Morphological characteristics of the reversed halo sign that may strongly suggest pulmonary infarction
Introduction
Pulmonary embolism (PE) is a common, potentially fatal condition associated with high morbidity and mortality. Early diagnosis of PE followed by adequate treatment reduces the risk of major complications, making the institution of effective therapy as quickly as possible imperative. Patients with acute PE, however, often have non-specific symptoms, and prompt recognition of PE remains a challenge.1, 2, 3, 4, 5
Imaging plays a critical role in the early diagnosis of PE. Computed tomography (CT) pulmonary angiography (PA) has been established as a first-line diagnostic technique in patients suspected of having PE. Although the diagnosis of PE is based on direct arterial findings, indirect parenchymal signs suggestive of pulmonary infarction (PI) are occasionally detected at unenhanced CT, increasing the diagnosis of unexpected PE.5
Although a variety of parenchymal CT signs suggesting PI have been reported,5, 6, 7 the reversed halo sign (RHS) has seldom been included among them.8, 9, 10 The RHS has been defined as a focal, rounded area of ground-glass opacity surrounded by a nearly complete ring of consolidation.11 Voloudaki et al.12 first described the RHS in patients with cryptogenic organising pneumonia (COP), and this sign was once considered to be specific to COP13; however, it was subsequently reported in association with a wide spectrum of diseases14, 15 and is now regarded as a non-specific sign.
The recognition of specific morphological CT characteristics of the RHS due to PI may raise the possibility of PE and indicate the need for urgent definitive investigations, such as CTPA. The aims of this study were to describe the characteristics of the RHS on unenhanced chest CT associated with PI, and compare them with those caused by diseases other than PI, with the ultimate aim of identifying CT characteristics that may raise the suspicion of PE.
Section snippets
Patient selection
The institutional review board approved this study and waived the requirement for informed patient consent. All data used in this study were anonymised. Patients with the RHS caused by PI were selected retrospectively from a total of 2,482 consecutive patients who underwent CTPA between January 2011 and December 2015 in three tertiary hospitals in Brazil. PE was detected in 410 (16.52%) of these patients, but eight cases were discarded because of movement artefacts that impaired parenchymal
Results
The study population comprised 145 patients with the RHS on chest CT. A total of 250 RHSs were identified. Single lesions were observed in 81 (55.9%) patients, two RHSs were present in each of 22 (15.2%) patients, and three or more RHSs were present in each of 42 (28.9%) patients. Low-attenuation areas were observed in 70 of 250 (28%) RHSs, but not in 180 (72%) RHSs. Reticulation inside the halo was found in 26 (10.4%) RHSs and ground-glass opacities were present in 148 (59.2%) RHSs. Sixty-six
Discussion
In this series of patients with the RHS caused by PI and other diseases, the main morphological characteristics of the RHS that favoured PI were the presence of internal areas of low attenuation (with or without reticulation) and predominance in the peripheral regions of the lower lobes.
Lung ischaemia may lead to a spectrum of injuries involving damage to the pulmonary and alveolar epithelial cells, resulting in haemorrhage and infarction in an area distal to the embolic obstruction.3, 6
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2018, Respiratory MedicineCitation Excerpt :We are additionally unable to comment on the sensitivity and specificity of the radiographic criteria that we used to confirm the presence of pulmonary infarction by CT because there remains no gold standard for its identification beyond CT characteristics [19]. A recent retrospective review suggested that the reversed halo sign may strongly suggest pulmonary infarction, and a combination of radiographic and clinical factors was used to confirm the diagnosis, in similar fashion to this study [20]. Of note, Parambil and colleagues published a series of infarction cases diagnosed via biopsy, which revealed necrotic tissue over an extended period of time [4].
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