Facet Cysts: Is There an Advantage to Treating Synovial Cysts with Minimally Invasive Techniques?

3 Facet Cysts: Is There an Advantage to Treating Synovial Cysts with Minimally Invasive Techniques?

MIS: Jose M. Torres-Campa, Marjan Alimi, and Roger Härtl
Open: Brian W. Su

3.1 Introduction

Synovial cysts are well-known (although relatively uncommon) pathologies in the spine involving the synovium of the facet joints. Synovial cysts were first described in the knee in 1885,1 and in the spine in 1950.² Their relationship to the facet joint, however, was not clearly described until 2010 by Spinner et al.³ Synovial cysts of the spine usually originate from degenerative facet joints, although occasional cases arising from microtraumatized joints have also been reported.⁴

Synovial cysts can be found throughout the spinal axis, but most commonly occur within the lumbar spine. Among all patients with synovial cysts on the magnetic resonance imaging (MRI), 0.5 to 2.3% are found to be symptomatic.⁵ Wilby et al demonstrated that osteoarthritis of the facet joints can result in the release of cartilage and bone fragments into the synovial fluid of the joint, which can then provoke granulation tissue and cyst formation.⁶ Synovial cysts of the lumbar spine typically cause nerve compression in the lateral recess adjacent to the joint. The traversing nerve root is more commonly affected (e.g., L5 nerve is affected by an L4/L5 cyst), although extension of the cysts into the foramen may also happen, resulting in compression of the exiting nerve root as well (e.g., L4 nerve becomes affected by an L4/L5 cyst). Symptomatic facet cysts present with pain and paresthesias within the distribution of the compressed nerve root. Although exceedingly rare, lumbar facet cysts have also been reported to present as cauda equina syndrome.^7,8,9

Since instability alters the biomechanics of the facet joint, lumbar synovial cysts may be associated with degenerative spondylolisthesis. Lumbar synovial cysts are more commonly seen at the L4/L5 level.^10,11 For evaluation of patients with synovial cysts, it is critical to obtain dynamic flexion/extension X-rays in order to rule out concomitant spondylolisthesis and instability. While the majority of facet cysts are fluid filled, chronic cysts may occasionally be calcified following percutaneous aspiration.¹² In such cases, computed tomography (CT) scans need to be done for evaluation and surgical planning.

3.2 Indications for Surgical Treatment of a Synovial Cyst

Initial treatment of synovial cyst is nonoperative, which includes oral medication, cyst injection or aspiration, and selective nerve root injections. Slipman et al reported 33% long-term improvement of symptoms with corticosteroid use.13 Martha et al proposed that fluoroscopy-guided injection results in concurrent rupture of the cyst and introduction of the corticosteroids into the synovial cyst space.¹⁴ They successfully treated 46% of their patients by injection, and the other 54% surgically. Cyst aspiration, however, may appear to be challenging, due to gelatinous consistency of the cyst fluid or presence of a calcified component within the cyst.^15,16

Surgical intervention should be considered after failure of nonoperative management and/or where the extremity pain interferes with the patient’s functionality and quality of life. While facet cysts can also cause axial back pain, surgical intervention should generally be reserved for patients with radiculopathy and/or weakness secondary to nerve compression.

Surgical treatment of the lumbar facet cyst involves resection of the cyst. Fusion is indicated only if concomitant dynamic instability of the spinal segment is detected or when over 30% of the facet joint is resected during surgery.

3.3 Advantages of Minimally Invasive Surgery

There are several advantages of using the techniques of minimally invasive surgery (MIS). MIS procedures allow for reduced retraction of muscles and result in less soft-tissue damage compared to open procedures. It has been shown that they allow earlier ambulation and shorten the hospital stay.17,18,19,20 MIS treatment of the herniated lumbar discs and MIS fusion, in particular, result in reduced muscle atrophy, as shown on the postoperative MRI.²¹

Treatment of synovial cysts using MIS technique has similar advantages. It is associated with reduced blood loss (MIS: 74– 158 mL; vs. open: 460–930 mL).^22,23 In this instability-prone pathology, a tubular approach can avoid fusion in patients without mechanical back pain and/or movement on the flexion/extension films.²⁴ The tubular approach preserves the majority of the posterior elements, thereby minimizing instability.^25,26,27 Moreover, a contralateral approach (contrary to an ipsilateral approach) allows for resection of the cyst through normal anatomy; the normal dura is identified first, therefore minimizing the risk of cerebrospinal fluid (CSF) leak. A contralateral approach also reduces the extent of the facet joint that needs to be removed.²⁴

CSF leaks, if they occur, can be treated with CSF sealants such as Tissucol (Baxter Healthcare SA Inc.; Zurich, Switzerland) or Duraseal (Confluent Surgical Inc.; Waltham, MA). Direct mechanical repair in our experience is rarely necessary and can be accomplished with endoscopic tools through tubular retractors.

3.4 Advantages of Open Surgery

Resection of facet cysts through an open ipsilateral microdiscectomy/microdecompression approach has several advantages. The open technique allows for avoidance of the demanding learning curve associated with minimally invasive approaches, particularly the contralateral approach. Facet cysts often require widespread resection of laminae and/or facet joints, to ensure complete removal of the facet cyst and decompression of the affected nerve root. The broader field of view in an ipsilateral open technique permits better visualization of the surgical region during resection. An incidental durotomy due to removal of an adherent cyst can easily be repaired through an ipsilateral open technique, as opposed to a contralateral minimally invasive approach. In addition, when fusion becomes necessary during the surgery, an open technique can rapidly be converted to a fusion procedure.16,28,29

Fig. 3.1 A case example of a patient with a synovial cyst on the left at L4–L5: the T2-weighted MRI.

3.5 Case Illustration

A 64-year-old woman presented with a 5-month history of severe left leg pain along L5 dermatome. There was no relief of the symptoms with the use of oral medications, physical therapy, and epidural steroid injections.

MRI and flexion/extension X-rays were obtained, showing a large left synovial cyst at L4–L5 level, without spondylolisthesis and no instability ( Fig. 3.1).

A minimally invasive tubular surgical resection and decompression via a contralateral approach was performed. The operative technique has been fully described following the current case example (under “The MIS Surgical Technique”). Briefly, under the microscope and through a 19-mm-diameter tubular retractor, the inferior edge of the lamina contralateral to the cyst was removed; the retractor was angled medially, and the spinous process and the contralateral lamina were undercut. The ligamentum flavum was exposed bilaterally, and the cyst was exposed from the contralateral, normal anatomy. The cyst was then carefully resected. The patient ambulated within a few hours after surgery and was discharged home within 24 hours.

At 4 years’ follow-up, the sciatic pain and neurological claudication remained resolved. No worsening of the spondylolisthesis was detected in any of the postoperative studies.

3.6 Surgical Technique in Minimally Invasive Surgery

The microendoscopic tubular approach was first described by Foley and Smith in 1997.30 We have been using a modification of this approach since 2004, by replacing the endoscope with an operating microscope.²³ In the operating room, patients under general anesthesia are placed prone on a Wilson frame. Fluoroscopy is used for localization of the correct level. A skin incision is made approximately 1.5 cm lateral to the midline on the side opposite to the juxtafacet cyst. A tubular retractor is placed over serial dilators and is fixed in place using a table-mounted arm; an 18- or 19-mm-diameter tubular retractor is used for this procedure. The correct level is confirmed. An operating microscope is brought in. The base of the spinous process and the inferior edge of the lamina contralateral to the cyst are identified and removed using a high-speed drill with a curved 3-mm matchstick attachment (Anspach; Palm Beach Gardens, FL). The yellow ligamentum flavum is identified and exposed bilaterally. Subsequently, the retractor is angled toward the midline, and the lamina and facet joint contralaterally are undercut. In the cases where lumbar spinal stenosis coexists with the cyst, a bilateral MIS laminectomy is performed. The operating table is then rotated away from the surgeon, which provides a wide access to the ligamentum flavum, which needs to be carefully resected for exposure of the facet cyst. The dura is then carefully dissected off the cyst wall.

During this maneuver, the dura is depressed using the suction device. After adequate exposure, the medial edge of the juxtafacet cyst is meticulously identified and carefully dissected off the dural attachment along the cranial, caudal, and medial aspect of the cyst. It is then typically possible to remove the juxtafacet cyst in a piecemeal manner using Kerrison rongeurs and other microsurgical instruments. Occasionally, when clearance cannot be achieved due to the large size of the cyst, in order to prevent excessive retraction of the dura, the cyst is deliberately ruptured and decompressed, which allows complete removal of the cyst. Resection of the facet joint is not required. If a dural tear is observed, it is covered at the end of the procedure by Tissucol or Duraseal, and the patient is kept flat after surgery. At the end of the procedure, the operative field is irrigated by antibiotic solution, the tubular retractor is removed, and every attempt is made to close the fascia before skin closure is obtained.