Osteoblastoma Is a Metabolically Active Benign Bone Tumor on 18F-FDG PET Imaging

Abstract

We describe a case of a 9-y-old girl who on 18 F-FDG PET imaging was found to have a highly metabolically active sacral tumor with an average standarized uptake value of 6.2. The tumor was proven to be osteoblastoma by pathologic examination. Osteoblastoma is a relatively rare benign primary bone tumor and occurs predominantly in patients younger than 20 y. The most common area of involvement is the spine. Osteoblastoma has been reported to be metabolically active on 18 F-FDG PET imaging, with an average standarized uptake value of 3.2, which renders 18 F-FDG PET imaging unable to differentiate benign from malignant primary bone tumors. To our knowledge, only 5 cases of osteoblastoma evaluated by 18 F-FDG PET imaging have been reported in the literature; all were metabolically active on 18 F-FDG PET imaging. The objective of this case report is to show that a metabolically active primary bone tumor on 18 F-FDG PET imaging might be benign and not necessarily malignant. PETi s an important imaging modality for a patient with malignancy. 18 F-FDG PET imaging is commonly used for staging and restaging cancer. 18 F-FDG accumulates in cancer cells because of their increased glucose metabolism. However, increased glucose metabolism is not specific to malignancy. Some benign bone lesions may accumulate 18 F-FDG in amounts similar to those seen for malignant bone tumors (1). Osteoblastoma is an uncommon benign and vascular osteoid-forming bone tumor (2). In the literature, we could find only 5 osteoblastoma cases involving 18 F-FDG PET evaluation, all of which revealed increased 18 F-FDG uptake (1-4). Here, we present another case of sacral osteoblastoma that revealed increased metabolic activity on 18 F-FDG PET imaging. The objective of this case report is to show that a metabolically active primary bone tumor on 18 F-FDG PET imaging may be a benign tumor such as osteoblastoma and not necessarily malignant. CASE REPORTThe orthopedic clinic referred a 9-y-old girl to the nuclear medicine department for whole-body bone scanning. She had a 1-mo history of left hip pain radiating to the left thigh. Two weeks before surgery, she started to complain of intermittent abdominal pain, constipation, and occasional difficulty with urination. Initially, she was evaluated by simple radiography of the hip, with normal results. Wholebody bone scanning was performed and found an isolated focal osteoblastic lesion involving the L5 and S1 vertebrae (Fig. 1). Three days later, the patient underwent lumbar spine MR imaging, which demonstrated a large mass (measuring 4 · 2.5 cm) originating from the left sacral ala at the S1 and S2 levels. The mass was invading the spinal canal and the left S1 and S2 foramina and extended upward to the left L5-S1 neural exit canal, causing L5-S1 neural foramina expansion (Fig. 2). Five days later, the patient underwent lumbar spine CT, which demonstrated an enhancing soft-tissue mass causing expansion of the left S1 intervertebral foramen and showing dumb-bell growth inside the spinal canal and outside the l...

Imaging algorithm and multimodality evaluation of spinal osteoblastoma

“…In short, owing to the flare phenomenon, it is difficult to accurately diagnose spinal OB based only on CT and/or MRI. [6]. Generally, osteoblastoma has high osteogenic activity, which consequently leads to high uptake of 18 F-FDG by tumors [14].…”

“…For instance, previous reports on spinal OB mostly used a single imaging technique with a small sample size [3][4][5]. Furthermore, studies with PET data are very limited [6][7][8][9]. In particular, the potential use of the flare sign (observed as the diffuse inflammatory reaction in soft tissues and marrow adjacent to bone tumors) to influence diagnosis has not been fully addressed [2,10].…”

Benign Bone Conditions That May Be FDG-avid and Mimic Malignancy

“…16). 96,97 However, clinical findings, location, and particularly CT findings may give clues toward the correct diagnosis. Osteoid osteoma most commonly occurs in the long bones (femur and tibia) and typically causes night pain that is relieved with salicylates.…”

“…Excisional biopsy revealed osteoblastoma. This research was originally published in the Journal of Nuclear Medicine Technology, © by the Society of Nuclear Medicine and Molecular Imaging, Inc 96.…”

PET/CT Imaging for Langerhans Cell Histiocytosis Involving Only Posterior Elements of the Cervical Vertebra

“…It usually shows mild FDG uptake 15 . Osteoblastoma is the most common benign tumor of the posterior elements in the cervical spine within a wide age range (6–75 years) and a variable degree of FDG uptake 16–18 . In our case, the lesion was located in the posterior elements of the cervical vertebra and had a high degree of FDG uptake.…”