Citation, DOI and article data
Osteoid osteomas are benign bone-forming tumors that typically occur in children (particularly adolescents). They have a characteristic lucent nidus less than 1.5 or 2 cm and surrounding osteosclerotic reaction, which classically causes night pain that is relieved by the use of NSAIDs.
Osteoid osteomas are usually found in children, adolescents, and young adults, between the ages of 10 and 35 years 2.
They account for ~10% of all benign bone lesions and there is a male predilection (M:F 2-4:1) 2.
Classically patients present with nocturnal pain that is relieved by aspirin/NSAIDs (aspirin is contraindicated in children <12 years old due to risk of Reye syndrome)
When in the spine they are a classic cause of painful scoliosis, concave on the side of lesion. This typical presentation is seen in over 75% of cases 2.
Soft tissue swelling may occur (see case 4) and if close to a growth plate, accelerated growth may be evident 2, presumably related to hyperemia.
When the lesion is intracapsular, the presentation is more atypical, and more likely mimics inflammatory arthropathy or synovitis. Joint effusion is often present 2,4.
An osteoid osteoma is composed of three concentric parts 1:
- nidus, representing the neoplastic process
- meshwork of dilated vessels, osteoblasts, osteoid, and woven bone
- may have a central region of mineralization 2
- fibrovascular rim
- surrounding reactive sclerosis
The nidus releases prostaglandins (via the enzymes cyclo-oxygenase-1 and cyclo-oxygenase-2) which in turn result in pain 2.
Most osteoid osteomas occur in long tubular bones of the limbs (especially the proximal femur), but any bone may be involved.
- long bones of the limbs: ~65-80% 1,2,7
- femur most common (especially neck of femur)
- mid-tibial diaphysis common also
- phalanges: ~20%
vertebrae: ~10%, predominantly posterior elements
- lumbar: 59% 2
- cervical: 27%
- thoracic: 12%
- sacrum: 2%
Furthermore, osteoid osteomas are usually cortical lesions but they can occur anywhere within the bone including medullary, subperiosteal (most commonly in the talus), and intracapsular 2. In intracapsular osteoid osteomas, periosteal reaction may be distant from the lesion itself 9.
It is important to remember that the sclerosis is reactive and does not represent the lesion itself. The nidus is usually <2 cm in diameter, and is typically ovoid. It may have a central region of mineralization 2.
May be normal or may show a solid periosteal reaction with cortical thickening. The nidus is sometimes visible as a well-circumscribed lucent region, occasionally with a central sclerotic dot. However, dense sclerosis may sometimes obscure the nidus.
CT is excellent at characterizing the lesion and is the modality of choice. It typically shows a focally lucent nidus within surrounding sclerotic reactive bone. A central sclerotic dot may also be seen.
Skeletal scintigraphy will show typical focal uptake and at times will show a double density sign (also known as the less catchy hotter spot within hot area sign) which if present is highly specific and helpful in distinguishing it from osteomyelitis. The central focus showing intense uptake within a surrounding lower - but nonetheless increased - uptake rim.
On ultrasound, focal cortical irregularity with adjacent hypoechoic synovitis may be present at the site of intra-articular lesions. The nidus can show hypoechogenicity with posterior acoustic enhancement. Ultrasound may be able to identify the nidus as a hypervascular nidus on Doppler examination 2.
Although MRI is sensitive, it is non-specific and is often unable to identify the nidus. The hyperemia and resultant bone marrow edema pattern may result in the scans being misinterpreted as representing aggressive pathology 2.
The signal intensity of the nidus is variable on all sequences as is the degree of contrast enhancement 2.
Treatment and prognosis
The lesion is benign and treatment has traditionally been with surgical resection. Historically, this has, on occasion, been difficult because of the inherent inability to locate the nidus during surgery 3. However, percutaneous radiofrequency ablation under CT guidance is being used with increasing frequency 5.
There is growing evidence, that osteoid osteoma naturally resolves spontaneously with time and can be treated conservatively with NSAIDs in certain groups of patients 6. The average time to resolution is 33 months.
General imaging differential considerations include:
- osteomyelitis (e.g. Brodie abscess): bone scan demonstrates central area of reduced uptake representing an avascular area of purulent material
- osteoblastoma: >1.5-2 cm in size
- stress fracture
- cortical desmoid
- enostosis (bone island)
- localized cortical thickening 8
- intracortical hemangioma 8
- reactive sclerosis around an osteolytic lesion 8
- 1. Bahk Y. Combined scintigraphic and radiographic diagnosis of bone and joint diseases. Springer Verlag. (2007) ISBN:3540228802. Read it at Google Books - Find it at Amazon
- 2. Greenspan A, Jundt G, Remagen W. Differential diagnosis in orthopaedic oncology. Lippincott Williams & Wilkins. (2006) ISBN:0781779308. Read it at Google Books - Find it at Amazon
- 3. Towbin R, Kaye R, Meza MP et-al. Osteoid osteoma: percutaneous excision using a CT-guided coaxial technique. AJR Am J Roentgenol. 1995;164 (4): 945-9. AJR Am J Roentgenol (abstract) - Pubmed citation
- 4. Schlesinger AE, Hernandez RJ. Intracapsular osteoid osteoma of the proximal femur: findings on plain film and CT. AJR Am J Roentgenol. 1990;154 (6): 1241-4. AJR Am J Roentgenol (citation) - Pubmed citation
- 5. Vogl TJ, Helmberger TK, Mack MG. Percutaneous Tumor Ablation in Medical Radiology. Springer Verlag. (2007) ISBN:3540225188. Read it at Google Books - Find it at Amazon
- 6. Feletar M, Hall S. Osteoid osteoma: a case for conservative management. Rheumatology (Oxford). 2002;41 (5): 585-6. doi:10.1093/rheumatology/41.5.585 - Pubmed citation
- 7. Unni KK, Inwards CY, Research MF. Dahlin's bone tumors, general aspects and data on 10,165 cases. Lippincott Williams & Wilkins. (2009) ISBN:0781762421. Read it at Google Books - Find it at Amazon
- 8. Chai JW, Hong SH, Choi JY, Koh YH, Lee JW, Choi JA, Kang HS. Radiologic diagnosis of osteoid osteoma: from simple to challenging findings. (2010) Radiographics : a review publication of the Radiological Society of North America, Inc. 30 (3): 737-49. doi:10.1148/rg.303095120 - Pubmed
- 9. Garg G, Malot R. Intra-articular Osteoid Osteoma of Femoral Neck Region: A Simplified Treatment Strategy and Review of Literature. (2017) Journal of orthopaedic case reports. 7 (6): 36-40. doi:10.13107/jocr.2250-0685.940 - Pubmed