Acute Isodense Subdural Hematoma

Plain and contrast-enhanced axial CT images of the brain show an isodense subdural hematoma (SDH, arrows) in the left cerebral convexity, much better appreciated on post-contrast image. There is also a thinner right frontal convexity SDH. 

Facts: Isodense Subdural Hematoma (SDH)

• Subdural blood collection that has similar attenuation with the gray matter
• Acute SDH appears as a high density collection with declining density with time. It passes "isodense" state mostly in subacute phase (2-6 weeks after initial trauma)
• Isodense SDH poses diagnostic dilemma because it is not apparently seen on CT
• In acute setting this can be seen in anemic patients (acute isodense SDH). Experimental data showed that Hb 8-10 g/dl will be isodense to the adjacent brain

Reference:

Smith, Jr., WP, Batnitzky S, Rengachary SS. Acute isodense subdural hematomas: a problem in anemic patients. AJR 1981; 136:543-546.