SC are a common cause of lumbar pain among adults, presenting more frequently between the sixth and seventh decade of life, with a slight predominance among females6. Such characteristics coincide with those observed in our case series.
The current gold standard for imaging diagnosis of SC is magnetic resonance imaging7, with a maximum reported sensitivity of 90%8. SSC presents as a compressive well-outlined, intracanal, extradural lesion, generally located adjacent to a facet joint, with higher intensity than cerebrospinal fluid (CSF) in T2 and low intensity in T19. However, signal intensity may vary according to the presence of protein and/or blood content within the cyst.
Of our sample, 63.77% of patients underwent instrumentation at the segment L4-L5, in accordance with the pathogenesis of SCs, since such level is the most involved4 as a result of having the greatest mobility of the lumbar spine and because of the instability generated there as part of the vertebral spine degenerative process. The latter also explains why this pathology is much less common at the dorsal spine, which is rigid and motionless10.
Presently, there is still no consensus regarding the optimal treatment of this condition, which is a constant subject of debate. Although cases of SSC with spontaneous remission have been reported, some kind of therapy is generally needed for symptom resolution.
The first line of treatment is CM, which is based on a combination of rest, analgesics and physical therapy, and it is indicated in patients without progressive or significant neurological deficit. However, results reported in the literature are not fully satisfactory3,4. Metellus et al9, conducted a retrospective study where they analyzed functional outcomes of 77 patients treated conservatively and observed a failure rate of 60% at six months. Likewise, Parlier-Cuau et al11, in their retrospective series of 30 cases, reported only 33% of excellent or good outcomes when using the CM and they had to choose surgical intervention in 47% of their sample. In 2003, Shah and Lutz4 carried out a literature review and identified 139 patients treated with a CM, in which 47% had to undergo surgical treatment as a result of an unsuccessful CM.
Another option within the CM is facet infiltration with steroids during the attempt to aspirate or rupture the cyst through a percutaneous approach. However, results do not seem to be better than those seen in other CM modalities. Allem et al12, in 2009, retrospectively analyzed 32 patients that underwent percutaneous rupture of the SC. A symptom relief was observed in 72% of patients at one year of follow-up. However, 37.5% presented cyst recurrence at 3 months and 55% required surgery for cyst resection. On the same year, Martha et al13 evaluated 101 patients who had undergone the same procedure, with confirmed cyst rupture in 81% of patients. Likewise, 54% of patients had to undergo surgical intervention after an average of 8 months. Other earlier studies such as the one by Parlier-Cuau et al11, report similar outcomes; and in case series in which steroid infiltration was selected, success rates were not higher than 57%14–16.
In our case series, 63 patients underwent steroid infiltration and cyst rupture, which was confirmed in 49 patients (77.8%). Although the main purpose of our study is not to assess the efficacy of the CM, as in the previously mentioned studies, individuals did not show long-term symptom relief, and had to be operated. Therefore, surgical intervention is recommended in patients in which CM does not evidence a significant improvement6.
Surgical technique and fusion together with instrumentation may vary depending on the location and the relation of the cyst to neural structures and the presence of concomitant local pathologies. Nevertheless, they remain a motive of debate.
Certain authors propose that the surgery of choice is a hemilaminectomy and partial facetectomy and cyst excision, without fusion (decompression and excision without fusion - DwF), the latter being the less invasive approach. Eventually, the potential risk entailed by such technic is the generation or increase of the instability of the compromised segment, that might theoretically increase recurrence of the condition or generate a chronic lumbar pain.
SC recurrence rates (development of a new SC at the same level, after surgical removal) have been reported to range from 15–25% among patients undergoing DwF procedures17,18, while case series in which decompression and excision with fusion (DF) was carried out reported rates close to 0%19,20, data in accordance with our case series.
The systematic review of the literature by Bydlon et al21, identified 966 patients of which 84% of these were treated with surgical DwF, reporting only a cystic recurrence rate of less than 2% and with postoperative back pain in 21.9% of the subjects, after a minimum follow-up of two years.
In 2000, de Lyons et al7 published a retrospective study in which 194 patients with SC were evaluated. Their results did not evidence a correlation between the degree of laminectomy and / or facetectomy and the development of postoperative symptomatic spondylolisthesis. Likewise, Trummer et al16 and Sabo et al22 failed to find significant differences between the different surgical techniques and the final outcome. They concluded that the requirement of DF will depend on the previous segment degree of instability and promoted the use of flexion / extension x-rays to assist in evidencing the instability.
It would appear that the association of isolated cyst resection with an increased risk of segmental instability is not entirely clear. Instrumented fusion must be targeted to the instability of the segment to be operated. Such instability may be identified in dynamic (flexion / extension) x-rays as a displacement greater than 3 mm or more than 10º angulations between adjacent vertebral bodies22,23. Blumenthal et al24, also recommend an instrumented arthrodesis in patients with a facet angle greater than 50º, disc height higher than 6.5 mm and a displacement greater than 1.25 mm between vertebrae.
Indirect signs of instability evidenced both in MR as well as in CT scan, such as intradiscal or intraarticular vacuum phenomenon, ligament flavum hypertrophy or presence of more than 1.5 mm effusion25 within the involved facet joints in conjunction with the presence of axial pain, might also strengthen the indication for instrumentation of the segment to be operated.
The requirement for an DF should be assessed individually in each case as it adds risks compared to DwF (longer hospital stay, higher risk of incidental durotomy, higher blood loss and higher rates of perioperative infection)20,21.
Finally, advances in minimally invasive surgery techniques have allowed the resection of the SC with less damage to the posterior stabilizing structures20, showing good results26, however there is still a lack of bibliography with a higher level of evidence to be able to determine if these procedures represent a significant advantage as well as to be able to determine which patients really need DwF.
The present study has an adequate number of patients, considering the low prevalence of this pathology, who were operated on by the same surgeon and with the same surgical technique, resulting in a homogeneous sample and a non-negligible follow-up period. The main limitation is the retrospective design, and the absence of a control group to contrast outcomes. The latter restricts the possibility of other analyses with our results. Also, in some patients the follow up completion was, by telephone, thus adding a memory bias to the study. prospective randomized studies with a control group are needed to assess the real association between good results and lower recurrence rate among patients undergoing instrumented arthrodesis.