A 60-year-old right-hand–dominant woman presented with a soft tissue mass in the posteromedial aspect of her right distal arm of 3 months’ duration. She denied any trauma to that area but stated the mass had slowly enlarged. She denied any pain, numbness, or tingling in the distal extremity. She also denied fevers, chills, weight loss, loss of energy, and loss of appetite but did have some occasional night sweats. She had a history of localized thyroid cancer in 1989 treated with thyroidectomy. She denied any lumps or bumps elsewhere.
Physical examination revealed a healthy-appearing woman with a palpable, firm, deep, slightly warm mass over the posteromedial aspect of her distal right arm that measured approximately 7 cm proximodistal by 4 cm mediolateral. Tinel’s test was negative, and there was no bruit, thrill, or tenderness to palpation over the mass.
The initial radiographic studies included plain radiographs and MRI of the extremity. The radiographs showed a slight soft tissue density at the posteromedial aspect of the arm without any evidence of periosteal reaction or calcification in the mass (Fig. ). Magnetic resonance imaging revealed a complex, heterogeneous, deeply situated intramuscular soft tissue mass adjacent and posterior to the neurovascular bundle on the medial aspect of the arm in the triceps muscle belly. The mass was predominantly dark with heterogeneity on the T1-weighted images (Fig. A) and bright with some heterogeneity on T2-weighted images (Fig. B). There was minimal soft tissue edema surrounding the mass. There was no bony involvement and no periosteal reaction, but it did appear to abut the humerus medially.
A plain radiograph of the elbow and distal arm shows only a nonmineralized soft tissue shadow.
Sagittal MRI of the distal upper arm soft tissue mass shows a (A) heterogeneous dark signal on the T1-weighted image and a (B) heterogeneous bright signal on the T2-weighted image.
The nonspecific MRI features of the deep, large heterogeneous soft tissue mass yielded a broad differential diagnosis, including benign and malignant entities such as malignant fibrous histiocytoma, fibrosarcoma, and even metastatic disease. Tissue for pathologic examination was obtained through a Tru-Cut core needle (Travenol Laboratories, Inc, Deerfield, IL) biopsy in the office. Staging studies, which included computed tomographic scans of the chest, abdomen, and pelvis, were negative for the presence of metastases. Laboratory values were all within normal limits, including a leukocyte count of 6000, erythrocyte sedimentation rate of 15 mm/hour, and C-reactive protein less than 0.5.
The Tru-Cut needle biopsy specimen revealed a tumor composed of nests and cords of cells with eosinophilic and vacuolated cytoplasm and relatively uniform round to oval nuclei. The cells were embedded in a myxoid and hyaline stroma and separated by broad fibrous septa (Fig. ). Foci of recent and remote hemorrhage were present, but necrosis was not identified. In addition, there was a low mitotic rate not exceeding one mitosis per 20 high-power fields (Fig. ).
A low-power photomicrograph of the tumor shows multinodular masses separated by broad collagen bands (Stain, hematoxylin and eosin; original magnification, ×20).
A high-power magnification with tumor cells shows vacuolated cytoplasm and lack of considerable nuclear atypia (Stain, hematoxylin and eosin; original magnification, ×400).
Differential diagnosis for these histologic findings included parachordoma, extraskeletal myxoid chondrosarcoma, and chordoma. Immunohistochemistry revealed expression of the cytokeratin CAM5.2 and S-100 protein by tumor cells with negative staining for cytokeratins AE1/AE3, cytokeratin 19, epithelial membrane antigen (EMA), muscle-specific actin, desmin, and carcinoembryonic antigen (CEA). An alcian blue stain was strongly positive in the stroma, with marked reduction of the staining after hyaluronidase digestion. The diffuse CAM5.2 and S-100 expression is an immunophenotype not seen in extraskeletal myxoid chondrosarcoma, although negative cytokeratin 19 and CEA with hyaluronidase digestion of the matrix favored parachordoma rather than chordoma. Because extraskeletal myxoid chondrosarcomas are characterized by the balanced chromosomal translocation t(9;22)(q22;q12), with the breakpoint involving the EWS gene on chromosome 22q12 and the CHN gene on 9q22, fluorescence in situ hybridization studies for the detection of the EWSR1 gene break-apart rearrangement were performed, and the results were negative.
The patient underwent wide resection of the tumor 2 weeks later. A curvilinear incision was made on the posteromedial aspect of the arm, which included excision of the biopsy tract. The ulnar nerve was identified and protected during the entire procedure. The mass was removed en bloc with negative intraoperative frozen section margins. She experienced some mild numbness along her small finger and the ulnar border of the ring finger but full abduction strength. The final pathologic results also were consistent with parachordoma. There has been no recurrence to date during the past 3 months of followup.