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: Pembrolizumab-induced Pneumonitis

Figure 1. Thoracic CT showing multifocal, bilateral extensive lung opacities consistent with consolidation with a striking peribronchovascular distribution. Note the opacities are primarily distributed along the airways. Peripheral lung opacity, both ground-glass opacity and consolidation, is also present.

Figure 2. Axial thoracic CT performed several months after Figure 1 following discontinuation of the pembrolizumab and initiation, and subsequent tapering, of corticosteroid therapy, shows significant regression in the previously noted extensive peribronchovascular consolidation. Residual areas of consolidation and ground-glass opacity associated with architectural distortion are consistent with scarring.

A 76-year-old man with metastatic melanoma, undergoing treatment with pembrolizumab, an antibody against programmed cell death 1 (PD-1), beginning 8 months ago developed low-grade fever, non-productive cough, and shortness of breath. A thoracic CT scan showed multifocal, bilateral extensive lung opacities (Figure 1). The patient underwent bronchoscopy with bronchoalveolar lavage which showed non-specific inflammatory changes associated with foci of organizing pneumonia. Microbiologic studies, including Coccioides antibody enzyme immunoassay and Aspergillus antigen, were negative.

The patient was begun on corticosteroid therapy for presumed medication-induced pulmonary injury, manifestation as an organizing pneumonia pattern, due to pembrolizumab. Over the ensuing months, his symptoms abated and his CT scan abnormalities regressed (Figure 2).

Organizing pneumonia may occur as an idiopathic, primary pulmonary process, often referred to as “cryptogenic organizing pneumonia,” or may occur in the context of a number of systemic conditions, a situation often referred to as secondary organizing pneumonia. Among the various etiologies of secondary organizing pneumonia, medication-induced pulmonary injury is fairly common and when imaging features of organizing pneumonia are seen, careful correlation regarding the possibility of a medication-induced etiology should be undertaken. Recently, three cases of pembrolizumab-induced pneumonitis were described, two being consistent with organizing pneumonia (1).

The thoracic CT findings of organizing pneumonia include peripheral and peribronchovascular consolidation and ground-glass opacity, areas of consolidation surrounding ground-glass opacity (often referred to as the “atoll” or reverse ground-glass halo” sign- see Medical Image of the Week: The Atoll Sign in Cryptogenic Organizing Pneumonia), single and multiple nodules, and perilobular consolidation. The case illustrates a dramatically peribronchovascular distribution of pulmonary consolidation as a manifestation of medication-induced organizing pneumonia.

Michael B. Gotway, MD

Department of Radiology

Mayo Clinic Arizona

Scottsdale, AZ USA

Reference

1. Leroy V, Templier C, Faivre JB, Scherpereel A, Fournier C, Mortier L, Wemeau-Stervinou L. Pembrolizumab-induced pneumonitis. ERJ Open Res. 2017 May 2;3(2). pii: 00081-2016. [CrossRef] [PubMed]

Cite as: Gotway MB. Medical image of the week: pembrolizumab-induced pneumonitis. Southwest J Pulm Crit Care. 2017;15(3):118-9. doi: https://doi.org/10.13175/swjpcc110-17 PDF 

Medical Image of the Week: The Atoll Sign in Cryptogenic Organizing Pneumonia

Figure 1. Portable chest X-ray shows bilateral airspace opacities (yellow arrows) and possible trace pleural effusion (blue arrow).

Figure 2. Computed tomography of the chest showing (A) patchy ground glass opacity in the upper lungs with additional scattered circular areas of opacity in a reverse halo configuration (blue arrows, atoll sign) and (B) extensive bibasilar consolidation with air bronchograms.

A 54-year-old woman presented to the emergency department with cough and worsening shortness of breath. Her cough began approximately 1 month prior to presentation, at which time she was diagnosed with pneumonia by her primary care physician based on a chest X-ray at an outside institution. She tried and failed courses of azithromycin, doxycycline, and levofloxacin.

The patient had an oxygen saturation of 55% and hyperpyrexia to 101.7 F in the emergency department. An initial chest X-ray was suggestive of moderate multifocal pneumonia with pleural effusion (Figure 1). Subsequent chest computed tomography (CT; Figure 2) revealed findings consistent with cryptogenic organizing pneumonia (COP) including multiple upper lobe atoll signs. Infectious and autoimmune workups were negative and the patient experienced a rapid recovery with pulse steroids, providing further evidence for the diagnosis of COP.

CT is the best imaging modality for evaluation of potential COP. Features include consolidations and nodules, bronchial wall thickening or dilatation, and ground glass opacities (1). The atoll sign, consisting of a central ground glass opacity and surrounding consolidation which may also be called a reverse halo sign, is highly specific but not sensitive for organizing pneumonia (2). Definitive diagnosis requires lung biopsy, although the disease is often managed based on a presumptive diagnosis (3).

Joseph Frankl, BS¹ and Veronica A. Arteaga, MD²

¹University of Arizona College of Medicine and ²Department of Medical Imaging

Banner University Medical Center Tucson

Tucson, AZ USA

References

1. Lee JW, Lee KS, Lee HY, Chung MP, Yi CA, Kim TS, Chung MJ. Cryptogenic organizing pneumonia: serial high-resolution CT findings in 22 patients. AJR Am J Roentgenol. 2010 Oct;195(4):916-22. [CrossRef] [PubMed]
2. Davidsen JR, Madsen HD, Laursen CB. Reversed halo sign in cryptogenic organising pneumonia. BMJ Case Rep. 2016 Feb 8;2016. pii: bcr2015213779. [CrossRef] [PubMed]
3. Bradley B, Branley HM, Egan JJ, et al. Interstitial lung disease guideline: the British Thoracic Society in collaboration with the Thoracic Society of Australia and New Zealand and the Irish Thoracic Society. Thorax. 2008 Sep;63 Suppl 5:v1-58. [CrossRef] [PubMed]

Cite as: Frankl J, Artega VA. Medical image of the week: the atoll sign in cryptogenic organizing pneumonia. Southwest J Pulm Crit Care. 2017;15(2):92-3. doi: https://doi.org/10.13175/swjpcc100-17 PDF