Osteoid Osteoma is a benign bone lesion with a nidus
of less than 2 cm surrounded by a zone of reactive bone. This lesion accounts
for approximately 10 % of benign bone tumors1.The tumor occurs
most frequently in the second decade and affects males twice as often
as females. The proximal femur is the most common location followed by
the tibia, posterior elements of the spine, and the humerus. Osteoid Osteoma
is found in the diaphysis or the metaphysis of the proximal end of the
bone more often than the distal end.
Osteoid osteoma has a distinct clinical picture of dull pain that is worse
at night and disappears within 20 to 30 minutes of treatment with non-steroidal
anti-inflammatory medication. Joint pain may be present with a periarticular
lesion and synovitis can occur secondary to an intraarticular lesion.
Local symptoms can include an increase in skin temperature, increased
sweating and tenderness. Epiphyseal lesions can cause abnormal growth.
The classic radiological presentation of an osteoid
osteoma is a radiolucent nidus surrounded by a dramatic reactive sclerosis
in the cortex of the bone. The center can range from partially mineralized
to osteolytic to entirely calcified. The lesion can occur only in the
cortex, in both the cortex and medulla, or only the medulla. The reactive
sclerosis may be present or absent. The four diagnostic features include
(1) a sharp round or oval lesion that is (2) less than 2 cm in diameter,
(3) has a homogeneous dense center and (4) a 1-2 mm peripheral radiolucent
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.
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.
Osteoid osteoma will resolve without treatment in
an average of 33 months. If the patient does not wish to endure the pain
and prolonged use of non-steroidal anti-inflammatory medications, surgical
removal or percutaneous ablation of the nucleus is indicated.
'Bloem, J and H. Kroon, Osseous Lesions, Radiologic Clinics of
North America,31(2):261-277, March, 1993. DGitelis, S, Wilkins, R and
Conrad, benign Bone Tumors, Instructional Course Lectures,
Bullough, Peter, Orthopaedic Patholoev (third edition), Times Mirror
International Publishers Limited, London, 1997.
Huvos, Andrew, Bone Tumors:Diagnosis, Treatment and Prognosis, W.B. Saunders,
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