diffuse, widespread decrease in transparency with less prominent interlobular septal thickening is observed.
What else to study on this topic
- Pathophysiology of pulmonary hypertension in various groups
- Differential diagnosis of chronic thromboembolic pulmonary hypertension
- Hereditary hemorrhagic telangiectasia: systemic manifestations
- Technique of CT angiography with volume rendering (VRT)
- Principles of embolotherapy for pulmonary arteriovenous malformations
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