Safe entry point for twist-drill craniostomy of a chronic subdural hematoma.

OBJECT Twist-drill craniostomy (TDC) with closed-system drainage is an effective treatment option for chronic subdural hematoma (CSDH). Because the entry point for TDC has not been described in a definitive area, the aim of this study was to define the optimal twist-drill entry point for CSDH. METHODS The authors selected 40 random cases involving selective catheter angiography of the external carotid artery, regardless of study purpose, to evaluate the course of the middle meningeal artery. Furthermore, 50 skull radiographs were reviewed to assess the relation of the vascular groove to the coronal suture. On the basis of the radiological anatomical study, the authors propose that the normal TDC entry point should be 1 cm anterior to the coronal suture at the level of the superior temporal line (STL). Thirty patients with symptomatic CSDH were treated using TDC with closed-system drainage at the proposed entry point. The thicknesses of the hematoma and the skull were measured at the proposed entry point. The congruence between the proposed entry point and postoperative craniostomy was estimated and complications were evaluated. RESULTS In the radiological study, all the branches of the middle meningeal artery ran posterior to the coronal suture and the vascular grooves were also located posterior to the coronal suture at the level of the STL. The average distance of the vascular grooves was 8.0 +/-5.8 mm. Thirty-five procedures were performed. The coronal suture and the STL could be identified clearly on brain CT scans. The mean thickness of the skull and the CSDH at the proposed point was 8 mm (range 5-13 mm) and 20 mm (range 10-28 mm), respectively. All the TDCs except 1 were congruent with the preoperative brain CT scans. One CSDH recurred 1 month after the first operation and was revised using the same procedure. No other complications occurred. CONCLUSIONS One centimeter anterior to the coronal suture at the level of the STL is suitable as the normal entry point of the TDC for symptomatic CSDH. The thickness of the CSDH can be measured at this point on a preoperative brain CT scan. Furthermore, the entry point on the scalp can be accurately estimated using surface landmarks.