PMC3335335_01
Radiograph of the right shoulder shows a large mass with extensive calcific density (arrow) overlying the right scapula.
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F1
However, a large densely calcified mass was incidentally seen in the soft tissues overlying the right scapula (Fig. 1).
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).
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F2
Associated thinning and irregularity of the underlying scapula were present, and were thought to be due to pressure erosion (Fig. 2). [99mTc]MDP bone scan demonstrated a large amount of activity associated with the primary mass.
Posterior view from a [99mTc]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).
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An additional focus of tracer accumulation in the right posterior seventh rib corresponded to a remote, healing rib fracture (Fig. 3).
(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. (c) Axial pre-contrast T1-weighted MRI with fat saturation. (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).
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A surrounding rim of fatty tissue showed minimal internal septation and hyperintense signal on T1-weighted imaging (Fig. 4A). 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.   
Histology of atypical lipomatous tumor with extensive ossification. (a) Non-ossified adipocytic component showing slight variation in adipocyte size, thickened fibrous septum, and occasional hyperchromatic cells. (b) The dominant ossified component was composed of mature trabecular bone. (c) Immunohistochemical staining for MDM2 showed positive nuclear staining, confirming the diagnosis.
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CDK4 by immunohistochemistry (Fig. 5). Cytogenetic analysis showed ring chromosomes.