Case Presentation

This active young man is 8 1/2. He has a fraternal twin brother. Just five days ago, he fell, injuring his left leg on a rock. He started having pain. And x-ray was made, and lesion is found in the mid tibia near the site of the pain.

On closer questioning, the child seems to have had pain in the area for a few weeks or longer. Precisely when the pain began is difficult to pin down. There is no history of injury when the pain actually began a few weeks ago.

There are no contributing past medical, surgical, social, or familial factors.

On examination, the patient is afebrile, and in no acute distress. There is limping, antalgic gait and station. Examination of the leg shows the area is slightly warm and slightly tender. There is no redness. There is no irritability of the knee or of the ankle. The neurologic status of the foot and the pulse in the foot are normal. The hip range of motion is normal. There is no regional or central lymphadenopathy.

Radiographs X1 X2 X3 X4 show a lesion in the mid tibia, within the medullary cavity.There is slight expansion of the cortex, with thining. There appears to be a faintly calcified matrix.

A bone scan shows abnormal uptake BS1 BS2 BS3, and a CT scan shows the lesion in better detail.CT1 CT2 CT3 The laboratory exam shows a mild elevation in the sedimentation rate and the C reactive protein.

I instructed her father to give the patient Naprosyn, and monitor his response. The patient had relief of pain from the Naprosyn. However, the improvement was not very dramatic.

Biopsy was performed and histopathology is shown in
P1 P2 P3 P4.

What is the differential?

There are two benign lesions that form bone - they differ in fairly subtle ways. What features of this case allow you to conclude which of these tumors is present in this case?

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