juxtafacet cysts ( jfcs ) are uncommon intraspinal , extradural lesions that arise from the facet joints . jfcs can be further distinguished as either synovial cysts , if histology confirms the presence of a synovial lining membrane , or alternatively as a ganglion cyst , if no such membrane is present . however , few differences exist between the two in terms of diagnosis and management.1 
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 7 their pathogenesis remains unclear , with most authors citing excessive joint mobility leading to synovial fluid herniation through joint capsule defects.2 
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  calcification in the cyst walls is a common finding on imaging for jfcs , appearing as peripheral areas of high attenuation on computed tomography ( ct ) and peripheral hypointensity on t1- and t2-weighted magnetic resonance imaging ( mri).8 
 9 
 10 but although calcification of the cyst walls are commonly reported findings,9 
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 11 complete calcification of the cyst is exceedingly rare.11 
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 13 we present here an unusual case of a jfc presenting as a giant , multilobular , completely calcified mass with significant extraforaminal extension . the patient was a 57-year - old woman who presented with a 2-year history of gradually worsening lower back and left leg pain . she also reported numbness in her left heel and foot and subjective weakness in the left foot . her past medical history was significant for hypothyroidism , hypertension , mild levoscoliosis , rheumatoid arthritis , and scleroderma managed on weekly methotrexate injection . her past surgical history was negative for any previous lumbar surgeries , but the patient had received multiple cervical surgeries resulting in c3c7 fusion . on neurologic exam , the patient was found to have decreased strength in plantarflexion and dorsiflexion of the left lower extremity but was otherwise nonfocal . the patient 's imaging was most notable for a large , multilobular mass , measuring 54    31    30  mm , arising from the left l5s1 facet joint that had caused destruction of the joint itself and that showed severe encroachment of the adjoining foramen , with coexisting grade i anterolisthesis of l5 on s1 . the lesion was hyperdense on plain radiograph ( fig . 1 ) and on ct imaging ( fig . 2a , 2b , and 2c ) and appeared hypointense on t1- and t2-weighted mri sequences ( fig . preoperative plain film of the lumbar spine showing a large , completely calcified lesion extending out from the l5s1 intervertebral space . ( a ) axial computed tomography ( ct ) image taken preoperatively , showing the origin of the lesion from the left l5s1 facet joint . ( b ) a preoperative midsagittal ct image demonstrating grade 1 anterolisthesis of l5 on s1 . ( c ) a preoperative sagittal ct image demonstrating foraminal stenosis at l5s1 caused by the lesion . 
 ( a ) t1-weighted magnetic resonance image ( mri ) of the same lesion , which appears uniformly hypointense . ( b ) the patient underwent an l5 laminectomy for excision of the mass along with an l5 to s1 fixation and fusion . intraoperatively , the lesion was noted to consist of a pastelike material that was compressing the thecal sac and that extended ventrally out of the foramen . histologic analysis identified the lesion as a mineralized simple pseudocyst , containing mineralized proteinaceous material that did not refract plane polarized light after ethanol fixation ( fig . 4a and 4b ) . ( a ) hematoxylin and eosin  stained sections of the resection reveal dense membranous fibrous connective tissue separating spaces associated with dense calcifications as well as smaller loculated spaces filled with calcium ( 20 magnification ) . ( b ) higher magnification ( 40 ) reveals the wall of the spaces to be associated with granular calcifications and no obvious cellular lining . the patient experienced no intraoperative or postoperative complications , and her postoperative hospital course was unremarkable . by postoperative day 2 , the patient had recovered full strength in her extremities but still had some residual numbness , and she was discharged to home in stable condition on postoperative day 3 . at 2-year follow - up , the patient continued to be free of her lower extremity pain and weakness and had not experienced any subsequent postsurgical complications ( fig . 5a and 5b ) . ( a ) postoperative plain film ( anterior - posterior ) showing removal of the mass and placement of fixation hardware . mineralized , extradural lesions of the lumbar spine arising from the facet joint are uncommon causes of spinal pathology . the differential diagnosis consists of several uncommon disorders , including synovial osteochondromatosis,14 tumoral calcinosis,15 tumoral calcium pyrophosphate dehydrate crystal deposition disease ( pseudogout),16 and lumbar presentation of ossification of the ligamentum flavum.17 the case we present here represents another potential consideration in that differential diagnosis . completely calcified jfcs are rare , with only a handful of instances existing in the literature . almefty et al presented four patients with multiple - level , bilateral , consistently calcified thoracic spinal cysts.12 these lesions were atypical due to their number , location , and mineralization . kasliwal and deutsch presented on the case of a unilateral lumbar jfc at the l4l5 level.13 similar to our case , the patient presented with radicular symptoms in the setting of a lumbar lesion that appeared hypointense on t1- and t2-weighted mri . it should be noted that calcification of jfcs can result from treatment as well , as mtellus et al noted a case of a cyst undergoing complete calcification after intracystic steroid injection therapy.11 
  the case presented here was remarkable not just for its mineralization but also for its size . jfcs have typically been recorded to be between 10 and 20  mm in diameter at their widest dimension on imaging.10 
 18 the case we report here , however , measured 54  mm at its widest dimension , showing significant extension into nearby structures . moreover , although jfcs frequently extend into the spinal canal and cause compression of the thecal sac,2 the majority of the lesion in our case existed outside the spinal canal . this may explain how the cyst grew to be so large before the patient presented for evaluation . it should also be noted that our patient 's medical history included rheumatoid arthritis and scleroderma , and systemic inflammatory diseases have been associated with jfcs in the past.1 
 19 moreover , inflammatory arthritides are known to contribute to the pathogenesis of synovial cysts outside of the spine.20 however , no studies to date have established systemic inflammation as a risk factor for jfc development , and the role of inflammatory joint disease in the pathogenesis jfcs remains unclear . many methods of treating jfcs have been described , including simple laminotomy with cystectomy and the potential addition of a laminectomy , hemilaminectomy , mesial facetectomy , or foraminotomy.3 
 4 minimally invasive approaches with tubular retractors have also been described.19 
 21 in terms of treatment of this patient , it was presumed that the symptoms of back pain were secondary to facet dysfunction and that the left - sided plantar flexion weakness was due to foraminal stenosis . due to the size and mineralization of the lesion , it was felt that a complete facetectomy was needed to adequately address the underlying pathology , necessitating a concurrent fusion . our case highlights the significant variation that exists in the size , location , and content of jfcs . although uncommon , jfcs should be considered in the differential diagnosis of lesions arising from the facet joint , even if they appear calcified and noncystic in nature .
study design  case report . 
 objective  to report the case of one patient who developed a giant , completely calcified , juxtafacet cyst . 
 methods  a 57-year - old woman presented with a 2-year history of progressively worsening lower back pain , left leg pain , weakness , and paresthesias . 
 imaging showed a giant , completely calcified mass arising from the left l5s1 facet joint , with coexisting grade i l5 on s1 anterolisthesis . 
 the patient was treated with laminectomy , excision of the mass , and l5s1 fixation and fusion . 
 results  the patient had an uncomplicated postoperative course and had complete resolution of her symptoms as of 1-year follow - up . 
 conclusions  when presented with a solid - appearing , calcified mass arising from the facet joint , a completely calcified juxtafacet cyst should be considered as part of the differential diagnosis .