Beyond the bones: Extraskeletal osteosarcoma of the thigh

Abstract

Extraskeletal osteosarcoma (ESOS) is a rare malignant mesenchymal soft tissue tumor that usually arises in the lower extremities. It is typically a high-grade malignancy that represents only around 1%-2% of all soft tissue sarcomas and 2%-4% of all osteosarcomas. In this report, we describe a case of a 67-year-old female who presented with a 4-day history of a painless lump in her posterior right thigh. Workup utilizing different imaging modalities yielded a diagnosis of ESOS. The radiologic features of ESOS, as well as the current treatment paradigm and prognosis of this rare malignancy, will be discussed based on a review of the literature.

Keywords: Chemotherapy; Extraskeletal osteosarcoma; Oncologic radiology; Osteogenic sarcoma; Osteoid matrix; Soft tissue sarcoma.

Fig. 1

Right femur radiograph showed an extraskeletal calcified mass in the right posteromedial thigh with osteoid matrix. There are ill-defined central calcifications and margins. No involvement of the right femur. No periosteal reaction.

Fig. 2

Targeted sonographic assessment of the right inner thigh showed a hypoechoic mass with dense calcification and significant posterior acoustic shadowing.

Fig. 3

COR STIR, COR TSE T1 FS pregadolinium, and COR TSE T1 FS postgadolinium sequences demonstrate heterogeneously enhancing mass in the posteromedial compartment of the right thigh with eccentric soft-tissue and predominately peripheral enhancement with perilesional edema. Central low signal intensity reflects known matrix.

Fig. 3

COR STIR, COR TSE T1 FS pregadolinium, and COR TSE T1 FS postgadolinium sequences demonstrate heterogeneously enhancing mass in the posteromedial compartment of the right thigh with eccentric soft-tissue and predominately peripheral enhancement with perilesional edema. Central low signal intensity reflects known matrix.

Fig. 3

COR STIR, COR TSE T1 FS pregadolinium, and COR TSE T1 FS postgadolinium sequences demonstrate heterogeneously enhancing mass in the posteromedial compartment of the right thigh with eccentric soft-tissue and predominately peripheral enhancement with perilesional edema. Central low signal intensity reflects known matrix.

Fig. 4

Axial unenhanced CT showing central calcification with ill-defined central mineralization and margins. No contiguity with the underlying femur. No periosteal reaction or aggressive features in the right femur.

Fig. 5

Bone scintigraphy showing increased uptake in the right posteromedial soft tissue mass in the thigh with greater uptake compared to the iliac crest. No suspicious uptake elsewhere.

Fig. 6

Six months repeat bone scintigraphy showing increased uptake in anterior iliac spines, right femur, and lumbar spine, consistent with metastatic disease.