Cortical bridging venous segment protruding into the inner skull depression: a potential site of hemorrhage at external ventriculostomy.

PURPOSE: The cortical bridging venous segment protruding into the inner skull depression (CBVISD), a distinctive structure found in the calvarial convexity, may be a potential risk factor for hemorrhagic complications resulting from trephination. However, this subject has not been documented. In the present study, we explore the CBVISD using magnetic resonance imaging (MRI).

METHODS

A total of 94 patients underwent contrast-enhanced MRI. Distributions of the CBVISDs were recorded in two symmetrical regions of the frontal calvarial convexity. The lateral dimensions on both hemispheres were defined to range between 25 and 35 mm from the midsagittal section. The anteroposterior axis was delimited anteriorly by the supraorbital bar and posteriorly by the coronal suture, which was further divided into four parts: the forehead (FH), anterior frontal (AF), FH-AF junctional, and posterior frontal (PF) regions.

RESULTS

Analysis of the delineations revealed that the CBVISDs had variable shapes and sizes. They were identified on the right side in 40% of the 94 patients and in 41% on the left side. Among the 91 identified CBVISDs, 5.5% of the CBVISDs were located in the FH, 17.6% in the FH-AF, 34.1% in the AF, and 42.9% in the PF.

CONCLUSIONS

The CBVISDs are most frequently located at the common trephination site of external ventriculostomy. Trephination performed in the FH and FH-AF junctional regions may be safer than that in more posterior frontal areas.