Acute subdural hematoma (ASDH), chronic subdural hematoma (CSDH) and subdural hygroma (SDG)
occur in the subdural space, usually after trauma. We tried to find a certain relationship
among these three traumatic subdural lesions in 436 consecutive patients. We included all
subdural lesions regardless of whether they were main or not. We evaluated the distribution,
age incidence and interval from injury to diagnosis of these lesions, and the frequency of
new subdural lesions in each lesion. ASDH constituted 68.6%, SDG 15.8%, and CSDH 15.6%, Age
incidence of CSDH was similar to that of SDG, but differed from that of ASDH. Mean interval
from injury to diagnosis was 0.4 days in ASDH, 13.4 days in SDG, and 51.6 days in CSDH.
Focal brain injuries accompanied in 37.5% of ASDH, 5.8% of SDG, and no CSDH. In ASDH, 2
recurrent ASDHs, 17 SDGs and 9 CSDHs occurred. In SDG, 3 postoperative ASDHs and 8 CSDHs
occurred. In CSDH, 2 postoperative ASDHs, 2 SDGs and 1 CSDH occurred. These results suggest
that the origin of CSDH is not only ASDH, but also SDG in upto a half of cases. SDG is produced
as an epiphenomenon by separation of the dural border cell layer when the potential subdural
space is sufficient. A half of CSDHs may originate from ASDHs. ASDH may occur in CSDH by either
a repeated trauma or surgery. Such transformation or development of new lesions is a function
of a premorbid condition and the dynamics between the absorption capacity and expansile force
of the lesion.
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