A 13 year-old female patient with no history of previous trauma, referred with lower back pain that has been present for two years. The orthopaedic surgeon requested an X-ray.
Our patient underwent conventional X-ray, computed tomography (CT) and magnetic resonance imaging (MRI).
Imaging revealed a radiolucent oval image (nidus) in the posterior aspect of the right iliac bone, with a sclerotic dot inside. Also, a thick solid regular sclerotic cortical thickening surrounding the nidus is seen. This is the typical presentation of an osteoid osteoma.
Osteoid osteomas (OO) are benign bone tumors composed of osteoblasts which tend to be small (less than 2 cm in diameter) and surrounded by a solid periosteal reaction. The histological appearance is that of a fibrovascular stroma with numerous osteoblasts, osteoid tissue, well-formed woven bone, and giant cells [1, 3].
It is a benign skeletal neoplasm of unknown aetiology which typically presents in children (particularly adolescents), although the age range of presentation is between the ages of 10 and 35 years. Males are affected more commonly than females. The classic presentation is that of progresive focal bone pain at the site of the tumour. The pain worsens at night and increases with activity; it is dramatically relieved with small doses of Nonsteroidal Anti-inflammatory Drugs. Soft tissue swelling may occur and if close to a growth plate, accelerated growth may be evident, presumably related to hyperaemia. When the lesion is intra-capsular, presentation is more atypical, and more likely mimics and inflammatory arthropathy or synovitis. Joint effusion is often present [2].
Radiography is the initial examination and may be the only examination required [1]. Although it can be normal, the typical features of osteoid osteomas in plain films are those of a solid periosteal reaction with cortical thickening and a well circumscribed lucent central region (nidus) [3]. CT is the technique of choice for the characterization of the lesion and is also useful for precise localization of the nidus. It may also be used for guiding percutaneous ablation and it typically shows a focally lucent nidus within surrounding sclerotic reactive bone and with or without a central sclerotic dot. The specificity of the MRI is lower compared to CT because the nidus is not as well depicted as in CT. Also, the hyperaemia and the bone marrow oedema secondary to it may lead to misinterpretation of the lesion as it being aggressive [1, 3].
The differential diagnosis that should be made when the aforementioned imaging features are found comprise eosinophilic granuloma (EG), stress fractures and septic cortical osteitis (SCO). SCO shows more irregular margins and the cortical is interrupted at some point. Stress fractures also show an interruption of the cortex. EG is more frequent in long bones and may show a soft-tissue mass and features of aggresivity [4, 5].
The treatment of OO may be conservative (NSAIDs for 3-6 months), surgical (curettage of the lesion) or minimally invasive (CT-guided radiofrequency ablation) [2, 6].
Our patient underwent open surgery and the OO was histologically confirmed.
Osteoid Osteoma
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This imaging examination includes a pelvic X-ray, plain CT, and MRI sequences. From the images, the following observations can be noted:
Based on the patient’s age (13 years), the typical symptom of pain worsening at night, and the imaging findings of a small cortical radiolucent lesion with reactive sclerosis, the following differential diagnoses should be considered:
Considering the patient’s 13-year-old age, nocturnal pain exacerbation relieved by NSAIDs, imaging findings of a localized radiolucent lesion with surrounding sclerosis, and the postsurgical histopathological results, the final diagnosis is Osteoid Osteoma.
Treatment Strategy:
Rehabilitation and Exercise Prescription (FITT-VP Principle):
The above content is for reference only and does not replace a professional physician’s in-person diagnosis and treatment advice. For specific diagnostic and treatment plans, please consult an orthopedic specialist or relevant healthcare provider and tailor them to the patient’s individual condition.
Osteoid Osteoma
