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Osteoid osteoma - Foot and Ankle

Summary

Approximately 11% of these painful, benign tumors occur in the bones of the foot.

At peak age of incidence is in the second decade.
Patients present with persistent pain and swelling, which is unrelated to activity. The pain may be more intense at night.
On plain radiographs, and CT scans a central nidus of less than 1 cm is seen within a larger zone of sclerotic reactive bone.
Patients who respond well to NSAIDs and aspirin may be successfully treated with these medications until the lesion disappears. The average time to resolution is 22 months.
Complete Information on this Tumor
Introduction and Definition: 

Approximately 11% of these painful, benign tumors occur in the bones of the foot. The neck of the talus is the most common location.

Incidence and Demographics: 
At peak age of incidence is in the second decade.
Symptoms and Presentation: 

Patients present with persistent pain and swelling, which is unrelated to activity. The pain may be more intense at night.

X-Ray Appearance and Advanced Imaging Findings: 
On plain radiographs, and CT scans a central nidus of less than 1 cm is seen within a larger zone of sclerotic reactive bone. If the nidus is larger than 2 cm, the diagnosis of osteoid osteoma is excluded. The sclerotic bone surrounding the nidus can be minimal when the tumor involves a small bone. Bone scan shows a small, very intense focus of abnormal uptake. CT is the preferred method of evaluation, especially if the lesion is in the spine or obscured by reactive sclerosis. The radiologic differential includes osteoblastoma, osteomyelitis, arthritis, stress fracture and enostosis. Characteristic plain radiograph, CT scan, and bone scan findings are sufficient to confirm the diagnosis of this tumor. MRI findings are nonspecific.
Histopathology findings: 
On gross examination, osteoid osteoma is a brownish-red, mottled and gritty lesion that is distinct from the surrounding bone. It can be present in the cortex or medullary canal. Osteoclasts are present. The nidus is surrounded by sclerotic bone with thickened trabeculae. Microscopically, the nidus consists of a combination of osteoid and woven bone surrounded by osteoblasts. The oval shaped nidus is welvascularized and clearly separate from the reactive woven or lamellar bone. path 1 path 2
Treatment Options for this Tumor: 
In most cases, nonsteroidal anti-inflammatory medicines give substantial relief, and any history of taking these medicines should be carefully reviewed. If there is absolutely no relief of pain from taking NSAIDs, the diagnosis of osteoid osteoma is less likely. Lesions adjacent to a joint may cause ankylosis or mimic a pauciarticular inflammatory arthritis, such as Reiter's disease. The local swelling, erythema and tenderness can mimic infection. When there is significant involvement of a nearby joint, the relief from nonsteroidal medicines can be less dramatic. Patients who respond well to NSAIDs and aspirin may be successfully treated with these medications until the lesion disappears. The average time to resolution is 22 months. Many patients will not be able to tolerate the pain this long, and request surgical removal. For these cases, the goal is complete removal of the lesion by the least invasive means possible. For lesions in the hindfoot and midfoot, radio thermal ablation by CT guided needle is the recommended technique. During radio thermal ablation, the tip of a radiofrequency generator electrode is placed into the center of the lesion under CT guidance and general anaesthesia. A radiofrequency generator forms an alternating high frequency radio wave that passes from the electrode tip into the surrounding tissue, where energy is dissipated as heat. The tissue itself is heated, not the radiofrequency probe. A sphere with a diameter of 1 cm can be effectively treated in this manner, making this treatment ideal for osteoid osteoma. In order to be treated with radial thermal ablation, the diagnosis should be confirmed based on the imaging studies with a high degree of confidence. There should be sufficient distance between the lesion and any major neurovascular structure. The lesion should have a clearly deformed nidus less than 1 cm in largest dimension. Although radio thermal ablation was previously only available in tertiary Medical Centers, it is now more widely available. The high success rate combined with the extremely low rate of complications strongly favor this technique. Radio thermal ablation can be difficult in the smaller bones because of difficulties with targeting the lesion in the CT scanner. In addition, when the lesion is in a small bone, there is risk of damage to nearby tendons or neurovascular structures. For superficial lesions in the forefoot, open surgery is still the preferred treatment. The surgeon needs to be able to locate the nidus using radiographs, anatomic landmarks, and direct observation. Other techniques for locating the nidus have been described. The surrounding reactive bone can be extremely dense, and it may also be hypervascular and somewhat porous.
Outcomes of Treatment and Prognosis: 
It is essential to remove the entire nidus because failure to do so will lead to recurrence. Surgical removal often leads to weakening of the affected bone, and bone grafting, plating, and prolonged nonweightbearing with activity restrictions may be necessary.
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