Juxtacortical tumors or surface tumors of bone are neoplasms [abnormal and excessive growth] arising from or just outside the cortex, and are composed of different histologic types.
Some of the important juxtacortical tumors are
- Periosteal or juxtacortical chondroma
- Periosteal or juxtacortical chondrosarcomas
- Periosteal or juxtacortical osteosarcomas
Juxtacortical tumors are divided into 5 major categories
- Cartilaginous [most common]
Juxtacortical chondroma and chondrosarcoma are cartilaginous, osteosarcoma is an example of the bony lesion.
Chondromyxoid fibroma is a fibrous lesions. Metastases and lipomatous juxtacortical tumors are less common.
Juxtacortical Chondroma or Periosteal Chondroma
Periosteal chondroma is a benign cartilage juxtacortical tumor that develops on the surface of bone under the periosteum and consists of mature hyaline cartilage.
Periosteal chondromas account for less than 1% of all chondromas.
A slight male predominance exists.
Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) genes are known to be associated.
Periosteal chondroma is known to grow into adulthood as well. Osteochondroma stops growing after skeletal growth stops.
The proximal humerus is most commonly affected [50%]. It may also involve the bones of the hands and feet.
Microscopic features are typical of a chondroma with a hyaline cartilage matrix. On average, juxtacortical chondromas can show mild nuclear atypia or binucleated chondrocytes. Scalloping and erosion of the outer cortex are seen microscopically.
Some periosteal chondromas may bulge for a short distance into intervening lamellar bone.
A fibrous capsule typically overlies the tumor. Occasional foci of necrosis and myxoid degeneration may be present.
This surface lesion most often presents as slowly progressive painful mass. The pain is due to enlargement of the lesion or from impingement on adjacent soft-tissue structures.
Physical examination reveals a firm and immobile mass which is painful to touch.
Deep-seated juxtacortical chondromas near tendon insertion sites may cause pain and local discomfort on activity.
Periosteal chondromas are always not symptomatic though. These are sometimes discovered incidentally on radiographs.
X-rays reveal a well-circumscribed surface lesion of bone, usually of size 1-5 cms, with variable punctate calcifications on radiographs. The cartilaginous nature of juxtacortical chondroma is easy to recognize on plain radiographs.
The cortex beneath the lesion is usually eroded but not completely disrupted. There would a varying degree of subcortical sclerosis beneath the lesion.
The elevated periosteum is seen as solid buttresses of mature subperiosteal bone. It can sometimes slightly overhang the edges of the central excavation especially in cases of the smaller periosteal chondromas
Computed tomography, magnetic resonance imaging, or both modalities also may be needed to evaluate the extent of involvement
Asymptomatic stable lesions can be monitored. Though the risk of malignant transformation is very small, asymptomatic periosteal chondromas should be followed regularly with clinical examination and x-rays.
A lesion that enlarges over a period or is symptomatic should be treated.
Complete local excision of juxtacortical chondroma is a curative procedure. Because periosteal chondromas may demonstrate radiologic overlap with juxtacortical chondrosarcoma, excision of the lesion is the preferred mode of the treatment.
Periosteal chondrosarcoma or juxtacortical chondrosarcoma is a malignant cartilage tumor that is seen in the second to fourth decades of life.
The patient presents with a slowly growing mass. Pain is less common. The distal femur is the most common site followed by proximal humerus.
Perioseal chondrosarcoma is difficult to differentiate from periosteal chondroma.The larger size and cortical breach [compare with juxtacortical chondroma] suggest chondrosarcoma.
MRI shows multilobulated lesions, confined to the juxtacortical area without medullary involvement.
Microscopically, the lesions are low-to-intermediate grade. An occasional high-grade area may be seen.
Increased of expression of matrix metalloproteinases 1, 2, and 9 is noted but less consistently than central or dedifferentiated chondrosarcoma.
Osseous metaplasia or enchondral ossification may lead to pockets of bone formation in the tumor.
Like juxtacortical chondrosarcomas, mutations in IDH1 and IDH2 have been noted.
Treatment consists of surgical removal with tumor-negative margins. With adequately resected margins, local recurrence is unusual. Metastases also are unusual, and if they occur, they occur late in the disease process. ]
Parosteal Osteosarcoma, periosteal osteosarcoma and high-grade surface osteosarcoma are three types of osteosarcomas that form juxtacortical osteosarcomas.
Parosteal osteosarcoma is the most common representing 65% of juxtacortical osteosarcomas. It forms 3-6% of all osteosarcomas
Posterior surface of the distal femur is most commonly involved. Occasionally proximal humerus is involved. Most of the cases are seen in persons aged 15-40 years.
There is a slight female predilection for this variant of osteosarcoma. Slowly growing painless mass is the usual presenting feature. Pain and swelling occur late.
There could be a decreased range of motion of the joint as the lesion is in the vicinity of the joint.
On x-rays, the lesions are seen as radiodense mass present on the bone surface. The lesion is broad-based and may encircle the bone.
Periosteal reaction is not seen [as compared to intramedullary osteosarcoma]. Lucent areas on x-ray films suggest either aggression or dedifferentiation [presence of immature cells] of the tumor.
A clear space, on CT, between the tumor and the bone cortex, is called clear plane or string sign. It reflects unmineralized, thickened periosteum. CT can delineate areas of cortical erosion.
MRI can identify soft tissue and intramedullary extent of the tumor. MRI is useful for preoperative planning and can reveal more aggressive areas within apparent parosteal osteosarcoma.
On gross examination, the dense mineralization of the tumor is noticed along with medullary involvement.
Being low grade, this variant does not express the higher MIB-1 indices [ percentage of immunoreactive tumor cells] or multiple chromosomal aberrations typically seen with higher-grade lesions.
But every tumor should be looked for pockets of high-grade changes.
Treatment of these juxtcortical tumors consists of wide resection and limb salvage when possible. Although low-grade, these tumors may recur locally with less than a wide resection margin, and dedifferentiation has been noted in cases with multiple local recurrences.
Among osteosarcomas, this variant carries the best prognosis.
However, wide margins may be difficult to achieve due to the vicinity of neurovascular structures.
Metastases in classic parosteal osteosarcoma are rare
Parosteal osteosarcoma that contains higher-grade dedifferentiated areas has a worse prognosis.
Periosteal osteosarcoma represents the second most common type of surface osteosarcoma. Its occurrence is similar to conventional osteosarcoma.
It is a purely cortical lesion, the thickened intact cortex is visible. It is high grade and does not go to medulla.
There is a male predilection has been noted.
Periosteal osteosarcoma most frequently is seen on the surface of the proximal tibia [compare with parosteal]. The patients present with a painful enlarged mass which has rapid clinical course.
X-rays show heterogeneous ossification. Radiolucent lesions are present in greater frequency than in parosteal osteosarcoma. Erosion or thickening of the underlying cortical bone may be noted.
Microscopically, the tumor is composed of moderately differentiated chondroblastic osteosarcoma. The spindle-cell component usually is of intermediate grade. Cartilage present within the tumor contributes to the lobulated appearance. However, the chondrocytes may show atypia [structural abnormalities of cells]
Treatment consists of wide surgical resection. This variant is reported to metastasize.
High-Grade Surface Osteosarcoma
It is the least common of the surface osteosarcomas. Most commonly, it affects people in the second or third decade
This variant is found more in the males.
Patients typically present with an enlarging painful mass and swelling. The natural course fo this tumor is shorter. Most of the patients present within 1-6 months. Just to compare, parosteal osteosarcoma takes about one year to present.
Midfemur or distal femur is the most common location. The tibial diaphysis is next in the list.
X-rays show a broad attachment to the cortex but there is no encircling of the cortex as seen in parosteal osteosarcoma. Involvement of the underlying cortex is seen as cortical erosion or thickening.
The lesion may be dense showing sunburst appearance or could be radiolucent.
Medullary involvement may be difficult to rule out. However, if there is substantial medullary involvement, the lesion is more likely to be conventional intramedullary osteosarcoma with extrabony extent.
The tumor is otherwise histologically identical to the conventional intramedullary form.
This tumor has the worst prognosis among the surface osteosarcomas and demands aggressive treatment.
Initial grade of the tumor, response to neoadjuvant chemotherapy, and the presence of local recurrence are prognostic factors.
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