Low-Grade Fibromyxoid Sarcoma of the Back

Abstract

A 29-year-old male presented with a seven-year history of a slow-growing, painless, firm, mobile mass in the right upper back that was bothersome when supine or with direct pressure. On initial presentation, a clinical diagnosis of lipoma was given. The mass progressively increased in size over several years but remained painless. The mass measured 15 x 10 cm on examination. Excision of the lesion was performed, which revealed a white cut surface with cystic degenerative changes. Histologically, the lesion revealed spindle cell morphology with occasional mitosis. Diffuse immunohistochemical staining with MUC4 supports a diagnosis of low-grade fibromyxoid sarcoma (LGFMS). Tumor was present with focal extension into the deep margin. However, serial magnetic resonance imaging studies performed suggest no residual disease and negative regional lymph node involvement. This case demonstrates the growth pattern of LGFMS, but also denotes the importance of correlating radiological and pathological features to accurately diagnose and treat these tumors in a timely fashion.

Keywords: lipoma; low-grade fibromyxoid sarcoma; magnetic resonance imaging; metastasis; soft tissue tumours.

Figure 1. Circumscribed lesion with a central cystic area filled with necrotic material and a peripheral rim of tan-white solid lesion extending to the ink margin

Figure 2. Pathologic specimen of back mass

(a,b,c) H&E stain showing (a, 4X) spindle cell proliferation with fibrous and myxoid areas, (b, 10X) hypocellular areas with curvilinear vessels, and (c, 20X) monomorphic cells with bland cytology. (d) MUC4, diffuse and strong staining of lesion.

Figure 3. Post-resection axial magnetic resonance imaging of back mass

Axial post-contrast T2 SPAIR (a) and axial T1 (b) MR images of right upper back status post resection of soft-tissue mass. Focal fluid collection measured to be approximately 1.4 x 0.5 x 2.3 cm, which was noted to be decreased in size from previous imaging study. SPAIR, spectral attenuated inversion recovery; MR, magnetic resonance.