Magnetic resonance imaging findings of osteoid osteoma of the proximal femur

Abstract

Osteoid osteoma (OO) is a benign bone tumor whose main radiological finding is nidus. OO of the proximal femur can also result in non-specific findings such as hip joint effusion, perinidal bone marrow edema and soft tissue mass. Since the nidus may be difficult to identify with MR, these non-specific findings can lead to erroneous diagnosis. Therefore, MR imaging technique should be optimized in order to identify nidus. Since MR imaging has assumed increasing importance in the evaluation of disorders of the hip, radiologists must be aware of the spectrum of findings of OO of the proximal femur. The aim of this pictorial review is to show the MR imaging findings of intra-articular and extra-articular OO of the proximal femur.

The healing pattern of osteoid osteomas on computed tomography and magnetic resonance imaging after thermocoagulation

“…The presence of reactive changes in association with osteoid osteoma has been described before [6]. Osteoid osteomas produce a large amount of prostaglandins.…”

“…Osteoid osteomas produce a large amount of prostaglandins. Elevations of the prostaglandin levels up to 100-1,000 times the normal level have been demonstrated within the nidus of osteoid osteomas [6]. The production of such high levels of prostaglandins generates inflammation of the peritumoral soft tissue, causing reactive changes (synovitis and/ or effusion, and "oedema-like" changes of bone marrow as well as soft tissue oedema) [6].…”

“…However, residual "oedemalike" changes of bone marrow were found in 69% (9/13) of treatment successes. From a theoretical point of view, one would expect a total absence of "oedema-like" changes of bone marrow (or soft tissue oedema) after successful thermocoagulation, reflecting the total heatinduced destruction of the hormonally active nidus [6]. It is unclear why these "oedema-like" changes of bone marrow persist after successful thermocoagulation.…”

“…It may be that pain decreases because of the destruction of nerve fibres in and around the nidus [14] after successful thermocoagulation, while hormone production is maintained. Other possible explanations include local mechanical or degenerative changes [6], or reaction to the procedure; in this latter case one would expect these "oedema-like" changes of bone marrow to diminish gradually or disappear after successful thermocoagulation. Further study is required to determine the exact nature and evolution of these residual "oedema-like" changes of bone marrow present in successfully treated patients.…”

“…The radiolucent nidus is best seen on thin slice (1 mm to 2 mm) axial CT images, because there is no overlap of surrounding reactive sclerosis and/or periosteal reaction [3][4][5]. More recent papers have focused on the appearance of osteoid osteoma on magnetic resonance imaging (MRI), describing the morphology of the nidus, the surrounding bone, and the adjacent soft tissues, as well as the enhancement pattern of the nidus during dynamic MRI imaging [6,7].…”