Benign Bone Tumors of the Foot - Section 2

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Chondroblastoma

Chondroblastoma often affects the talus and other hindfoot bones may be affected. The peak age of incidence is 20 with most patients in the second and third decade. Patients complain of swelling or a mass near a joint, with pain that may be severe. Synovitis of the nearby joint may be present. Pathological fracture is rare.

Radiologically, the tumor is almost exclusively located in the epiphysis. The cortex may be scalloped or expanded. The lesion has a chondroid matrix and stippled calcification may be seen on plain radiographs. Cysts are present about 20% of the time and both MRI and CT can define the fluid levels. CT is also useful for defining the relationship of the tumor to the joint, integrity of the cortex, and intralesional calcifications. The differential diagnosis includes enchondroma, central chondrosarcoma and aneurysmal bone cyst.

Chondroblastoma may behave aggressively and invade soft tissue, and pulmonary metastasis of this benign tumor has been observed. Treatment of chondroblastoma is biopsy and curettage with possible use of adjuvant liquid nitrogen or phenol, or a mechanical burr. The lesions are located near open growth plates and care is necessary to prevent damage. It may be necessary to reconstruct articular surfaces due to subchondral erosion. Any joint invasion is usually secondary to previous instrumentation. Recurrence is common and recurrent lesions should be treated with repeat curettage. All pulmonary nodules should be excised.

Osteoid osteoma

Osteoid osteoma comprises 10 to 14% of bone tumors of the foot. It presents predominately in teenagers, usually boys. The most common location is the neck of the talus and the calcaneous, but it may occur in any bone. Patients complain of significant, often severe pain, worse at night, which is usually dramatically improved with NSAID medicines or aspirin.

Osteoid osteoma is the only condition known to the author that will cause a teenage boy to take medicine on a regular basis without prompting. In lesions located within the bone, the diagnosis of osteoid osteoma should be reconsidered if the patient does not report significant pain relief from taking aspirin.

Occasionally, the lesion is located so close to a joint that the presentation is that of monoarticular arthritis. Symptoms and signs include pain, a significant effusion, loss of ROM, erythema, and exquisite point tenderness of the synovium. In these unusual cases the pain relief from NSAID's and aspirin is less dramatic.

Radiologically, the lesion has a lucent "nidus" that is normally less than 1 cm in size, and never larger than 2 cms. In large bones there is a zone of sclerosis that surrounds the lesion, but this is variable in smaller bones and absent if the lesion is adjacent to a joint or in the joint. Occasionally the nidus has a calcific center that can be seen on plain radiographs.

CT scan demonstrates the radiographic features of this lesion particularly well and may be diagnostic. MRI is not as helpful as CT in bone lesions but may be useful in lesions near joints. Bone scan is helpful since the bone lesions demonstrate intense, highly focal uptake, and this is a unique feature of osteoid osteoma.Normally, a plain radiograph, a CT scan and bone scan are sufficient to make the diagnosis. Biopsy is not usually necessary for diagnosis.

Patients who respond well to NSAIDs and aspirin may be successfully treated with these medications until the lesion disappears. The lesion will spontaneously resolve in time, but many months or years of treatment may be required. (Simon JBJS ) Many or most patients prefer more rapid relief and newer surgical techniques now allow the lesion to be precisely destroyed with little or no morbidity, rapid recovery, and few recurrences. (click here for info)

Traditional treatment involves surgical removal of the nidus. This can be accomplished easily if the lesion is superficially located and the surgeon can pinpoint the location by referencing nearby anatomic landmarks. The overlying bone may be visibly abnormal, appearing hypervascular and slightly porous. Surgeons should be careful to remove the entire nidus to prevent recurrence. Recurrence rates of 10% or more have been reported.

The authors believe recurrence risk is strongly related to the difficulty the surgeon has in locating the nidus. Thus recurrence is more likely in deep-seated lesions and lesions located on the endosteal surface of larger bones. Lesions deep within the calcaneous or talus are better treated with image guided techniques such as RTA. During conventional surgical removal, it may be so difficult to locate or access the lesion that the surgical trauma and resulting morbidity may be far worse than the lesion itself.

Many techniques for locating the nidus have been described and are outside the scope of this review. The author's preferred technique for deep-seated lesions is to precisely ablate the nidus by inserting a thermal probe under CT guidance (RTA). This procedure is done under general anaesthesia in an outpatient setting. Morbidity is minimal and most patient return immediately to full activities. The rate of recurrence is comparable to or better than conventional techniques.

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