Focal bone lesions are not uncommon findings in the daily practice of radiology. Therefore, it is essential to differentiate between lesions with aggressive, malignant potential that require action and those that have no clinical significance, many of which are variants or benign lesions, sometimes self-limited and related to reactive processes. In some cases, a diagnostic error can have catastrophic results. For example, a biopsy performed in a patient with myositis ossificans can lead to an incorrect diagnosis of sarcomatous lesions and consequently to mutilating surgical procedures. The present study reviews the main radiological aspects of the lesions that are most commonly seen in daily practice and have the potential to be confused with aggressive, malignant bone processes. We also illustrate these entities by presenting cases seen at our institution.

Keywords: Bone diseases; Muscular diseases; Diagnostic imaging; Myositis ossificans; Bone neoplasms.

OBJECTIVE: To evaluate progression rate of Bosniak category IIF complex renal cysts and the malignancy rate among surgically resected cysts. MATERIALS AND METHODS: We performed a database search for complex renal cysts classified as Bosniak category IIF on computed tomography or magnetic resonance imaging between January 2008 and April 2016. Follow-up examinations (computed tomography or magnetic resonance imaging) were used in order to evaluate progression (Bosniak category reclassification) and stability, the latter being defined as remaining stable for a minimum of six months. Pathology reports were used as the reference to assess the malignancy rate of surgically resected cysts. RESULTS: A total of 152 cysts in 143 patients were included in the final analysis. Seven cysts (4.6%) were reclassified on follow-up studies, and mean time to progression was 20 months (range, 1 month to 4 years). Three cysts were surgically resected. All three were diagnosed as low-grade malignant renal cell carcinomas (RCCs): one clear cell RCC and two papillary RCCs. The remaining 145 cysts remained unchanged after a mean follow-up period of 28 months (range, 6 to 118 months). CONCLUSION: The progression rate in Bosniak category IIF cysts was low. Even lesions that were upgraded on follow-up remained stable, indicating an indolent behavior. Our data support the idea of conservative management of Bosniak IIF renal cyst.

Keywords: Tomography, X-ray computed; Magnetic resonance imaging; Cysts/classification; Carcinoma, renal cell; Kidney/diagnostic imaging.

The term avascular necrosis describes any one of a number of bone diseases that have a common mechanism: the death of bone components due to lack of blood supply. Avascular necrosis can occur in diverse parts of the skeleton, each location-specific form not only receiving a distinct designation but also presenting unique epidemiologic characteristics. However, the imaging findings are similar in all of the forms, which pass through well-described radiological phases, regardless of the site of involvement. Because avascular necrosis can cause considerable morbidity if not properly detected and managed, the radiologist plays a fundamental role. The present study provides a brief review of the main radiological aspects of the various forms of avascular necrosis, illustrated on the basis of a collection of cases from our institution.

Keywords: Osteonecrosis/diagnostic imaging; Radiography; Tomography, X-ray computed; Magnetic resonance imaging.

Hip arthroplasty is a widely used and successful orthopedic procedure for the treatment of degenerative, inflammatory, or traumatic joint disease. The procedure promotes significant pain relief, as well as recovery of limb function, reduction of disability, and better quality of life. However, there are related complications, which have characteristic imaging aspects. In the present study, we review the literature and exemplify such complications using images obtained at our facility, illustrating the main radiological aspects of complications such as heterotopic ossification, periprosthetic fractures, osteolysis, infection, wear, and dislocation.

Keywords: Hip joint/physiopathology; Hip joint/diagnostic imaging; Arthroplasty, replacement, hip/diagnostic imaging; Arthroplasty, replacement, hip/adverse effects.

Radiologists should be familiar with the main techniques of knee cartilage repair and the imaging methods available for its evaluation, in order to optimize the postoperative follow-up of patients. The objective of this study was to present a series of clinical cases seen at our facility, illustrating the main techniques necessary for the repair of knee cartilage, as well as the magnetic resonance imaging techniques used in the postoperative evaluation and the relevant radiological findings.

Keywords: Knee; Cartilage; Magnetic resonance imaging.

The disease caused by the new coronavirus (COVID-19) was restricted to China but quickly spread to other Asian countries and later to the Western countries, categorized as a pandemic by the World Health Organization. Its diagnosis is primarily dependent on viral detection in the airways. The available kits are, however, limited, do not have high sensitivity and their result takes time. In this scenario, computed tomography emerges as an efficient and available method with high sensitivity. It is up to us radiologists to readily recognize the findings related to this disease. The aim of this article is to demonstrate the main tomographic findings in symptomatic respiratory patients infected with COVID-19 in order to assist colleagues in this critical moment.

Keywords: Coronavirus; COVID-19; Multislice computed tomography.

Radiotherapy plays a central role in the palliative and curative treatment of neoplasms of the chest wall or intrathoracic structures. However, despite technical advances, radiotherapy can alter previously normal organs and tissues, those alterations presenting as various types of imaging findings. Post-radiation alterations must be promptly recognized by radiologists, in order to avoid confusion between complications of radiotherapy and the recurrence of a tumor. This pictorial essay aims to illustrate different thoracic changes after radiotherapy.

Keywords: Radiotherapy; Tomography, X-ray computed; Magnetic resonance imaging; Diagnostic imaging; Thoracic neoplasms.

Advances in cardiac magnetic resonance have promoted tissue characterization with high spatial and contrast resolution, and late gadolinium enhancement (LGE) sequences have improved the detection of myocardial fibrosis. The distribution pattern of LGE facilitates differentiation between ischemic and nonischemic etiologies and aids in refining diagnoses within nonischemic cardiomyopathies, suggesting specific etiological factors. A distinctive nonischemic LGE pattern that has recently gained prominence is the ring-like pattern, defined as a subepicardial or mid-wall circumferential or semi-circumferential enhancement, which involves at least three contiguous segments within the same short-axis slice. Initially identified as a diagnostic marker for desmoplakin and filamin C-related cardiomyopathies, the pattern has been reported in nongenetic conditions; nevertheless, it remains an uncommon finding in these diseases. In this article, we aim to present the differential diagnoses of ring-like LGE and its mimics. The combination of epidemiological, clinical, electrocardiographic, and additional features enables a focused refinement of the differential diagnosis associated with ring-like LGE.

Keywords: Cardiomyopathies; Arrhythmogenic right ventricular cardiomyopathy; Magnetic resonance imaging; Gadolinium.

The sternum and the sternoclavicular joints can exhibit a wide range of anatomical variations and serve as sites for numerous diseases, many of which are diagnosed solely through imaging studies. Recognizing these variations and differentiating them from pathological conditions is essential for radiologists, because accurate identification helps prevent misdiagnoses and treatment delays. This study provides a comprehensive review of the sternal anatomy, addressing anatomical variations, as well as mechanical, inflammatory, and traumatic pathologies, discussing their radiographic characteristics across different imaging modalities. Thus, it provides an overview of the key radiological findings.

Keywords: Sternum; Manubrium; Xiphoid bone; X-Rays; Multidetector computed tomography; Magnetic resonance imaging.

OBJECTIVE: To characterize the main causes of the reversed halo sign (RHS) on computed tomography (CT) of the chest and its imaging features.
MATERIALS AND METHODS: This was a retrospective study reviewing all chest CT scans for which the report contained the term "reversed halo sign" among those performed between 2015 and 2020 at a tertiary care hospital.
RESULTS: A total of 286 cases were identified, and the corresponding CT images and clinical data were reviewed. In this population, the most common cause of an RHS was pulmonary infarction (in 42%), followed by cryptogenic organizing pneumonia (in 17%) and bacterial pneumonia (in 16%). In addition, the CT characteristics of the RHS were identified in various conditions, such as pulmonary thromboembolism with pulmonary infarction, in which the RHS was typically smooth-walled and solitary with a peripheral distribution.
CONCLUSION: The RHS can be observed in many contexts, and its CT characteristics, in combination with the clinical picture, can help narrow the differential diagnosis.

Keywords: Tomography, X-ray computed/methods; Respiratory tract infections/diagnostic imaging; Pulmonary embolism/diagnostic imaging; Lung diseases, interstitial/diagnostic imaging.