A 27 year-old farmer was referred to our hospital for orthopaedic investigation of the right foot. He complained of tenderness over the dorsal region of the foot at night and with activity. The onset of the pain was one year before initial presentation. The pain was relieved easily with NSAID.
There was no prior medical history.
Conventional radiography of the feet showed no lesions.
An MR examination was performed. T1-weighted, T2-weighted and T2 STIR-weighted sequences in coronal, sagittal and transverse planes were acquired. T2 STIR-weighted images demonstrated bone marrow edema of the intermediate and lateral cuneiform bones with involvement of the surrounding soft tissues.
On the T2 STIR-weighted MRI images, a small mass with intermediate to hypointense signal was seen adjacent to the intermediate cuneiform bone. A small, dot-like signal void in the center of this lesion is in keeping with calcification.
Because of the nidus-like structure of the subperiostal lesion, osteoid osteoma of the midfoot was suspected.
The presence of a nidus with central calcification was confirmed by CT examination. A small hypodense nidus with a central calcification was seen adjacent to the cortex of the intermediate cuneiform bone. Retrospectively, the conventional radiography demonstrated subtle erosion and discrete scaffolding of the cortex of both cuneiform bones.
The patient was treated with CT-guided laser ablation of the osteoid osteoma. Recovery was uneventful.
Osteoid osteoma (OO) is a benign skeletal neoplasm that consists of an ovoid or spherical nidus of osteoid tissue and interconnected bone trabeculae, superimposed on a background of highly vascularized connective tissue. The amount of osseous and osteoid tissue varies within the nidus and is reflected in its density. The average size of the nidus varies between 0.5-2 cm, but the lesion is usually smaller than 1.5 cm in diameter.
OO account for 11% of all benign bone tumours and 3% of all primary bone tumours. The prevalence of the tumour is highest in the second and third decades of life.
OO is mostly found in the diaphysis or the metaphysis of the long tubular bones. The proximal femur is the most common location followed by the tibia, the posterior elements of the spine and the humerus. Locations in the hands and the feet are less common.
The classic clinical presentation is that of focal bone pain at the site of the tumour. The pain worsens at night, increases with activity and is easily relieved by use of non-steroidal anti-inflammatory medication.
OO are classified as cortical, cancellous or subperiosteal and may occur extra- or intra-articular.
Typical radiographic findings of OO include a nidus which may display a variable amount of mineralization, accompanied by cortical thickening and reactive sclerosis. The nidus is seen as a radiolucent focus, located in the center of an area of reactive sclerosis.
On CT imaging, the nidus is well defined and round or oval with low attenuation. An area of high attenuation may be seen centrally, a finding that represents mineralized osteoid. Reactive sclerosis around the nidus can easily be depicted by CT.
MR imaging does not only demonstrate the nidus and accompanying sclerosis but also the adjacent bone marrow. The nidus has a low to intermediate signal intensity on T1-weighted images and variable signal intensity on T2-weighted images, depending on the amount of mineralization present in the center of the nidus. Edema in the adjacent bone marrow and soft tissue can easily be depicted by MRI.
Intra-articular OO, irrespective of their subperiostal, cortical or cancellous origin, are poorly seen on conventional radiography since intra-articular periosteum is less active and thus reactive sclerosis is not seen. Intra-articular osteoid osteoma may be associated with joint-space widening as a result of joint effusion or synovitis.
Tarsal OO display a lesser degree of reactive sclerosis compared to lesions in the long bones. Because of the proximity of the bones in the feet, an inflammatory reaction that originates from one tarsal lesion often spreads to adjacent bones and joints. Moreover, soft tissue swelling may be prominent in OO of the feet, and this finding may resemble infection or inflammatory arthritis.
Current management of OO is surgical resection or CT-guided percutaneous treatment with radiofrequency ablation or laser photocoagulation.
Subperiostal osteoid osteoma of the foot
Based on the provided X-ray, CT, and MRI images, the following observations are noted:
1. The lesion is located in the tarsal region of the right foot, presenting as a small round or oval-shaped “nidus” (central focus) with varying degrees of sclerotic reaction surrounding it;
2. On conventional X-ray, localized increased bone density or sclerosis is noted on the affected side of the foot bones, though the reaction is relatively mild compared to lesions in long bones;
3. CT shows a well-defined lesion with a low-density center that commonly exhibits high-density calcification or residual bone in the center;
4. On MRI, the lesion typically appears as low to intermediate signal on T1 and variable signal on T2 (related to the degree of calcification and ossification within the lesion). Edema and inflammatory response signals may be noted in the surrounding bone marrow and soft tissues.
Considering the patient’s age (27 years), the typical nocturnal and activity-related pain, responsiveness to NSAIDs, and imaging findings of a clear nidus with limited surrounding sclerosis, the most consistent diagnosis is Osteoid Osteoma of the Foot.
Conservative treatment: If pain is well controlled with oral analgesics (such as NSAIDs) and lesion progression is slow, close follow-up and observation can be considered.
Minimally invasive treatment: CT-guided radiofrequency ablation (RFA) or laser photocoagulation are common minimally invasive procedures with small incisions and quick recovery, suitable for smaller lesions in accessible locations.
Surgical resection: For cases where conservative measures fail, minimally invasive procedures offer limited benefits, or the lesion’s location is more complex, surgical curettage or localized resection may be considered. Bone grafting may be performed if necessary.
Given the foot’s weight-bearing role, special attention should be paid to gradual weight-bearing and pain management during rehabilitation. The following is a general guideline; adjustments should be made according to the individual patient’s condition:
Early Stage (1-2 weeks post-surgery or post-intervention):
- Recommend immobilizing and elevating the affected limb to reduce weight-bearing time;
- Use assistive devices (crutches or a walker) under medical guidance to decrease pressure on the foot;
- Perform passive range of motion or light active exercises of the foot and ankle to prevent joint stiffness, avoiding excessive stimulation of the painful site.
Intermediate Stage (2-6 weeks):
- Gradually increase weight-bearing as symptoms improve, beginning with short periods of walking while ensuring no significant increase in pain;
- Perform active ankle dorsiflexion-plantarflexion, toe-grasp exercises, and basic balance training to maintain or improve muscle strength;
- Exercise frequency is typically 3-4 times per week, 15-30 minutes per session, stopping at mild pain or slight fatigue.
Late Stage (6 weeks and beyond):
- As bone healing and local symptoms improve significantly, gradually return to normal walking and daily activities;
- Introduce moderate-intensity exercises such as standing balance training, light jogging, and resistance band exercises, progressively increasing intensity;
- Exercise frequency can be increased to 4-5 times per week, about 30 minutes each session, closely monitoring pain and load tolerance.
Throughout the entire rehabilitation process, regular follow-up is essential to monitor local bone healing and the outcome of the surgery/intervention. Adjust the training plan as necessary. If persistent, worsening pain or other discomfort occurs, seek medical evaluation promptly.
This report is based on the current imaging data and clinical history and is for reference only. It should not replace an in-person consultation or professional medical advice. Specific treatment plans should be determined by a specialist physician after a comprehensive clinical evaluation.
Subperiostal osteoid osteoma of the foot
