A Progressively Enlarging Soft Tissue Mass in a 51-Year-Old Man

A 51-year-old man presented with an enlarging and progressively painful mass in the left posterolateral shoulder. He initially noticed a small firm mass approximately 4 to 5 months before presentation and had no history of antecedent trauma. The pain was present mostly with overhead activity; there were no significant rest or nocturnal symptoms. His medical history included noninsulin dependent diabetes mellitus and hypertension. On physical examination, there was a firm, moderately tender, immobile, and nonpulsatile mass over the posterolateral aspect of the left shoulder. The lesion measured 12 cm in maximal dimension; there were no overlying skin abnormalities and no other clinically apparent masses or adenopathy. There was no associated bruit on ausculation of the mass. He had full range of motion (ROM) of the left shoulder with discomfort beyond 90° abduction and with resisted external rotation. The peripheral neurovascular examination was normal. Admission laboratory data including complete blood count, erythrocyte sedimentation rate, and serum chemistries were normal. Plain radiographs, computed tomography (CT), and magnetic resonance (MR) images were performed(Figs 1-4).Fig 1: Transscapular lateral radiograph of the left shoulder.Fig 2: Noncontrast transaxial CT at the level of the lesion.Fig 3: T1 weighted spin echo MR image of the left shoulder.Fig 4: T2 weighted spin echo MR image of the left shoulder.Based on the history, physical findings, and imaging studies, what is the differential diagnosis? RADIOLOGIC INTERPRETATION A transscapular lateral view of the left shoulder reveals a soft tissue mass posterior to the scapula with subtle flocculent calcifications associated with a chondroid matrix (Fig 1). Noncontrast transaxial CT (Fig 2) confirms the presence of a smoothly marginated soft tissue mass within the infraspinatus muscle posterior and lateral to the scapula without underlying osseous involvement. The mass is composed of fat peripherally and soft tissue of lower attenuation centrally. Punctate calcifications are seen within the soft tissue component of the mass. Magnetic resonance imaging confirms the presence of fat around the periphery of the tumor whereas the central component shows intermediate signal on T1 pulse sequences (Fig 3). The mass is heterogeneous on T2 weighted images with increased signal centrally, linear areas of low signal consistent with fibrous septae, and focal ill defined areas of intermediate signal consistent with fat (Fig 4). Extraskeletal myxoid chondrosarcoma Myxoid liposarcoma Myxoid malignant fibrous histiocytoma Parosteal lipoma Lipoma with fat necrosis and dystrophic calcification Extraskeletal osteosarcoma Infection Myositis ossificans Chondromyxoid lipoma An open biopsy was performed and the retrieved specimen consisted of firm, well encapsulated, whitish glistening tissue intermixed with fat. The photomicrographs are shown in Figures 5 and 6.Fig 5: Low power photomicrograph of the lesion(Stain, hematoxylin and eosin; magnification, ×15).Fig 6: Higher power photomicrograph of the lesion(Stain, hematoxylin and eosin; magnification, ×100).Based on the history, physical findings, radiographic studies, and histologic pictures, what is the diagnosis? HISTOLOGY At low power magnification the edge from one of the chondromyxolipomatous nodules is seen. The soft tissue capsule is composed primarily of compressed skeletal muscle and connective tissue, surrounding multiple, variably sized chondroid nodules within a lipomatous background (Fig 5). At higher power magnification a chondroid nodule with myxoid and hyaline features is seen. Emerging myxoid and chondroid metaplastic changes are arising within the adjacent lipomatous component, reflecting the fundamental pathophysiology of this lesion (Fig 6). DIAGNOSIS Chondromyxoid lipoma TREATMENT AND DISCUSSION Chondromyxoid lipoma shares radiographic and histologic similarities to other benign soft tissue tumors, such as chondroid lipoma,10 extraskeletal chondroma,4 and chondroangiolipoma,9,11 that are composed of varying amounts of fat and cartilage. As such, it is classified as a mesenchymoma whereby at least two different mesenchymal components are found that usually are not associated with one another in a single tumor.14 This lesion is more common in women than in men probably reflecting the increased ratio of fat to muscle in women compared with men. Clinically, patients usually present with a painless mass of fairly long duration in the fourth and fifth decades of life, although wide age ranges are reported.10,11 They range in size from 1 to 2 cm in the feet and hands to 12 cm in the proximal limb girdle in this case.4,5,10,11 They are most common in the proximal appendicular skeleton followed by the trunk and head and neck region in one study of 20 so called chondroid lipomas.10 They may occur in or between muscle, subcutaneously or in association with fascial structures. Radiographically, mineral densities are seen on radiographs and may appear stippled or flocculent. Heterogeneity is seen on CT with low and high attenuation areas reflecting the different mesenchymal components. Magnetic resonance imaging shows high signal areas on T1 and T2 in areas consistent with the high water content in the myxoid and cartilage components of the tumor. Similar to other predominately cartilage tumors of bone and soft tissue, this lesion has a lobular appearance with prominent fibrous septae that enhance with Gd.1,3 Grossly, these lesions have a smooth glistening surface that is encapsulated by a thin fibrous capsule. Sectioning reveals a gritty grayish white firm tumor with a lobular appearance with areas of calcification and ossification. Histologically, there are nests or cords of benign appearing uniloculated or multiloculated fat to varying degrees intermixed with myxoid matrix with well differentiated chondroid areas. The etiology of chondromyxoid lipomatous tumors is controversial,4-6,11,12 but it is thought that under certain conditions, fat can modulate and undergo either myxoid change or cartilage metaplasia or a combination of both. Hence, there seems to be a spectrum of benign chondromyxoid lipomatous lesions of soft parts with varying degrees of lipomatous, myxoid, and cartilaginous differentiation perhaps depending on the location in which this occurs and the time interval during which the process evolves. Clinically, however, they are benign and rarely recur after marginal and even intralesional resection.10 It is important to exclude other lesions such as myxoid liposarcoma (which can appear deceptively benign on CT and MR7), myxoid malignant fibrous histiocytoma, and extraskeletal chondrosarcoma that require more aggressive surgical treatment.2,15 Because of tumor heterogeneity seen in cartilage tumors in general and in this lesion in particular, needle biopsies can be misinterpreted easily leading to errors in diagnosis and treatment.8,13 For this reason, open biopsy may be more appropriate in leading to the correct diagnosis and subsequent treatment. This patient was treated with marginal resection of the mass and has had no evidence of local recurrence for 2 years. He is pain free and has full active ROM.