Obstruction of the superior vena cava (SVC) or inferior vena cava (IVC) is most commonly an acquired condition, typically caused by malignancy, benign conditions such as mediastinal fibrosis, and iatrogenic causes such as venous catheterization. In the event of chronic occlusion, collateral pathways must develop to maintain venous drainage. The major collateral pathways seen with SVC or IVC obstruction are well described and include the azygos-hemiazygos, internal and external mammary, lateral thoracic, and vertebral pathways. In addition, several unusual collateral pathways may be seen with SVC or IVC obstruction; these include systemic-to-pulmonary venous, cavoportal, and intrahepatic collateral pathways. In patients with systemic-to-pulmonary venous collateral vessels, the systemic veins drain directly into the left side of the heart, resulting in a right-to-left shunt. The collateral veins consist of mediastinal connections between the innominate veins and the superior pulmonary veins through bronchial venous plexuses around the airways, hilar vessels, and pleura. The cavoportal collateral pathways consist of collateral formation between the SVC or IVC and a tributary to the portal system. They include the caval-superficial-umbilical-portal pathway, caval-mammary-phrenic-hepatic capsule-portal pathway, caval-mesenteric-portal pathway, caval-renal-portal pathway, caval-retroperitoneal-portal pathway, and intrahepatic cavoportal pathway. These types of collateral pathways may result in unusual enhancement patterns in the liver. An understanding of these unusual collateral pathways is essential in a patient with caval occlusion who presents with signs and symptoms of a right-to-left shunt or has unusual enhancing lesions in the liver.

A n acute lower respiratory tract infection caused by the 2019 novel coronavirus was first reported in China in December 2019 (1,2). The clinical spectrum of disease with coronavirus disease 2019 (COVID-19) infection is variable and ranges from an asymptomatic infection or mild upper respiratory tract illness to severe viral pneumonia with respiratory failure and occasionally death (2). Although the case fatality ratio has been as high as 15%, the incidence of critical illness has been reported to be 7%-26% (3). Patient factors that have been associated with a higher incidence of critical illness and death include male sex, age older than 60 years, obesity, diabetes, hypertension, cardiopulmonary comorbidities, and higher d-dimer and interleukin 6 values (3).At the time of writing this article, more than 8 million cases and 450 000 deaths worldwide have been reported. The COVID-19 pandemic has resulted in an unprecedented health care crisis with immense strain on health care resources and disruptions in both routine and emergency health care delivery (4). The lack of adequate diagnostic testing has resulted in suboptimal early detection and containment of this infection, which has contributed to rapid and widespread transmission by individuals with mild or no symptoms (5). The primary diagnostic test, reverse transcriptase polymerase chain reaction (RT-PCR) assay for COVID-19, has variable sensitivity ranging from 37% to 71% (5), depending on the rate of viral expression at the time of collection and the site of specimen collection (6). Obstacles to the use of RT-PCR testing include shortage of kits and extended processing period.Chest CT in COVID-19 pneumonia demonstrates bilateral, peripheral, and basal predominant ground-glass opacities (GGOs) and/or consolidation in nearly 85% of patients with superimposed irregular lines and interfaces; the imaging findings peak 9-13 days after infection (7,8) (Fig 1). Subsequently, a mixed pattern evolves with crazy paving, architectural distortion, and perilobular abnormalities superimposed on GGOs with slow resolution (7) (Fig 1). Importantly, CT scans may be normal in an infected patient, particularly early in the disease (8). Atypical chest CT findings include upper lobe or peribronchovascular distribution of GGOs, cavitation, tree in bud nodules, lymphadenopathy, and pleural thickening (9). Tables 1 and 2 summarize common and uncommon CT findings of COVID-19 (10-21). It is vitally important to remember