Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon.
Department of Anatomy, University of New England, College of Osteopathic Medicine, Biddeford, Maine.
Pain Med. 2020 Mar 1;21(3):570-575. doi: 10.1093/pm/pnz298.
The S1 dorsal foramen is the route for 30% of lumbar transforaminal epidural injections; it is therefore important to identify structures impeding S1 foraminal access. The study objective was to characterize the imaging findings, prevalence, and anatomic origin of synovial cysts presenting within the S1 neural foramen.
A case series (N = 14) established imaging characteristics of S1 synovial cysts. Imaging studies of 400 patients undergoing epidural injections were reviewed for lesions compromising S1 foraminal access. Cadaveric dissections defined the relationship of the inferior recess of the L5-S1 facet to the S1 dorsal foramen.
Elderly patients (mean age = 76) exhibited S1 synovial cysts. Synovial cysts were typically 1-2 cm in diameter, hyperintense on sagittal T2 weighted magnetic resonance images (MRIs), fluid-density on computed tomography, and dorsal to the S1 spinal nerve. Sixty percent of cysts exhibited complex MRI signal characteristics (thick wall, internal structure). Tarlov cysts, in contrast, were larger, lobular, and exhibited pure fluid intensity. Lesions impeded access to the S1 dorsal foramina in 5% of reviewed imaging studies (16 Tarlov cysts, three synovial cysts, one conjoint S1-S2 nerve root). The multifidus muscle was interposed between the L5-S1 facet inferior recess and the S1 dorsal foramen on dissection specimens; severe atrophy of the ipsilateral multifidus was noted on imaging in 17/18 synovial cysts.
The S1 neural foramina should be inspected on sagittal MRI, when available, for confounding lesions before performing S1 epidural injections. Tarlov cysts are more common than synovial cysts; the latter are seen in elderly patients with severe multifidus atrophy.
S1 背侧孔是 30%腰椎经椎间孔硬膜外注射的途径；因此，识别妨碍 S1 孔进入的结构非常重要。本研究的目的是描述 S1 神经孔内滑膜囊肿的影像学表现、发生率和解剖学来源。
通过病例系列（N=14）确定 S1 滑膜囊肿的影像学特征。对 400 例接受硬膜外注射的患者的影像学研究进行了回顾，以确定是否有病变影响 S1 孔的进入。尸体解剖确定了 L5-S1 关节突下隐窝与 S1 背侧孔的关系。
老年患者（平均年龄=76 岁）出现 S1 滑膜囊肿。滑膜囊肿通常直径为 1-2cm，矢状面 T2 加权磁共振成像（MRI）上呈高信号，CT 上呈液性密度，位于 S1 脊神经背侧。60%的囊肿表现出复杂的 MRI 信号特征（厚壁、内部结构）。相比之下，Tarlov 囊肿更大、呈分叶状，表现出纯液性强度。在 5%的回顾性影像学研究中（16 个 Tarlov 囊肿、3 个滑膜囊肿、1 个 S1-S2 神经根）发现病变妨碍了 S1 背侧孔的进入。在解剖标本中，多裂肌位于 L5-S1 关节突下隐窝和 S1 背侧孔之间；在 17/18 个滑膜囊肿的影像学上均观察到同侧多裂肌严重萎缩。
在进行 S1 硬膜外注射之前，如果有矢状面 MRI，应检查 S1 神经孔，以寻找干扰性病变。Tarlov 囊肿比滑膜囊肿更常见；后者见于老年患者，伴有严重的多裂肌萎缩。
