Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft-tissue sarcoma that usually presents in young adults as a painless, slow-growing mass. Evans first described LGFMS in 1987 as a spindle-cell sarcoma with bland histological features and paradoxically aggressive behavior. Although young adults are most frequently affected, recent reports describe pediatric cases being increasingly more common. Males and females are affected approximately equally and common locations include the deep soft tissue of the lower extremity, particularly the thigh and trunk. Primary occurrence within the chest cavity is exceedingly rare. Local recurrence and metastasis are not uncommon and present the clinician and radiologist with challenges regarding follow-up recommendations. Review of the literature reveals many cases of slowly progressive symptoms related to a mass effect. We present a healthy 12-year-old African-American girl who interestingly developed acute symptoms of shortness of breath and chest pain while playing with her brother.