4. Fibrous Cortical Defects
The fibrous cortical defect is a very small metaphyseal lesion seen
in long bones, typically around the knee joint in children. They are
usually picked up on a routine radiograph as an incidental finding.
They are considered dysplastic or hamartomatous lesions and are
very common, with about a 25% incidence in normal children
around the age of four to five years. As the child matures, the
lesions will disappear by a process of skeletal remodeling and,
in most cases, the diagnosis is obvious based on a simple radio-
graphic study. Microscopically, the lesions are filled with benign
fibroblastic cells forming collagen and usually demonstrate no
macrophage or inflammatory activity.
18. Non-ossifying Fibroma
The non-ossifying fibroma is considered to be a larger form of the
fibrous cortical defect seen in the lower extremities of children.
The lesions are usually eccentrically located but the larger ones can
become more central. Radiographically, they have a soap-bubbly
appearance with slight thinning and dilitation of the adjacent
cortical structure. The diagnosis can usually be established by x-ray
alone without biopsy. These lesions are a common cause for path-
ologic fracture in children. They are usually asymptomatic until
the day of injury. There can be multiple lesions in the same patient,
similar to fibrous dysplasia, and can even be associated with café-
au-laite skin lesions.
Histologically, the lesion consists of benign fibrous tissue
speckled with giant cells, histiocytes, and occasional foam cells
and even cholesterol deposits. Treatment usually consists of curette-
ment and bone grafting in high risk athletic males.
19. CLASSIC Case #132
22 year female with non-ossifying fibroma proximal tibia
44. Fibrous Dysplasia
Fibrous dysplasia of bone is a relatively common hamartomatous
developmental process in the skeletal system that can be either
monostotic or polyostotic. In the case of polyostotic, there can also
be endrocrine abnormalities such as precocious puberty in females
with the McCune-Albright syndrome. This condition occurs
primarily in females and can be associated with café-au-laite spots
on the skin which have a rough serrated edge compared to the
smooth edges in neurofibromatosis. The monostotic form has an
appearance similar to non-ossifying fibroma except that the lytic
component has a typical smokey appearance caused by metaplastic
bone formation in the fibrous tissue. In the more severe polyostotic
form, representing only about 10% of fibrous dysplasia, the disease
tends to amplify on one side of the body more than the other
causing leg length discrepancy, especially when there is a character-
istic chronic deformity of the proximal femur; referred to in the
45. literature as the shepherd’s crook deformity; that frequently
requires surgical correction.
The most common locations for fibrous dysplasia are the
proximal femur, followed by the tibia, humerus, ribs and,
occasionally, caranio-facial anatomy. Other endrocrinopathies
associated with polyostotic fibrous dysplasia include hyperpara-
thyroidism, acromegaly, Cushing’s disease and, occasionally,
hypophosphatemic osteomalacia. Occasionally, one will see soft
tissue myxomas with fibrous dysplasia which is referred to as the
Mazabraud’s syndrome. Radiographically, there will be diffuse
dysplastic changes throughout the involved bones with gradual
dilation and thinning of the cortices, and a soap-bubbly appear-
ance but with a smoky look compared to non-ossifing fibroma.
Histologically, there is evidence of benign fibrous tissue matrix
studded with islands of metaplastic bone with a so-called
alphabet soup appearance but without osteoblastic rimming of the
46. trabeculae. Occasionally one will see macrophages, osteoclasts,
foam cells and even cholesterol deposits similar to what is found
in non-ossifying fibroma. In approximately 1% of cases, there will
be a conversion to a secondary sarcoma in adult life that could
present as an osteosarcoma, or malignant fibrous histiocytoma or
even a chondrosarcoma.
Treatment usually consists of corrective osteotomies for secondary
developmental deformities, along with bone grafting, including
fibular strut grafts and occasionally intramedullary devices to prevent
repeated stress fractures. Recently there has been enthusiasm for
the use of biphosphonates to inhibit the osteoclastic activity in
growing children that produces weakening of the bone. It is best
not to perform bone grafting procedures in children because of the
high recurrence rate in children under 16 years of age.
250. Cibagram showing the
difference between the
rough serrated edges of
the café-au-lait spots of
fibrous dysplasia on top
compared to the smooth
edges of neurofibromatosis
seen on the bottom
251. Case #760
35 year female with Albright’s disease
279. Desmoplastic Fibroma of Bone
Desmoplastic fibroma of bone is an extremely aggressive, but
benign, fibrous lesion seen in long bones as well as the mandible.
It represents 1% of all bone tumors and occurs typically in children
and young adults with equal sex distribution. The long bones
involved include the distal femur, proximal tibia, proximal
humerus and the lower half of the pelvis. Radiographically, these
lesions have an aggressive and moth-eaten appearance, eroding
into cortical bone and breaking out into the adjacent soft tissue,
much like the low grade fibrosarcoma. Histologically, the tumor
appears identical to aggressive fibromatosis seen in soft tissue with
intense collagen formation by aggressive-appearing fibroblasts with
an occasional mitotic figure. With curettement alone, the recurr-
ence rate is very high, in the neighborhood of 40%, and for this
reason most authorities suggest a wide resection and possible
prosthetic replacement. This tumor will not metastasize to the lung.
311. Fibrosarcoma of Bone
Fibrosarcoma of bone is a malignant spindle cell sarcoma seen in
an older age group with a peak incidence in the fourth decade of
life. It is ten times less frequent than osteosarcoma but involves
similar bones including the distal femur, proximal tibia, pelvis,
proximal femur and proximal humerus. It is rare in the spine, hand
or foot. Radiographically, the fibrosarcoma has a permeative lytic
appearance in the metaphyseal ends of long bones, similar to that
seen in lymphomas or malignant fibrous histiocytoma. Histo-
logically, the tumor demonstrates aggressive fibroblastic activity
with collagen formation similar to what is seen in desmoplastic
fibromas but with a much higher mitotic index. The lesions can be
low grade or high grade. The low grade lesions carry a good
prognosis with a low incidence of metastasis to the lung, whereas
the high grade lesions, just like with osteosarcoma, are more
aggressive with a worse prognosis and a higher potential for
312. metastasis. Treatment consists of wide local resection of the tumor,
if possible. If the lesion is high grade, adjuvant therapies including
local radiation therapy and chemotherapy are frequently implemented
to reduce the chance of pulmonary metastasis. Limb salvage
prosthetic reconstructions are frequently utilized as in the case of
osteosarcoma.
367. Malignant Fibrous Histiocytoma of Bone
Malignant fibrous histiocytoma of bone is a relatively new patho-
logical entity in bone tumors, compared to soft tissue tumors
where malignant fibrous histiocytoma is a more common tumor.
Malignant fibrous histiocytoma (MFH) of bone occurs in a middle
or older age group, more commonly in males than females. It is
found typically in the same locations as fibrosarcoma or osteo-
sarcoma, including the distal femur, proximal tibia, and proximal
humerus. Radiographically, it is an aggressive permeative lesion
in metaphyseal bone with significant cortical destruction that can
break out into the adjacent soft tissue. Histologically, there is
evidence of malignant fibroblasts as well as atypical histiocytes
and giant cells, exactly as we see in soft tissue MFH. Because this
is usually a high grade tumor, the prognosis is quite guarded with
a high potential for metastasis to the lung, similar to fibrosarcoma
and osteosarcoma. Treatment consists of a wide surgical resection
368. with prosthetic reconstruction when possible, along with
adjuvant chemotherapy to reduce the chance of pulmonary
metastases.
482. Leiomyosarcoma of Bone
Leiomyosarcoma of bone is an extremely rare diagnosis with
fewer than 50 cases in the world literature. It occurs typically in
middle to older age adults in the same location in the skeleton as
fibrosarcoma, MFH, and osteosarcoma are found in; distal femur,
proximal tibia and upper humerus. Radiographically, these lesions
have a permeative lytic appearance, similar to a lymphoma,with
extensive cortical breakdown and extension into the surrounding
soft tissue. Histologically, the malignant spindle cells with collagen
formation look like a fibrosarcoma or MFH so that the only way
a diagnosis can be established is by using the specific immuno-
histochemical staining for smooth muscle protein. Treatment usually
consists of wide surgical resection and prosthetic implantation.
Because of the poor prognosis with high grade lesions, they are
frequently treated with adjuvant systemic chemotherapy and
radiation which is not very effective, especially in old patients.
483. CLASSIC Case #144
69 year female with leiomysarcoma proximal humerus