metaplastic ossification within atypical lipomatous tumor / well - differentiated liposarcoma ( alt / wdlps ) is a rare occurrence , and when present is often associated with a dedifferentiated component . we report the radiologic and pathologic features of a rare case of alt / wdlps with extensive metaplastic ossification , however without an element of dedifferentiated liposarcoma ( ddlps ) . however , a large densely calcified mass was incidentally seen in the soft tissues overlying the right scapula ( fig . the patient was unaware of the mass and denied trauma to the site , focal or asymmetric pain , weight loss , other constitutional symptoms , or known history of malignancy . the possibilities of heterotopic ossification , myositis ossificans , tumoral calcinosis , and soft tissue sarcoma were raised ; the patient was thus referred for further clinical and radiographic evaluation . figure 1radiograph of the right shoulder shows a large mass with extensive calcific density ( arrow ) overlying the right scapula . radiograph of the right shoulder shows a large mass with extensive calcific density ( arrow ) overlying the right scapula . a computed tomography ( ct ) scan of the chest , abdomen and pelvis , technetium-99  m - methylene diphosphonate [ tc]mdp ) bone scan , and magnetic resonance imaging ( mri ) were performed . ct scan demonstrated a large 13    8    5  cm well - circumscribed mass with a thin capsule medially located in the right posterior shoulder , superficial to the scapula . centrally the mass revealed dense , cloud - like calcification , which made up the bulk of the lesion . this was surrounded by a rim of mostly simple appearing fat . associated thinning and irregularity of the underlying scapula were present , and were thought to be due to pressure erosion ( fig . [ tc]mdp bone scan demonstrated a large amount of activity associated with the primary mass . an additional focus of tracer accumulation in the right posterior seventh rib corresponded to a remote , healing rib fracture ( fig . 3 ) . mri demonstrated a large , lobulated , circumscribed mass adjacent to the rotator cuff musculature , displacing the infraspinatous and teres minor . a large central area of hypointensity on both t1 and t2 sequences corresponded to areas of dense calcification seen on radiograph and ct . a surrounding rim of fatty tissue showed minimal internal septation and hyperintense signal on t1-weighted imaging ( fig . post - contrast t1 fat - saturated images revealed thin linear areas of enhancement traversing both the calcified and fatty component ( fig . 4b ) , with suppression of hyperintense signal of the fatty component . 
 figure 2axial ct scan of the right shoulder in ( a ) bone and ( b ) soft tissue windows reveals the mass in question . the bone window reveals a central cloud - like area of high density , consistent with ossification ( arrow ) . thinning and irregularity of the adjacent scapula , likely secondary to chronic pressure erosion ( arrow head ) is also present . the soft tissue window reveals to advantage the encapsulated fatty component at the periphery of the mass ( arrow ) . figure 3posterior view from a [ tc]mdp bone scan reveals intense tracer accumulation within the primary tumor , most intensely in the central area of ossification ( arrow ) . a remote , healing seventh rib fracture was seen incidentally ( arrow head ) . figure 4(a ) oblique coronal t1-weighted mri of the right shoulder reveals a large mass overlying the right scapula and displacing the infraspinatous and teres minor . the central area of signal dropout corresponds to the ossified portion of the mass ( arrow ) , and the surrounding area of hyperintensity is consistent with fat ( arrowhead ) . ( b ) oblique coronal post - contrast t1-weighted mri with fat saturation demonstrates the area of signal drop out within the tumor corresponding to fat ( arrowhead ) . minimal linear enhancement extending throughout the mass and faint enhancement of the central ossified portion ( arrow ) is seen . ( d ) axial post - contrast t1-weighted mri with fat saturation demonstrates minimal linear enhancement extending throughout the mass and faint enhancement of the central ossified portion ( arrows ) . axial ct scan of the right shoulder in ( a ) bone and ( b ) soft tissue windows reveals the mass in question . the bone window reveals a central cloud - like area of high density , consistent with ossification ( arrow ) . thinning and irregularity of the adjacent scapula , likely secondary to chronic pressure erosion ( arrow head ) is also present . the soft tissue window reveals to advantage the encapsulated fatty component at the periphery of the mass ( arrow ) . posterior view from a [ tc]mdp bone scan reveals intense tracer accumulation within the primary tumor , most intensely in the central area of ossification ( arrow ) . ( a ) oblique coronal t1-weighted mri of the right shoulder reveals a large mass overlying the right scapula and displacing the infraspinatous and teres minor . the central area of signal dropout corresponds to the ossified portion of the mass ( arrow ) , and the surrounding area of hyperintensity is consistent with fat ( arrowhead ) . ( b ) oblique coronal post - contrast t1-weighted mri with fat saturation demonstrates the area of signal drop out within the tumor corresponding to fat ( arrowhead ) . minimal linear enhancement extending throughout the mass and faint enhancement of the central ossified portion ( arrow ) is seen . ( d ) axial post - contrast t1-weighted mri with fat saturation demonstrates minimal linear enhancement extending throughout the mass and faint enhancement of the central ossified portion ( arrows ) . based on the imaging , the differential diagnosis for the mass included both benign and malignant entities . benign entities included metastatic calcification , benign lipoma with calcified fat necrosis , variants of benign lipoma such as osteolipoma and chondrolipoma , parosteal lipoma , and myositis ossificans ; malignant entities included extraskeletal osteosarcoma and liposarcoma with osteosarcomatous dedifferentiation . the patient was subsequently referred for percutaneous biopsy , and samples of both the calcified and non - calcified portions of the mass were obtained . ct - guided core - needle biopsy of the right upper back mass was performed using a 13.5-gauge introducer , an 18-gauge    15-cm temno biopsy needle and lateral to medial approach . four core biopsies were obtained through the soft tissue component of the mass ; a single core was obtained through the calcified portion of the mass using a bonopty drill advanced though the introducer . tumor seeding along a needle path is sufficiently rare as not to be an issue in clinical practice for sarcomas . histologically , the peripheral , non - calcified portion of the mass consisted of adipose tissue with slight variation in adipocyte size and occasional hyperchromatic stromal cells that were focally positive for mdm2 and cdk4 by immunohistochemistry ( fig . 5 ) . alt / wdlps contains ring and giant marker chromosomes composed of amplified material from the long arm of chromosome 12 ( 12q1315 ) , which leads to overexpression of both mdm2 and cdk4 . immunohistochemistry or fluorescence in situ hybridization ( fish ) can therefore be used to confirm the diagnosis , because benign lipomatous tumors do not harbor these genetic abnormalities . ( a ) non - ossified adipocytic component showing slight variation in adipocyte size , thickened fibrous septum , and occasional hyperchromatic cells . ( c ) immunohistochemical staining for mdm2 showed positive nuclear staining , confirming the diagnosis . ( a ) non - ossified adipocytic component showing slight variation in adipocyte size , thickened fibrous septum , and occasional hyperchromatic cells . ( c ) immunohistochemical staining for mdm2 showed positive nuclear staining , confirming the diagnosis . with the diagnosis of alt , the patient went on to full surgical excision for definitive treatment . the lesion was easily excised from the surrounding soft tissues , and no bony invasion was seen intra - operatively . gross examination revealed a mass that was over 95% ossified , with the remainder being composed of lobulated adipose tissue . no adjuvant therapy was recommended , although due to the unusual finding of metaplastic ossification , the patient was closely followed clinically and radiographically . approximately 3 years after resection , the patient remains without evidence of local recurrence or distant metastasis . lipogenic tumors , both benign and malignant , are common entities that have been reported throughout the body , accounting for nearly 50% of soft tissue neoplasms clinically encountered . both benign and malignant lipogenic tumors have varying radiologic presentations with significant overlap in appearance ; final diagnosis is often made by genetic and histologic analysis . for example , in a study by gaskin and helms in which 126 consecutive fatty masses were evaluated by mri , the positive predictive value was only 38% when the diagnosis of well - differentiated lps was suggested , with final pathologic diagnosis often being that of simple lipoma or a benign lipoma variant . similarly , the presence of calcification or ossification within an adipocytic lesion can be a diagnostic dilemma for the radiologist . benign entities such as lipoma should be considered , as trauma or ischemia can lead to central fat necrosis and subsequent calcification , although the extent of ossification and homogeneity seen in our case would be atypical . myositis ossificans in the late stages ( more than 6 months ) presents as a densely ossified mass and can therefore appear similar , particularly on radiographs , although the presence of fat as in this case would be unusual . history of trauma and various stages of maturation of myositis ossificans on imaging are important differentiating features . moreover , zonal pattern of ossification toward the periphery on histology is a characteristic feature . other rare , benign lipoma variants including chondrolipoma and osteolipoma can have grossly visible metaplastic bone formation . chondrolipoma , furthermore , has a propensity to present in the proximal extremities and limb girdles . parosteal lipoma , a benign lipoma adherent to the underlying bone , was a consideration in our case , as the scapula is a common location for this lesion and the mass itself can cause reactive changes in the associated bone . malignant tumors should always be considered in the differential for adipocytic masses with calcification or ossification . for example , rarely , metaplastic bone formation can be seen associated with well - differentiated lps , and ddlps not uncommonly shows metaplastic bone formation and heterologous elements , including osteosarcomatous differentiation . ossification in the soft tissues without surrounding fatty tissue should also raise concern for extraskeletal osteosarcoma . the term atypical lipomatous tumor and well - differentiated liposarcoma are indeed two names for the same entity . histologically and genetically , the tumors are identical , consisting of well - differentiated adipocytic tissue with sometimes subtle histologic differences from benign lipoma ( including variation in adipocyte size , thickened fibrous septa , and atypical hyperchromatic stromal cells ) and ring or giant marker chromosomes containing amplified material from the long arm of chromosome 12 ( 12q1315 ) , resulting in mdm2 and cdk4 overexpression in most cases . subtypes of benign lipomatous lesion are initially distinguished from well - differentiated liposarcoma by the image - guided percutaneous core - needle biopsies . fish for mdm2 performed on core - needle biopsy material is reported to be more sensitive and specific than immunohistochemistry for well - differentiated liposarcoma ; however , fish and immunohistochemistry have similar results on resection specimens.the behavior of the tumors , furthermore , is the same in that they have no metastatic potential . the true distinction , therefore , is solely anatomic , with tumors presenting in the extremities and subcutaneous tissues being labeled as alt and tumors in the mediastinum , retroperitoneum , mesentery , spermatic cord , or other locations being labeled as wdlps . this developed from the idea that tumors presenting in the extremities or superficial tissues , the so - called atypical lipomatous tumors , have higher rates of complete surgical excision , lower rates of local recurrence , and lower risk of undergoing dedifferentiation compared with tumors arising in the mediastinum , retroperitoneum , or spermatic cord ; hence the term well - differentiated liposarcoma . the entities of alt / wdlps and ddlps are often considered together due to their common genetic alterations , with the distinction of ddlps based on the histologic finding of a non - lipogenic component . the histologic appearances of ddlps vary greatly , ranging from a relatively uniform spindle cell morphology to a highly pleomorphic undifferentiated appearance . certain patterns , including a meningothelial - like whorling pattern of dedifferentiation , have been recently linked to bone formation within ddlps in some cases . our case is rare in that it demonstrates extensive metaplastic ossification within an alt / wdlps not associated with meningothelial - like , osteosarcomatous , or other types of dedifferentiated tissue . although a rare entity , alt / wdlps with metaplastic ossification should be considered in the differential diagnosis for a calcified soft tissue mass . although our case represents an instance when no dedifferentiation was seen , it is important to be aware that metaplastic bone formation is often associated with tumors harboring a dedifferentiated component .