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Neuroradiology Case of the Week

Case 187

Salman S. Mirza, DO and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 71-year-old female with history of bilateral subdural hematomas.

Radiological Findings: Axial CT images demonstrate bilateral isodense subdural hematomas with areas of high density which is indicative of hemorrhage of different ages.

Diagnosis: Bilateral isodense subdural hematomas

Discussion: Subdural hematoma is a collection of blood below the inner layer of the dura but external to the brain parenchyma and arachnoid membrane. Subdural hematomas can be acute, subacute, and chronic and each type has distinct imaging characteristics.
     Subdural hematomas occur when low pressure venous bleeding of bridging veins dissect the arachnoid away from the dura and layers out along the cerebral hemisphere. Subdural hematomas are commonly caused by blunt head trauma.
     Subdural hematomas undergo a predictable temporal change in their normal evolution. As the hemoglobin, platelet clots, and other cellular elements are broken down there will be a gradual decrease in the size and density of the SDH. The initial hyperdensity may persist for up to 7 to 10 days. As a SDH progressively decreases in density, it will eventually reach a point where it is isodense to the brain parenchyma, which usually occurs at 1-2 weeks. During this time period SDHs are particularly difficult to diagnose. Ultimately, as the SDH undergoes further evolution, it will become hypodense to the brain parenchyma.
     On nonenhanced CT scans, isodense SDH can be recognized by the mass effect they exert on the lateral ventricles. There will also be effacement of cortical sulci with inability to follow the cortical sulci to the inner table of the skull. Other things to look for include unusually thick gray matter and medially displaced gray-white matter junction.
     Enhanced CT scan studies will demonstrate enhancement of the subdural membrane along with displacement of the cortical veins on the surface of the brain away from the skull. On delayed images there will also be layering of contrast material within the SDH. However, the study of choice currently for diagnosing isodense SDHs is MRI.

References:

1. Orrison, William: Neuroimaging. W.B. Saunders Company, 2000, pp 891-895.
2. Osborn, Anne G: Diagnostic Imaging, Brain. Amirsys, 2004, pp I 2.12-I 2.21.