Medical Image of the Week: Pulmonary Infarction- the “Reverse Halo Sign”

Figure 1. CT Chest with contrast. Two different levels in the same patient displayed on mediastinal windows. Several triangular shaped subpleural lesions with annular peripheral solid appearance are depicted, better characterized in the lung windows below (yellow arrows). Note the partial filling defect (red arrow on B), indicating a non-occlusive thrombus(arrow). Bilateral pleural effusions are also identified.

Figure 2. CT Chest with contrast, lung window corresponding to the levels in Figure 1 above. Note the triangular shaped subpleural lesions with peripheral solid appearance and ground glass center, characteristic of the atoll sign (arrows). As above, bilateral pleural effusions are present.

Pulmonary infarction is a known complication of pulmonary embolism (PE), a common disorder that results in 100,000-200,000 deaths annually in the United States. Computed tomography (CT) is the first-line modality to assess the pulmonary circulation with the ability to directly the visualize pulmonary emboli as well as pleuro-parenchymal abnormalities.

The appearance of a pulmonary infarct varies depending on the degree of ischemic injury in the setting of a dual blood supply to the lung. Infarcts occur more commonly in the periphery of the lung, given, the alternate blood supply by the bronchial arteries, is not as efficient as it is centrally. This location is also favored by the more common occurrence after occlusion of small peripheral arteries of 3 mm or less in caliber.

On CT lung infarcts can take the can take the “reverse halo” sign, also known as the “atoll” sign configuration, representing a focal area of decreased enhancement, and surrounding solid appearance. In the case of lung infarcts, the lesions typically have a broad pleural base triangular form with apex toward the hilum (1). Pathologically this corresponds to a hemorrhagic consolidation. The center of the lesion appears to correspond to aerated non-infarcted lung coexisting side by side with infarcted lung in the same lobule. The broad-based configuration is explained by the fan shaped distribution of the arteries as they extend out into the periphery. The convex border reflects the extravasated blood within the infarcted lung. Once the hemorrhage reabsorbs, the infarct heals completely or may leave behind a linear band of scarring.

From the imaging stand point, the reverse halo sign initially described in cryptogenic organizing pneumonia, has also been noted in patients with fungal disease, granulomatosis with polyangiitis, sarcoidosis and neoplastic disease among others (2).

George R Wu MS IV¹, Berndt Schmit MD², Veronica Arteaga MD², and Diana Palacio MD²

¹Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ USA

²Division of Thoracic Imaging, University of Arizona, Tucson, AZ USA

References

1. He H, Stein MW, Zalta B, Haramati LB. Pulmonary infarction: spectrum of findings on multidetector helical CT. J Thorac Imaging. 2006;21(1):1-7. [CrossRef] [PubMed]
2. Godoy MC, Viswanathan C, Marchiori E, et al. The reversed halo sign: update and differential diagnosis. Br J Radiol. 2012;85(1017):1226-35. [CrossRef] [PubMed]

Cite as: Wu GR, Schmit B, Arteaga V, Palacio D. Medical image of the week: pulmonary infarction- the “reverse halo sign”. Southwest J Pulm Crit Care. 2017;15(4):162-3. doi: https://doi.org/10.13175/swjpcc124-17 PDF 

Medical Image of the Week: Pulmonary Artery Sling

Figure 1. Computerized tomography (CT) of the chest showing the aberrant origin of the left pulmonary artery from the right pulmonary artery creating a pulmonary artery sling with mild tracheal narrowing (arrow).

Figure 2. Cardiac magnetic resonance imaging (MRI) confirming the presence of a pulmonary artery sling with aberrant origin of the left pulmonary artery from the right pulmonary artery.

A 42-year-old year woman with asthma was admitted to the hospital with an asthma exacerbation. The patient complained of dyspnea on exertion, two-pillow orthopnea and bipedal edema. An echocardiogram showed a severely dilated right ventricle (RV) with elevated right ventricular systolic pressure of 71 mmHg. The systolic left ventricular (LV) function was also reduced with an ejection fraction of 45%. Computerized tomography (CT) of the chest showed an aberrant origin of the left pulmonary artery (PA) creating a pulmonary artery sling with mild tracheal narrowing (Figure 1, arrow). Cardiac magnetic resonance imaging (MRI) confirmed the presence of a pulmonary artery sling with the aberrant origin of the left PA from the right PA (Figure 2). Cardiac catheterization showed a mean PA pressure of 46mmHg with LV end diastolic pressure of 12mm Hg. The patient was diagnosed with WHO Group I pulmonary hypertension and started on treatment with sildenafil with a stable outpatient course.

Pulmonary artery sling is an uncommon form of vascular ring. The anomaly is a result of formation of the left PA from the right sixth vascular arch (rather than the left), leading to the left PA arising from the posterior aspect of the right PA (1). Pulmonary artery slings may produce symptoms of airway compression and esophageal compression and usually presents in childhood (2). In asymptomatic cases, a PA sling may mimic a mediastinal mass on chest radiographs and CT and MRI may be used to establish the diagnosis (3).

Abhinav Agrawal MD¹, Stuart L Cohen MD², Rakesh Shah MD², Arunabh Talwar MD FCCP¹

¹Division of Pulmonary, Critical Care & Sleep Medicine, Department of Medicine

²Division of Thoracic Radiology, Department of Radiology

Hofstra-Northwell School of Medicine

New Hyde Park, NY USA

References

1. Casta-er E, Gallardo X, Rimola J, Pallardó Y, Mata JM, Perendreu J, Martin C, Gil D. Congenital and acquired pulmonary artery anomalies in the adult: radiologic overview. Radiographics. 2006 Mar-Apr;26(2):349-71. [CrossRef] [PubMed]
2. Odell DD, Gangadharan SP, Majid A. Pulmonary artery sling: a rare cause of tracheomalacia in the adult. J Bronchology Interv Pulmonol. 2011 Jul;18(3):278-80. [CrossRef] [PubMed]
3. Ganesh V, Hoey ET, Gopalan D. Pulmonary artery sling: an unexpected finding on cardiac multidetector CT. Postgrad Med J. 2009 Mar;85(1001):128. [CrossRef] [PubMed] 

Cite as: Agrawal A, Cohen SL, Shah R, Talwar A. Medical image of the week: pulmonary artery sling. Southwest J Pulm Crit Care. 2017;15:160-61. doi: https://doi.org/10.13175/swjpcc116-17 PDF