Usefulness of PET/CT for diagnosis of periosteal chondrosarcoma of the femur: A case report

Abstract

Periosteal chondrosarcoma is an extremely rare low-grade malignant cartilaginous tumor arising from the external bone surface. Diagnosis of periosteal chondrosarcomas may be challenging, since this condition closely resembles periosteal chondromas. It has been reported that positron emission tomography (PET) is useful in distinguishing benign from malignant cartilaginous tumors using a maximum standardized uptake value (SUV_max) cut-off of 2.0 or 2.3. This report presents the case of a 40-year-old female with an 18-month history of a tender mass in the left distal femur. Radiological findings demonstrated periosteal buttressing. Magnetic resonance imaging (MRI) revealed a chondrogenic tumor of 3 cm in size developing from the external bone surface. It was difficult to differentiate periosteal chondrosarcoma from periosteal chondroma on the basis of size and the radiological and MRI findings. PET/computed tomography (CT) revealed abnormal linear uptake with an SUV_max of 2.7, indicating a malignant tumor. A diagnosis of periosteal chondrosarcoma was made, and wide resection was performed. Tumor histology was consistent with grade II chondrosarcoma. PET/CT is thus useful in differentiating periosteal chondrosarcoma from periosteal chondroma.

Keywords: PET; chondrosarcoma; imaging; periosteal tumor.

Figure 1

Anteroposterior radiograph revealing a well formed sclerotic periosteal reaction in the metaphysis of the distal femur.

Figure 2

Axial computed tomography revealing that the tumor contained calcific densities characteristic of the external bone surface and associated with a thickened cortex, which indicates a periosteal chondrogenic tumor.

Figure 3

(A) Axial T1-weighted MRI showing a sharply delineated mass 3 cm in diameter with low to intermediate signal intensity in the bone surface of the metaphyseal region. (B) Axial T2-weighted MRI with a bright signal and associated lobulated structure with hypo-intense septa. (C) Gadolinium-enhanced T1-weighted MRI with peripheral and septal enhancements. No intramedullary extension or edema was identified.

Figure 4

(A) Whole-body PET revealing abnormal ¹⁸F-fluorodeoxyglucose uptake in the distal aspect of femur (arrow). No evidence of metastasis was identified. (B) PET/computed tomography of the distal femur showing periosteal buttressing with abnormal uptake, indicating a malignant cartilaginous tumor. PET, positron emission tomography.

Figure 5

Histological examination revealing atypical spindle cells proliferating in a myxomatous background. Cellular atypia and marked myxomatous change indicated grade II chondrosarcoma (bar, 200 μm). Magnification, ×100.