ACR Imaging Criteria for Suspected Pulmonary Hypertension

Chest X-Ray of Lungs.
Chest X-Ray of Lungs.
New criteria by the American College of Radiology detail appropriateness of various imaging techniques for suspected pulmonary hypertension.

A wide range of diseases can cause pulmonary hypertension (PH), and the symptoms — such as dyspnea, syncope, fatigue, and edema — are nonspecific.1,2 For these reasons, diagnosis of PH can be difficult. A thorough history and clinical evaluation are essential, and numerous imaging modalities can further guide diagnosis and determination of etiology.

The American College of Radiology recently published criteria regarding the appropriateness of these various imaging techniques for suspected PH, as briefly highlighted below.3

Chest X-ray (CXR). While CXR has been found to demonstrate high sensitivity (96.9%) and specificity (99.1%) for PH detection, its sensitivity in detecting mild PH is low.4 “Thus, a normal CXR does not exclude PH and further imaging evaluation should be pursued if there are persistent unexplained symptoms such as dyspnea or risk factors for PH,” wrote the investigators. CXR may reveal the following findings of PH: Enlarged main pulmonary artery, right heart chamber enlargement, right interlobar artery >15 mm in women and >16 mm in men at the hilum, and diffuse lung diseases that may be linked to PH.

Resting transthoracic echocardiography. The sensitivity and specificity of Doppler echocardiography in detecting moderate PH is 79% to 100% and 68% to 98%, respectively. This testing should be performed any time PH is suspected. “Continuous-wave Doppler measurement of the peak tricuspid regurgitation velocity is used in combination with additional echocardiographic signs suggestive of PH to assign an echocardiographic probability of PH,” according to the paper. When there is intermediate or high echocardiographic probability of PH, right heart catheterization (RHC) is required for confirmation.

Transesophageal Echocardiography (TEE). TEE is more invasive than resting transthoracic echocardiography and may result in pharyngeal or esophageal trauma, although these complications are rare. While TEE may be used to detect the presence of congenital shunts, cardiac magnetic resonance imaging (MRI) and computed tomography (CT) are also effective for this purpose and are less invasive, and are thus recommended over TEE. 

Ventilation/perfusion (V/Q) Scans. American College of Cardiology algorithms recommend V/Q scans in all patients with unexplained PH, mainly for the assessment of chronic thromboembolic pulmonary hypertension (CTEPH).5,6 “V/Q scans are the examination of choice in evaluating for CTEPH and differentiating CTEPH from other causes of PH,” with a sensitivity of 90% to 100% and specificity of 94% to 100% for differentiating between IPAH and CTEPH,” the investigators stated. “A normal or low-probability scan essentially excludes the diagnosis of CTEPH with a sensitivity of 90% to 100% and a specificity of 94% to 100%,” although the scan may be normal with other PH etiologies.

CT and CT pulmonary angiography (CTPA). When the main pulmonary artery is larger than the adjacent ascending aorta, this is almost always an indication of PH, with a positive predictive value of 96%. Additional CT-CTPA findings suggestive of PH are “a ratio of segmental pulmonary artery to accompanying bronchus >1:1, mosaic attenuation of the lungs, pericardial thickening or effusion, enlargement of the right ventricle, and straightening of the interventricular septum,” as well as bronchial artery diameter >1.5 mm.

MRI and MR Angiography (MRA). MRI is the best noninvasive imaging technique for assessing right ventricular morphology and function. Morphologic findings of PH shown on cardiac MRI and pulmonary MRA are similar to the findings from CT/CTPA: pulmonary artery enlargement and pruning of peripheral vasculature on MRA, right ventricular hypertrophy and dilation, and straightening of the interventricular septum on cardiac MRI. These techniques are also often used to assess for early changes in right ventricular function in patients with an established PH diagnosis.

RHC. As the gold standard for diagnosing pulmonary arterial hypertension (PAH), RHC is typically performed to confirm a PH diagnosis and assess severity after all noninvasive examinations have been performed.

In addition, the investigators noted that the utility of catheter pulmonary angiography and fluorodeoxyglucose-positron emission tomography (FDG-PET)/CT are limited. The former is now mainly used for thrombolysis, and the latter is primarily used to distinguish rare mimics of CTEPH.

The paper also includes an indication of the relative radiation level (RRL) for each type of examination to facilitate the clinician’s consideration of potential adverse effects from radiation. 

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