Ligamentum Flavum Cyst: Rare Presentation Report and Literature Review
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.299172
Source of Support: None, Conflict of Interest: None
Keywords: Formainal stenosis, ligamentum flavus cyst, lumbar canal stenosis, neurogenic claudication
Ligamentum flavum cysts (LFC) are rarer entities, stirring a diagnostic dilemma on initial imaging studies. Pathological changes in ligamentum flavum, leading to cyst formation, are not completely understood.
We report a rare case of ligamentum flavum cyst in the lumbar spine, mimicking as epidural mass, presenting with neurogenic claudication and then discuss the origin of these cysts.
An 88 years old Asian male presented with progressively increasing left leg pain for the last 1 year. The pain progressively limited his activities and walking was painful beyond fifty steps. Visual analog score (VAS) for leg pain was 8 and for backache was 2. Neurological examination revealed normal sensation and motor strength with preserved bowel and bladder function. Magnetic resonance imaging (MRI) of the lumbar spine demonstrated lumbar canal stenosis at the L4–L5 vertebral level [Figure 1]a. A cystic mass was appreciated in proximity to the left L4–5 facet joint in the epidural space [Figure 1]b. Mass was hyperintense on T2-weighted images and hypointense on T1-weighted images of the axial MRI, appearing as a synovial cyst arising from the facet joints.
Due to his unrelenting symptoms, surgical decompression was planned in the background of no obvious instability, as evidenced by dynamic radiographs [Figure 2]a and [Figure 2]b. Bilateral midline sparing L4 laminotomy and foraminotomy was done to expose the ligamentum flavum. The en-bloc excision of flavum was done on both sides. A cystic swelling was noticed arising from the ventral surface of flavum on the left side [Figure 3]. It was found non-adherent to the dura and compressing the thecal sac, displacing it to the right side. A tissue sample was sent for histopathological examination which demonstrated fibro-collagenous tissue consistent with connective tissue cyst [Figure 4]a and [Figure 4]b. The cyst wall was devoid of the synovial lining. The patient had immediate relief in leg symptoms after surgery.
We describe a rare case of LFC causing neurogenic claudication and discuss the pathogenesis and clinical implications in this report. LFC was first described by Moiel et al. in 1967, compressing the thecal sac and presenting as radicular leg pain. Kao et al. in 1974 have first coined the term “Juxta-facetal cysts” to represent cysts arising from periarticular regions in the spine. “Juxta-facetal” has been recently used to describe these entities owing to their common location around the facet joints, overlying the thecal sac and presenting as radicular or claudication leg pain.
The exact pathogenic mechanism in the formation of ligamentum flavum cyst is not well elucidated. It is believed that persistent micro-instability at motion segment with concomitant micro-trauma predisposes to cyst formation. Nevertheless, abnormal micro-movement owing to motion-segment instability is challenging to demonstrate on imaging studies.
Ligamentum flavum is composed predominantly of elastic fibers and fewer collagen fibers. The predominance of elastic fibers distinguishes the ligamentum flavum from other spinal ligaments. Micro-traumatic events in ligament lead to regeneration with type-2 collagen formation with a reactive decrease in the elasticity. The deposition of collagen results in further degeneration and ongoing myxoid changes culminates in cyst formation.
Cysts appear on the ventral surface of the ligament without any connections to articular facets. This peculiarity is in contrast with the formation of a synovial cyst and ganglion cyst which arise from the articular synovial lining.
Other types of the cystic formation may include amyloid deposition in ligamentum flavum, in association with the normal aging process as well as with systemic amyloidosis. At times, calcifications and ossifications are also seen within these cysts. Proteolytic enzyme released from neutrophils in the vicinity of calcium deposits has been seen.
The most commonly reported location for LFCs is the lumbar spine [Table 1] There are few reported cases of cervical flavum cysts. It is interesting to note that no case of LFCs has been reported at thoracic locations, which further supports the theory of segmental instability in the genesis of LFCs. L4-L5 segment seemingly, is the most common level for the development of these cysts, as seen in our case. However, we did not observe appreciable instability on dynamic radiographs in our case. This observation supports the role of subtle micro-instability in the cyst formation. The cervicothoracic junction is the most commonly affected level in the cervical spine. There have been few reports of cysts at other locations in the sub-axial spine as well.
Most of the LFCs are located in close vicinity to the facet joint. Few authors suggested the origin of these cysts from fluid migration through the defect into the ligament. Others refute this observation, stating no connection exists between facet joints and ligamentum flavum.
There are no specific symptoms pertaining to LFCs and presentation depends on location, size and growth rate of the cyst. Asymmetric compression may present with unilateral radicular pain and mimic foraminal stenosis. The central location of cyst occluding the spinal canal may present with symptoms of canal stenosis and claudication type leg pain. Shah et al. reported the case of midline cyst embedded in ligamentum flavum without connections to facet joints and presenting with bilateral claudicant leg pain. The most common presentations are radicular pain (97%), motor deficit (39%), sensory changes (55%), abnormal reflexes (18%), and positive Lasegue's test (33%). Surgical emergencies arising from cysts are rare. There are few reports of Cauda equina syndrome with concomitant LFCs complicated by infection and hemorrhage within the cyst.
Differential diagnosis of these intraspinal epidural mass is ligamentum flavum cyst, juxta-articular cysts, perineural cyst, dermoid cyst, schwannoma, neurofibroma, ependymal cyst or infected cyst. MRI may help to differentiate LFCs from the synovial cysts, however at times, differentiation is possible only during surgery.
Conservative treatment can achieve a varying degree of success. Percutaneous steroid injection of synovial and juxta-facetal cyst has reportedly not achieved good results. Surgical excision is a reasonable choice when conservative measures fail. The goal of surgical excision is decompression and complete removal of cyst along with ligamentum flavum. Most of the cyst are non-adherent to the dura and only require careful dissection before excision. LFCs represent a rare cause of nerve compression and radicular or claudication pain and it should be considered in the differentials along with synovial and ganglionic cysts, in the setting of neurogenic leg pain and imaging studies suggestive of the epidural cystic lesion.
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The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]