The lumbar spinal canal fat filling the epidural space is a crucial component of the lumbar spinal canal that provides the dural sac with sufficient buffer space. However, excessive deposition of lumbar spinal canal fat compresses the lumbar dural sac and nerve root, causing nerve compression symptoms such as lumbar epidural lipomatosis (LEL) (1). The LEL can be idiopathic or secondary to Cushing's syndrome, obesity, or endocrine diseases, all of which are linked to excessive visceral fat accumulation (2). LEL is a rare disease in clinical practice; however, approximately 6% of symptomatic cases of lumbar spinal stenosis are associated with LEL (2, 3). Clinical manifestations include nerve root and cauda equina compression injury symptoms, such as neurogenic claudication, loss of sensation, lower limb weakness, cauda equina syndrome, and so on (3, 4). If symptoms are mild, conservative treatment should be administered. If the symptoms are severe combined with nerve or cauda equina compression symptoms, repeated conservative treatment is ineffective, or if the symptoms are progressively aggravated, surgical decompression is required (2, 3).

Recent studies have indicated that the diagnosis rate of LEF is only 8%, and it is easily missed or misdiagnosed in clinical practice, which may delay the optimal treatment time and affect a patient's quality of life (4, 5). Research on the diagnosis and treatment of LEF has increased in recent years, and numerous effective treatment methods have been proposed (6). It has been reported that 97% of the patients with LEF who undergo surgical treatment have improved symptoms (7). Currently, the surgical methods for LEF mainly include laminectomy, fat tissue removal, single-channel endoscopic-guided fat aspiration, spinal canal decompression, and intervertebral fusion decompression, all of which can achieve better clinical efficacy (8). A narrative review by Kim et al. (9) observed that most patients with SEL with acute symptoms who failed conservative treatment must undergo laminectomy and epidural fat removal to achieve good clinical efficacy. Bayerl et al. (10) have demonstrated that microscopic discectomy and decompression for LEF can result in favorable clinical outcomes. Traditional laminectomy and surgery to remove the excessive accumulation of adipose tissue requires wide incisions and extensive paravertebral muscle dissection to obtain a sufficient surgical field. However, this may lead to postoperative pain and a slow recovery (9, 10). Compared with open decompression surgery, minimally invasive endoscopic surgery is preferred by surgeons because of the shorter operation time, less intraoperative bleeding, fewer postoperative complications, and shorter postoperative recovery time (11). Studies have shown that single-channel spinal endoscopy exhibits optimal short-term clinical efficacy for treating LEF; however, it has a small operation space, narrow decompression range, difficult operation, and steep learning curve. These deficiencies limit the clinical application of single-channel endoscopy for LEF treatment (12, 13). Bilateral decompression is frequently required in patients with LEF complicated by severe lumbar spinal stenosis. However, the steep learning curve of single-channel spinal endoscopy and limited operating equipment consisting of a single rigid working cannula makes bilateral decompression difficult and high-risk (14). With the development of spinal endoscopic techniques, unilateral biportal endoscopy has been employed to treat severe lumbar spinal stenosis. Unilateral biportal endoscopy–unilateral laminectomy bilateral decompression (UBE-ULBD) is an effective, safe, and sufficient decompression surgery that can achieve excellent clinical efficacy for treating severe lumbar spinal stenosis (15). However, to date, no prospective study has compared the therapeutic effectiveness of UBE-ULBD and open lumbar decompression (OLD) for treating LEL, and the surgical approach remains controversial. This research aimed to investigate the clinical efficacy of UBE-ULBD for treating LEL and compare it with that of traditional OLD.

The LEL is a normal intraspinal fat space-occupying lesion caused by pathological hyperproliferation and accumulation of epidural fat (17). Because of stimulation or compression of the adjacent nerve root by abnormal hyperplasia of adipose tissue, patients often have a series of clinical symptoms, including lumbar pain, numbness, pain, and weakness of one or both lower limbs (2, 3, 17). Mild symptoms can be alleviated by conservative treatment; however, some patients often require surgical treatment when conservative treatment is ineffective. Traditional OLD is considered an effective surgical method for treating LEL; however, this procedure has defects (18). The UBE-ULBD aims to reduce these disadvantages because it can achieve complete resection of the diseased tissue in the spinal canal and full decompression of the spinal canal, with less tissue damage (15, 19). Our preliminary clinical results of UBE-ULBD and OLD for treating LEL disclosed that (1) after one year of follow-up, UBE-ULBD and OLD can achieve the same short-term clinical efficacy for treating LEL. (2) Compared with OLD, UBE-ULBD had lower postoperative lumbar pain NRS and ODI scores at 1 week of follow-up. (3) Compared with OLD, UBE-ULBD had less blood loss, shorter hospital stays, and less paravertebral muscle injury, which is beneficial to the postoperative rehabilitation of patients. (4) In our preliminary study, none of the patients had complications linked to this technique. Both groups achieved clinical improvement at the same time, and the overall benefit time was 1 year. The satisfaction rates of the patients in the UBE-ULBD and OLD groups were 80% and 77.8%, respectively. The two groups achieved considerable short-term clinical efficacy.

As stated previously, traditional OLD has consistently been the standard lumbar decompression technique and has yielded good clinical outcomes (20). Interestingly, in the presence of LEL with lumbar spinal stenosis, compared with other open surgeries, OLD can remove the hyperplasia and abnormal adipose tissue that compresses the dural sac and nerve root under direct vision and preserves the normal anatomy of the spine to the greatest extent (21, 22). However, the OLD approach requires extensive dissection of the paravertebral muscle tissue to expose the surgical field and greater force to continuously pull the paravertebral muscle, causing ischemic injury of the paravertebral muscle and the formation of surrounding scars (23). Increasing evidence suggests that muscle atrophy after paraspinal muscle injury accelerates spinal degeneration, leading to decreased spinal stability, postoperative pain, and dysfunction (22–24). Patients with LEL are often obese and have a thick fat layer on their waists. Simultaneously, OLD surgery can achieve a much wider range of decompression than endoscopic surgery; however, the surgical wound is larger, and the risks of incision fat liquefaction, delayed wound healing, and infection can easily occur after surgery (21, 22). Our results revealed that EBL, hospital stay duration, postoperative creatine kinase level, postoperative lumbar muscle atrophy, and postoperative incision infection rate were significantly higher in the OLD group than in the UBE-ULBD group. This demonstrates that UBE-ULBD for treating LEL can reduce the disadvantages of OLD technology and postoperative risks while achieving the same clinical efficacy as OLD technology.

The UBE-ULBD technology has several advantages over the OLD technology for the surgical treatment of LEL. First, UBE-ULBD allows the surgeon to reach the surgical target area quickly and provides a well-illuminated surgical field of view and appropriate magnification. The surgery was completed under full visualization. Second, the technique avoids unnecessary dissection of the surrounding muscle tissue and preserves the facet joints and joint capsule, which provides advantages for the rapid recovery of patients, such as reducing postoperative pain and early recovery of daily activities. Our results indicated that the EBL, hospital stay duration, postoperative creatine kinase level, postoperative lowbar muscle atrophy, and postoperative incision infection rate were significantly lower in the UBE-ULBD group than in the OLD group. The short-term (1 week after surgery) lower lumbar pain NRS and ODI scores in the UBE-ULBD group were substantially better than those in the OLD group. Third, the spinal canal of LEL is filled with abnormal hyperplasia of adipose tissue, accompanied mainly by bilateral nerve root compression, and may even be accompanied by disc herniation and bone stenosis of the nerve root canal. UBE-ULBD can visually remove abnormal adipose tissue in the spinal canal and completely decompress bilateral nerve roots, making it wider and safer than the OLD technology. Fourth, UBE-ULBD has the advantages of a shorter learning curve, wider decompression range, and higher safety than uniaxial transforaminal endoscopy for LEL. Our results disclosed that the cross-sectional area of the dural sac in the two groups was significantly improved compared to that before the operation, and there was no significant difference in the improvement percentage of the dural sac CSA between the two groups. In many cases, LEL combined with bilateral nerve root canal stenosis is difficult in traditional hemilaminectomy decompression.

Conversely, total laminectomy decompression aggravates iatrogenic injury to the posterior structure of the spine (25). To the best of our knowledge, no prospective study has compared the advantages, disadvantages, and clinical efficacy of UBE-ULBD and OLD for treating patients with LEL. In this study, we emphasize that the UBE-ULBD technique is safe and successful in treating patients with LEL, and significant clinical improvement in patients with LEL persists for at least 1 year. We believe that this is the first prospective comparison of UBE-ULBD and OLD for treating patients with LEL.

The characteristics of the LEL patient cohort in this investigation were comparable to those reported in other studies. The LEL mostly occurs in the lumbosacral segment, and 32% of the patients have glucocorticoid-related LEL. More than 50% of the patients had metabolic syndrome, and LEL patients were mostly male. Overall, these data are consistent with previous research results (16, 18). Visceral fat distribution may be associated with epidural fat accumulation in the spinal canal. In this research, UBE-ULBD or OLD surgery was performed according to the individual decisions of the spine surgeon and patient's wishes. Since the LEL lesion is not limited to the level of the intervertebral disc but is located at the entire height of the vertebral body, hemilaminectomy may be necessary in some multisegmental cases. Unilateral hemilaminectomy and bilateral spinal canal decompression were performed in both groups. This technique allows decompression of the dural sac along the entire path and reduces perioperative bleeding and tissue damage.

One limitation of this study was the small number of recruited patients, which was associated with a low prevalence of symptomatic LEL. Moreover, the outcomes of patients who received the best drug treatment for LEL have not been investigated. Consequently, there is a comparison between surgical and conservative treatments of symptomatic LEL, and this comparison should be conducted in future studies. Finally, this was a single-center prospective observational study. The sample size was relatively small, and the follow-up time was short. These results require further confirmation in prospective multicenter studies.

Among the patients who underwent spinal MRI, the prevalence of spinal epidural lipomatosis was 2.5% in those with and without spinal-related symptoms (26). The prevalence of symptomatic spinal stenosis is approximately 6% (27). Correspondingly, spine-related symptoms, such as low lumbar pain and sciatica caused by LEL, are easily missed or misdiagnosed as lumbar degenerative diseases (28). Therefore, it is crucial to evaluate the application of standardized and risk-free treatment alternatives. This study demonstrated that UBE-ULBD decompression for LEL patients is a surgical method with less trauma, safety, low complication rate, and long clinical benefit time.

In the current study, UBE-ULBD achieved good surgical results after decompression without complications in patients with LEL. To treat LEL patients with bilateral nerve root stenosis, UBE-ULBD overcomes the limitations associated with intervertebral foramen and microscope channel technology. Compared with open surgery, it achieved a more consistent clinical effect, less trauma to the paravertebral muscles, faster clinical recovery, and a reduced incidence of paravertebral muscle atrophy and late low lumbar pain. Accurate diagnosis based on MRI and clinical symptoms is necessary, and thorough decompression based on analysis of the pathological anatomy of the spinal and nerve root canals is essential. The UBE technology may replace traditional surgery as the standard procedure for treating LEL.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

The studies involving humans were approved by Ethics Committee of Mianyang Third People's Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

BT: Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Supervision, Validation, Writing—original draft, Writing—review & editing. Y-hZ: Data curation, Formal analysis, Project administration, Resources, Writing—original draft. CL: Conceptualization, Data curation, Writing—original draft. J-yO: Data curation, Formal analysis, Software, Writing—review & editing. Y-bW: Data curation, Software, Writing—original draft. Z-hS: Writing—review & editing. Q-YY: Investigation, Supervision, Writing—review & editing.