The Circle of Willis (COW) is an important collateral pathway to protect the persistence of cerebral blood perfusion. This study aims to investigate the morphological variants of this significant vascular structure with a large study population. 867 patients who had undergone MR angiography (MRA) evaluation were enrolled in this study. The MRA images of these patients obtained by the three-dimensional time-of-flight technique were re-interpreted to measure the vessel diameters of all components of the COW and classify the COW variations. In addition, correlations of the vessel calibers and the integrity of the COW with gender and age groups were presented. There was female dominance in the study population, and the mean age was 48. Type A was the most common variation in anterior (75.78%) and posterior (53.98%) circulation. Types G and H were the other common variation in the anterior circulation, and types E and D were the second and third common variations in the posterior COW, respectively. Smaller calibration for both ICAs, both P1s and BA were observed in females compared with the male group. Diameters of the BA, and both P1 segments were lower, and the left PCom diameter was significantly higher in the patients with a complete circle. There was a significant sex and age difference regarding the distribution of the complete, partially complete, and incomplete circle groups. The significant differences in the vessel calibers of specific components of the COW for complete, partial, and incomplete circulations revealed by this study should be explained with further research. In addition, meta-analyses with other studies in the literature might be a guide to understanding the morphological alterations of the COW and their relationships with a complete and non-complete circle.

BACKGROUND The data obtained on the anatomical knowledge of the tracheobronchial system can be used for diagnosis, treatment and interventional interventions in areas such as anesthesia, thoracic surgery, pulmonary physiology. AIM To determine the tracheobronchial branching angles in pediatric and adult populations by using the multislice computed tomography (CT) and minimum intensity projection (MinIP) technique, which is a non-invasive method. METHODS Our study was carried out retrospectively. Patients who underwent contrast and non-contrast CT examination, whose anatomically and pathophysiologically good tracheobronchial system and lung parenchyma images were obtained, were included in the study. Measurements were made in the coronal plane of the lung parenchyma. In the coronal plane, right main bronchus-left main bronchus angle, right upper lobe bronchus-intermedius bronchus angle, right middle lobe bronchus-right lower lobe bronchus angle, left upper lobe bronchus-left lower lobe bronchus angle were measured. RESULTS The study population consisted of 1511 patients, 753 pediatric (mean age: 13.4 ± 4.3; range: 1-18 years) and 758 adults (mean age: 54.3 ± 17.3; range: 19-94 years). In our study, tracheal bifurcation angle was found to be 73.3° ± 13.7° (59.6°-87°) in the whole population. In the pediatric group, the right-left main coronal level was found to be higher in boys compared to girls (74.6° ± 12.9° vs 71.2° ± 13.9°, P = 0.001). In the adult group, the right-left main coronal level was found to be lower in males compared to females (71.9° ± 12.9° vs 75.8° ± 14.7°, P < 0.001). CONCLUSIONS Our study, with the number of 1511 patients, is the first study in the literature with the largest number of patient populations including pediatric and adult demographic data, measuring the angle values of the tracheobronchial system using multislice CT and MinIP technique. Study data will not only be a guide during invasive procedures, but it can also guide studies to be done with imaging methods.

Coronavirus disease 2019 (COVID-19) is caused by the virus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In the literature, this virus has been associated with coagulation dysfunction and arterial thromboembolism. In clinical practice, corpus callosum infarcts are very rare, and the incidence of isolated splenium infarct is very low. Here, two cases of isolated splenium infarct after COVID-19 are reported with clinical and imaging findings. These findings are thought to be useful in daily practice for our colleagues. In addition, differential diagnoses of this entity will also be discussed in this case report.