CSH is a common type of intracranial hemorrhage and many factors related to recurrence have been reported (5, 8, 20).
Motoie et al. reported that age and sex associated with recurrence hemorrhage, however in our study, we found that age and sex were not associated with hematoma recurrence (13).Our study population was younger than theirs, their mean age was 79 years, ours was 70 years old. Less brain atrophy in younger patients, which didn’t examine in this study, may make the difference. Also, Kim et al. reported that male gender was associated with recurrence hemorrhage and they explained: estrogen is related to the repair of damaged vessels (6). However, estrogen levels are higher in older men than in postmenopausal women (10).
Many publications stated that history of head trauma was not related to hemorrhage recurrence (2, 7). We also found similar results. In this study; DM, hypertension, using anticoagulant and/or antiaggregant drugs were not predictive factors for hematoma recurrence. Yamato et al. suggested that hyperviscosity of the blood induced by hyperglycemia could play a role in decreasing recurrence rate in diabetic patients (22). Motoie et al claimed that using antiaggregant and/or anticoagulant drugs do not increase the recurrence rate, because these prevent the formation of clots in subdural space, but further studies are required to accept such a claim (13).
Similar to the results of the study conducted by Song et al., we found that preoperative midline shift was associated with hemorrhage recurrence (19). Kim et al. suggested that preoperative midline shift causes impaired adhesion between inner and outer membrane, therefore recurrence risk increases due to insufficient postoperative brain expansion (7). As a more objective indicator of brain compression, ambient cistern compression was found to be highly correlated with recurrence. To our knowledge, there is only one study examining the relationship between ambient cistern compression and recurrence of CSH in the English literature (13).
The density of hematoma reflects the amount of fresh blood clot in the hematoma cavity, and shows that blood vessels are actively growing into the membrane of CSH, therefore high hematoma density reflects active capillary network formation (9). Similarly, we established a relationship between mixed-density hematoma (hyperdense area were present) and recurrence. Also, the recurrence rate was found associated with multiple layer hematoma in which the excessive neo-membrane structures and blood vessel formation is active. However, contradictory results have been reported, Ohba et al. reported that the recurrence rate is not related to hematoma density (15).
Nakaguchi and et al. classified CSD into the four stage, based on the internal architecture and density of hematomas (14). They reported that CSD initiate as the homogeneous type and sometimes beginning into the laminar type, and then matures as the separated type and is finally absorbed as the trabecular type (14). Experimental studies have shown that blood in the subdural space causes an inflammatory response and increases the amount of cytokines. Separated stage is the most active period of inflammation because the amount of cytokine is measured the most (4). In the publications, they reported that the recurrence is high in separated architecture, like the results we obtained (3, 17).
Surgical technique (single/double burr-hole/craniotomy) were not found associated with recurrence. However, the recurrence rate was found to be significantly higher in patients who underwent membranectomy. The optimal surgical technique for CSH is unclear, but it has been reported that postoperative mortality and morbidity rates do not differ between burr-hole craniostomy, and craniotomy with or without membranectomy (16). We know that the outer membrane is highly vascularized and the exudation is critical for CSH accumulation (18). Although a wide membranectomy may be performed, it will not be total, bleeding may occur from residual membrane. On the other hand, fenestration or partial resection of the outer membrane may prevent blood/excuda accumulation in the long term (1). In our study, the procedures performed in patients with recurrence were: 10,7% with double burr hole craniostomy, 28,6% with single burr hole craniostomy and 60,7% with craniotomy. According to our experience, the double burr hole craniostomy method has been found to be the most reliable method, in which the integrity of the outer membrane was sufficiently impaired but widely membranectomy was not performed.