Teaching Case

Recurrent confusion. No history of trauma.

One week prior to admission had an episode of confusion that resolved without neurological deficit. On the day of admission he had increasing headache and confusion. No history of trauma. Not taking any medications. On examination, a right sided facial weakness was noted.

Subdural hematoma (SH) can be acute (usually hyperdense on CT), subacute (1-2 weeks after injury, isodense) and chronic (3-4 weeks after injury, usually hypodense). Up to 50% of subacute and chronic hematomata do not have a history of trauma. An acute subdural hematoma can appear isodense in anemia and clotting disorders. A chronic SH may appear isodense on CT due to recurrent acute bleeds. True isodensity is rare. High resolution images will usually show slightly abnormal attenuation with the SH. The separation of isodense collections into hypodense serum anteriorly and hyperdense blood posteriorly is enhanced if the patient supine for at least 30 minutes before the study. CT detection of isodense SH relies on effacement of sulci,ipsilateral ventricular compression, displacement of the grey-white matter away from the ipsilateral inner table and, in unilateral SH, midline shift. Intravenous contrast enhances the inner table and the cortical-subdural interface. Magnetic Resonance (MR) is the imaging modality of choice. In subacute SH it shows as a bright lesion on T1 due to the high sensitivity to met hemoglobin. Small subdural hematomata oriented in the CT plane e.g. tentorial subdurals may be missed on CT but are detected on MR.