The Hughes-Stovin Syndrome (HSS) International Study Group developed a reference “atlas” regarding the radiographic characteristics of HSS, which can inform early diagnosis and management of HSS-related pulmonary vasculitis. The report was published in Clinical Rheumatology.

The HSS International Study Group reviewed computed tomography pulmonary angiography (CTPA) data collected from 42 patients with HSS. Images were reviewed and selected for inclusion in the atlas, based on quality and content, such that it included information on radiologic signs of HSS.

After review of the CTPA images, the study group classified pulmonary aneurysms into 6 radiographic patterns with varied associated risk levels.


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Aneurysmal Wall Enhancement on Postcontrast CTPA

According to the report, arterial wall enhancement is the earliest radiologic sign of pulmonary vasculitis in HSS. Enhancement was defined as an “enhancing aneurysmal wall”, which appears on CTPA images in the mediastinal window during sequential arterial and venous postcontrast phases.

True “Stable” Pulmonary Artery Aneurysms (PAAs)

The authors noted that PAA was a dilation involving all 3 layers of the vessel wall, including the main pulmonary artery and its branches. Radiographically, true stable PAA can be defined as an “aneurysmal lesion (contrast-filled) of the affected PA branch with a well-defined aneurysmal wall and associated with intra-aneurysmal adherent in-situ thrombosis (filling defects) without any perianeurysmal parenchymal ground-glass opacification.”

Unstable Leaking True PAA (“Acute Phase”)

In contrast to stable PAA, leaking PAA was defined by the study group as aneurysm formation of the affected vessel with loss of aneurysmal wall definition. Leaking PAA may also present as “perianeurysmal alveolar hemorrhage (ground glass opacification and/or consolidation) with ‘air-bronchograms.’” ‘Air-bronchograms refers to the opacification of surrounding alveoli causing air-filled bronchi to become visible on imaging. This finding can typically be observed as a result of hemorrhage and is “best visualized in the lung window.” The study group noted that leaking vs stable PAA presented significantly increased risk for rupture.

Pulmonary Artery Pseudoaneurysm (PAP; “Chronic Phase”)

The report indicated that PAP was not associated with adjacent ground glass opacification or consolidation, thus distinguishing it from leaking PAA. Instead, PAP has been defined radiologically as “sharply demarcated contrast-filled aneurysmal lesions with a variably sized marginal hypodense perianeurysmal component (‘marginal thrombosis’) entangling a contrast-filled ectatic lumen.” Air bronchograms may be associated with the hypodense component. PAP also presents a high risk for rupture.

Unstable PAP

Unstable PAP can be referred to as PAP with an added adjacent ground glass opacification or frank consolidation due to “active hemorrhage from the leaking ectatic lumen.” Unstable PAP also presents urgent risk for rupture.

Right Ventricular Strain (RVS) With or Without Intracardiac Thrombosis

According to the authors of the report, RVS can be characterized by a right ventricle size, which exceeds that of the left ventricle. Radiologically, RVS has been defined by CTPA as “interventricular septal flattening or paradoxical interventricular septal bowing towards the left ventricle, which occurs secondary to the altered pulmonary hemodynamics in the context of pulmonary hypertension.” Intracardiac thrombosis was defined on imaging as a “low attenuation non-enhancing filling defect” in the involved chambers.

Conclusions Drawn From the Report

According to the HSS study group, the classification of pulmonary lesions in HSS is important for risk assessment and therapeutic management. In particular, the delineation of PAA categories can facilitate risk assessment regarding the “threat…[of] individual pulmonary lesions…for subsequent rupture.” Leaking unstable PAA and/or bronchial artery aneurysms and unstable PAP lesions pose the greatest risk for rupture. Interventions such as immunomodulators and PAA embolization and/or coiling may be indicated in the case of urgent or emergent unstable/leaking PAA or PAP.

“This reference atlas will assist treating physicians to reach the diagnosis and precisely characterize the specific pulmonary vascular lesions at an early stage of the disease process,” the authors wrote. “In addition, the atlas defines the most serious CTPA radiological signs that warrant special consideration and show the clinicians when urgent interventions are necessary in order to avoid adverse or fatal outcomes.”

Reference

Emad Y, Ragab Y, Robinson C, et al. Pulmonary vasculitis in Hughes-Stovin syndrome (HSS): a reference atlas and computed tomography pulmonary angiography guide-a report by the HSS International Study Group. Clin Rheumatol. Published online September 17, 2021. doi:10.1007/s10067-021-05912-3