Synovial cysts, also referred to as “juxta-facet cysts,” are dilations of synovial sheaths that originate in the zygapophyseal joint capsule of the lumbar spine. The exact cause of facet cysts is not fully understood, but it is believed to be associated with joint destabilization due to degenerative or traumatic changes in the ligamentum flavum and the facet joints. Facet cysts were initially reported by Vosschulte and Börger in 1950 [1–3]. The prevalence in radiological studies ranges from 0.5% to 1.1% in older studies [2]. However, with the improved diagnostic possibilities of MRI, the number of identified cysts has increased to 5.8% in recent decades [4]. These cysts are mostly found in the lumbar spine, particularly at the L4–L5 level, and can cause symptoms such as neurogenic claudication, radiculopathy, or even cauda equina syndrome. This cyst can be classified as either a true synovial cyst or a pseudocyst [5]. A true synovial cyst is characterized by a visible connection between the joint and the cyst on the MRI, while a pseudocyst, like a ganglion, does not show this relationship (Fig. 8.1) [6, 7].