Our group previously presented a case series aided by a three-dimensional (3D) magnetic resonance imaging (MRI) reconstruction that described injection into the space of Okada as a possible cause of unsuccessful epidural analgesia or injection following the commonly used loss of resistance to air (LORA) technique (Reina et al., 2021). We proposed at the time that a possible cause of the epidural block or injection failure may have been that the epidural needle (or catheter) was placed inside the space of Okada rather than into the epidural space (Lehman et al., 2015; Murthy et al., 2011; Okada, 1981; Reina et al., 2021).

This space was initially described at the cervical spine (Okada, 1981), but it was later also described at the lumbar region between the ligamentum flavum and the vertebral lamina (Iwanaga; et al., 2020; Reina et al., 2016). The space caused the contrast medium used after LORA for epidurographic confirmation of epidural needle placement to spread between the adjacent ipsilateral and contralateral facet joints, the adjacent neural foramen, the paraspinal musculature and the spinous process adventitial bursae (Lehman et al., 2015; Murthy et al., 2011; Okada, 1981; Reina et al., 2021). This space is retrodural and does not communicate with the epidural space (Lehman et al., 2015; Murthy et al., 2011; Okada, 1981; Reina et al., 2021).

We now present an additional case of this phenomenon. A 64-year-old woman with lumbar pain and bilateral radicular pain mainly radiating to her left buttock and posterior leg was diagnosed by MRI with bilateral L4–L5 radiculopathy (L > R) and spinal stenosis refractory to conservative treatment regimens. The patient was scheduled for a left paramedian L4–L5 interlaminar epidural steroid injection in the prone position with fluoroscopic guidance. After local skin infiltration with 1% lidocaine, an 18-gauge Tuohy epidural needle was introduced via the left paramedian approach. LORA was initially used to identify the epidural space. After apparent successful placement as confirmed with positive LORA, we used anteroposterior and lateral fluoroscopic views and attempted epidurography to confirm epidural placement by injecting a 2-ml dose of 1 ml of iodixanol (270 mg/ml of Visipaque, GE Healthcare Biosciences, S.A.U) through the needle prior to steroid injection. Fluoroscopy revealed an unexpected spread of contrast medium into the interspinous region in addition to both L4–L5 facet joints. This spread was typical for the space of Okada (Lehman et al., 2015; Murthy et al., 2011; Okada, 1981; Reina et al., 2021); however, a less common feature, namely cranial contrast medium spread in a ‘V’ shape, was also seen in this patient (Figure 1a). The lateral fluoroscopic view showed the retrodural space without epidural spread (Figure 1b).

Afterward, we again used 3D reconstruction of the MRI of the lumbar spine of another similar-sized healthy patient (Reina et al., 2021; Figure 2) and overlaid the fluoroscopic images at similar enlargements to demonstrate the spread in our patient. This reconstruction demonstrated the position of the space of Okada and its ‘V’ shape. It also demonstrated that the ligamentum flavum extended beyond the articular joint surfaces (Iwanaga et al., 2020; Reina et al., 2016) and overlapped at the lower half of the laminae (Figure 2).

These findings correspond with the findings we described in detail previously (Reina et al., 2021) and further support those in other studies (Lehman et al., 2015; Murthy et al., 2011; Okada, 1981; Reina et al., 2016). This report further enhances our understanding of unexpected events such as failed epidural blockade.

我们小组先前提出了一个由三维 (3D) 磁共振成像 (MRI) 重建辅助的病例系列，其中描述了注射到冈田空间中作为硬膜外镇痛失败的可能原因或在常用的空气阻力丧失后注射(LORA) 技术（Reina 等人，  2021 年）。我们当时提出硬膜外阻滞或注射失败的一个可能原因可能是硬膜外针（或导管）放置在冈田间隙内，而不是进入硬膜外间隙（Lehman 等人，  2015 年；Murthy 等人） al.，  2011 年；冈田，  1981 年；Reina 等人，  2021 年）。

这个空间最初被描述在颈椎（Okada，  1981），但后来也被描述在黄韧带和椎板之间的腰部区域（Iwanaga; et al.,  2020 ; Reina et al.,  2016）。该空间导致 LORA 后用于硬膜外穿刺术确认硬膜外穿刺针放置的造影剂在相邻的同侧和对侧小关节、相邻神经孔、椎旁肌肉组织和棘突外膜囊之间扩散（Lehman 等人，  2015 年；Murthy等人，  2011 年；冈田，  1981 年；雷纳等人，  2021 年）。该空间是硬膜后腔，不与硬膜外腔连通（Lehman 等，  2015；Murthy 等，  2011；Okada，  1981；Reina 等，  2021）。

我们现在介绍这种现象的另一个案例。一名 64 岁女性腰痛，双侧神经根性疼痛主要向左臀部和后腿放射，经 MRI 诊断为双侧 L4-L5 神经根病（L>R）和保守治疗无效的椎管狭窄。该患者被安排在透视引导下以俯卧位进行左侧旁正中 L4-L5 层间硬膜外类固醇注射。用 1% 利多卡因局部浸润皮肤后，通过左侧旁正中入路引入 18 号 Tuohy 硬膜外针。LORA 最初用于识别硬膜外腔。经 LORA 阳性确认明显成功放置后，在注射类固醇之前，我们使用前后位透视和侧位透视并尝试硬膜外造影，通过针头注射 2 毫升剂量的 1 毫升碘克沙醇（270 毫克/毫升 Visipaque，GE Healthcare Biosciences，SAU）来确认硬膜外放置。透视显示除了 L4 – L5 小关节外，造影剂意外扩散到棘突间区域。这种价差是 Okada 空间的典型特征（Lehman 等人， 2015 年；Murthy 等人，  2011 年；冈田，  1981 年；雷纳等人，  2021 年）；然而，在该患者中也发现了一个不太常见的特征，即颅内造影剂呈“V”形扩散（图 1a）。侧位透视显示硬膜后间隙没有硬膜外扩散（图 1b）。

之后，我们再次使用了另一名类似尺寸的健康患者的腰椎 MRI 的 3D 重建（Reina 等人，  2021 年；图 2），并以类似的放大倍数叠加透视图像以证明我们患者的扩散。这次重建展示了冈田空间的位置及其“V”形。它还表明黄韧带延伸到关节面之外（Iwanaga 等人，  2020 年；Reina 等人，  2016 年）并在椎板的下半部分重叠（图 2）。

这些发现与我们之前详细描述的发现一致（Reina 等人，2021 年），并进一步支持了其他研究中的发现（Lehman 等人，2015 年；Murthy 等人，  2011 年；Okada，  1981 年；Reina 等人 ，  2021 年）  2016 年）。该报告进一步增强了我们对诸如硬膜外阻滞失败等意外事件的理解。