Periosteal chondrosarcoma

Periosteal chondrosarcomas, previously also known as juxta-cortical chondrosarcomas, arecartilagineous or chondroid matrix-generating neoplasms originating in close association with the periosteum from the bony surface ^1-3.

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 3^rd 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 tumour as well as the invasion of the bony cortex or tumour size and can be eventually confirmed by histology ^1-4.

Diagnostic criteria

Diagnostic criteria according to theWHO classification of soft tissue and bone tumours (5th edition edition)¹:

• cartilaginous tumour originating from the surface of the bone in close association with the periosteum

• tumour invasion of the underlying osseous cortex or tumour 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.

Aetiology

The aetiology 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.

Aetiology

The aetiology 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 characterised by the following features ^1,3:

• lobulated mass on the bony surface sometimes extending into the soft tissues

• often large tumours >5 cm, rarely they can be small <3 cm

• greyish-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 tumour 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 signalling 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 tumours (>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

• periosteal reaction

• 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 favours an intermediate to high-grade over a low-grade tumour^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 mineralisation

• T1 C+ (Gd): peripheral and septal enhancement

Rarely tumours 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:

• tumour size and location (metaphysis, diaphysis)

• tumour 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 tumours ^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 ¹⁶⁶, 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

• parosteal lipoma

See also

• chondrosarcoma

• chondrosarcoma grading