Features of Osteoma
- Loc: Craniofacial bones, can protrude to sinuses/orbit
- Rx: Radiodense mass
- Micro:
Dense, mature lamellar bone.
Features of Osteoid osteoma
- Clinical: 10-30 yo. Pain relieved by NSAIDS
- Loc: Any bone. Common: long bones, H&F, vertebra
- Rx: Radiolucent central nidus +/- radiodense center & peripheral sclerotic reaction
- Micro:
Nidus has anastomosing trabeculae of woven bone/osteoid lined by osteoblasts (variably calcified).
Fibrovascular stroma in b/w trabeculae +/- MN giant cells.
Nidus surrounded by dense bone.
Features of Osteoblastoma
- Clinical: 5-30 years old. Progressive pain
- Loc: Post elements of vertebrae, long bones
- Rx: Radiolucent, well defined, >2cm +/- calcium foci
- Micro: (like an ostoid osteoma but bigger)
Anastomosing trabeculae of woven bone/osteoid lined by osteoblasts (variably calcified).
Ectatic vessels in the fibrovascular stroma +/- MN giant cells.
Features of Osteosarcoma
-Clinical: Progressive pain.
10-25yo.
Second peak: >40 years old, associated with pre-exiting disorder: Paget, Radiation, Chemothx, foreign body (i.e at site of THJR, etc), pre-existing benign bone lesion (fibrous dysplasia, OI, bone infarct) and genetic predisposition (hereditary RB, Li-Fraumeni sdme).
-Location:
Metaphysis of long bones (> common around knee).
- Rx: Destruction of medullary cavity & cortical bone, aggressive pattern of periosteal reaction.
- Micro:
* Production of bone or osteoid by the tumour cells: ‘lace-like’ deposition of osteoid +/- calcified matrix.
* No osteoblastic rimming
*Spindled, oval or round cells with cytologic features of malignancy.
* Osteoblastic, chondroblastic & fibroblastic patterns usually coexist.
* Permeative growth.
* +/- HPC like vessels.
* +/- MN gant cells.
- IHC: SATB2 useful to establish osteoblastic lineage.
Bone conditions that predispose to malignancy (4)
- Paget disease
- Enchondromatosis
- Osteochondromatosis
- Fibrous dysplasia
Differential diagnosis of bone lesions with giant cells (9)
- GCT
- ABC
- LCH
- Giant cell rich osteosarcoma
- Giant cell reparative granuloma
- Non-ossifying fibroma
- Chondromyxoid fibroma
- Chondroblastoma
- Brown tumour of hyperparathyroidism
Features of Chondrosarcoma (page 1764-1767 Rosai)
- Clinical: Adults >50 years old. Slow clinical evolution with pain, swelling +/- pathological #. Can metastasize to lung.
- Location:
Central: Medulla of long or flat bones.
Peripheral: From the cartilaginous cap of an Osteochondroma (> freq in MHE patients).
Most common: trunk (including shoulder and pelvic girdles), upper end of humerus & femur, skull. - Rx: Large radiolucent lesion with areas of calcification, ill-defined margins, expansile remodelling of bone with endosteal scalloping to cortical destruction with soft tissue mass.
- Micro:
Wide range of differentiation. Common denominators:
Production of cartilaginous matrix.
Lack of bone/osteoid formation by tumour cells.
Permeation of bone & invasion into soft tissues.
Also:
Lobulated growth (+/- rings of reactive bone).
Myxoid change in the cartilaginous matrix.
+/- Foci of necrosis
Two classifications of Chondrosarcoma (page 1766 Rosai)
- 1ry: Arising de novo.
- 2ry: Associated with a pre-existing benign condition. Eg. Osteochondroma.
- Conventional
- Variants:
- Clear cell: Cells w abundant clear cytoplasm & sharply defined borders, large N w prominent nucleoli admixed w small trabeculae of woven bone/osteoid (not produced by the cells) & MN giant cells.
- Myxoid: (> common in ST). Looks like chordoma. Rows of round to spindle cells separated by a myxoid background.
- Dedifferentiated: Transition from a low grade CS to a high grade sarcomatous component (OS, MFH, UPS, Rhabdosarc, etc)
- Mesenchymal: Rare, 2nd or 3rd decades. In extraosseous sites like orbit, paraspinal region, meninges or ST of extremities. In bone: axial skeleton or craniofacial bones. Biphasic pattern with areas of cellular cartilage (S100+) and population of small, undifferentiated round to spindle cells (CD99 +, S100 -). HPC vessels. Other IHC: SOX9 and Osteocalcin +.
Grading of Chondrosarcoma (page 1766 Rosai)
Grading based on cellularity and cytologic atypia, to a lesser degree mitotic activity (Overall uncommon).
- Grade 1: Resembles normal cartilage or an enchondroma, mild atypia (but permeative).
- Grade 2: > cellular, abundant myxoid stroma, > atypia (nuclear enlargement, hyerchromasia, binucleation).
- Grade 3: High cellularity, marked atypia.
Molecular analysis Chondrosarcoma and variants
- Central/conventional CS: IDH1 & IDH2 mutations common.
- Clear cell CS: Chromosome 9 & 20 abnormalities.
- Myxoid CS: EWSR1 & NR4A3 gene rearrangements.
- Dediff CS: Overexpression of TP53 & HRAS.
- Mesenchymal CS: HEY1-NCOA2 fusion
Variants of Osteosarcoma (page 1754- 1758)
- Telangiectatic: Blood filled spaces separated by septae containing pleomorphic mononuclear &MNG cells with ++mitosis, +/- areas of necrosis. DD: ABC.
- Small cell: Small, uniform round or spindled cells. Need to identify osteoid & exclude other high grade neoplasms. IHC: SATB2 +, CD99 -.
- Paraosteal (most common variant): Originates from the surface of cortex. Posterior aspect of distal femur. Broad beams of ostoid in a hypocellular fibrous stroma with minimal atypia.
- Low grade central (rare): Similar to paraosteal OS.
- Periosteal: Less common. Encases the bone like a glove. Diaphysis location.
- Osteosarcoma of jaw: approx 35yo. Body of mandible or alveolar ridge of maxilla.
- Other: Osteoblastoma-like OS, Chondroblastoma-like OS, giant cell rich OS, Secondary OS (due to Paget diease, etc.
DD of Osteosarcoma
Depending of predominant pattern:
fracture callus, fibrous dysplasia, metastatic carcinoma, osteoblastoma, fibrosarcoma, chondrosarcoma, GCT.
