Computed-tomography of bilateral isodense chronic subdural hematomas.

While unilateral chronic isodense subdural hematomas as a result of indirect signs of a space-occupying lesion are easily recognizable on computed tomography (CT) and clearly diagnosed on the angiogram, bilateral chronic isodense subdural hematomas may cause considerable difficulty. In two cases with CT false negative findings we observed, retrospectively, significant small cellae mediae and also the main part of the anterior horns sharply pointed and approaching one another. Three further cases showed the same ventricular configuration, which we called "hare's ears sign". This sign together with clinical data is always suspicious of chronic bilateral isodense subdural hematomas and carotid angiography is indicated. Other possible signs are: subtle midline shift if the size of the hematoma varies, changed formation of density of brain tissue, non-appearance of cerebral sulci especially in elderly patients, and eventually the visualization of a membrane after intrevenous injection of contrast material.