Discal cysts have been reported as intraspinal extradural cysts connected with corresponding intervertebral discs ^[1]. While these pathologies are rare as a cause of low back pain or radiculopathy, the exact pathology remains unclear [2-5]. The hemilaminectomy and microscopic resection were good result as surgical procedure, but now, the resection under the microendoscope has also illustrated an effectivity, which is alternative to conventional open surgery for cystic lesions in the lumbar spine [6,7]. Now, we experienced a much larger discal cyst which caused radiculopathy. It seemed to be difficult to resect all of them under the microendoscope safety. Therefore, we developed a novel strategy to treat under microendoscope without neurological deficit and any additional fusion surgery.

The patient was a 21-year-old man. He has been one of the top swimmers in Japan. He had experienced pain in the right lower limb for at least a month and was diagnosed with radiculopathy of the right S1 nerve root. Magnetic resonance image (MRI) showed that mild disc degeneration and cyst at L5/S1. The cyst was hypointense on T1-weighted images, hyperintense on T2-weighted images, and the surrounding rim and the enhancement of contents of the cyst on gadolinium MRI (Fig. 1). The cyst measured 12.0 mm on the sagittal view, accounted for 71.1% of the sagittal diameter of the spinal canal. He underwent hemi-flavectomy and the resection of the cyst under the microendoscope because he would like to minimize the surgical invasion and return to the competition at early stage. During surgery, we found that there was not enough space in the epidural to remove the cyst safety without the laminectomy. The right S1 nerve root was strongly pushed to the dorsal side, adhered, and stretched by the cyst (Fig. 2a), which was filled with the pale yellow-colored serious component. We thought that it has several risks of the nerve root injury due to the surgical procedure, for example, excessive retraction of the nerve root or dura and removal of the adhesion. Hence, we have tried to drain the context of the cyst and decrease the volume of the cyst to make the enough epidural space to perform the surgical procedure safety. The context of the cyst was drained through a needle puncture (Fig. 2b, c, f) whereupon the cyst shrank. We dissected the adhesion between the nerve root and the wall, followed by the resection safety, which procedure made the nerve root loosen (Fig. 2d). The cyst was connected by the corresponding intervertebral disc (Fig. 2e) but did not contain any disc tissues. Clinical follow-up of the patient after 24 months showed no symptoms and signs with satisfactory results and he has returned to the competition.

We have experienced a case of the large discal cyst, which occupied 71.1% of the epidural space on sagittal view. We have tried to the resect the cyst safety without excessive laminectomy. The combination of the microendoscope and drainage by the needle puncture enabled us to resect the cyst safety and preserve the bony construct. The etiology and pathogenesis of an intervertebral discal cyst remain unknown. Two hypotheses for the formation of these cysts have been suggested. Past report ^[8] proposed that an epidural hematoma is initially formed from hemorrhage of the epidural venous plexus, resulting from either a disc herniation or an underlying disc injury. The discal cyst appeared as a result of an unspecified impairment in hematoma resorption, but pathology could not explain fully how epidural vasculature forms the connection between intervertebral disc and cyst form [3, 4]. The others hypothesize that discal cysts result from focal degeneration of an intervertebral disc producing a herniated disc with subsequent spilling of fluid, which incites an inflammatory response leading to reactive pseudomembrane formation and the development of the disc cyst ^[5]. In our case, we recognized the connection between the cyst and corresponding intervertebral disc and the cyst wall consisted of the fibrous tissues, which might support the second hypothesis. Several reports described that conservative therapies were managed limited to the cases without the neurologic deficit and surgical treatment was considered when these conservative therapies were failed [2, 3]. Most report showed that hemilaminectomy and microscopic resection were good result [2, 3]. Nowadays, several papers suggested that microendoscopic resection could be an effective alternative to conventional open surgery for cystic lesions in the lumbar spine [6, 7]. However, there are no reports about the size of the discal cyst and the surgical selection based on the size. It was seemed that our case is larger than past and difficult to resect under the microendoscope. The operative indications for discal cysts were likely to be similar to those of lumbar disc herniation [2, 9]. The definition of giant lumbar disc herniation varies across the literature, but herniation affecting 50% of the sagittal diameter of the spinal canal is widely accepted ^[10]. In our case, the size of the cyst was 12.0 mm, and 71.1% of the sagittal diameter, which implied that our case was applied as a giant discal cyst. In general, the surgical treatment of giant lumbar disc herniation is the removal of the compressive lesion through an interlaminar approach or laminectomy ^[11]. Narrow exposition needs excessive retract during lumbar discectomy and may cause permanent paralysis ^[12]. Although the laminectomy is more useful for giant fragments to perform gentle retraction and discectomy [13, 14], it can induce post-operative instability resulting in the need for additional fusion surgery. Microendoscopic laminotomy was originally developed to preserve posterior elements and was achieved by the medial trumpet facetectomy. This procedure could secure a working space, which avoided post-operative instability even in patients with pre-operative degenerative spondylolisthesis ^[15]. However, the adaptation under the microendoscopic surgery for the larger size of the discal cyst seemed to be limited. In this case, we have tried several steps to complete the surgical procedure safety. First, we punctured the cyst to make it smaller and easier to secure enough working space to preserve the articular surface of the facet joint and posterior elements to endure the competition load of the top level. Second, we ensured the nerve root safety by carefully dissecting the adhesions, which enabled to resect the cyst without any injury for nerve root. We believe that this method is adaptable for the several larger discal cysts which have been resected by the open technique so far, but it seemed to be limited to the discal cyst at the lower lumbar lesion. These are larger space than upper lumbar, so we can easily ensure the working space by using these techniques. However, the common site of the discal cyst was L4/5, followed by the L5/S1, so we believe that the combination of the microendoscope and drainage enabled us to secure enough working space, prevent nerve root injury, and allowed the patient to return to competitive swimming at a high level.

We experienced a case of the giant discal cyst who get the good result using the combination of the drainage of the liquid context and resection of the wall of the cyst under the microendoscope. This strategy has ability to secure the enough working space, prevent the nerve root injury, minimize the surgical invasion, and can expand the surgical indication for the larger cystic lesion, which have been performed by the open surgery so far.

We experienced a case of the giant discal cyst who get the good result by the combination of the drainage of the liquid context and resection of the wall of the cyst under the microendoscope. This method minimized the surgical invasion safety and allowed patients to return the social life.