Age / Sex : 77 / F

Courtesy :  이경규(Gyung Kyu Lee), 한림의대 한강성심병원(Hallym University College of Medicine, Hangang Sacred Heart Hospital)

Cyst of the ligamentum flavum

Discussion

Findings :

Sagittal T1-weighted spin-echo and corresponding sagittal fat saturated T2-weighted turbo spin-echo MR images show a round cystic mass in the spinal canal at the L4–L5 level. The mass is isointense relative to intervertebral disc on T1-weighted spin-echo image and high signal intensity with a hypointense rim on T2-weighted turbo spin-echo image. Axial T2-weighted spin-echo MR image shows a cystic mass adjacent to the right-sided ligamentum flavum displacing the dural sac anteriorly and resulting in central canal stenosis. There is bilateral facet joint degenerative change at this level but the lesion is no communication with the facet joint.

Differential Diagnosis :

1) Intraspinal extradural cysts, such as Synovial cyst or Ganglion cyst, Disc cyst, PLL cyst, Ligamentum flavum cyst, Perineural cyst, Arachnoid cyst, etc

2) herniated disc (can migrate to a posterolateral position)

3) schwannoma with cystic degeneration

Diagnosis : Cyst of the ligamentum flavum

Discussion :

- Cysts of the ligamentum flavum arise from or are partially embedded in the inner surface of the ligament and are not closely related to the facet joint such as synovial cysts.

- Pathogenesis of the cyst formation is related to ligamentous and fibrocollagenous tissue degeneration and hypermobility of the spinal segment. Hypermobility associated with degenerative disc disease, and particularly with degenerative spondylolisthesis and subluxation of the facet joints, can subject the ligament to stress between its points of attachment. The development of cysts of the ligamentum flavum may be related to necrosis or myxoid degeneration occurring in a hypertrophied ligamentum flavum. Pathologically, ligamentum flavum cysts can contain hemorrhage.

- On T1-wheighted images, the cysts have a variable signal. The cysts show a hyperintense mass with a hypointense rim on T2-wheighted images. Differential diagnosis on imaging studies between ligamentum flavum cysts and synovial cysts is useful to the surgeon, as the latter are more difficult to resect requiring exploration of the facet joint. Synovial cysts remain clearly outside the ligamentum flavum and are typically attached to the facet joint, whereas ligamentum flavum cysts are attached to or located within the ligament. Evidence of attachment to the facet joint or the ligament may be helpful in distinguishing between these two lesions.

References:

1) Gazzeri R, Canova A, Fiore C, Galarza M, Neroni M, Giordano M. Acute hemorrhagic cyst of the ligamentum flavum. J Spinal Disord Tech. 2007;20:536-538.

2) Cakir E, Kuzeyli K, Usul H, Peksoylu B, Yazar U, Reis A, Karaarslan G. Ligamentum flavum cyst. J Clin Neurosci. 2004;11:67-69.

3) Mahallati H, Wallace CJ, Hunter KM, Bilbao JM, Clark AW. MR imaging of a hemorrhagic and granulomatous cyst of the ligamentum flavum with pathologic correlation. AJNR Am J Neuroradiol. 1999;20:1166-1168.