different etiologies for cystic lesions in the lumbar spinal canal have been reported in the literature , among them hemorrhagic cysts , perineural cysts , dermoid cysts , and parasitic cysts . the most common lesion seems to originate from the facet joints : the synovial cyst , which represents a protrusion of the synovial membrane into the surrounding tissue . the literature remains imprecise about the histopathologic nature of cystic lesions in the lumbar region of the spine . some authors differentiate between the terms  synovial cyst  ( with a synovial lining ) and  ganglion pseudocyst ligamentum flavum pseudocyst , as a cystic lesion in the lumbar spine , has only rarely been mentioned [ 4 , 5 , 7 , 25 , 28 , 29 ] . a 70-year - old woman presented with 5-year history of gradually developing gait disturbance as well as pain in the lumbar area , buttock , and right leg , particularly the right knee , involving mostly the l4 distribution . in the meantime an artificial knee joint was implanted with inadequate recovery of the pain . motor function was normal and there was no sensory disturbance on examination of the legs . magnetic resonance imaging revealed at l3l4 level a right - sided voluminous epidural cystic lesion , 10  mm in diameter , which was hypointense on t1-weighted images and hyperintense on t2-weighted images and its wall was enhanced with contrast material . the mass displaced the dural sac anteriorly and resulted in marked stenosis of the spinal canal . the mass was surgically resected together with the hypertrophied ligamentum flavum after partial l3l4 hemilaminectomy ( fig .  1 ) . a round , yellowish cyst of about 10  mm in diameter filled with somewhat gelatinous fluid and barely adhered to the dura mater pathological examination of the cyst revealed myxoid and pseudocystic degeneration of the ligamentum flavum ( fig .  2 ) . intraoperative view via the surgical microscope showing part of the cyst and degenerated ligamentum flavum ( arrow ) , regular ligamentum flavum ( notched arrow ) , and dura mater spinalis ( arrowhead ) histopathologic section of operative specimen reveals degenerative changes in the ligamentum flavum with infiltration of inflammatory cells and no synovial cell lining ( hematoxylin and eosin ) several studies have shown that the usual aging process of the ligamentum flavum causes thickening and loss of elasticity . change in proteoglycans , loss of elastic fibers , and increase in collagen tissue and chondroid metaplasia due to mechanical stress have been described . additionally and closely related to age this amyloid deposition has been reported in only a few cases to be associated with systemic amyloidosis . a diffuse form of calcification contributing to the loss of elasticity and the thickening and a focal form of calcified material accumulation as well as granulomatous inflammation and tophaceous depositions of calcium pyrophosphate crystals can occur . these depositions have been ascribed to decreasing cellularity of the ligamentum flavum with age and resultant diminished calcification inhibiting factor production by fibroblastic - like cells . the tophaceous type of lesion seems to be closely related to previous degeneration of the affected ligament by minor trauma predisposing to calcium deposition . activity of proteolytic enzymes within the ligament , produced by neutrophils localizing to calcified nodules , has been found . .   found only four patients with calcium pyrophosphate depositions , suggesting that they play a minor role in the pathogenesis of ligamentum flavum pseudocysts . this seems to follow a sequential process of chondroid metaplasia and eventual enchondral ossification mainly at the insertion site of the ligament . all these factors , resulting partially from mechanical stress , seem to contribute to loss of the natural structure of the ligamentum flavum , making them again susceptible to new mechanical stress , forming a vicious circle . the degenerated bony structure of the lumbar spine and the facet joints suggest a major pathogenic role of degenerative segmental instability in pseudocyst formation of the ligamentum flavum , as found by other authors too . most ligamentum flavum cysts reported in the literature were also located laterally within the spinal canal . while possibly a consequence of chronic bony degenerative disease , this phenomenon may be further elucidated in certain cases by the observation that the yellow ligaments are not as thick laterally as they are medially . these recesses are filled with epidural fat   and offer an area of decreased resistance and may , as a result , tolerate cyst formation . the pathogenesis of ligamentous degeneration remains to be elucidated , but it may be considered in the context of degenerative spinal changes . the spine is divided into alternating mobile and fixed segments , and the transitional zones between the mobile and fixed regions incur the most severe stress during motion . the anatomic disposition , histologic characteristics , and biomechanical properties of the ligamentum flavum indicate that it is markedly different from other spinal ligaments . the ligamentum flavum is a well - defined elastic structure composed of 80% elastic and 20% collagen fibers . this composition of dense connective tissue with elastic fiber predominance is rarely seen in other tissues , although it can be seen in the vestibular folds of the larynx and the media of large arteries . when a change occurs in the ligamentum flavum , regeneration of elastic fibers that includes the formation of collagen fibers and degenerative changes occurs , and this regenerative process leads to decrease in elasticity . moreover , this process in the ligamentum flavum is markedly different from other spinal ligamentous reactions . thus , chronic irritative or degenerative changes of the ligamentum flavum in the area of the cyst could predispose it to mechanical stress , even after a minor repeated injury . cysts of the ligamentum flavum have myxoid degeneration and arise from or are partially embedded in the inner surface of this ligament , and in contrast to juxta - articular cysts , are not related to the facet joint cavity . pathogenesis of the cyst formation is secondary to ligamentous and fibrocollagenous tissue degeneration and hypermobility of the spinal segment , mainly at the transitional zones between the mobile and the fixed segments of the spine . pathologic ligamentum flavum cysts can contain hemorrhage , and previous degeneration of the ligament may create conditions for the formation of hematoma . rupture of vessels in degenerated lumbar ligamentum flavum may develop secondary to stretching forces on the back . the pathogenesis of the hematoma may originate from minor acute or chronic trauma such as minor back injury , physical exertion or heavy lifting [ 20 , 26 ] . intraspinal ligamentum flavum cysts are rare ; they occur preferentially in the lower lumbar region [ 5 , 15 , 32 ] , while cervical localization is uncommon . in most of the cases , ligamentum flavum cysts in the lumbar spine occur at l4l5 , the most mobile segment within the lumbar spine , and are frequently associated with lumbar degenerative spondylolisthesis . continuous stress to the ligamentum flavum due to minor chronic trauma such as listhesis may predispose to the formation of the cyst . only in a few cases no reports have described the appearance of these cysts in any region other than the mobile spine . the t210 vertebrae mainly act with the ribs to form the thorax and are not generally considered to be part of the mobile spine ( table  1).table  1reported cases of ligamentum flavum cysts occurring in the spineliterature 
 n 
 cervical  takano et  al . 1  yamamoto et  al . 1lumbar  haase 1  abdullah et  al . 4  vernet et  al . 6  savitz et  al . 6  baker and hanson 1  bloch et  al . 6  mahallati et  al . 1  brlocher and seiler 1  terada et  al 33  dimario et  al . 4  asamoto et  al . 1  gazzeri et  al . 2  our case1 reported cases of ligamentum flavum cysts occurring in the spine there are no specific clinical symptoms for ligamentum flavum cyst . cysts in the spinal canal can impinge upon and displace neural structures and can lead to neurologic symptoms . the majority of symptomatic cysts usually presents with radiculopathy , such as sciatica in the case of lumbar cysts , and can mimic symptoms related to intervertebral disc herniation . in the study of wildi et  al . , 97% patients complained of radicular pain , 39% showed motor deficits , 55% had sensory changes , 18% had abnormal reflexes , and 33% showed a positive lasque sign . our patient presented with gradually developing right - sided radicular pain involving mostly the l4 distribution with patellar reflex loss on the same side . on myelography , these lesions are recognized as intraspinal extradural masses and on postmyelogram computed tomography as a faint cyst adjacent to the ligamentum flavum . magnetic resonance imaging provides the best images [ 14 , 20 , 25 , 28 ] : on t1-weighted images , the cysts have a variable signal , and on t2-weighted images , the cysts have a high - intensity signal [ 20 , 28 ] . differential diagnosis of 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 . magnetic resonance imaging , in some cases of synovial cysts , reveals demonstrable communication with the facet joint with enhancement of the synovial cyst wall and of the adjacent facet joint . synovial cysts often have a calcified rim , while ligamentum flavum cysts do not . in our study , magnetic resonance imaging revealed at l3l4 level a right - sided voluminous epidural cystic lesion , 10  mm in diameter , which was hypointense on t1-weighted images ( fig . 3a , b ) and hyperintense on t2-weighted images ( fig .  4 ) and the computed tomography appearance of synovial cysts is often diagnostic and correlates well with pathologic findings . they typically consist of a cystic formation whose walls show calcification , and are located adjacent to facet joints that frequently show signs of degeneration . juxtafacet cysts appear as well - delineated cystic masses ; the rim of synovial cysts is typically isointense to slightly hyperintense compared with cerebrospinal fluid in t1 and hypointense in t2 , and its contents have variable intensities and several classifications have been proposed . in the case of ligamentum flavum cysts , they are seen adjacent to the ligamentum flavum   and there is no observable communication with the spinal facet joint . when intraluminal hemorrhage occurs in a minority of cases , they are easier to distinguish from herniated disk fragments and most neoplasms . in addition to other cystic lesions that may affect the lumbar spine , calcium pyrophosphate dihydrate deposits have been observed in the ligamentum flavum among patients presenting with lumbar pain and/or radiculopathy , and typically are hypointense on magnetic resonance imaging and show calcifications on computed tomography imaging.fig .  3t1-weighted magnetic resonance image demonstrating a hypointense intraspinal extradural right - sided ligamentum flavum cyst ( white arrow ) : a sagittal pre - gadolinium , b axial pre - gadolinium , c sagittal post - gadolinium , d axial post - gadoliniumfig .  4t2-weighted magnetic resonance image showing a hyperintense signal of the above - mentioned cyst ( white arrow ) : a sagittal , b axial t1-weighted magnetic resonance image demonstrating a hypointense intraspinal extradural right - sided ligamentum flavum cyst ( white arrow ) : a sagittal pre - gadolinium , b axial pre - gadolinium , c sagittal post - gadolinium , d axial post - gadolinium t2-weighted magnetic resonance image showing a hyperintense signal of the above - mentioned cyst ( white arrow ) : a sagittal , b axial differential diagnosis of intraspinal extradural mass lesions includes ligamentum flavum cyst , juxta - articular cysts ( ganglion and synovial cysts ) , arachnoid cyst , perineural cyst , dermoid cyst , infectious cyst , schwannoma , meningioma , and metastasis or nontumorous - type mass lesions including neurofibromas , fibrous dysplasia , ependymal cyst , and rheumatoid arthritis pannus [ 15 , 20 , 23 ] . ligamentum flavum and juxta - articular cysts can be definitely distinguished only by their pathological findings . the goal of surgery is spinal decompression as well as resection of the cyst and affected ligamentum flavum . complete excision at the base of the ligamentous insertion of the cyst assures a minimal rate of recurrence . reported recurrence of the cyst in the remaining ligamentum flavum in two patients 1  year after surgery . while nearly 95% of all operated cysts can be removed in their entirety , a major reported intraoperative difficulty lies in the presence of adhesions to the dural wall , which is the main causative factor of incomplete resection . complete removal of pseudocystic lesions generally has excellent results [ 2 , 9 , 14 , 27 , 28 , 30 ] . ligamentum flavum cysts represent a rare cause of lumbar nerve root compression or spinal stenosis . histologically , these degenerative changes represent a distinct entity different from ganglion or synovial cysts . radical removal of pseudocyst guarantees in nearly all cases complete relief of radiculopathy and seems to prevent recurrence of such a lesion at the same level .