Primary Fibroblastic Osteosarcoma of the Lumbar Vertebra on Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography

A 37-year-old man presented with one year history of lower back and right buttock pain. He was investigated with contrast-enhanced computed tomography (CT), magnetic resonance imaging (MRI), and fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography. Enhanced CT and MRI images show an T1 iso-to-slight high-signal intensity mass with irregular osteolytic lesion in the vertebral body, both pedicle, transverse, and spinous process of L4 with bony cortical expansion and destruction. Moreover, 18F-FDG PET/CT demonstrated an area of increased 18F-FDG uptake with a maximum standardized value (SUVmax) of 3.2, corresponding to an osteolytic lesion occupying the right vertebral body, both pedicle, transverse, and spinous process of L4 spine suspicious for malignant bone tumor [Figure 1]. No other areas of abnormal 18F-FDG uptake were detected in the rest of the body. Based on this PET/CT finding, the patient had a biopsy of the L4 lesion. Histology demonstrated the presence of a fibroblastic osteosarcoma (OS), and the patient was addressed to surgical resection.

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Figure 1 An fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography scan (Biograph 2, Siemens, Germany) was performed after the injection of 370 MBq (10 mCi) of fluorine-18-fluorodeoxyglucose with a blood glucose level of 90 mg/dl for lower back and right buttock pain. The fusion sagittal (a), transverse (b), and maximum intensity projection (f) images showing an increased fluorodeoxyglucose uptake of the L4 spine with a maximum standardized uptake value (SUVmax) of 3.2, which suggest a primary malignancy of vertebra. Enhanced computed tomography (c-e) and magnetic resonance imaging (d) images show an T1 iso to slight high signal intensity mass with irregular osteolytic lesion in vertebral body, both pedicle, transverse, and spinous process of L4 with bony cortical expansion and destruction

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OS is a highly malignant sarcoma with the production of osteoid matrix. The most common sites of origin are the metaphyseal regions of the distal femur, proximal tibia, and proximal humerus.[1]

Vertebral involvement is very rare with 2%–4% of all cases and fibroblastic subtype is a low rate with 25% of all conventional OS.[2] It tends to occur in a slightly older age group, with a mean age of 38 years, than OS of the extremity.[3]

The role of 18F-FDG PET/CT in patients with appendicular OS is well known for initial staging, detecting recurrence, and/or response monitoring, whereas only a little articles evaluated the usefulness of primary vertebral OS.[45]

The present case 18F-FDG PET/CT was useful in evaluating a malignant potential of the spine mimicking bone metastasis or benign bone tumor in a patient with back pain. Although rare, primary fibroblastic OS should be considered one of the differential diagnoses of vertebral lesions detected by 18F-FDG PET/CT.