Osseous Tumour Reporting and Data System (OT-RADS)

Osseous Tumour Reporting and Data System (OT-RADS) is a reporting and communication tool designed to reliably identify benign and malignant bone tumours and to communicate them in a standardised way, using BI-RADS as an example ^1-3.

History and etymology

The Osseous Tumour Reporting and Data System has been developed and validated by a group of radiologists and orthopaedic surgeons from UT Southwestern Medical Centre in Dallas around the American Radiologist Avneesh Chhabra and has been published in the Journal of Computer Assisted Tomography in 2021 ¹.

Usage

The reliability of the OT-RADS system was validated by the above study group mainly based on a "complete MR imaging study" with the following predefined requirements ¹:

full tumour coverage in each of the following sequences in at least one plane

• T1 weighted imaging (T1)

• fluid sensitive imaging (T2FS/STIR)

• postcontrast fat-saturated T1 weighted imaging (T1FS C+)

An additional complementary set of MRI sequences is considered sufficient if acquired within two weeks of the initial incomplete imaging set ¹.

The following are considered optional supplemental imaging features for the diagnosis ^1,3:

• diffusion-weighted imaging (DWI) with the apparent diffusion coefficient (ADC)

• corresponding radiographic imaging features (if available)

Assessment categories

The assessment categories were created using the BI-RADS system as an example and based on the WHO classification of bone tumours. The assignment of categories in the OT-RADS seems to be based more on the typical MRI appearance of representative lesions with lesion-specific predefined imaging criteria than on generalised MRI signal characteristics ^2,3 with some exceptions, such as about appearance on diffusion imaging and post-contrast enhancement.

OT-RADS 0

• interpretation: incomplete imaging (see above)

• probability of malignancy: not applicable

• management: additional imaging or prior imaging examinations required

• imaging criteria: not applicable

OT-RADS 1

• interpretation: no bone tumour/lesion

• probability of malignancy: substantially 0%

• management: no further imaging follow-up is required

• imaging criteria: normal bone anatomy

OT-RADS 2

• interpretation: definitely benign bone lesion

• probability of malignancy: substantially 0%

• management: imaging follow-up as per recommendations of the clinical team

• representative lesions:

  • intraosseous lipoma: uniform typical fat signal on all sequences and no enhancement

  • simple bone cyst

  • geode

  • classic aneurysmal bone cyst: fluid-fluid levels and no solid component

  • non-ossifying fibroma: subcortical location, mixed signal intensity

  • osteoid osteoma: with well-defined nidus (<1.5 cm)

  • small enchondroma: <4-5 cm, endosteal scalloping <50%, no bone marrow oedema or periosteal oedema

  • classic haemangioma of bone: T1 signal hyperintensity

  • osteochondroma: exostosis, cartilage cap ≤1.5 cm

• enhancement patterns:

  • no enhancement

  • thin or septal enhancement

  • nidus-like enhancement (osteoid osteoma)

  • variable enhancement

• diffusion-weighted imaging:

  • moderate to marked hyperintensity in both DWI and ADC images

  • T2 shine through effect

  • mean ADC values: >1.5-3.0 x 10^-3 mm²/s with exception of fat-containing tumours

OT-RADS 3

• interpretation: probably benign bone lesion

• probability of malignancy: ≤2%

• management:

  • imaging follow-up in 3 months, 6 months, 1 year and 2 years or <2 years

  • follow-up might be shorter in the setting of lesion regression or resolution

• representative lesions:

  • Langerhans cell histiocytosis: in children and young adults

  • intraosseous myxoma

  • chondromyxoid fibroma

  • giant cell tumour of bone

  • chondroblastoma

  • synovial chondromatosis with involvement of bone

  • enchondroma protuberans: in hands and feet

  • desmoplastic fibroma

  • fibrous dysplasia

  • Paget disease

  • epithelioid haemangioma of bone

• enhancement patterns: usually variable enhancement

• diffusion-weighted imaging:

  • moderate to marked hyperintensity in both DWI and ADC images

  • mean ADC values: >1.2-2.0 x 10^-3 mm²/s with caution in myxoid lesions and giant cell tumour of bone

OT-RADS 4

• interpretation: indeterminate or suspicious for malignancy

• probability of malignancy: >2% and <50%

• management:

  • histology or short-term follow-up in 4-6 weeks

  • imaging follow-up as per OT-RADS 3 category in the setting of negative or indeterminate histology

• MR imaging criteria: mixed intensity, solid appearance, up to 5 cm in length

• representative lesions:

  • enchondroma with deep endosteal scalloping (>50% of cortex)

  • atypical cartilaginous tumour/chondrosarcoma grade 1

  • osteoblastoma

• enhancement patterns: variable

• diffusion-weighted imaging:

  • moderate to marked hyperintensity on DWI and mild-to-moderate hyperintensity on ADC images

  • mean ADC values: >1.1-1.2 x 10^-3 mm²/s with caution in myxoid lesions and giant cell tumour of bone

OT-RADS 5

• interpretation: highly suspicious for malignancy

• probability of malignancy: ≥50%

• management: histology required

• MR imaging criteria: mixed intensity, solid appearance

• representative lesions:

  • osteosarcoma

  • Ewing sarcoma

  • pleomorphic sarcoma

  • bone lymphoma

  • multiple myeloma

  • bone metastasis

• enhancement patterns: variable

• diffusion-weighted imaging:

  • diffusion restriction

  • mean ADC values: <1.1-1.2 x 10^-3 mm²/s with caution in myxoid lesions and giant cell tumour of bone

OT-RADS 6

• interpretation: histologically proven malignancy or known tumour recurrence

• probability of malignancy: not applicable / proven

• management: surgical excision and/or treatment as clinically appropriate

• imaging criteria: solid nodule or residual mass in tumour bed with pre-interventional imaging features

See also

• Solitary bone tumour imaging reporting and data system (BTI-RADS)

• Bone Reporting and Data System (Bone-RADS)

• Reporting and Data Systems (RADS): list of all RADS