Chronic thromboembolic pulmonary hypertension: Presentation on ECG-gated CT

A 78-year-old male patient presented with worsening exertional dyspnea. Echocardiogram revealed signs of right ventricle dysfunction and elevation of pulmonary artery systolic pressure (PASP) to 81 mmHg (41 mmHg the year before), suggesting severe pulmonary hypertension (PH). Moderate tricuspid regurgitation was also noted. The patient underwent CT for further evaluation.

Computer tomography pulmonary angiography (CTPA) with ECG gating revealed bilateral partial pulmonary artery filling defects, with eccentric thrombus and endoluminal bands and webs (Figure 1). There were also signs of PH, such as enlargement of the pulmonary trunk and narrowing of peripheral pulmonary arteries in the affected segments (Figure 2). Furthermore, the right ventricle was dilated and hypertrophied with an accentuated trabecular pattern and was also noted opacification of hepatic veins due to retrograde flow of contrast material (Figure 3). Also, bronchial arteries were prominent, suggesting increased systemic collateral lung supply (Figure 2). Lung parenchyma revealed a mosaic perfusion pattern, with hypoattenuating areas in the affected segments due to oligoemia (Figure 4).

Ventilation/perfusion (V/Q) scintigraphy revealed mismatched segmental perfusion defects corresponding to the hypoattenuating areas with narrowed peripheral pulmonary arteries on CTPA (Figure 4).

Chronic thromboembolic pulmonary hypertension (CTEPH) is a sequela of pulmonary embolism (PE) due to persistence of residual clots that ultimately lead to increased pulmonary vascular resistance [1]. Endothelial dysfunction and small vessel remodelling also contribute to PH.

The prevalence of CTEPH is underestimated; the incidence after acute PE is approximately 4% [2]. This condition affects women slightly more and is associated with underlying malignancy, cardiovascular or pulmonary disease, some autoimmune and haematological disorders, multiple PE episodes, larger perfusion defects, and younger age [3]. In this case, no risk factors were present.

Clinical scenario is crucial for raising suspicion of CTEPH, but symptoms are nonspecific, related to PH, and may include exertional dyspnea, chronic cough, chest pain, tachycardia, or syncope [1]. The extent of vascular obstruction influences the severity of PH (>40% of the pulmonary vascular bed obstructed in symptomatic patients [2].

Conventional pulmonary angiography with right heart catheterisation has been considered the gold standard method for diagnosing CTEPH, but it is an invasive procedure [1,4].

Echocardiography is useful for PH detection due to its high sensitivity, but it is not specific for CTEPH [2].

CTPA is a diagnostic method with high sensitivity and specificity for detecting CTEPH [1,2,4]. Imaging findings vary based on vascular obstruction and PH severity [1]:

• Vascular signs: complete occlusion of pulmonary arteries with vessel cut-off; partial occlusion with peripheral crescent-shaped thrombus, and bands/webs; and abrupt vessel narrowing [2,4].
• PH signs: main pulmonary artery dilation, right ventricle enlargement, hypertrabeculation or hypertrophy [2,4], and bowing of the interventricular septum to the left, features that are better assessed with ECG gating technique; reduced right pulmonary artery distensibility, measured on ECG-gated CT, was shown to be an accurate noninvasive marker of CTEPH [5]; bronchial arteries dilation and tortuosity due to long-term PH [2,4].
• Lung parenchymal signs: scars from prior infarctions (irregular linear and peripheral wedge-shaped opacities), and mosaic lung attenuation pattern, with pathological low attenuated areas intercalated with normal attenuated parenchyma regions [2,4].

V/Q lung scintigraphy helps detect segmental mismatched perfusion defects [1,2].

CTEPH has a 30% 3-year survival but is potentially curable [1,2]. Treatment involves lifelong anticoagulation to prevent recurrent thromboembolism [1]. Surgical pulmonary thromboendarterectomy is the primary approach, with operability determined by the location and extent of obstruction [1,2].

The presented case shows the importance of CTPA in detecting CTEPH, which frequently presents as a diagnostic challenge, and is often forgotten and easily misdiagnosed. Consequently, its early recognition is crucial for its potential curative treatment and to prevent progressive PE, morbidity, and mortality [1–4].