beyond the ventral epidural space?

Sacral Transforaminal Approach

The patient is positioned prone, and an AP view of radiograph is obtained to identify the level to be injected. The C-arm should be tilted cephalad to line up the sacral end plate. The C-arm may need to be ipsilaterally rotated slightly oblique to optimize visualization of the dorsal sacral foramen. The oblique approach reduces the procedure length, radiation exposure, and intravascular injection rate [41, 42].The dorsal S1 foramen is located just inferior to the S1 pedicle and to the medial side of the lateral sacral line. Once the optimal foramina view is obtained, a 22- or 25-gauge 1.5–3.5 inch spinal needle is placed coaxially and advanced to the medial side of the foramen to avoid the nerve running inferolaterally, as well as to allow for a more effective spread of the contrast and reduced incidence of intravascular uptake [43]. The position is then checked in the lateral view, and the needle is advanced just beyond the ventral epidural space. Following negative aspiration, 0.5–1.0 mL of nonionized contrast is infused through an extension tubing under live fluoroscopy. The contrast should outline the sacral nerve root and spread medially through the neural foramen into the lateral epidural space (Fig. 22.2). Once confirmed, the local anesthetic and steroid admixture may be injected. Ensure that the needle and tract are cleared of steroid with either saline or local anesthetic flush before removing the needle.

经骶后孔入路

患者俯卧位，使用X线正位片来定位穿刺节段。C臂应向头侧倾斜，与骶骨终板对齐。为优化骶后孔的视图，C形臂可能需要向同侧轻微倾斜旋转。倾斜入路可以减少了操作时间、放射暴露和血管内注射的发生率[41-42]。S 骶后孔位于S 椎弓根正下方和骶外侧线内侧。一旦获得最优的骶后孔视图，为避开向外下方走行的神经、有利于造影剂有效地扩散和减少误入血管的发生率，沿X线方向推进22或25G 1.5～3.5英寸穿刺针至骶后孔内侧[43]。然后在侧位片中核对该位置，确保针尖刚好到达腹侧硬膜外腔之外。回抽后通过延长导管注入0.5～1.0 mL 非离子造影剂，在透视中造影剂应能显示出骶神经根的轮廓，并通过神经孔向内侧扩散至硬膜外间隙（图22.2）。一旦明确针尖的正确位置，可注射局部麻醉药和类固醇混合物。在取出针头之前，确保用生理盐水或局部麻醉药冲洗针头和导管内的类固醇药物。

不明白什么叫“腹侧硬膜外腔之外”，硬膜外穿刺不是从“背侧”开始吗？谢谢