Case Author(s): Bart Rydzewski M.D., Ph.D. and Jerold Wallis M.D. , 8/23/00 . Rating: #D2, #Q3

Diagnosis: Osteoid osteoma vs osteoblastoma.

Brief history:

17-year-old female with left lower back pain of 4-5 months duration

Images:

Anterior and posterior spot images of the pelvis and lumbar spine.

View main image(bs) in a separate image viewer

View second image(mm). Axial, coronal and sagittal SPECT images of the lumbar spine

View third image(xr). Oblique plain radiographs of the lumbar spine.

Full history/Diagnosis is available below

Diagnosis: Osteoid osteoma vs osteoblastoma.

Full history:

17-year-old female with left lateral lower back pain of 4-5 months duration which occurred suddenly while playing basketball. Plain radiographs performed at an outside hospital two months ago were reportedly negative.

Radiopharmaceutical:

15.4 mCi Tc-99m MDP i.v.

Findings:

The delayed spot images demonstrate a focus of moderately increased activity in the region of the left posterior elements of L5. The location of this abnormality was confirmed by SPECT examination of the lumbar spine. Based on the bone scintigraphy alone, the abnormality may represent a left pars interarticularis fracture, facet osteoarthritis, or a lesion of the pedicle of L5.

Plain Radiographs were obtained including oblique and coned examination of the lower lumbar spine. There was no radiographic evidence of a pars interarticularis defect. Instead, there is a lytic lesion involving the inferior aspect of the left L5 pedicle best seen on the oblique view. Differential diagnosis includes benign primary bone tumors including osteoblastoma or osteoid osteoma. Less likely etiologies would include an aneurysmal bone cyst or giant cell tumor.

Discussion:

The most common reasons for a focal increase in Tc-99m MDP uptake within the posterior elements of the vertebrae include pars interarticularis defect and benign neoplasms of the vertebrae such as osteoid osteoma, osteoblastoma, giant cell tumor and aneurysmal bone cyst. Usually, limited resolution of bone scintigraphy and SPECT of the spine does not allow for a specific diagnosis based on the nuclear medicine study alone. Plain radiography and in some instances computed tomography can effectively narrow the differential possibilities by distinguishing between pars interarticularis fracture and benign or less commonly malignant tumors as happened in this case.

Osteoid osteoma is the most common benign tumor of the spine. Patients are young and commonly present with pain and occasionally scoliosis with apex away from side of the lesion. All three stages of the triple phase bone scan are abnormal showing initially increased blood flow and increased radiopharmaceutical deposition on the later images at the site of the lesion. Classically, there is a “hot” nidus related to hypervascularity in the center of the lesion and a less intense peripheral zone related to the rim of bone sclerosis. Osteoblastomas, are larger (> 1.5 cm) than osteoid osteomas, are commonly less painful and have a natural history of progressive growth rather than spontaneous remission.

Treatment options of osteoid osteomas are limited. Non-steroidal anti-inflammatory medications are the most commonly used option. Radiofrequency (RF) ablation has been used successfully on these lesions and involves introduction of a metallic probe into the center of lesion under CT-guidance and ablation of the by controlled increase in the temperature around the tip of the probe.

References:

Textbook of Nuclear Medicine ed. Michael A. Wilson, Lippincott-Raven Publishers 1998

Clinical Nuclear Medicine Ed. MN Maisey, KE Britton, BD Collier Chapman and Hall Medical 3rd edition 1998

Differential Diagnosis List

osteoid osteoma, osteoblastoma, giant cell tumor, pars interarticularis fracture

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Spine and Contents, Category:Neoplasm, Neoplastic-like condition)

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Case number: bs122

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