Revision surgery for symptomatic postoperative pseudocyst following full-endoscopic lumbar discectomy: clinical characteristics and surgical strategies

The characteristics of PP seemed to be similar to those of discal cysts as reported [17]. In all the reviewed studies, PP was found to be more common in young male patients at L4–5 level. The same could be observed for this study in general. The highest prevalence of herniated lumbar disc was among people aged 30 to 50 years, with a male to female ratio of 2:1 [18]. In the people younger than 35 years, the male to female ratio was significantly higher than that of other age groups, and men were more likely to suffer from lumbar disc herniation. In this study, we found that the male to female ratio of PP is 2.5:1, which was similar to the prevalence rate of lumbar disc herniation. More male patients may have more PP cases. The diagnosis and differential diagnosis of symptomatic PP mainly depend on clinical manifestations and imaging scans. The 14 cases that ended up with revision surgeries had similar disease progression: (1) Most of them were young male patients with a definite diagnosis of lumbar disc herniation, and the clinical manifestations were related to compression of nerve root(s) by the herniated disc. All patients received FELD surgeries; (2) The symptoms that the patients experienced were alleviated after the first surgery; (3) Radicular pain of lower extremity, similar to that experienced before surgery, reoccurred after 40.5 (Q1: 30, Q3: 60) days without obvious inducement; (4) Severe pain median NRS score = 7.5 (Q1: 6, Q3: 8) persisted, or the pain was progressively affecting normal life. The degree of pain that the some of the patients felt during the recurrence was higher than that before surgery, and the conservative treatment that they received was ineffective; (5) MRI imaging revealed the formation of a cystic lesion at the discectomy site, with low intensity on a T1WI and high intensity on a T2WI, that was compressing the dural sac and nerve root. PP exhibited the following characteristics, in relation to that of the initial herniated lumbar disc: larger, up- or down-migrated, located in lateral recess or foraminal zone; (6) The patients received revision surgeries within a very short period of time median = 9.5 (Q1: 6, Q3: 22) days; (7) Most of the surgical outcomes were satisfactory. In contrast to lumbar discal cyst with spontaneous regression [5, 19], 13 out of 14 of the PP cases in our study exhibited at least one of the following three characteristics: larger, up- or down-migrated, located in lateral recess or foraminal zone; which might lead to severe compression of the dural sac and nerve root. As the pain progressed rapidly due to the severe compression and the patients did not respond to conservative treatment, revision surgery was eventually performed.

The common clinical manifestation of PP is postoperative recurrent radicular pain, which is similar to that of the recurrence of disc herniation [20]. As such, MRI is required for a differential diagnosis. While a disc herniation is presented with a low intensity on both T1WI and T2WI, a PP is typically presented with a high signal, clear boundary and cystic change on a T2WI. However, it may not always hold true [21]. Hence, intraoperative identification is also important. Generally, PP has a dark-red capsule without disc fragments or hematoma. While the MRI scan of case 14 revealed a well-defined cystic lesion at L4–5 level, the cystic lesion was presented with a medium signal on a T2WI. This is different from those of the other patients. In the endoscopic view of case 14, the surgeon found the new prolapsed disc tissue inside the cyst wall, thereby suggesting that the PP might consist of not only cystic tissue but also disc components. Shiboi et al. [7] reported a case of recurrent LDH that mimicked a symptomatic PP. Hence, such cases should be considered carefully to rule out LDH recurrence. This might also be the reason why this case was treated with a revision surgery despite the absence of the three aforementioned characteristics of PP.

In all the reviewed studies, the pathology and pathogenesis of PP were still unclear. Young et al. hypothesized that granulation tissue may form a pseudocapsule around the herniated disc fragment [16]. If the disc fragment is removed without disrupting the pseudocapsule, fluid may accumulate and PP may be formed. The pathological results of the cystic wall indicated that its main component is fibrous connective tissue (Fig. 4), which might be the result of an inflammatory response of the connective tissue due to postoperative annular defects. As most of the patients in our study are young, the strong ability of granulation or fibrous tissue formation as well as self-repair of annular fibrosus might be the cause of symptomatic PP formation. Male patients may return to work and resume daily activities earlier than female patients, and in the early postoperative period, the increased pressure on the intervertebral disc may promote the formation and enlargement of PP. However, a large cohort is needed to prove this hypothesis. Additionally, the inadequate treatment and resection of the annular fibrosus might have led to the formation of the pseudocyst. Together with that, an insufficient resection of the facet joint might have limited the opening of the spinal canal thereby leading to symptomatic PP. It has been reported that the interlaminar approach, in comparison to the transforaminal approach, was correlated with PP formation [4]. However, the transforaminal approach was performed in 13 out of 14 cases in this study. This implies that the surgical approach may not be significantly related to the formation of PP.

In all the reviewed studies, conservative treatment, C arm/computed tomography (CT)-guided aspiration and/or injection, microdiscectomy, microendoscopic discectomy, and PELD had been used to treat the patients for PP. Clinical and radiological recovery of the symptomatic lumbar discal cyst could only be obtained through conservative therapy [5, 19, 22]. In our cases with severe pain caused by the compression of dural sac or nerve root by cystic lesions as confirmed by MRI, however, conservative treatment was ineffective, and revision surgery was required. It should be noted that, the patient in Case 12 felt a relief of pain after the puncture of the intervertebral foramen and did not undergo endoscopic revision surgery, thereby suggesting that percutaneous aspiration (PA) could be an alternative treatment with less trauma [6, 15, 16]. However, C arm/CT-guided aspiration and/or injection cannot remove the capsule wall, thereby risking the recurrence of PP. [8] Furthermore, it will also be difficult to aspirate completely if the PP is a multicystic cavity. This was evident in Case 13, where the pain was not improved after PA and the patient eventually underwent an endoscopic revision surgery.

Endoscopic lumbar discectomy has been reported for the treatment of discal cysts [23‐25]. In this study, FELD was performed for the revision surgeries of 13 cases and the postoperative recoveries were satisfactory. The mean operative time of revision surgery was less than that of the first surgery. Because we operated through the original surgical path in the revision surgery, there was no need for facetectomy and discectomy again. In the endoscopic view, we generally found severe adhesion surrounding the PP (Fig. 5), dural sac, ligamentum flavum, and disc material, as well as well-developed vasculatures which causes bleeding when removing PP. Hence, we should separate the adherent tissues carefully and remove as much of the capsule of PP as possible during the revision surgery to minimize having to perform another revision surgery. This is evident in Case 2, where we performed two revision surgeries with a 14 days interval. If it is difficult to completely resect the cyst, the potential for recurrence may be reduced by annuloplasty using radiofrequency coagulation [8].

This study had some limitations. The exact total number of patients treated in 7 minimally invasive spine centers is not available. Therefore, the prevalence of PP requiring revision surgery is not measured correctly. In addition, the lack of surgeon standardization is another limitation. The data is collected from 8 surgeons. A further clinical study will be needed to figure out the definite pathology and pathogenesis of PP.