Percutaneous endoscopic spine surgery has been evolving rapidly these years with the development of endoscopic philosophy, technology, and equipment (1, 2). Consequently, the indications of endoscopic spine surgery are ever expanding, from the initial lumbar intervertebral disk disease to other types of pathologies located in the whole spinal column (3, 4). The obvious advantages of working-channel endoscopic spinal surgery include the reduction of the surgical corridor, avoiding soft tissue and muscular stripping, minimizing bony resection, as well as obtaining excellent visualization (1, 2, 4).

Since Lee et al. first reported a case of spinal epidural lipomatosis (SEL) in 1975 (5), more and more studies on this disease have been retrieved in the literature (6–12). SEL is defined as an abnormal accumulation of adipose tissue in the epidural space within the spinal canal resulting in compression to the spinal cord and/or cauda equina. Clinical manifestations of SEL in lumbar include low back pain, lower extremity weakness, lower extremity numbness, and neurogenic intermittent claudication, which are identical to that of degenerative lumbar stenosis. The treatment measures of SEL include conservative therapy and surgical decompression. Although there is still no clear consensus on the treatment of SEL, the approach to patients with SEL should initially be conservative involving weight reduction and endocrine therapy (13, 14). Surgery interventions should be considered when conservative treatments fail and clinical symptoms deteriorate rapidly (14). As for the surgical methods, extensive laminectomy and excision of the adipose tissue are the most commonly used options (15). So far, there has been no report to treat lumbar lipomatosis using the percutaneous uniportal full-endoscopic technique. In this report, we describe a case of lumbar epidural lipomatosis, which was successfully treated with percutaneous uniportal full-endoscopic surgery (Figure 1). The objective of this article is to validate the feasibility of the approach and describe several operative pearls based on our experience.

The study was conducted in accordance with the guidelines of the 1964 Declaration of Helsinki and was approved by the ethics committee of Zhongshan Hospital, Fudan University (Institutional Review Board approval number 2021-042), as well as Minhang Hospital, Fudan University (Institutional Review Board approval number 2021-037-01X). The patient signed informed consent forms for the surgery procedure.

After the procedure, his leg pain decreased and his walking capacity improved. One day postoperatively, the pain decreased sufficiently with 2/10 on VAS. There were no surgery-related complications, such as cerebrospinal fluid leakage, incision infection, etc. During the follow-up, 3- and 12-month postoperatively, the VAS scores were 2/10 and 1/10 points. He was able to walk 500 m without obvious numbness and pain in his lower limbs at the last follow-up. Postoperative MRI and CT scans indicated the successful decompression of the neural structure at the L4–5 and L5–S1 levels (Figure 2).

Under physiologic conditions, the epidural fat tissue in the spine canna is thought to serve as a cushion for nerve structures. However, the excessive accumulation of fat tissue, which is referred to as SEL, can cause compression damage to the spinal cord and cauda equina. As a result, patients with SEL often develop neurological symptoms, such as sensory and motor disturbance, claudication, lower back pain, and radiculopathy (14). The pathogenesis of SEL may include the following disease states: endogenous steroid hormonal disease, long periods of exogenous steroid use, surgery-induced, obesity, and idiopathic disease (18, 19). Malone et al. reported a rate of 6.26% for symptomatic SEL in their population, with an incidence rate of 2.5% per year (9). Thus, it can be seen that SEL seems to be more than people originally thought. The patient we presented in this report had difficulty in walking less than 50 m, leg weakness, and sensory loss in L4, L5, and S1 distribution. He had no history of endocrine diseases and steroid use. Therefore, he was diagnosed with idiopathic SEL.

For this idiopathic SEL patient, with clinical symptoms have been deteriorating progressively, surgical treatment should be considered (14). Although there is no consensus about surgical methods, laminectomy with excision of the hypertrophic fatty tissues is considered the mainstay (6, 12, 14, 20, 21). However, the traditional laminectomy and microsurgery of excision of the hypertrophic fatty tissue need a wide incision, significant paravertebral muscle stripped, and bone dissection for adequate visualization, which can result in postoperative pain and slow recovery (22). During the past three decades, percutaneous endoscopic spine surgery has evolved dramatically with the development of endoscopic equipment and techniques. As a result, the indications of endoscopic spine surgery are ever expanding, from the initial lumbar disc disease to other types of pathologies located in the whole spine column (4). The obvious advantages of percutaneous working-channel endoscopic spine surgery are as follows: reduction of the surgical corridor, avoiding muscular dissection, reduction of bony resection to prevent iatrogenic instability, close observation to obtain excellent visualization, and reduction of bleeding under water perfusion pressure (4). In the operation of this case, we used Delta endoscopic surgical system with a larger manipulation channel (diameter of 1 cm) than the previous traditional endoscopy (Figure 3). This character facilitated us to use larger sizes of endoscopic Kerrison punches in the procedure, in which the size of the rongeur bite part can be up to 5 mm. Hence, the ligamentum flavum and its enthesis are convenient to be removed (17). Owing to this, the efficiency of surgery was greatly enhanced. The operation duration was within 2 h for two segments (L4–5, L5–S1) in this case. Kang et al. reported that the biportal endoscopic technique had been used to achieve successful neural decompression for symptomatic SEL (22). It is indeed a minimally invasive technique possessing the traits of percutaneous spinal endoscopy, such as close observation and clear field of vision under water irrigation. Compared with this technique, our uniportal technique had less damage to soft tissue because we neither need two skin incisions and two ports nor need to remove part of the muscle and muscle fascia to make room for the procedure and continuous irrigation. In this case, our experience has proved that the full endoscopic uniportal technique is fully suitable for decompression treatment for SEL.

In addition, compared with microscopic channel surgery, our endoscopic surgery has great strengths to manipulate the opposite side lesion. The outer working cannula can be inserted toward the contralateral side using sub-spinous process space. The camera’s eye with 15 view angles can be put closer to the opposite side lesion, providing high-definition images on a video monitor for the operator (4, 22). Therefore, it makes the removal of excessive adipose tissue safer and easier, facilitating the reduction of the possibility of dura tear and neural damage.

Thanks to the high-definition vision of endoscopy, we had an interesting discovery during the operation. We found that there were many bands among the dura, ligamentum flavum, and nerve roots in the epidural space (Figures 6E,F). These bands separated the epidural space into multitudinous small spaces, and the hyperplastic adipose tissue was bound in these small spaces. It can explain why although adipose tissue is soft, it causes compression of the nerve roots and dura sac (Figure 7). In this case, the thecal sac has a striking stellate appearance on lumbar axial imaging. Kuhn et al. named this configuration as the “Y-sign” which is characteristic of lumbar SEL (23). The stretch action of these bands may interpret the “Y-sign.” During the operation, cutting off these bands to eliminate the stretch action is very important to release the compression of the sac and nerve roots. Cutting off these bands also makes it easier to remove fatty tissues and reduces bleeding and dura involvement. Frank reported an endoscopic suction technique for the treatment of idiopathic epidural lipomatosis (24). In his article, he noted that sharp microsurgical techniques should be used in the area that the fat was well vascularized and adherent to the dura. Otherwise, suction of adipose tissue is insufficient to achieve success. Our experience verified that in current uniportal full-endoscopy technology, all the procedures can be accomplished in a single channel.

The case with SEL was successfully treated with a percutaneous full-endoscopic uniportal surgery, which has the advantages of excellent presentation of anatomical structures, expanded field of vision, less surgical-related trauma, and bleeding. The key point of the procedure is to release and cut off the bands which divide the epidural space into small rooms filled with excess adipose tissue.