QUESTION-1:

You are shown a lateral radiograph (Figure 3A) and a non-contrast CT (Figure 3B) of a 9-year-old boy with anterior leg bowing. What is the MOST likely diagnosis?:

Correct Answer: Osteofibrous dysplasia

A. Incorrect. Intracortical osteosarcoma is the most uncommon form of osteosarcoma. They are diaphyseal, usually arising in the femur or tibia. Intracortical osteosarcoma generally presents as lucency within the cortex that measures less than 4 cm, with surrounding sclerosis. If small, they may be mistaken for an osteoid osteoma or fibrous cortical defect.
B. Incorrect. Nonossifying fibromas may be mildly expansile, but they are not associated with bowing of the bone.
C. Correct. Osteofibrous dysplasia is a benign fibro-osseous lesion that is almost exclusively found in the tibia or fibula. It is a disorder of childhood, usually seen within the first 2 decades of life and often under 10 years of age. The lesion is centered in the anterior cortex, and may be associated with anterior bowing. A lobulated lucency is seen, often with surrounding sclerosis. The appearance may mimic a nonossifying fibroma, but the location and bow are key. Adamantinoma may be present in association with osteofibrous dysplasia. The two disorders cannot be differentiated one from the other by imaging.
D. Incorrect. Aneurysmal bone cysts are eccentric, lytic lesions that are usually found in the medullary cavity. They are most often metaphyseal, but may be present anywhere along a bone. Cortical and periosteal locations have been reported, but are unusual. The cortex overlying the lesion is expanded and if growth is rapid, it may be destroyed.

Differential Diagnosis:

There is a cortically based, expansile lesion involving the anterior tibia shaft.
The tibia is mildly bowed anteriorly.
The majority of the lesion is lucent, with a lobulated contour and sclerotic margins.

References:

Huvos AG. Bone Tumors: Diagnosis, Treatment, and Prognosis, 2nd Ed. WB Saunders Company, Philadelphia, PA, 1991.
Unni KK, Ed. Dahlin’s Bone Tumors: General Aspects and Data on 11, 087 cases, 5th ed. Lippincott-Raven Publishers, Philadelphia, PA, 1996

QUESTION-1:

Correct Answer: Osteofibrous dysplasia

Differential Diagnosis:

References:

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