The computed tomographic attenuation and the age of subdural hematomas

Abstract

The sequential change in density (attenuation coefficient) of subdural hematomas (SDHs) in computed tomography (CT) is important in understanding the pathogenesis and evolution of SDHs. We retrospectively investigated the age of SDHs by CT in 446 cases. We included 30 cases of chronic SDHs, in whom the density was directly measured in the CT. The density of acute (within 7 days) SDH was hyperdense in 98.6%, isodense in 1.1%, and hypodense in 0.3% of the cases. In subacute (8-22 days) SDHs, it was hypodense in 45.7%, isodense in 42.9%, and hyperdense in 11.4%. In chronic (over 22 days) SDHs, 86.7% was isodense and only 13.3% was hypodense. In hypodense SDHs, 64.0% was the subacute, and 73.2% of the isodense SDHs was the chronic one. The mean interval from injury to CT was 0.5 +/- 1.6 days in hyperdense SDHs, 20.9 +/- 20.7 days in hypodense SDHs, and 54.9 +/- 44.0 days in isodense SDHs. In 30 cases of chronic SDH, the average density was 38.0 +/- 6.9 Hounsfield number(H) in 20 approximately 30 days, 43.8 +/- 12.8 H in 31 approximately 60 days, 51.8 +/- 5.1 H in 61 approximately 90 days, and 44.2 +/- 8.3 H in over 90 days. The density of acute SDH is usually hyperdense. It becomes hypodense within 3 weeks. Then the density progressively increases by the repeated microhemorrhage, which is the mechanism of enlargement of chronic SDH. The density of chronic SDH increases with time up to 90 days, then decreases again after maturation of the neomembrane, which is the mechanism of spontaneous resolution.

What Determines the Laterality of the Chronic Subdural Hematoma?

“…The density of the CSDHs was most often isodense in this study. The age of the isodense hematoma is older than the hypodense hematoma 12) . The density of the CSDH originated from SDGs would be hypodense at first.…”

“…That is the reason why bilateral hematomas were more common in the hypodense group in this study. Even the hyperdense ASDHs usually become hypodense within 3 weeks 12) . Then, it becomes isodense by the repeated microhemorrhage, which is the mechanism of enlargement of CSDH 12) .…”

“…Even the hyperdense ASDHs usually become hypodense within 3 weeks 12) . Then, it becomes isodense by the repeated microhemorrhage, which is the mechanism of enlargement of CSDH 12) . The laterality of CSDH is dependent on the initial site of ASDH and pressure difference produced by either dynamics between expansion and resorption or tilting of the cranium.…”

“…There was no statistically significant difference in terms of laterality in the acute or subacute subdural hematomas 16) . There are reports indicating that the laterality of the CSDH depends on the cranial morphology 2,12) . The brain is asymmetric in structure and function 6,10) .…”

Neuroimaging in traumatic brain imaging

“…CT is also the imaging modality of choice in revealing delayed cerebral hematoma, which should be suspected in anyone who exhibits worsening level of consciousness, new third nerve palsy, or increasing ICP, can detect delayed extraaxial hematomas, but may miss small subdural hematomas caught by MRI. 74,96 As time progresses, hematomas decrease in attenuation until they becomes isodense with normal brain parenchyma 3-10 weeks after the bleed, making it difficult to detect on CT. 97,98 Because old blood still emits high signal intensity on T1-weighted imaging, MRI is better at detecting chronic hemorrhage. 99,100 Chronic subdural hematomas rarely spontaneously resolve, and therefore, surgical or nonsurgical (e.g., mannitol, glucocorticoids) treatment may be necessary.…”