Telangiectatic osteosarcoma

Telangiectatic osteosarcomas (TOS/TAEOS) are an uncommon variant of osteosarcoma ^1-3. 

Epidemiology

Telangiectatic osteosarcomas make up for 2-12% of high-grade osteosarcomas with varying frequencies between studies ^1-6. They have similar demographics to that of conventional osteosarcoma and typically occur in adolescents and young adults ^4,5 (reported age range of 3-67 years ^ref with a median age of 15- 20 years ⁵). There is a recognized male preference ^4,5.

Diagnosis

Telangiectatic osteosarcoma is considered a subtype of conventional osteosarcoma. Similarly, the diagnostic criteria are based on a combination of typical radiographic and pathological features.

Diagnostic criteria

Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5^th edition) ⁴:

• imaging features of a bone tumor

• osteoid matrix with neoplastic bone formation

• permeative and destructive growth pattern

and in addition, the following criterion is required:

• empty or blood-filled cystic spaces separated by septa

As with conventional osteosarcoma, the following histological criteria are desirable ⁴:

• high-grade atypia of tumor cells

• frequent atypical mitotic figures

Diagnostic clues

Clinical and imaging-related characteristics indicating the diagnosis without the pathological information:

• in adolescents (10-20 years)

• bone tumor with osteoid matrix, cystic spaces with fluid-fluid levels, enhancing septae, permeative features and cortical destruction

• location in a metaphyseal-diaphyseal region with epiphyseal extension

Pathology

Telangiectatic osteosarcomas are a subtype of osteosarcoma characterized by empty or blood-filled cystic spaces separated by septa ^1-6. A small telangiectatic component is present in most osteosarcomas, but to classify as telangiectatic osteosarcoma, the telangiectatic component should comprise >90% ⁷.

Location 

The most common sites are the metaphyses of long bones possibly with extension into the epiphysis or diaphysis especially around the knee (~60) ^4-6:

• distal femur: ~40-45%

• proximal tibia: ~15-20%

• proximal humerus: ~8-10%

• proximal femur: ~7-8%

The femoral, humeral and tibial diaphyseal regions as well as the pelvic bones are less common with frequencies ranging from ~5-7% for the mid-femur to ~3% in the pelvis ⁵.

Rare locations are the fibula, skull and ribs with a frequency <2% each ^5,8.

Macroscopic appearance

Grossly, telangiectatic osteosarcomas are characterized by the following features ^1-5:

• cystic, blood-filled spaces

• multiple thin fibrous septa with sponge-like or honeycomb appearance

• fish-flesh appearance of solid tumor portions

• tumor size is 5-13 cm on average ³

Microscopic appearance

Microscopically, telangiectatic osteosarcomas display a similar picture to an aneurysmal bone cyst with the following histological features ^1-5:

• hemorrhage and necrotic debris

• blood pools without endothelial lining

• septa of variable thickness

• atypical stromal cells among osteoclast-like giant cells

• atypical mitoses with moderate to high mitotic rate

• nuclear hyperchromasia and pleomorphism

• focal osteoid formation and sometimes lacelike osteoid matrix (maybe absent in biopsy sample) ^4,5

Radiographic features

Plain radiograph

Typically seen as an expansile lytic bone lesion at the metaphysis:

• geographic bony destruction with a wide zone of transition tends to be more common than permeative bony destruction ⁹

• less osteoid matrix than the conventional type

• pathological fractures are frequent

CT

• low attenuating fluid-fluid levels within the lesion (in ~80% of cases)

• useful at assessing associated cortical destruction

• thick peripheral and nodular septal enhancement

• osteoid matrix mineralization

MRI

• commonly shows fluid-fluid levels within the lesion (~90% of cases) with variable signal intensity

• allows appreciation of surrounding soft tissue components

• signal characteristics are often heterogeneous

• enhancement of septa with nodularity as well as the soft tissue component may be observed ¹⁰

• hemorrhage appears as hyperintense on T1 and variable signal intensity on T2

Nuclear medicine

Overall, lesions tend to show marked but heterogeneous uptake on bone scans. May demonstrate a region of central photopenia representing a doughnut sign ^9,10.

Radiology report

The radiological report should include a description of the following ⁴:

• form and location

• blood-filled or empty cystic spaces, fluid-fluid levels

• thickened fibrous septa, nodular/solid components

• tumor margins and transition zone

• cortical striations indicating prominent intraosseous veins

• cortical destruction

• soft tissue extension

• pathological fractures

Treatment and prognosis

The treatment of telangiectatic osteosarcoma is often similar to that of conventional osteosarcoma: chemotherapy followed by wide surgical resection and limb salvage or amputation. 

The survival rate of telangiectatic osteosarcoma (estimated at ~70%) is similar to that of conventional osteosarcoma.

Complications

They are associated with a high rate of pathological fractures ^6,11 and fracture risk is higher than conventional osteosarcoma ⁶.

History and etymology

Telangiectatic osteosarcoma was first described by the English surgeon Sir James Paget (1814-1899) in 1854 as a ‘medullary cancer of bone with excessive vessels and blood cysts’ ¹³. Later in 1903, the entity has been called ‘malignant bone aneurism’ by the American surgeon Gaylord ¹⁴ before the American pathologist James Ewing designated it as an osteosarcoma variant in 1922 and 1939 ¹⁵.

Differential diagnosis

Considerations on plain film include ⁵:

• aneurysmal bone cyst (ABC): should not have any soft tissue component outside the lesion and will have a narrower transitional zone. Smooth septal and rim enhancement is seen without nodularity, osteoid matrix mineralization or aggressive features like cortical destruction and infiltration into surrounding tissue (unlike telangiectatic osteosarcoma) ¹¹

• giant cell tumor of bone: no soft tissue component

• osteolytic metastatic bone lesions: should not have any fluid levels