3. Osteoid Osteoma
The osteoid osteoma is the most common osteoid-forming tumor
seen in the skeletal system, accounting for 10% of all benign
bone tumors. It is more common in males than females with the
peak incidence in the second decade of life. The lesions produce
symptoms of dull, aching pain that is more severe at night. The
pain is relieved with anti-inflammatory medication such as
aspirin or non-steroidal anti-inflammatory drugs (NSAID)
that inhibit the high concentration of prostaglandins found in
the nidus of the osteoid osteoma. The lesions occur typically in
the cortical structures of long bones such as the femur or tibia
but can also be found in the small bones of the ankle, wrist or
vertebral column. The lesion is characteristic for its dense,
sclerotic response in the cortical bone resulting in a fusiform
enlargement on the surface of the cortex as a response to the
small inflammatory nidus or granuloma (measuring up to one
4. centimeter in diameter) in the central area of the sclerotic
response. If the lesion is located in a central medullary area,
such as the metaphysis or on the very superficial surface of a
bone, the sclerotic response is less severe. If the nidus is
located close to or within a joint structure, as in the femoral
neck area, there will be a significant inflammatory synovitis
in the adjacent joint that gives the clinical appearance of a
pyarthrosis. In the spine, the lesions are usually located in the
posterior elements of the spine such as the laminae or pedicles.
The lumbar spine is the most common location followed second
by the dorsal spine. Atypical secondary painful scoliosis will
develope with the convexity seen on the side opposite the
inflammatory lesion.
The two most significant diagnostic imaging studies are a CT
scan through the nidus area to identify its anatomic location and a
bone isotope scan which is invariably positive, especially in a
symptomatic lesion. It is the current feeling that the osteoid
.
5. osteoma is a true benign neoplasm of bone in which a com-
bination of osteoclastic and osteoblastic activity are seen.
There are no inflammatory cells such as lymphocytes or
plasma cells as would be seen in a Brodie’s abscess. Non-
steroidal anti-inflammatory medications such as prostaglandin
inhibitors can be very effective in controlling the disabling
symptoms and helping the patient get thru a period of one or
two years during which time the lesion will typically involute
into a painless lesion that does not require surgery. However,
if the patient is unable to live with the pain during this time,
a surgical approach is indicated. Following exposure of the
lesion, a high speed burr is used to burr into the inflammatory
bone that is characterized by a pinkish hyperemia. When the
nidus is found, a small curette is used to core the inflammatory
nidus for pathological diagnosis and the cavity of the nidus
is burred an additional 2 or 3 mm which usually results in a very
dramatic relief of symptoms and a permanent cure from the
6. disease process. It is not necessary to remove the large
dense sclerotic bone surrounding the nidus; doing so could
result in a pathologic fracture following surgery. In the spine,
a simple laminectomy is frequently carried out. If the lesion is
located in the pedicle a simple burring into the pedicle will
relieve the patient of the inflammatory pain.
More recently, relatively non-invasive techniques have been
tried to remove the nidus of the osteoid osteoma by means of a
CT guided burr placed through a protective trocar or by place-
ment of a heat-producing radio frequency probe that, when
properly positioned, can destroy the nidus through thermal
coagulation. These techniques are particularly valuable for deep-
seated lesions located in the acetabulum. For lesions located in
the pedicle of a vertebra one must be careful not to damage an
adjacent spinal root or spinal cord.
143. Osteoblastoma
The so-called osteoblastoma is considered by most to be a large
or giant form of the similar clinical entity known as the osteoid
osteoma. As with the osteoid osteoma, it is found in children and
young adults, more often in males than females. It is less common
than the osteoid osteoma, representing approximately 1% of all
bone tumors. It is found mostly in metaphyseal areas of long bone
and in the posterolateral elements of the axial skeleton where
nearly 50% of the lesions are identified. Radiographically these
lesions are more osteolytic than the osteoid osteoma and have a
central nidus that measures more than 1.5 cm in diameter with
less reactive sclerosis seen at the periphery than an osteoid
osteoma. It is not unusual for an aneurysmal component to be
associated with the osteoblastoma, similar to the reaction seen
adjacent to chondroblastomas and giant cell tumors. The micro-
scopic appearance of the nidus material is almost identical to
144. that of the osteoid osteoma and under higher power cannot be
differentiated by even the most competent pathologists. The
major concern is a microscopic appearance similar to an osteo-
sarcoma and, for this reason, multiple samples must be evaluated
in order to establish the correct diagnosis in cases where these
lesions arise from the metaphyseal areas of long bone.
In the spinal area, the osteoblastoma is typically located in the
posterolateral elements where it can cause problems with spinal
cord or nerve root compression that may require aggressive
surgical decompression and even spinal stabilization. On occasion
an osteoblastoma will spontaneously convert into an osteo-
sacoma, especially if it has been treated with radiation therapy.
The primary treatment for the osteoblastoma is a surgical one with
a fairly aggressive curettement of the lesion. There is no particular
reason to take wide margins because the recurrence rate is quite
low and in some cases the lesions resolve spontaneously with out
any surgery at all, similar to what occurs with osteoid osteomas.
145. A variant of the osteoblastoma, the so-called aggressive or
“malignant” osteoblastoma, is a clinical entity halfway between the
classic benign osteoblastoma and a full blown malignant osteo-
sarcoma. This “malignant” osteoblastoma appears and behaves
clinically at the local site like an osteosarcoma but has no potential
to metastasize to distant parts. In this situation, local treatment
must be more aggressive and probably would require a wide local
resection to avoid a local recurrence because radiation therapy or
even systemic chemotherapy is not effective for this aggressive but
benign entity.
350. Osteofibrous Dysplasia
Osteofibrous dysplasia is a rare condition occurring
in children less than 10 years of age. This benign lesion
has radiographic and microscopic features similar to fibrous
dysplasia of the tibia, the main difference being the presence
of more heavily ossified tissue at the periphery of the lesion
giving it a soap-bubbly appearance on x-ray. Microscopically
it has a similar “alphabet-soup” metablastic bone appearance
in a benign fibrous tissue stroma but with the additional feature
of heavy osteoblastic rimming of the trabeculae not seen in
fibrous dysplasia. It typically arises from the anterior cortex of
the tibia at mid shaft and causes a progressive anterior bowing
of the tibia over time, creating a cosmetic deformity associated
with pain of a dull, aching nature. The radiographic appearance
is very similar to and impossible to separate from that of the
malignant adamantinoma that also affects the tibia in children
351. and, for this reason, a biopsy must be performed to rule out the
malignant possibility. Occasionally osteofibrous dysplasia of the
tibia can progress gradually into a well-differentiated form
of the adamantinoma, which will have the microscopic
features of both osteofibrous dysplasia and adamantinoma
in the same lesion. As far as treatment is concerned, early
surgical debriedment and bone grafting before age 15 years
results in a high local recurrence rate and thus should be
discouraged until the child reaches full bone maturity at which
time a definitive debriedment and bone grafting procedure
can be performed without significant risk of recurrence. This
lesion occurs bilaterally in a very small percentage of cases
and can also involve the fibula on the same side. This process
in newborns appears to be more osteolytic and destructive in
nature.
385. Ossifying Fibroma of Jawbone
Ossifying fibroma of jawbone is a benign condition similar to
osteofibrous dysplasia of the tibia in that histologically they are
almost identical. It is also a condition that is related to fibrous
dysplasia, which can have a very similar radiographic appearance,
but in the case of fibrous dysplasia of jawbone osteoblastic
rimming of the trabecular bone is not seen under microscopic
evaluation. As with fibrous dysplasia, this condition is found in
children and is almost always an asymptomatic process resulting
in cosmetic deformation of the maxilla or mandible, usually on
one side but can be bilateral. The condition can result in
significant malocclusion of the teeth because of deformation
of the subadjacent alveolar ridge or maxillary structures. It also
can create problems with normal drainage from the air sinuses in
the maxilla that can lead to infection requiring surgical drainage.
Most of the surgical treatment for this condition is for cosmetic
deformity.
386. Case #102
5 yr female
ossifying fibroma
maxilla
