Simple Bone Cyst
Simple (unicameral or solitary) bone cysts are solitary, fluid-filled cystic
lesions located in the metaphysis of long bones near the epiphyseal plate of
children and adolescents. These lesions predominately occur in the proximal
humerus and the proximal femur, although they have been reported in the bones
of the forearm, leg, and foot. A solitary bone cyst is often asymptomatic. It
commonly presents as a radiographic finding in a child with a fracture associated
with minimal trauma. The pathogenesis of this lesion is unclear. It may result
from resorption and cystic changes at the site of a posttraumatic hematoma or
arise from a local disturbance of bone growth with the formation of fibrous
tissue and the accumulation of fluid within the bone. Radiographically, it appears
as a radiolucent, trabeculated lesion with well-defined borders. The cyst contains
straw-colored or blood-tinged fluid with thin, bony ridges that give the lesion
its multiloculated appearance on x-ray. The cyst is lined with a loose connective
tissue membrane containing small numbers of fibroblasts, giant cells, and hemosiderin-laden
macrophages. The treatment of a simple bone cyst varies with its location and
the age of the patient. Up to 15 percent of cysts may heal after fracture with
observation alone. A nonsurgical approach of aspiration and multiple steroid
injections has proven to be effective in the healing of cysts. A surgical approach
of curettage and bone grafting improves the healing rate and provides mechanical
support. A higher rate of recurrence is associated with large lesions (involving
more than one-eighth of the overall length of the bone), proximal humeral cysts,
and cysts occurring in young (<10 years of age) males.
Aneurysmal
Bone Cyst
An aneurysmal bone cyst is a solitary expansile lesion located in the metaphysis
of long bones, flat bones, and vertebrae. It presents in the second decade of
life and, unlike a simple bone cyst, pain is the presenting complaint along
with tenderness and swelling at the site of the lesion. There may be an associated
limitation of motion of nearby joints. Vertebral lesions can present with the
signs and symptoms of cord or root compression due to bony expansion of the
posterior elements. Radiographs demonstrate an expansile eccentric lesion surrounded
by a thinned cortex with periosteal new bone formation and a characteristic
"fluid-fluid" level within the cavity may be seen on CT scan or MRI.
The etiology of this lesion is unknown. A vascular disturbance in bone such
as arteriovenous communication or an alteration of a preexisting fibro-osseous
lesion has been offered as possible causes for aneurylsmal bone cysts. Gross
inspection of these lesions reveals a honeycombed appearance of bony trabeculae
or fibrous tissue bands enclosing cystic spaces of various sizes filled with
unclotted blood. Microscopically, the blood spaces are separated by cellular
septa lacking an endothelial cell lining and containing a variety of cells such
as fibroblasts, multinucleated giant cells, and histiocytes with hemosiderin
deposits, as well as metaplastic bone. Large, solid cellular areas may also
be seen. Aneurysmal bone cysts can be treated by excision, curettage, and bone
grafting. A wide margin resection may be performed when the lesion is located
in areas of nonessential bone. Cryosurgery and chemical cautery have also been
employed successfully in the treatment of these lesions.
Intraosseous
Ganglion
It is a benign cystic lesion located in the subchondral region adjacent to the
joint. It occurs in adults and has a predilection for the bones of the knee,
ankle, hip, wrist, and carpal joints. The lesion may be incidentally found,
but most often pain near the joint is a common presentation. Radiographs demonstrate
a well-outlined lytic defect in the subchondral bone, usually measuring 1 to
2 cm in the greatest dimension. The lesion extends to the articular cartilage
and has sclerotic margins. The afflected joint shows minimal or no evidence
of osteoarthritis. Grossly, it consists of fibromembranous tissue with mucinous
material. Histologically, the cyst wall contains fibrous tissue and may have
myxoid areas.
The pathogenesis of this lesion is unknown and probably is a reactive process.
The cyst usually does not communicate with the joint. Intraosseous ganglion
should not be confused with subchondral cysts of osteoarthritis. If pain persists
treatment is by curettage and bone grafting.
Fibrous Dysplasia
Fibrous dysplasia is a dysplasic disorder of bone characterized by the presence
of trabeculae of immature bone presenting at one or many skeletal sites. It
may represent disordered bone maturation, and often results in progressive bony
deformity that may be associated with pathologic fracture. It often presents
during the second or third decade of life with local pain and swelling. This
condition can be monostotic or polyostotic. A rare polyostotic variant associated
with precocious puberty and café-au-lait spots predominately seen in
young girls is known as Albright’s syndrome. On x-ray, the lesion has
a "ground glass" appearance and is sharply marginated with a rim of
sclerotic bone. There is expansion, endosteal scalloping, and deformity of the
affected bone. The classic "shepherd’s crook" deformity of the
proximal femur arises from bowing of the bone and multiple pathologic fractures.
The lesion may contain numerous cysts surrounded by a dense fibrous tissue with
a gritty consistency. Histologically, a collagenous matrix containing proliferating
fibroblasts surrounds irregularly shaped trabeculae of immature bone arranged
in haphazard pattern classically described as "Chinese letters." The
paucity of osteoblasts rimming the bony trabeculae distinguishes this lesion
from osteofibrous dysplasia. Cartilaginous tissue may occasionally be present
in this condition. Monostotic fibrous dysplasia in the non-weightbearing skeleton
can be treated with observation while bone grafting and internal fixation is
often necessary for proximal femoral lesions. The prognosis of fibrous dysplasia
is good, although sarcomatous transformation has been reported on very rare
occasion in the polyostotic form.
Osteofibrous Dysplasia
Osteofibrous dysplasia is an infrequent benign fibro-osseous lesion of bone,
originally described by Kempson under the name ossifying fibroma. This lesion
has a strong predilection for the tibia and occurs in the first two decades
of life. Radiographs reveal lytic defects involving the anterior cortex of the
tibial shaft. There is usually associated sclerosis surrounding the lesions
and anterior bowing deformity is not uncommon. Histologically, there is a fibroblastic
stroma associated with trabecular bone resembling fibrous dysplasia. The trabeculae,
however, are lined by prominent osteoblasts. This and the cortical location
in the tibia distinguish osteofibrous dysplasia from fibrous dysplasia, which
is a disorder of the medullary bone. There is strong evidence in the literature
to suggest a relationship between osteofibrous dysplasia and adamantinoma .
Both lesions involve the anterior cortex of the tibia, and it is known that
adamantinoma may have areas that resemble osteofibrous dysplasia. In addition,
osteofibrous dysplasia often shows keratin-positive cells in the fibrous stroma.
The relationship between these two disorders is still unclear. The treatment
of osteofibrous dysplasia is curettage, particularly in enlarging lesions during
the second decade of life. Recurrence may occur.
Nonossifying Fibroma
A nonossifying fibroma is a well-defined, eccentric metaphyseal fibrous lesion
of long bones, particularly around the knee. It is distinguished from a fibrous
cortical defect, which is characterized as a localized area involving the cortex.
Most authors consider nonossifying fibromas as advanced forms of fibrous cortical
defects because they are no longer confined to the cortex but extend into the
medullary canal. These lesions appear to arise as a result of some nonspecific
developmental aberration of the tissue or as a consequence of an intraosseous
hemorrhage. Fibrous cortical defects are usually asymptomatic and present on
radiographs taken for unrelated conditions in the distal femur and proximal
tibia of children. They may also be seen in the distal radius. Nonossifying
fibromas may be painful and can present with pathologic fracture. They appear
as clearly demarcated, eccentric, multiocular expansile lesions with scalloped,
sclerotic margins. Multiple and bilateral cortical defects are common. The cortex
may be attenuated in areas adjacent to the lesion but remains intact unless
pathologic fracture has occurred. Histologic examination reveals spindle cells
arranged in a storiform pattern. These whorls of connective tissue are often
interspersed with multinucleated giant cells and lipid-laden macrophages (foam
cells). The giant cells tend to be widely scattered, unlike the more uniform
distribution seen with a giant cell tumor. Nonossifying fibromas and fibrous
cortical defects are self-limited lesions that eventually ossify by the third
decade of life and therefore may be managed with observation. Large lesions
that encompass more than half of the bone diameter may require curettage and
bone grafting to prevent pathologic fracture.
Langerhans Cell Granulomatosis
It is a nonneoplastic proliferation of Langerhans cells associated with eosinophils,
and other chronic inflammatory cells. Eosinophilic granulomas present as solitary
lesions in the long bones, pelvis, ribs, and vertebrae of young children, most
commonly between the ages of 5 to 10 years. Histiocytosis X was a term used
in the past for this condition that comprises eosinophilic granuloma, Hand-Schüller-Christian
disease, and Letterer-Siwe disease. They often manifest with local symptoms
of pain and swelling. When the lesions appear in long bones, they are found
in the metaphysis or diaphysis and may show end osteal scalloping, and there
may be a periosteal reaction if there is local cortical destruction. These lesions
may be more sharply defined when they present in the cranial or mandibular bones.
Spinal lesions may manifest with vertebra plana due to compression of the vertebral
body. Grossly, the tissue is soft with a loose consistency and is yellow in
color. Histologically, it consists of Langerhans cells containing a vesicular,
indented nucleus with a small, centrally placed nucleolus and abundant pale,
granular eosinophilic cytoplasm. These cells are arrayed in sheets or clusters,
and they are surrounded by eosinophilis, various chronic inflammatory cells,
and macrophages. Small areas of necrosis may be seen. Electron microscopy of
the Langerhans cells reveals the characteristic "Birbeck granules":
racquet-shaped cytoplasmic structures. The Langerhans cells react immunohistochemically
with S-100 protein. The surgical treatment of esinophilic granuloma includes
simple intraosseous curettage and bone grafting. In other cases, a conservative
approach by intralesional injection of steroids has proved to be effective.
Other clinical manifestations of Langerhans cell granulomatosis include Hand-Schüller-Christian
and Letterer-Siwe disease. Hand-Schüller-Christian disease is a systemic
process involving multiple bones, particularly the skull, as well as the liver,
lungs, spleen, and skin. Letterer-Siwe disease demonstrates fewer skeletal lesions
but has an aggressive clinical course due to widespread involvement of the skin,
viscera, and lymphatics. The histologic features of these two conditions are
similar to eosinophilic granuloma.
Giant Cell Reparative
Granuloma
It is a benign process that was originally described in the jaw but was found
also to occur in the short tubular bones of the hands and feet. A few cases
have been recently described in long bones. It is more common in children and
young adults but has a wide age distribution. Radiographs show a lytic intramedullary
lesion in the phalanges, metacarpals, or metatarsals, sometimes associated with
bone expansion and thinning of the cortex. Histologically, there is fibroblastic
proliferation associated with scattered aggregates of giant cells, stromal hemorrhage,
and bone reaction.
Giant cell reparative granuloma is a reactive nonneoplastic process. It usually
can be distinguished histologically from giant cell tumor, where the giant cells
are distributed uniformly in the tissue. The lesion has histologic similarities
with aneurysmal bone cyst, particularly the solid areas, and probably the two
processes are closely related. It is indistinguishable from brown tumor of hyperparathyroidism,
but the patients have normal serum calcium and phosphate levels. As far as distinction
from nonossifying fibroma, it is exceedingly rare in the bones of the hands
and feet. Curettege is the recommended treatment. Recurrence is not uncommon.
