The above NECT images demonstrate a right sided extra-axial crescentic collection that has similar attenuation to gray matter. The collection causes effacement of right sided sulci, and mass effect with midline shift. The isodensity to underlying cortical tissue makes this consistent with an isodense/subacute subdural hematoma indicating that its age ranges from ~3 days to 3 weeks. In patients with anemia, an isodense subdural hematoma can occur in the acute setting.
Kim KS, Hemmati M, Weinberg PE. Computed tomography in isodense subdural hematoma. Radiology 1978;128:71-4.