Morphological characteristics of infected subdural hematoma: Comparison with images of chronic subdural hematoma

•A biconvex shaped hematoma would be useful to detect infected subdural hematoma.•To detect an infection of the hematoma is difficult, especially in elderly patients.•The infected subdural hematoma is clinically important due to its high mortality. Infected subdural hematoma (ISH) is a rare type of subdural empyema, with fewer than 50 cases reported to date. Its radiological features have not been adequately described, making diagnosis challenging. At our institution, two adults presented with ISH, which exhibited a characteristic shape on preoperative imaging. This study examined ISH cases and chronic subdural hematoma (CSH) cases that underwent surgery at the Ishikawa Prefectural Central Hospital between January 2016 and March 2018. To distinguish ISH from CSH, we focused on three specific radiological features: the biconvex shape of the hematoma, presence of a high-density region at the lower end of the hematoma on plain computed tomography (CT), and presence of a hyper-intense signal within the hematoma on diffusion weighted imaging (DWI). We analyzed 30 ISH (current and previously reported) and 102 CSH cases in our study. We found no statistically significant associations between the hematoma type (ISH or CSH) and the presence of a high-density region at the lower end of the hematoma on plain CT (p = 0.13) or the presence of hyperintensity in the hematoma on DWI (p = 1.00). Conversely, a statistically significant association was found between the hematoma type and the biconvex shape of the hematoma (p