Biportal Endoscopic Spine Surgery for Symptomatic Postoperative Discal Pseudocyst Following Percutaneous Endoscopic Interlaminar Discectomy: A Case Report and Literature Review

1. Pathogenesis

PDP is an extremely rare complication following lumbar discectomy. The pathogenesis of this condition is not well understood and has not been thoroughly described. PDP was first reported by Young et al. [6] in 2009, who described 2 cases of PDP following microdiscectomy for LDH. The author originated the term “postoperative annular pseudocyst” to describe this condition, suggesting that the pseudocyst formation might result from the continued migration of miniscule disc fragments after surgery. These fragments may trigger a localized inflammatory response, leading to the development of a “pseudo-capsule” that encapsulates these disc fragments. Kono et al. [15] supported this hypothesis, reporting 2 cases of operatively confirmed discal cysts (DCs) and proposing that the pathogenesis of these cysts is similar to that of meniscal cysts in the knees and synovial cysts in the facet joints. They hypothesized that DC result from degeneration of the intervertebral disc, leading to herniation and the subsequent leakage of fluid from the herniated disc material. This extruded fluid triggers an inflammatory response, which leads to the formation of a reactive “pseudo-membrane” and the development of a DC. Similarly, Chiba's earlier understanding of the formation of spontaneous intraspinal cysts in the lumbar spine involves 3 factors: the resorption of a preexisting herniation, hematoma associated with disc prolapse, and mucoid degeneration, which is believed to be the cause of ganglion cysts in the peri-discal tissues [16].

Chung et al. [10] proposed that PDP formation is linked to axial loading on a mildly degenerated nucleus pulposus. This theory aligns with Aydin’s findings [17], which indicate that spontaneous DC occurs at a mean age of 33.5 years, significantly younger than typical cases of degenerative LDH, and is more common in physically active males. The authors suggest that, similar to spontaneous DC formation, in PDP, physical activity pumps fluid through an annular cleft in the degenerated nucleus, combine with a "pseudo-membrane" contributing to pseudocyst development.

In summary, there are 3 main hypotheses presented in the literature regarding the formation of PDP: a response to an epidural hematoma; pseudo-membrane formation following a local annulus fibrosus tear and disc degeneration; and an inflammatory response to the protrusion of tiny nucleus pulposus [7,10,15-17]. During revision surgery, we observed characteristics of PDP in our case that are consistent with these hypotheses. First, upon gross examination, the cyst appeared dark red, resembling the color of chronic hematoma, and was enclosed in a thick membranous structure. When we used a penfield to rupture the cyst and observed under endoscopic magnification, we noted that the cyst contained a mixture of materials, not merely fluid. This PDP was observed around the fourth week postoperatively, and MRI images showed that the cyst’s location was closely related to the disc space. Moreover, we believe that the PEID procedure, performed in a continuous water environment with pressure maintained around 30 mmHg, may have allowed water from the endoscopic system to infiltrate and remain within the already degenerated nucleus pulposus. Fibrin fibers formed from blood at the surgical site likely contributed to the formation of a membranous structure, preventing the escape and absorption of this fluid. These factors, combined with the mechanisms mentioned above, contribute to the formation of a thick-walled cystic structure (Figure 7). These hypotheses were reinforced when we performed a pathological examination of the removed cyst. The results revealed that the cyst wall had a heterogeneous structure, consisting of various components such as fibrous tissue, blood degradation products, and chronic inflammatory cells (Figure 8). This was similarly described in the report of Kang and Park [7].

Figure 7.

Illustration of the hypothesis for postoperative discal pseudocyst (PDP) formation after percutaneous endoscopic interlaminar discectomy. (A) Water enters the surgical field through the endoscope with medium pressure along the vertical axis, a small amount of this fluid may infiltrate the already degenerated disc nucleus. (B) A fibrin sheath formed by the inflammatory response and hematoma contributes to preventing the escape of this small amount of fluid. (C) Axial loading forces drive the retained fluid out of the disc nucleus, but it is blocked by the fibrin sheath, resulting in the formation of PDP.

Figure 8.

Pathological findings. The tissue exhibits a cystic structure with a fibrous wall accompanied by cholesterol crystals, old hemorrhage, and calcification. (A) Gross examination (original magnification ×40) shows three tissue samples, each measuring approximately 0.3–0.5 cm in diameter. (B) Microscopic examination (hematoxylin and eosin staining, original magnification ×100) demonstrates a cystic structure with a fibrous wall containing cholesterol crystals, old hemorrhage, and calcification. The cyst wall is infiltrated by chronic inflammatory cells and hemosiderin-laden giant cells.

2. Clinical Features

We summarized the literature of PDP in Table 1. Data were sourced from PubMed and Cochrane using keywords in the title and abstract, including "postoperative discal pseudocyst," "postoperative annular pseudocyst," "post discectomy pseudocyst," "postoperative pseudocyst," "pseudocyst," and "lumbar." The diagram showing the screening and selection of papers analyzed in the systematic literature review is presented as Figure 9. After screening, we identified 16 studies published in English up to 2023. The data show that regardless of the initial surgical technique—whether traditional open discectomy, microscopic, PEID, or percutaneous endoscopic transforaminal discectomy (PETD)—PDP formation is closely related to the location of the previous disc herniation. PDP may be asymptomatic and only detected through postoperative MRI, or it may cause symptoms ranging from mild to severe nerve root compression. Symptoms typically reappear within a few weeks postoperation. PDP occurs predominantly in males (84.7%) with an average age of 34.2 years.

Table 1.

Summary of the studies of postoperative discal pseudocyst found in a PubMed search

Figure 9.

Diagram showing the screening and selection of papers in the systematic literature review.

Chung's report on 12 PDP cases shows that after discectomy using microscopic or endoscopic, the mean time to relapsing radiculopathy was 23.3 days (range, 9–38 days) with an average VAS score of 6.8±1.3. PDP were detected on MRI at an average of 31.2 days (range, 14–60 days) after the initial surgery [10].

Manabe et al. [18] reported a case of a 21-year-old male requiring revision surgery for a PDP that developed 6 weeks after an endoscopic transforaminal L4–5 discectomy. Kang and Park [7] noted that PDP after endoscopic discectomy were reported at a 1% incidence in a study of 1,503 cases, with a mean postoperative interval of 53.7 days. The interlaminar approach showed a higher risk compared to the transforaminal approach, with 6 PDP occurring at L4–5 via transforaminal and 9 at L5–S1 via interlaminar out of 15 cases. The author did not establish whether differences between irrigation fluid and cystic fluid in these approaches contribute to this variation.

Among the 59 cases reported in the literature (Table 1), the highest incidence of PDP occurred after uniportal endoscopic lumbar discectomy (UELD), including both PETD and PEID, with 41 cases (69.5%) (Table 2). We did not find any report of PDP following biportal endoscopic lumbar discectomy (BELD). We believe that, although BELD is performed in a similar medium-pressure water environment as UELD, the distinct inflow and outflow pathways might contribute to a reduced residual water in the disc space during surgery. This could potentially explain the lower incidence of PDP observed. Figure 7 illustrates a hypothesis regarding the water flow during PEID surgery, which results in water retention in the degenerated nucleus pulposus and may be a contributing factor to the development of PDP.

Table 2.

Initial technique for lumbar discectomy

We categorized "initial technique using for lumbar discectomy" into 2 groups: endoscopic-related (group A) and nonendoscopic-related (group B). The rationale for this division is that spinal endoscopic surgeries are generally performed in a water environment with specific water pressure, which is different from traditional open and microscopic surgeries. The presence of a water environment in general and the maintained water pressure during the surgical process, in particular, may lead to the infiltration of water into the previously degenerated disc space, thereby increasing the risk of PDP formation. We observed a significant difference in the incidence of PDP between the 2 groups of initial techniques used for lumbar discectomy (p<0.001, chi-square test).

3. Management Strategies

Some cases have been reported to respond well to conservative treatment with NSAIDs, pain relief, and physical therapy [10,11,19-21]. Others may require simpler interventions, such as steroid injections and/or percutaneous cyst aspiration under fluoroscopic or CT guidance [6,10,22,23]. For cases with large cysts causing severe nerve root compression and not responding to conservative, surgical intervention to remove the pseudocyst may be necessary (Table 3). In most cases requiring revision surgery, authors prefer to use the same technique as was initially performed [9,12-14,24].

Table 3.

Management options for postoperative discal pseudocyst

Kang and Park [7] reported that 10 out of 15 cases improved with conservative treatment. The results showed no significant clinical differences between the groups requiring reoperation and those treated conservatively, with an average follow-up period of over 2 years. Jadhav et al.[11] also managed 4 cases—2 spontaneous DC and 2 PDP—conservatively using analgesia, neuropathic agents, and physiotherapy when needed, without strict bed rest. After 12 months of follow-up, all 4 patients showed clinical improvement, and the cysts spontaneously regressed on MRI. The author suggests that for patients with mild to moderate symptoms, conservative treatment should be the first option, as it can lead to significant improvement, even inducing spontaneous regression.

None of the cases requiring revision surgery in the literature reviewed reported subsequent recurrence of the PDP. In the study of Zhu et al. [12], reoperation was necessary in 13 out of 14 cases of PDP. Most of these PDP were larger than the previously excised herniated disc fragments. The author also noted a case that required PETD after an unsuccessful with percutaneous aspiration (PA). The author suggests that PA could be an alternative treatment with less trauma. However, C-arm or CT-guided aspiration and/or injection cannot remove the cyst wall, thereby risking recurrence of the pseudocyst. Additionally, complete aspiration may be difficult if the pseudocyst has a multi-cystic cavity.

PELD has been reported for the treatment of spontaneous DC and PDP via both the interlaminar and transforaminal approaches [7,8,12,13,18,24-27]. Wang et al. [13] presented 2 cases of PDP treated with PETD, where drainage was placed before closing the wound. In 1 case, the drain was removed on the seventh postoperative day, and in the other, on the fourth day. The author strongly recommends routine indwelling drainage during surgery to reduce nerve root irritation from local inflammatory factors and relieve radiculopathy. They also offered suggestions to prevent pseudocyst formation: (1) complete hemostasis during surgery and minimize coagulation and cauterization; (2) absolute bed rest on the first postoperative day; (3) wearing a lumbar brace for 2–3 months after surgery, along with moderate physical exercise. In our practice, we routinely place a drain in all cases of ED procedures (uniportal or biportal) and remove it on the second postoperative day. We believe this drainage helps reduce residual fluid at the surgical site, as water used during the endoscopic procedure may infiltrate and remain in the loose connective tissue around the spine. As mentioned earlier, when reoperating to remove the PDP, we prefer the BESS over PEID primarily to maintain a separate channel for water outflow, thereby reducing the risk of residual fluid in the surgical cavity.