Joint Program in Nuclear Medicine

Atypical Appearance of Osteoid Osteoma

George T. LeClercq, Jr, MD
Sabah S. Tumeh, MD

May 20, 1986

Presentation

A 35 year-old male chef presented after ten months of persistent pain and swelling of the distal right fifth digit; the onset occurred soon after he cut the finger at work. Various non-steroidal anti-inflammatory agents did little to relieve his symptoms. Physical exam revealed a swollen, tender area in the region of the middle phalanx of the right fifth digit.

Imaging Findings

Plain radiographs demonstrated a 1 cm circular subchrondral lucency in the distal aspect of the middle phalanx (arrow) surrounded by a dense rim of sclerosis and mild bony expansion. Minimal periosteal reaction and significant surrounding soft tissue swelling were noted. Chronic osteomyelitis was suspected and the patient was sent for a bone scan. On blood pool images (palmar, volar) at ten minutes and delayed images revealed a focal, well-delineated area of markedly increased activity was observed in the region corresponding to the radiographic abnormality. On delayed bone scintigraphy (palmar, volar, lateral), a focal region of marked increased activity was seen in the same region. An osteoid osteoma was diagnosed at biopsy.

Diagnosis

Osteoid Osteoma

Discussion

The clinical and radiographic appearance of osteoid osteoma can simulate that of an infection. Typically osteoid osteoma involves the long bones and spine. The associated pain is often releived by aspirin. As in this case, radiographs usually disclose a lucent nidus surrounded by significant sclerosis; however, this appearance can be seen in an abscess as well. If calcium is seen within the lucent zone, the diagnosis of osteoid osteoma can be made with certainty. Periosteal reaction (absent in this case) is usually present in either disease process, and (unlike this case) soft tissue swelling is not usually significant as it is in chronic osteomyelitis.

Because of the history of penetrating trauma, the poor response to anti-inflammatory medication, the atypical location, and the significant soft tissue swelling, osteoid osteoma was not considered.

Often bone scintigraphy is performed in osteoid osteoma as the primary diagnostic modality when the clinical history is atypical or vague, or when the radiographs are equivocal or normal. Because the scintigraphic appearance of osteoid osteoma on delayed images may vary from an extremely localized mild increased activity (1), blood pool images at five minutes should be performed. On blood pool imaging, osteoid osteoma invariably shows a localized increase in activity whereas osteomyelitis shows more diffuse activity.

In those cases where bone scan is equivocal, Lisbona and Rosenthall (2) suggest that Ga-67 imaging may be helpful in distinguishing acute/subacute osteomyelitis from osteoid osteoma. Although reporting on a series of only five patients, all cases of osteoid osteoma with intense Tc-99m-MDP deposition demonstrate low grade Ga-67, unlike osteomyelitis where radiogallium is known to concentrate intensely. These studies must be interpreted cautiously since avid Tc-99m-MDP deposition with very low gallium uptake can be seen with fracture, infarction, chronic osteomyelitis and acute osteomyelitis under antibiotic treatment (2).

When a patient presents with bone pain localized to a particular region, plain radiographs should be obtained. If a characteristics lesion is found, other imaging modalities are unnecessary. Both blood pool and delayed bone scans should be reserved for cases where it is difficult clinically to determine the exact site of pain. Bone scintigraphy can localize the site where subsequent radiographs should be centered. When radiographs are negative, a positive bone scan can direct a biopsy. A bone scan is also useful to determine whether a nondescript bone lesion on radiographs is active or not and whether synchronous lesions exist.

References

1) Smith FW, et al. Scintigraphic appearances of osteoid osteoma. Radiology 1980; 137:191-195.

2) Lisbona R, Rosenthall L. Role of radionuclide imaging in osteoid osteoma. Am J Roentgenol 1979; 132:77-80.