Diffusion-Weighted Imaging Reveals Distinct Patterns of Cytotoxic Edema in Patients with Subdural Hematomas

Abstract

Subdural hematomas (SDHs) are increasingly common and can cause ischemic brain injury. Previous work has suggested that this is driven largely by vascular compression from herniation, although this work was done before the era of magnetic resonance imaging (MRI). We thus sought to study SDH-related ischemic brain injury by looking at patterns of cytotoxic edema on diffusion-weighted MRI. To do so, we identified all SDH patients at a single institution from 2015 to 2019 who received an MRI within 2 weeks of presentation. We reviewed all MRIs for evidence of restricted diffusion consistent with cytotoxic edema. Cases were excluded if the restricted diffusion could have occurred as a result of alternative etiologies (e.g., cardioembolic stroke or diffuse axonal injury). We identified 450 SDH patients who received an MRI within 2 weeks of presentation. Twenty-nine patients (∼6.5% of all MRIs) had SDH-related cytotoxic edema, which occurred in two distinct patterns. In one pattern (N = 9), patients presented as comatose with severe midline shift and were found to have cytotoxic edema in the vascular territories of the anterior and posterior cerebral artery, consistent with herniation-related vascular compression. In the other pattern (N = 19), patients often presented as awake with less midline shift and developed cytotoxic edema in the cortex adjacent to the SDH outside of typical vascular territories (peri-SDH cytotoxic edema). Both patterns occurred in 1 patient. The peri-SDH cytotoxic edema pattern is a newly described type of secondary injury and may involve direct toxic effects of the SDH, spreading depolarizations, or other mechanisms.

Keywords: ischemia; secondary insult; subdural hematoma.

FIG. 1.

Flow diagram of study. *Includes atherosclerosis, moderate-severe vasospasm, and blunt cerebrovascular injury from trauma. ICD, International Classification of Diseases; IPH, intraparenchymal hemorrhage; MRI, magnetic resonance imaging; SAH, subarachnoid hemorrhage SDH, subdural hematoma.

FIG. 2.

Patterns of cytotoxic edema. Cytotoxic edema is identified with green arrows; SDHs are identified with red arrows. (A-D) Representative patients with peri-SDH cytotoxic edema. (E,F) Representative patients with ACA/PCA pattern of cytotoxic edema. ACA, anterior cerebral artery; PCA, posterior cerebral artery; SDH, subdural hematoma.

FIG. 3.

Representative long-term follow-up images for 2 patients with peri-SDH cytotoxic edema. (A) Initial diffusion-weighted MRI image shows cytotoxic edema in the right frontal lobe (left panel, red arrow), and follow-up CT at 2 months shows persistent encephalomalacia (right panel, red arrow). (B) Initial diffusion-weighted MRI shows cytotoxic edema in the right lateral temporal lobe (left panel, red arrow), and follow-up MRI at 1 year shows encephalomalacia and focal atrophy (right panel, red arrow). CT, computed tomography; MRI, magnetic resonance imaging, SDH, subdural hematoma.