Immediate Postoperative Outcomes of Burr-Hole versus Bone Flap: A Hounsfield Unit Threshold in Subacute Subdural...

Choosing between two-burr-hole craniostomy and bone-flap elevation for subdural hematoma (SDH) drainage is usually straightforward; however, in subacute cases there is often uncertainty about whether burr holes will achieve adequate evacuation. A hematoma density threshold in Hounsfield units (HU) on non-contrast computed tomography (CT) may offer an objective guide.

We retrospectively analyzed 281 surgically treated SDHs. Mean hematoma density was measured on standardized NCCT using a polygonal region of interest at the axial slice of maximal thickness. The primary outcome ("bone-flap need") included initial bone-flap elevation, intraoperative conversion, or immediate postoperative evacuation <80%. Threshold derivation was restricted to subacute cases (n = 114). As a secondary analysis, chronic-with-rebleeding cases underwent receiver operating characteristic evaluation without threshold derivation (n = 93). Diagnostic performance was assessed using receiver operating characteristic curves with bootstrap estimation of the area under the ROC curve and 95% confidence interval. Threshold selection used Youden's index, and operating characteristics were also reported at a fixed reference of 40 HU.

In subacute cases, mean density discriminated the primary outcome (area under the ROC curve 0.846; 95% confidence interval 0.758-0.914). A threshold near 40 HU provided sensitivity 85% and specificity 79%. Burr-hole success decreased progressively with increasing density: 96% (63/66) for HU < 40, 57% (12/21) for HU 40-45, and 46% (5/11) for HU > 45. In chronic cases with rebleeding, no evaluated variable demonstrated clinically meaningful discrimination.

A threshold near 40 HU may serve as an adjunct to guide burr-hole versus bone-flap selection in subacute SDH. Prospective multicenter validation is needed.