Periosteal chondrosarcomas, previously also known as juxta-cortical chondrosarcomas, are cartilagineous or chondroid matrix-generating neoplasms originating in close association with the periosteum from the bony surface 1-3.
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Terminology
The term ‘juxta-cortical chondrosarcoma’ is no longer recommended 1.
Epidemiology
Periosteal chondrosarcomas are rare and make up for about ~2-2.5% of all chondrosarcomas 1,2. They occur in a wide age range with a peak in the 3rd decade and a male gender preference 1-4.
Diagnosis
The diagnosis of periosteal chondrosarcoma is made by a combination of clinical information, location and origin of the tumor as well as the invasion of the bony cortex or tumor size and can be eventually confirmed by histology 1-4.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
cartilaginous tumor originating from the surface of the bone in close association with the periosteum
tumor invasion of the underlying osseous cortex or tumor size >5 cm
Clinical presentation
Clinically periosteal chondrosarcomas can present with swelling and/or pain and sometimes even motion restriction due to the swelling or neurological symptoms 1,2.
Pathology
Unlike conventional chondrosarcomas, periosteal chondrosarcomas arise from the surface of the bone in close association with the periosteum, lifting the periosteum over themselves. The underlying cortex is usually thickened and cortical invasion is seen in the majority of cases 3.
Etiology
The etiology of periosteal chondrosarcoma is unknown 1.
Location
They typically arise from long bones, with a predilection for the posterior aspect of the distal femur.
Pathology
Unlike conventional chondrosarcomas, periosteal chondrosarcomas arise from the surface of the bone in close association with the periosteum, lifting the periosteum over themselves. The underlying cortex is usually thickened and is seen in the majority of cases 3,4.
Etiology
The etiology of periosteal chondrosarcoma is unknown 1.
Location
The most common sites involved are the metaphyses of tubular long bones especially the distal femur and the proximal humerus 1-3.
Macroscopic appearance
Grossly, periosteal chondrosarcomas are characterized by the following features 1,3:
lobulated mass on the bony surface sometimes extending into the soft tissues
often large tumors >5 cm, rarely they can be small <3 cm
grayish-glistening cut surface with gritty-white spots of calcification
erosion of the bony cortex
Microscopic appearance
Histomorphologically, periosteal chondrosarcomas display the following microscopical features 1,3,4:
lobular moderately cellular cartilaginous tumor with myxoid matrix
similarity to conventional central chondrosarcoma
no direct bone or osteoid formation
neocortex formation or metaplastic bone formation at the periphery in almost half of the cases
commonly invasion of the underlying bony cortex
intramedullary extension can be seen
clear delineation from the soft tissues
Immunophenotype
Immunohistochemistry stains are negative for CDK4 or MDM2 1.
Genetics
IDH1 and IDH2 mutations which can be found in conventional central chondrosarcoma are expressed in a subset of cases. EXT1 is expressed normally without mutations that are found in secondary peripheral chondrosarcomas 1,3. There might be dysregulations of RB1 signaling pathways. Unlike in parosteal osteosarcoma CDK4 or MDM2 amplification is absent 1,3.
Radiographic features
General radiographic signs of periosteal chondrosarcomas include the following 1-4, 6-8:
lobulated morphology
altered underlying bony cortex (can be thinned or thickened) 1,5
often large tumors (>5 cm)
periosteal shell (metaplastic ossification)
Plain radiograph/CT
Radiographic features of periosteal chondrosarcomas include the following 1-3,,6-8:
osteolytic lesion with intralesional calcifications
cortical bone erosion
calcification, ossification of the periosteal shell
MRI
They appear as a lobulated cartilaginous mass with a chondroid or myxoid matrix, lifting the periosteum from the cortex. Cortical invasion or destruction is often present. Intraosseous/intramedullary extension might not always be appreciated on MRI 5-8, but if present favors an intermediate to high-grade over a low-grade tumor 9,10. Soft tissue extension might be present 6,7.
Signal characteristics
T1: low to intermediate signal vs muscle
T2/STIR: high signal intensity with punctate or curvilinear signal voids indicating matrix mineralization
T1 C+ (Gd): peripheral and septal enhancement
Rarely tumors are <3 cm then they are difficult to diagnose on imaging 5 and special attention should be paid to cortical destruction and/or intramedullary invasion even though the latter is not always apparent on MRI 5.
Nuclear medicine
PET-CT shows increased uptake of FDG 8.
Radiology report
The radiological report should include a description of the following 5-10:
tumor size and location (metaphysis, diaphysis)
tumor margins/surface
intralesional calcifications
cortical erosion/destruction
association to the periosteum/periosteal shell
extension into the medullary cavity
soft tissue extension
Treatment and prognosis
Surgical excision is recommended 1. Most recommend wide/en-bloc excision, whereas others conclude that marginal excision is adequate 2-4. Clinical and morphological parameters do not predict the outcome of those tumors 1,4.
Complications
Complications include local recurrences and distant metastases mainly to the lungs in up to 12% 1,4.
History and etymology
Periosteal chondrosarcoma was first described by the American bone pathologist Louis Liechtenstein in 1955 11.
Differential diagnosis
The main differential diagnoses of low-grade peripheral chondrosarcomas are 1,5,12:
periosteal chondroma (most difficult if small lesion): lesion size usually <3 cm 6, no cortical destruction
periosteal osteosarcoma: osteoid areas, sunburst or hair-on-end pattern, no IDH mutations
parosteal osteosarcoma: bony stalk
peripheral chondrosarcoma: arising from osteochondroma
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