myolipoma is a rare benign tumor , first described by meis and enzinger in 1991 ( 1 ) , which occurs most frequently in adults . these tumors are composed of irregularly admixed mature adipose tissue and smooth muscle fibers ( 2 ) . myolipoma has been described in the retroperitoneum ( 1 - 3 ) , the orbital region ( 4 ) , subcutaneous locations ( 1 ) , the pericardium ( 5 ) , the rectus sheath of the anterior abdominal wall , and the abdominal cavity with attachment to the abdominal wall ( 1 ) . however , there is a paucity of literature describing the radiologic appearance of myolipoma , particularly that of soft tissue . no magnetic resonance imaging ( mri ) findings in subcutaneous myolipoma of an extremity have been reported . here , we present mri findings on a subcutaneous myolipoma of the ankle . a 34-year - old woman was admitted to our hospital with a 3-year history of a palpable mass in the left ankle . physical examination revealed a non - tender , non - fluctuant , and non - pulsatile mass in the left ankle region . on plain ankle radiography , mild soft tissue bulging was observed around the medial malleolus . in order to better characterize the lesion , we performed mri of the left ankle ( fig . the lesion was located in the subcutaneous region at the level of the posteromedial ankle joint . the mass was lobulated in contour , with some septations , and showed a hyperintense t1 , t2 signal intensity ( si ) . on fat - suppressed t2-weighted imaging ( wi ) , however , focal , non fat - suppressed , intermediate t1 and t2 si were noted at the medial peripheral aspect of the mass . following administration of gadolinium diethylenetriamene pentaacetate ( dtpa ) , the main lesion showed no remarkable enhancement ; however , the peripheral portion of the mass showed heterogeneous enhancement . the mass was well - defined , multi - lobulated , and oval - shaped in character , and was located in the medial subcutaneous tissue of the ankle . the mass measured 4.5  3.2  2.4 cm and was made up of yellowish soft tissue . upon gross pathologic examination ( fig . 1 g ) , the tumor was found to be completely encapsulated and was yellow - to - light pink in color . histologic analysis showed a variable admixture of smooth muscle and mature adipose tissue ( fig . such lesions are usually located in the retroperitoneum or abdomen , including the inguinal region and the abdominal wall ( 1 - 3 , 6 ) . less common locations include subcutaneous tissue , the orbit , the mediastinum , and the erector spinae ( 1 , 4 , 5 , 7 , 8) . in the uterus patients may present with evidence of a soft tissue mass ; however , large retroperitoneal lesions may be identified as incidental findings ( 1 ) . because they can be detected earlier , the condition is most prevalent in the fifth and sixth decades of life , with a slight predilection for woman ( 8) . neither local recurrence nor metastatic disease has been reported ( 7 ) . the tumor is benign , and is composed of variable amounts of smooth muscle fibers and mature adipose tissue , but with no lipoblasts , floret - like giant cells , or zones of atypia ( 2 ) . histopathologically , the smooth muscle component of the tumor is usually regularly interspersed with adipose tissue , resulting in a sieve like appearance ( 1 ) . only a few reports on the radiological appearance of myolipoma have appeared in the literature ( 2 , 6 , 8 , 9 ) . imaging reflects the histologic composition of the lesion , in which the proportions of adipose and non - adipose tissue can vary . due to hyperechogenicity of the lipomatous regions of the tumor , ultrasound findings are suggestive , but not diagnostic . . however , the non - lipomatous component exhibits nonspecific solid intrinsic features with soft tissue attenuation on ct scans and an intermediate si on t1-weighted mr images and an intermediate to high si on t2-weighted images ( 9 ) . in our patient , most of the mass yielded an si characteristic of fat , whereas the peripheral region showed an intermediate t1 si value , but with a t2 si value isointense to muscle , with heterogeneous enhancement , indicative of the presence of both fat and muscle components . tumors consisting of a mix of mature adipose and smooth muscle tissue , including those designated as lipoleiomyomas , fibrolipoleiomyomas , and myolipomas are exceedingly rare . however , on histological examination , the mass of the patient in our case consisted mainly of a fatty component with only a small amount of muscle component , which differed from the known findings reported in the literature of myolipomas involving other regions of the body . in order to define the typical radiologic findings of myolipoma affecting the extremities soft tissue myolipoma is a benign lesion , which must be distinguished from lesions with malignant or uncertain biologic behavior . there are two main theories , namely adipose metaplasia and a multipotential mullerian cell origin ( 2 ) . the main differential diagnoses of myolipoma include well - differentiated liposarcoma , spindle - cell lipoma , angiomyolipoma , leiomyoma with fatty degeneration , and lipoleiomyosarcoma ( 2 , 3 ) . liposarcomas contain lipoblasts or floret - like giant cells ( enlarged eosinophilic cells with atypical nuclei ) or zones of atypia . due to similar fat content , a well - differentiated liposarcoma can mimic myolipoma . internal thick , irregular fibrous septations of well - differentiated liposarcomas show ct attenuation and mr signal intensity similar to those of muscle , and may become enhanced after gadolinium administration ( 10 ) . however , a well - differentiated liposarcoma shows a fatty mass with poorly defined internal areas of non - adipose tissue . non - adipose components are most often seen as prominent thick septa ( > 2 mm ) , which may show nodularity . focal nodular or globular non - adipose areas may show significant enhancement ( 6 , 10 ) . histopathologically , myolipoma differs from liposarcoma ; the former tumor type is encapsulated , and myolipoma is non - invasive . in addition , when examined microscopically , a myolipoma does not contain lipoblasts , atypical cells , or mitotic figures ( 3 ) . spindle cell lipomas in the typical locations of myolipoma are rare , and are composed of bland spindle - shaped cells , lacking smooth muscle differentiation ( 8) . on mri , non - adipose components have an si value similar to that of muscle on t1wi and equal to or greater than that of fat on t2wi , and marked enhancement is evident ( 9 ) . angiomyolipoma differs from myolipoma in that the former tumor shows a regular arrangement of medium - sized arteries with thick muscular walls and narrow lumina , contains epithelioid smooth muscle cells showing occasional cellular atypia , displays melanoma marker positivity , and is frequently associated with tuberous sclerosis ( 3 ) . heterogeneous soft tissue attenuation ( due to hemorrhage or fibrosis or representing muscular and vascular components ) may be evident . contrast enhancement is variable and is dependent on the amount of soft tissue and vascularity ( 10 ) . a leiomyoma with fatty degeneration lacks the regular distribution of fat characteristic of a myolipoma ( 2 - 4 , 8) . myolipoma also differs significantly from lipoleiomyosarcoma in that the former does not show the histologic features of a well - differentiated liposarcoma and shows entirely banal smooth muscle tissue . this is unlike the mild - to - moderate extent of muscle atypia seen in lipoleiomyosarcoma ( 3 ) . no reports of local recurrence , metastatic disease , or malignant transformation have appeared in the literature . in conclusion , we report our mri findings of a tumor occurring in an extremity , a location where myolipomas have not been previously documented . despite the benign nature of these tumors , radiological investigations and correct diagnosis are of significant importance , because such masses need to be considered in the differential diagnosis of fat - containing lesions of soft tissue .
myolipoma is a rare benign tumor , composed of irregularly admixed adipose tissue and smooth muscle fibers . 
 few literature studies have described the radiologic appearance of myolipoma , especially in the soft tissue . 
 no mri findings in subcutaneous myolipoma of an extremity have been reported . here 
 , we report on the case of a 34-year - old woman with myolipoma in the subcutaneous tissue of the ankle and describe mri features of the lesion .