eMedicine Specialties > Radiology > Musculoskeletal

Osteoid Osteoma

Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, Consultant Radiologist and Honorary Professor, North Manchester General Hospital Pennine Acute NHS Trust, UK
Muthusamy Chandramohan, MBBS, DMRD, FRCR, Consultant Radiologist, Bradford Teaching Hospitals, UK; Ian Turnbull, MB, ChB, MD, DMRD, FRCR, Lecturer, Department of Radiology, University of Manchester; Consulting Neuroradiologist, Hope Hospital, Salford, Manchester and North Manchester General Hospital, UK; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute

Updated: Sep 1, 2009

Introduction

Background

Osteoid osteoma is a benign skeletal neoplasm of unknown etiology that is composed of osteoid and woven bone. The tumor is usually smaller than 1.5 cm in diameter. Osteoid osteoma can occur in any bone, but in approximately two thirds of patients, the appendicular skeleton is involved. The skull and facial bones are involved exceptionally.

Most patients with osteoid osteoma are young. Rarely, an ossification center is affected. The classic presentation is that of focal bone pain at the site of the tumor. The pain worsens at night and increases with activity; it is dramatically relieved with small doses of aspirin. The lesion initially appears as a small sclerotic bone island within a circular lucent defect. This central nidus is seldom larger than 1.5 cm in diameter, and it may be associated with considerable overlying cortical and endosteal bone sclerosis. The tumors may regress spontaneously. The mechanism of this involution is not known, but tumor infarction is a possibility.

Radiograph of the right great toe in a 24-year-old woman shows a partly calcified lesion in the medulla of the distal phalanx, with no periosteal new bone formation suggestive of osteoid osteoma.

Transaxial CT scan in a 52-year-old man who had a biopsy-proven giant osteoid osteoma (osteoblastoma) and who presented with severe low back pain (same patient as in Images 15-16 and 18-19 in Multimedia) shows the sharply demarcated radiolucent nidus of the osteoid osteoma extending to the left pedicle.

Sagittal T1-weighted MRI in a 52-year-old man who had a biopsy-proven giant osteoid osteoma (osteoblastoma) and who presented with severe low back pain (same patient as in Images 15-17 and 19 in Multimedia). Osteoid osteoma of the L4 vertebral body was diagnosed. The nidus is hyperintense to the bone marrow but less intense than the fat. In this patient, MRI findings do not add to the CT findings.

Radionuclide bone scan in a 25-year-old man with cortical osteoid osteoma (same patient as in Image 1 in Multimedia) shows focal intense uptake of radioisotope corresponding to the site of radiographic abnormality, which is consistent with osteoid osteoma.

Recent studies

Shukla et al performed a retrospective review of radiographic, CT, and MRI images in 9 patients with osteoid osteoma of the foot and found that in young patients with chronic hindfoot pain and a normal radiograph, MRI features suggestive of possible osteoid osteoma include extensive bone marrow edema limited to a single bone, with a possible nidus demonstrated in two thirds of cases. The authors in the Shukla study noted that the presence or absence of a nidus should be confirmed with high-resolution CT.¹

In the Shukla study, classic symptoms (ie, night pain, relief with aspirin) were identified in 5 of 8 cases. In 5 patients, the lesion was located in the hindfoot (4 calcaneus, 1 talus), while 4 were in the midfoot or forefoot (2 metatarsal, 2 phalangeal). Radiographs were normal in all patients with hindfoot lesions, and CT identified the nidus in all cases except in a case of terminal phalanx lesion; MRI demonstrated a nidus in 6 of 9 cases.The nidus was of predominantly intermediate signal intensity on T1-weighted images and of intermediate to high signal intensity on T2-weighted images. High-grade bone marrow edema limited to the affected bone and adjacent soft-tissue edema was identified in all cases.¹

von Kalle et al retrospectively correlated the results of dynamic contrast-enhanced MRI with histologic and clinical diagnoses in 54 patients with osteoid osteoma who were diagnosed by MRI. In 49 of 54 patients (90.7%), the diagnosis of osteoid osteoma was determined to be certain or highly probable, and 38 of 54 osteoid osteomas were histologically proven. Five MRI diagnoses were regarded as false positives. According to the authors, tailored high-resolution MRI with dynamic contrast enhancement can reliably diagnose osteoid osteomas and pinpoint the nidus. The authors proposed a stepwise approach with STIR sequences, dynamic contrast-enhanced scanning, and high-resolution postcontrast T1 spin echo sequences with fat saturation.²

Pathophysiology

Features of the tumor

The tumor consists of an ovoid or spherical nidus of osteoid-rich tissue and interconnected bone trabeculae superimposed on a background of highly vascularized connective tissue containing large dilated vascular channels. The amount of osseous and osteoid tissue varies within the nidus and is reflected in its radiologic opacity. The average size of the nidus is approximately 1.5 cm, but its size can be 0.5-2 cm. Generally, the amount of osteoid tissue exceeds that of mineralized bone. Multicentric nidi with osteoid osteoma have been reported in 24 cases in the world literature.³

Multinucleated giant cells and osteoclasts are frequently observed. The degree of bone sclerosis varies around the central nidus, but such reactions may be minimal and are sometimes absent. The sclerosis and osteoblastic rimming are indistinguishable from findings in osteoblastoma. Unlike in osteoblastoma, neural staining techniques reveal many axons throughout an osteoid osteoma, which probably accounts for the pain. Levels of prostaglandin E₂ are markedly elevated in the nidus; this is presumably the cause of pain and vasodilatation.⁴

Classification

Osteoid osteoma is classified as cortical, cancellous, or subperiosteal.

Cortical tumors are the most common. The radiolucent nidus is within the cortical bone, where it is surrounded by a fusiform cortical thickening or solid or laminated periosteal new bone formation.

Cancellous osteoid osteoma has an intramedullary location. Intra-articular osteoid osteomas are difficult to identify, and a delay of 4 months to 5 years before diagnosis is not unusual. The most common sites affected by cancellous osteoid osteomas include the juxta-articular region of the femoral neck, the posterior elements of the spine, and the small bones of the hands and feet. Usually, little sclerosis occurs around the nidus. Intra-articular tumors are associated with joint-space widening as a result of joint effusion or synovitis.

Subperiosteal osteoid osteoma is a rare form of the disease that usually presents as a rounded soft-tissue mass adjacent to a bony cortex, which it excavates. Surrounding reactive changes are usually absent. The common sites involved include juxta- or intra-articular regions of the medial aspect of the femoral neck and the hands and feet, in particular, the neck of the talus.

Frequency

United States

In a series of 8542 patients with primary bone tumors, investigators from the Mayo Clinic reported that osteoid osteomas accounted for 12.1% of benign tumors and 2.9% of all tumors. The most common skeletal sites are the metaphysis or diaphysis of long bones, which are affected in 73% of patients. The spine is affected in 10-14% of patients; these predominantly involve the posterior spinal elements. The hands are affected in 8%, and the feet, in 4%. The tumor has been reported in all parts of the skeleton.

International

The overall incidence in Europe is the same as in the United States, but the international incidence is not known.

Mortality/Morbidity

The tumor has no malignant potential. The tumor usually does not grow, and it occasionally regresses spontaneously or becomes dormant, leaving residual sclerosis.

Osteoid osteoma may induce scoliosis, which is initially postural; however, with time, structural changes may occur. The degree of rotational anomaly of the spine is related to the patient's age at onset and the duration of symptoms. The incidence of structural scoliosis in patients with mature skeletons is low, even when symptoms last longer than 2 years.
The effect of surgery on spinal rotational deformity depends on the skeletal maturity and length of time symptoms have lasted. In most patients, scoliosis improves or resolves if the tumor is removed within 15 months of the onset of symptoms.
Regression has been documented both clinically and radiologically, but usually, complete surgical excision of the nidus is required. Reactive sclerosis subsequently resolves spontaneously.⁵

Race

Osteoid osteomas are uncommon in blacks.

Sex

Osteoid osteoma more commonly affects males than females. The male-to-female ratio is 2:1.

Age

The age range in patients is 5-56 years.

Three quarters of patients are aged 10-30 years, and more than 90% of patients are aged 5-25 years.
The tumor is uncommon in children younger than 5 years or in adults older than 40 years.

Anatomy

As many as 80% of cases involve the cortical bone; the remainder of the tumors are intramedullary.

Presentation

The classic presentation includes focal skeletal bone pain, which worsens at night and is frequently relieved with a small dose of aspirin. Pain that increases with activity and at night occurs in 95% of patients with spinal tumors. In 29% of patients, the pain is severe enough to waken the patient. The site of involvement may be tender to touch or pressure. Constitutional symptoms are usually absent.

When the spinal column is involved, muscle spasms may cause abnormal alignment. A painful scoliosis may be concave toward the lesion. Kyphoscoliosis, torticollis, and exaggerated lordosis may also be seen. The onset of scoliosis may be acute and is frequently initiated by physical exertion. Osteoid osteoma has been called the most common cause of painful scoliosis.

Definite neurologic abnormalities are seen in 6.5% of patients with spinal osteoid osteomas. An osteoid osteoma affecting the hip may cause referred pain, simulating that associated with nerve root compression by an intervertebral disc lesion. An intracapsular lesion often provokes a considerable intra-articular inflammatory response, mimicking erosive arthropathy, crystal arthropathy, or infective arthritis. Approximately one half of patients with intra-articular lesions have complications of osteoarthrosis 1.5-22 years after the onset of symptoms. Rarely, marked weakness associated with muscular atrophy may affect the involved limb, particularly when the tumor is long-standing.

Preferred Examination

Radiography is the initial examination of choice and may be the only examination required. CT is used for precise localization of the nidus and may be used for guiding percutaneous ablation.^6,7,8 MRI is a useful imaging technique, but CT appears superior for precise localization. The roles of conventional and Doppler ultrasonography have not been established. Angiography may be useful in differentiating the tumor from a Brodie abscess. Single-photon emission computed tomography (SPECT) is useful in the localization of the tumor when the spinal arch or spinous process is involved.

Radionuclide scanning for technetium-99m diphosphonate uptake shows fairly intense activity at the tumor site. This examination may also be used to localize the tumor preoperatively and to establish complete removal of the nidus by using a hand-held radioactivity detector. Radionuclide scanning is a sensitive technique, and findings may be positive before radiographic changes are apparent.^9,10

Limitations of Techniques

The nidus in spinal involvement may be difficult to detect by using plain radiographs. Intra-articular tumors are difficult to detect on plain radiographs because of the absent or limited sclerosis around the nidus.

CT has the disadvantage of ionizing radiation. On MRIs, tumors are not as conspicuous as they are on CT scans. Angiography is an invasive procedure, and a minor overlap of angiographic features occurs with a Brodie abscess. The specificity of radionuclide bone scanning is low.

Differential Diagnoses

Bone Infarct	Lymphoma, Bone
Bone Island	Osteoblastoma
Bone Metastases	Osteomyelitis, Chronic
Legg-Calve-Perthes Disease	Stress Fracture

Radiography

Findings

Plain radiograph in a 25-year-old man with cortical osteoid osteoma. Lateral view of the right tibia shows a radiolucent nidus surrounded by fusiform cortical thickening.

Plain radiograph of the pelvis in a 6-year-old child who presented with left hip pain. The radiograph shows a well-defined area of sclerosis surrounded by a ring of radiolucency in the left femoral neck. Note the absence of periosteal reaction that suggests intramedullary or cancellous osteoid osteoma.

Radiograph of the hip in an 8-year-old child who presented with left hip pain and restriction of movement. An intra-articular osteoid osteoma in the medial aspect of the femoral neck has resulted in periosteal new bone formation.

Radiograph of the right great toe in a 24-year-old woman shows a partly calcified lesion in the medulla of the distal phalanx, with no periosteal new bone formation suggestive of osteoid osteoma.

Lateral view of the thoracic spine in a 56-year-old woman who presented with abdominal pain. Initial findings of chest radiography, intravenous pyelography, barium enema, and cholecystogram were normal. An isotope bone scan showed focal increased uptake in the vertebral body of the lower thoracic spine. Plain radiograph corresponding to the site of the abnormality shows a radiolucent lesion in the posterior aspect of the T11 vertebral body with surrounding sclerosis that was diagnosed as giant osteoid osteoma and later was confirmed at histologic analysis.

Anteroposterior radiograph of the lumbar spine in a 52-year-old man who had a biopsy-proven giant osteoid osteoma (osteoblastoma) and who presented with severe low back pain. Radiograph shows a well-defined sclerotic lesion in the left side of the L4 vertebral body.

Lateral view of the lumbar spine in a 52-year-old man who had a biopsy-proven giant osteoid osteoma (osteoblastoma) and who presented with severe low back pain (same patient as in Images 15 and 17-19 in Multimedia) The radiolucent nidus is seen clearly; a central area of sclerosis consistent with osteoid osteoma is visible.

Radiographic features depend on the site of involvement, the duration of symptoms, and the age of the patient (see Images above and Images 1, 7, 9, 11, 13, 15-16 in Multimedia).

A circular or ovoid lucent defect is seen in 75% of patients. This defect is usually smaller than 1.5 cm in diameter and is associated with a variable degree of cortical and endosteal sclerosis.

The site of the tumor determines the degree of bone sclerosis. In medullary tumors, sclerosis is minimal or absent. Cortical and subperiosteal tumors provoke considerable sclerosis. Long-standing tumors demonstrate more sclerosis. Children also mount more of a sclerotic response than do adults.

In subarticular and intracapsular tumors, reactive sclerosis may be absent or minimal, or it may occur relatively distant to the lesion. This sclerosis usually occurs in tumors of the femoral neck because no periosteum covered by articular cartilage is present on the surface. However, whatever periosteum exists beyond the areas covered by the articular cartilage cannot be elevated because it is bound down by enhancing Sharpey fibers.

Intra-articular tumors may show joint effusion associated with the premature loss of cartilage. Osteoarthrosis affects approximately one half of patients with intra-articular tumors. Rarely, patients experience regional osteoporosis, presumably as a result of disuse. Regional osteoporosis may appear as an area of osteopenia around a joint.

With spinal involvement, alignment abnormalities may be obvious, such as scoliosis, kyphosis, or hyperlordosis. In children with a long-standing tumor, the involved bone may demonstrate overgrowth.

Supplementary radiographic methods, such as overpenetrated radiographs or thin-section planning radiographs, may be useful in locating tumors in portions of the skeleton with complex anatomy.

Degree of Confidence

Radiographs remain the mainstay of imaging in an orthopedic workup. Usually, radiography is the first examination performed in patients with bone pain. In three quarters of patients, a diagnosis may be suggested on the basis of the plain radiographic findings. However, some areas of the skeleton are difficult to assess by using plain radiographs in patients with a suspected osteoid osteoma. These areas include the spine, the femoral neck, and the small bones of the hands and feet. In the spine, overlapping shadows of the vertebral column can easily obscure the tumor.

False Positives/Negatives

A long list of conditions may mimic an osteoid osteoma (see Differentials). If excessive, new bone formation can mask the nidus, resulting in a false-negative diagnosis. When the tumor is in a long bone, a periosteal reaction may occur distant to the lesion or in an adjacent bone; these may cause diagnostic problems. However, this difficulty should not deter the radiologist from making the diagnosis.

Particular pitfalls include a Brodie abscess and a tumor in the long bones of children where overgrowth may occur. Both osteoblastoma and osteoid osteoma have a propensity for the posterior elements of the spine. Both are osteoblastic tumors; they are differentiated primarily by their sizes. Osteoblastomas become considerably larger than osteoid osteomas and are better depicted on plain radiographs.