Diagnostic imaging studies are shown from five different patients with the same condition. What is the most likely diagosis?
PROBLEM:
Diagnostic imaging studies are shown from five different
patients with the same condition. What is the most likely
diagnosis?
DISCUSSION:
The etiology of osteoid osteoma is undetermined, though the
lesion may be a tumor or an inflammatory process. These distinctive
osteoblastic lesions contain a central nidus, characterized by
osteoid, and highly vascular, fibrous tissue. The nidus usually is
less than 1 cm in size and is surrounded by a zone of reactive
sclerosis. Osteoid osteomas, observed most frequently in the second
and third decades of life, are found more commonly in men than
women, by a ratio of approximately 2:1. Frequent sites of
involvement are the femur (figure 1), tibia, humerus, and spine,
although virtually any bone may be affected (figure 2). Signs and
symptoms include pain, which is worse at night and usually relieved
by aspirin, muscle wasting, and growth disturbance. Spinal osteoid
osteomas may be associated with scoliosis.
Identification of an osteoid osteoma can be difficult, due to
the degree of surrounding bony proliferation. The three classes of
osteoid osteomas–cortical, medullary, and
periosteal–are determined by the lesion’s
location within a bone. On radiographs, cortical osteoid osteomas
produce a round or oval area of lucency that is surrounded by
significant sclerosis and periostitis. The nidus may be entirely
lucent or may be partially or totally calcified. Such cortical
lesions occasionally possess more than a single nidus, may evoke a
periosteal reaction in a closely situated neighboring bone, and can
recur after treatment. Rarely, a second nidus can be located in an
adjacent bone. Radiography of the bone specimen during surgery will
document that the nidus has been removed. Computed tomography,
arteriography, and scintigraphy can be useful additional diagnostic
modalities.
Medullary osteoid osteomas may be associated with a lucent
defect in bone, or one that is partially or completely calcified.
The degree of bony reaction is less striking than in cortical
osteomas and, when present, the reactive bone may be located at a
considerable distance from the nidus (figure 3).
Periosteal osteoid osteomas of the spine are located most
commonly in the posterior elements, including the pedicles,
laminae, and spinous and transverse processes. An increase in the
density of the corresponding neural arch, located along the concave
aspect at the apex of an accompanying scoliotic curve, may be
identified. Osteoid osteomas that arise in a vertebral body can
extend across the adjacent intervertebral disc space, and those
that arise in an intraarticular location (figure 4,5) can produce
significant joint symptoms and signs, including a lymphofollicular
synovitis with accumulation of articular fluid. The clinical and
radiographic appearance simulates that of an infection or of
rheumatoid arthritis.
REFERENCES
1. Resnick D: Diagnosis of Bone and Joint Disorders.
Philadelphia, WB Saunders, ed 3, 1994.