myxoma is a benign neoplasm of mesenchymal origin composed of undifferentiated stellate cells in a myxoid stroma , which were differentiated into altered fibroblasts and lost their ability to produce normal collagen18 ) .
myxoma can arise in a variety of locations ; heart , subcutaneous and aponeurotic tissues , bone , genitourinary tract and skin , etc .
the most frequent site for myxoma is the heart , and bony myxoma is almost exclusively limited to the jaws and palate , representing 40 - 50% of all head and neck myxomas216 ) .
the soft tissue myxoma is rare , and occurs mostly in the large skeletal muscles .
the myxomas that arise in the skeletal muscles are generally called intramuscular myxomas ( ims ) .
the most of ims are detected in the fourth to sixth decades of life with slight female predominance16 ) .
i m accounts for about 3 - 17% of the all myxomas , and the incidence is about 1 case per million population per a year51823 ) . to our knowledge ,
we report the eighth case of a myxoma developed within the lumbosacral paraspinal muscle ( including thoracolumbar paraspinal muscle ) , which had some different characteristics from the typical i m , and brief review of the literature will be followed .
a 62-year - old female was referred to our hospital for mass - like lesion detected on magnetic resonance imaging ( mri ) of her spine .
she presented with low - back pain just for 3 months without radiating leg pain , and the symptom was slowly progressive .
but , interestingly , she had the previous history of bone harvest on the right posterior superior iliac spine ( psis ) for the cervical fusion operation 15 years ago in the other hospital . physical examination revealed a large palpable mass on the right paraspinal area in the lumbosacral region , but there was no associated tenderness in this region .
her neurologic examination at the time of admission was fully normal , and there was no abnormal finding on the laboratory tests and the electrophysiological studies such as electromyography ( emg ) and somatosensory evoked potential ( ssep ) .
mri demonstrated a multi - lobulated mass in the right lumbosacral paraspinal muscles in contact with the posterior elements of the l4 and l5 vertebra ( fig .
this well - circumscribed mass was measured approximately 4.03.56.5 cm in size , and the lesion was hypointense on t1-weighted image ( t1wi ) and hyperintense on t2-weighted image ( t2wi ) .
there were heterogenously enhancing foci inside the mass with peripheral and septal enhancement on the post - contrast t1wi . on computed tomography ( ct )
scan of the lumbosacral region , this mass had low density and some calcification particularly on the inferior portion of the mass ( fig .
there was no bony destruction or invasion around the mass . in the process of a full diagnostic workup
, we found her previous abdominal ct images in picture archiving computer system ( pacs ) , which had been performed for evaluation of her abdominal pain 4 months ago ( fig . 2c ,
d ) . in the previous abdominal ct , although it was slightly smaller than the mass of recent lumbar ct , the hypodense lesion was also seen at the same area .
it was notable that calcification inside the mass was not detected on the previous abdominal ct .
we planned to conduct the complete excision , instead of simple biopsy ( for example , ct - guided biopsy ) , because the tumor was not only symptomatic , but also the operation had fairly limited risk to the patient .
the tumor was encapsulated and lobulated with grayish white surface , and there was no evidence of the infiltration or invasion into the surrounding bony structures .
3 ) . according to the frozen biopsy during the operation , the mass was revealed to myxoid tumor , and the final histopathological findings were consistent with intramuscular myxoma .
this mass was composed of prominent myxoid stroma with a distinct presence of spindle and stellate cells , and while pyknotic nuclei and karyorrhectic nuclei were also seen ( fig .
numerous micro - calcifications were also found , especially in the peripheral capsular area of the tumor .
the patient was neurologically free and experienced complete relief of her low - back pain postoperatively .
since stout et al18 ) . outlined the diagnostic criteria and defined myxoma at 1948 , the intramuscular myxoma has been known as the most rare sub - type in these tumor category .
ims have been reported at the various locations such as thighs , buttocks , upper limbs , shoulders , and paravertebral area . of those ims ,
paraspinal regions are the most uncommon site , and so far , only 14 cases of paraspinal ims have been reported .
and to the best of our knowledge , this report is just the eighth case of paraspinal i m in the lumbosacral area including one case of thoracolumbar lesion , and the first case in asian population ( table 1)891114151720 ) .
ims usually appear as well - circumscribed homogeneous low - density lesions within the skeletal muscle on ct scan , and have low - signal intensity on t1wi and high - signal intensity on t2wi .
bancroft el al.1 ) described that the peri - tumoral fat rind on t1wi and increased signal in the adjacent muscle on t2wi are the most reliable radiologic features for distinguishing intramuscular myxoma from other myxoid tumor .
but in this case , this finding was not definite on the mri . on gross inspection , the tumor has usually oval shape and shows well - circumscribed appearance , however its fibrous tissue often has incomplete pseudocapsule to result in infiltration of adjacent musculature510 ) . and
in general the tumor has a glistering gray - white appearance and contains gelatinous material and cyst filled with fluid inside the mass .
histologically , ims are composed of well - localized myxomatous connective tissue surrounded by a collagenous fibrous connective tissue22 ) .
ims are often confused with other pathologic conditions such as ganglion or neurofibroma , and furthermore , with other mucoid sarcomas such as liposarcomas , chondrosarcomas , low - grade fibromyxoid sarcoma and malignant histiocytomas , because these sarcomas are also accompanied by the myxomatous degeneration .
however , several critical clues had been presented , which help to distinguish ims from other myxoid lesions .
first , ims have poor vascularization and a paucity of cells ( lipoblasts or chondroblasts ) , in contrast to myxoid liposarcoma which has a rich , delicate , plexiform capillary vascular network . secondly , ims lack nuclear atypia , necrosis , and prominent mitotic activity .
in addition , on the enhanced mri , soft tissue sarcomas showed heterogeneity , intense enhancement , septation , ill - defined margins and invasion of adjacent structure against the ims .
moreover , ims often do not have a true capsule , and therefore could infiltrate to the adjacent striated muscle , resulting in muscle atrophy which appear as a peri - tumoral fat rind on t1wi .
additionally , doyle et al.4 ) presented the muc4 protein as a specific marker for distinguishing from low - grade fibromyxoid sarcroma .
ims usually present as a solitary slow growing painless mass , however multiple myxomas can occur on rare specific condition , for example , mazabraud 's syndrome .
the clinical manifestations of ims generally are non - specific , but rather presenting symptoms depend on the affected locations . in our case ,
the patient also presented with ambiguous low back pain and this symptom was resolved after total resection of the tumor . in general , ims are known as slowly growing and painless tumors , whereas there are some differences from typical natures of ims in this case .
first , it had been just asymptomatic mass , but it developed to symptomatic lesion in a very short time ( about 3 months ) .
there was demonstrable difference in size of the tumor ; widthlengthheight=3.03.05.4 cm to 4.03.56.5 cm .
in addition , a new calcification inside the mass was accompanied with tumor growth , while there is no internal calcification in most cases of i m .
third , the location of i m was adjacent to the previous operation site ( iliac bone harvest site ) .
although the pathogenesis of ims remains obscure , there are several theories for explaining the pathogenesis . according to one of the theories ,
stellate cells may be altered fibroblasts that fail to produce mature collagen5 ) . by glazunov and puckov , " viral origin "
wirth et al.24 ) proposed the fibrous dysplasia as another theory for the pathogenesis of ims , and fibrous dysplasia usually precedes the ims by several years .
we assumed that interruption of paraspinal muscles by previous operation could induce fibrous dysplasia to arise i m .
though there was no report about the prevalence by race due to the rarity of the incidence of ims , previous many reports were almost confined to the western population .
our case is the first case of i m in asian people , which developed in the lumbosacral paraspinal musculature .
the clinical course of ims is known to be nearly benign , and the treatment for ims is the total surgical resection . there is no report of metastasis or malignant change , but occasionally local recurrence resulting from incomplete resection has been reported6913 ) .
therefore , if possible , wide excision with clean margins is recommended to avoid local recurrence , since ims have an infiltrative tendency to surrounding muscles .
we report the first case of the paraspinal intramuscular myxoma developed in the lumbosacral area in asian population .
intramuscular myxomas are uncommon benign tumors , especially in the paraspinal area , and moreover it is difficult to make a diagnosis before operation because of the lack of characteristic clinical history and radiographic findings , however , neurosurgeons should be aware of this entity .
 intramuscular myxoma ( i m ) is a benign neoplasm of mesenchymal origin . 
 we report a rare case of i m which was located in the lumbosacral paraspinal muscles . 
 a 62-year - old female patient presented with progressive low back pain for 2 months , and the radiologic findings showed a large mass ( 4.03.56.5 cm ) in the right lumbosacral paraspinal area . 
 total resection of the tumor was performed and the symptom was nearly resolved after surgery . although the immuno - histopathological analysis was consistent with i m , there were some different findings from typical pathological characteristics of i m in this case . 
 firstly , the symptomatic change of the mass took relatively short time ( less than 3 months ) , and this change was accompanied by partial calcification inside the mass . 
 moreover , iatrogenic interruption of paravertebral muscle by the other previous operation might be the promoting factor of the fibrous dysplasia , which can explain the pathogenesis of i m . 
 to our knowledge , this is the eighth case of the lumbar paraspinal myxoma reported in the literatures and the first case in asian population . 