Morphological characteristics of the reversed halo sign that may strongly suggest pulmonary infarction

Target sign in COVID-19, radiological interpretation and diagnostic contribution of digital thoracic tomosynthesis

INTRODUCTION

Our objectives are: To describe the radiological semiology, clinical-analytical features and prognosis related to the target sign (TS) in COVID-19. To determine whether digital thoracic tomosynthesis (DTT) improves the diagnostic ability of radiography.

MATERIAL AND METHODS

Retrospective, descriptive, single-centre, case series study, accepted by our ethical committee. Radiological, clinical, analytical and follow-up characteristics of patients with COVID-19 and TS on radiography and DTT between November 2020 and January 2021 were analysed.

RESULTS

Eleven TS were collected in 7 patients, median age 35 years, 57% male. All TS presented with a central nodule and a peripheral ring, and in at least 82%, the lung in between was of normal density. All TS were located in peripheral, basal regions and 91% in posterior regions. TS were multiple in 43%. Contiguous TS shared the peripheral ring. Other findings related to pneumonia were associated in 86% of patients. DTT detected 82% more TS than radiography. Only one patient underwent a CT angiography of the pulmonary arteries, positive for acute pulmonary thromboembolism. Seventy-one per cent presented with pleuritic pain. No distinctive laboratory findings or prognostic worsening were detected.

CONCLUSIONS

TS in COVID-19 predominates in peripheral and declining regions and can be multiple. Pulmonary thromboembolism was detected in one case. It occurs in young people, frequently with pleuritic pain and does not worsen the prognosis. DTT detects more than 80 % of TS than radiography.

The Reversed Halo Sign in Pulmonary Infarction due to Acute Pulmonary Embolism

The reversed halo sign, or atoll sign, is a specific sign with ring-shaped consolidation and central lucency, which is historically considered typical for cryptogenic organising pneumonia. The presence of this sign in subpleural, posterior basal parts of the lower lobes, especially when solitary, should however raise suspicion for other causes, such as pulmonary infarction. Here, we present a case of pulmonary embolism with pulmonary infarction that was detected on HRCT without contrast. Teaching Point: The presence of a reversed halo sign, especially when solitary and located in the periphery of the lower lobes, should raise suspicion of a pulmonary infarction.

Differentiating Imaging Features of Post-lobectomy Right Middle Lobe Torsion

PURPOSE

The purpose of this study was to identify differences in imaging features between patients with confirmed right middle lobe (RML) torsion compared to those suspected yet without torsion.

MATERIALS AND METHODS

This retrospective study entailing a search of radiology reports from April 1, 2014, to April 15, 2021, resulted in 52 patients with suspected yet without lobar torsion and 4 with confirmed torsion, supplemented by 2 additional cases before the search period for a total of 6 confirmed cases. Four thoracic radiologists (1 an adjudicator) evaluated chest radiographs and computed tomography (CT) examinations, and Fisher exact and Mann-Whitney tests were used to identify any significant differences in imaging features (P<0.05).

RESULTS

A reversed halo sign was more frequent for all readers (P=0.001) in confirmed RML torsion than patients without torsion (83.3% vs. 0% for 3 readers, one the adjudicator). The CT coronal bronchial angle between RML bronchus and bronchus intermedius was larger (P=0.035) in torsion (121.28 degrees) than nontorsion cases (98.26 degrees). Patients with torsion had a higher percentage of ground-glass opacity in the affected lobe (P=0.031). A convex fissure towards the adjacent lobe on CT (P=0.009) and increased lobe volume on CT (P=0.001) occurred more often in confirmed torsion.

CONCLUSION

A reversed halo sign, larger CT coronal bronchial angle, greater proportion of ground-glass opacity, fissural convexity, and larger lobe volume on CT may aid in early recognition of the rare yet highly significant diagnosis of lobar torsion.

When pneumonia is not COVID-19

During the COVID-19 epidemic, the prevalence of the disease means that practically any lung opacity on an X-ray could represent pneumonia due to infection with SARS-CoV-2. Nevertheless, atypical radiologic findings add weight to negative microbiological or serological tests. Likewise, outside the epidemic wave and with the return of other respiratory diseases, radiologists can play an important role in decision making about diagnoses, treatment, or preventive measures (isolation), provided they know the key findings for entities that can simulate COVID-19 pneumonia. Unifocal opacities or opacities located in upper lung fields and predominant airway involvement, in addition to other key radiologic and clinical findings detailed in this paper, make it necessary to widen the spectrum of possible diagnoses.

When pneumonia is not COVID-19

During the COVID-19 epidemic, the prevalence of the disease means that practically any lung opacity on an X-ray could represent pneumonia due to infection with SARS-CoV-2. Nevertheless, atypical radiologic findings add weight to negative microbiological or serological tests. Likewise, outside the epidemic wave and with the return of other respiratory diseases, radiologists can play an important role in decision making about diagnoses, treatment, or preventive measures (isolation), provided they know the key findings for entities that can simulate COVID-19 pneumonia. Unifocal opacities or opacities located in upper lung fields and predominant airway involvement, in addition to other key radiologic and clinical findings detailed in this paper, make it necessary to widen the spectrum of possible diagnoses.

Multimodal indirect imaging signs of pulmonary embolism

The clinical diagnosis of pulmonary embolism is often difficult, as symptoms range from syncope and chest pain to shock and sudden death. Adding complexity to this picture, some patients with non-diagnosed pulmonary embolism may undergo unenhanced imaging examinations for a number of reasons, including the prevention of contrast medium-related nephrotoxicity, anaphylactic/anaphylactoid reactions and nephrogenic systemic fibrosis, as well as due to patients' refusal or lack of venous access. In this context, radiologists' awareness and recognition of indirect signs are cornerstones in the diagnosis of pulmonary embolism. This article describes the indirect signs of pulmonary embolism on chest X-ray, unenhanced CT, and MRI.

Pulmonary arteries: imaging of pulmonary embolism and beyond

The pulmonary arteries are not just affected by thrombus. Various acquired and congenital conditions can also affect the pulmonary arteries. In this review we discuss cross sectional imaging modalities utilized for the imaging of the pulmonary arteries. Acquired pulmonary artery entities, including pulmonary artery sarcoma (PAS), vasculitis, aneurysm, and arteriovenous malformations, and congenital anomalies in adults, including proximal interruption of the pulmonary artery, pulmonary sling, pulmonary artery stenosis, and idiopathic dilatation of the pulmonary trunk, are also discussed. An awareness of these entities and their imaging findings is important for radiologists interpreting chest imaging.

Incidence and morphological characteristics of the reversed halo sign in patients with acute pulmonary embolism and pulmonary infarction undergoing computed tomography angiography of the pulmonary arteries

OBJECTIVE

To determine the incidence of the reversed halo sign (RHS) in patients with pulmonary infarction (PI) due to acute pulmonary embolism (PE), detected by computed tomography angiography (CTA) of the pulmonary arteries, and to describe the main morphological features of the RHS.

METHODS

We evaluated 993 CTA scans, stratified by the risk of PE, performed between January of 2010 and December of 2014. Although PE was detected in 164 scans (16.5%), three of those scans were excluded because of respiratory motion artifacts. Of the remaining 161 scans, 75 (46.6%) showed lesions consistent with PI, totaling 86 lesions. Among those lesions, the RHS was seen in 33 (38.4%, in 29 patients).

RESULTS

Among the 29 patients with scans showing lesions characteristic of PI with the RHS, 25 (86.2%) had a single lesion and 4 (13.8%) had two, totaling 33 lesions. In all cases, the RHS was in a subpleural location. To standardize the analysis, all images were interpreted in the axial plane. Among those 33 lesions, the RHS was in the right lower lobe in 17 (51.5%), in the left lower lobe in 10 (30.3%), in the lingula in 5 (15.2%), and in the right upper lobe in 1 (3.0%). Among those same 33 lesions, areas of low attenuation were seen in 29 (87.9%). The RHS was oval in 24 (72.7%) of the cases and round in 9 (27.3%). Pleural effusion was seen in 21 (72.4%) of the 29 patients with PI and the RHS.

CONCLUSIONS

A diagnosis of PE should be considered when there are findings such as those described here, even in patients with nonspecific clinical symptoms.

Clinical characteristics of patients with pulmonary infarction - A retrospective review

BACKGROUND

Pulmonary infarction is an infrequent complication of pulmonary embolism. Traditionally, it has been regarded as a sign of worse outcome because ischemia can only occur by the simultaneous failure of all oxygenation sources to the area of infarct, but supporting evidence is limited.

METHODS

We identified 74 cases of pulmonary infarction over 5 years at a single academic center via review of radiographic reports. Contrast-enhanced chest CT scans were examined to confirm evidence of pulmonary infarction, and patient clinical characteristics and imaging results were studied.

RESULTS

Survival to discharge was high (97%). Patients most commonly presented with dyspnea (69%), chest pain (46%), and swelling or pain in the lower extremities (31%), while underlying risk factors included history of malignancy (41%) and surgery within 30 days (24%). Many patients had concurrent cardiovascular (59%) and pulmonary disease (22%). Infarction disproportionately affected the lower lobes.

CONCLUSIONS

Survival after diagnosis of pulmonary infarction is comparable to uncomplicated pulmonary embolism, suggesting that outcome is not worse. While emboli occurred in multiple lobar sites, pulmonary infarction occurred most commonly in the lower lobes, suggesting unique underlying physiological mechanisms in pulmonary infarction development.