Neuroradiology Case of the Month

July 2002

Edward P. Lin, Sven Ekholm, MD, PhD
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 5-year old-female presented with a six month history of severe back pain which woke her at night. The pain radiated along the abdominal wall to the umbilicus and was relieved by Ibuprofen.

Radiological Findings: Skeletal scintigraphy with 99m Technicium demonstrates increased uptake on the left aspect of the T10 vertebral body (Fig. 1).

Axial CT scan with contrast (Fig. 2) revealed a sharply defined non-enhancing lesion in the left pedicle of T10 measuring 0.9 x 0.9 cm. There was destruction of the cortex medially and slight sclerosis of the vertebral body. The lesion contained calcifications.

Diagnosis: Osteoid osteoma.

Figure 1: Skeletal scintigraphy (posterior projection) with 99m Technicium demonstrates focal intensity (arrow) of increased uptake in left aspect of T10.

Figure 2: Axial (left) CT and reconstructed CT with bone settings (right) reveal 0.9 x 0.9 cm lytic lesion (arrowheads) in the left pedicle of T10 with sclerosis of the vertebral body and calcifications (arrows) present within the lesion.

Discussion: Osteoid osteoma is a common, benign, bone neoplasm of highly vascularized osteoid tissue [1,2]. Seventy-five percent of cases occur between the ages of 11 and 26 with a predilection for males (3:1 male to female ratio) [1,2]. The tumor most commonly affects the tibia and femur, but it may also be found in the humerus, vertebrae, and bones of the hands and feet [1-3]. Ten percent of cases involve the spine [4].

The etiology is unclear, but it most likely involves an inflammatory process [2,3]. Patients typically present with progressive bone pain that is worse at night [1-3]. Non-steroidal anti inflammatory medications often relieve the pain [1-3].

Osteoid osteoma consists of a nidus that measures 1.5 cm or less [1]. If greater than 1.5 cm, the tumor is classified as an osteoblastoma [1]. Most osteoid osteomas arise in the bone cortex, but they can occur in the periosteum or medulla adjacent to a joint [1]. Osteoid osteomas of the spine are found in the posterior elements and can lead to painful scoliosis [1,2].

On radiographs, cortical osteoid osteomas appear as a lucent area of several millimeters surrounded by dense, compact sclerosis [1]. The center of the nidus may also contain calcifications [1]. The periosteal reaction, or sclerotic wall, tends to blend in with the normal cortex [1].

Although routine radiographs are usually diagnostic they do not detect 25% of cases [3]. Bone scan or CT imaging is usually required to detect the location of the nidus [5]. A double density sign on skeletal scintigraphy is diagnostic and helps differentiate it from a bone abscess [1]. It is a focal area of increased activity with a second smaller area of increased uptake superimposed [5]. On CT scans, the nidus is a well-defined area of low attenuation with smooth borders [1]. MR imaging aids in the detection of non-cortical tumors that contain little reactive bone formation [6]. T1-weighted imaging typically reveals low to intermediate signal with variable enhancement of the nidus [6]. T2-weighted imaging with fat saturation has shown variable signal intensity but can easily display marrow edema [6].

The differential includes osteomyelitis, a granuloma, or metastatic tumor. Treatment involves image-guided biopsy and surgical removal of the nidus. This patient successfully underwent surgical removal of the tumor.

References:

1. Miller SL: Malignant and benign bone tumors. Radiol Clin North Am, 2001; 39(4):673-99
2. Juhl: Paul and Juhl's Essentials of Radiologic Imaging. Lippincott Williams & Wilkins, 1998, p. 140-1
3. Behrman: Nelson Textbook of Pediatrics, 16th ed., W. B. Saunders Company, 2000, p. 1568
4. Abeloff: Clinical Oncology. Churchill Livingstone, 2000, p. 2231
5. Canale: Campbell's Operative Orthopaedics. Mosby, 1998, p. 691-2
6. Spouge AR. Osteoid osteoma: MR imaging revisited. Clin Imaging, 2000; 24(1):19-27