Osteoid osteoma: MR imaging revisited

Abstract

To assess and compare with computed tomography (CT) the performance of magnetic resonance (MR) imaging in the detection of osteoid osteoma, and determine the features of this lesion on MR imaging. The prospective MR imaging and CT diagnosis of osteoid osteoma was determined from original radiology reports. MR images were assessed retrospectively with regard to the location and signal intensity of the nidus and surrounding bone marrow and soft tissue edema. These findings were correlated with the age of the patient, duration of symptoms, and drug therapy. Ten patients with histologically proven osteoid osteoma who underwent MR imaging were reviewed. All 10 lesions were correctly diagnosed at the time of MR imaging. None of the lesions was intracortical. Nine lesions were intra-articular. Two out of five patients with extracortical lesions had false negative CT preceding the MR study. Signal intensity of the nidus, marrow, and soft tissue edema on MR imaging were variable. Perinidal edema was most pronounced in younger patients and had no apparent relation to drug therapy. MR imaging reliably demonstrates the nidus of an osteoid osteoma, which has a variable appearance related to its position relative to the cortex of the bone. A predominance of cancellous osteoid osteomas are encountered in patients referred for MR imaging. Marrow edema in the vicinity of the lesion improves the conspicuity of the nidus. CT may fail to diagnose osteoid osteoma when the nidus is in a cancellous location, due to the lack of perinidal density alteration.

Introduction

Osteoid osteoma is a common bone tumor, comprising approximately 12% of all benign skeletal lesions [1], [2]. Its diagnosis has previously relied on a combination of clinical history and radiographs, complemented by computed tomography (CT) and scintigraphy [3]. Although magnetic resonance (MR) imaging is regarded as the modality of choice for assessment of many musculoskeletal neoplasms, it is currently believed to have limited value for diagnosis of osteoid osteoma [4], [5]. Published reports indicate that osteoid osteoma has a misleading appearance, often leading to the diagnosis of infection or a more aggressive bone tumor on MR imaging and cite CT as being more accurate than MR imaging for detection of the nidus [5], [6], [7], [8]. The relatively low resolution MR imaging techniques employed in previous studies, combined with the unfamiliar and variable findings, which may be present on MR imaging, could have contributed to misdiagnosis in the past.

A retrospective evaluation of 10 patients with histologically proven osteoid osteoma who underwent MR imaging using higher resolution techniques than previously reported [5], [6] was undertaken. The performance of MR imaging in the detection and diagnosis of osteoid osteoma and the features of these lesions on MR imaging were assessed. MR imaging was compared to CT for lesion diagnosis in those patients who had CT prior to the MR examination.