Bone and joints

Question 1

fracture callus (vs neoplasm)

Answer 1

well circumscribed

zonation

well formed trabeculae

cartilage with enchondral ossification

osteoblastic rimming

no atypia

no mitoses

Question 2

benign mimics of malignancy

Answer 2

fracture callus

AVN

osetomyelitis (acute and chronic)

synovial chondromatosis

BPOP

Question 3

low grade chondrosarcoma (vs benign chondroid lesions)

Answer 3

PAGODA-6

painful, axial skeleton, rapid growth, old people,

bone destruction on radiology

atypia, mitoses, cellular, permeative

>6cm (or osteochondroma cap >2cm)

Question 4

telangiectatic osteosarcoma vs ABC

Answer 4

markedly atypical cells in septa

(radiology and macro look the same!)

Question 5

nodular joint lesions

Answer 5

PVNS

synovial chondromatosis

synovial lipomatosis

Question 6

ABC associations

Answer 6

chondroblastoma

giant cell tumour

fibrous dysplasia

BUT also any other benign or malignant bone lesion!

Question 7

giant cells

Answer 7

giant cell tumour

chondroblastoma

SBC and ABC

MFD

giant cell (reparative) granuloma (=solid ABC)

Brown tumour (hyperparathyroidism only distinguishes from GCG)

osteosarcoma

Question 8

epithelioid/histiocytoid

Answer 8

LCH

mastocytoma

lymphoma

Question 9

osteoid producing lesions

Answer 9

fracture callus

osteoid osteoma/osteoblastoma

ABC

osteosarcoma

Question 10

osteosarcoma vs benign osteoid producing lesion

Answer 10

permeative

lace-like osteoid

no osteoblastic rimming

severe atypia

mitoses

Question 11

mets in kids

Answer 11

neuroblastoma

rhabdomyosarcoma

retinoblastoma

Question 12

mets in adults

Answer 12

5 B’s

bronchus

breast

bidney

byroid

brostate

(and melanoma)

Question 13

OA vs RA

Answer 13

RA: joint destruction, inflamed synovium (hyperplasia, plasma cells and lymphocytes)

OA: reparative tissue, proliferative cartilage, bone sclerosis, osteophytes, less inflammation

Question 14

gout vs pseudogout vs calcification

Answer 14

gout: needle shaped crystals, negative birefringence

pseudogout (calcium pyrophosphate): rhomboid shaped crystals, positive birefringence

‘calcification’ (usu soft tissues):

metastatic - disturbed calcium metabolism (eg Pagets, parathyroid)

dystrophic - dead tissue (eg coagulation necrosis, fat necrosis)

Question 15

PVNS vs haemosiderotic and detritic synovitis

Answer 15

PVNS: mononuclear and giant cell proliferation

(both have pigment)

Question 16

chondroblastoma vs GCT

Answer 16

CB: younger, sclerotic rim, S100+, chicken wire calcifications

Question 17

adamantinoma vs osteofibrous dysplasia

Answer 17

OFD: single CK+ cells (cf nests in adamantinoma)

Question 18

metaphyseal defect vs benign FH

Answer 18

same histology!

MFD: skeletally immature, metaphysis of long bones

if not in right age/location can call BFH

Question 19

chondrosarcoma vs chordoma (esp at skull base)

Answer 19

chordoma: CK and brachyury+

Question 20

giant cell reparative granuloma (features)

(=solid ABC)

Answer 20

on a spectrum between GCT and MFD

craniofacial bones, mainly jaw

small bones hand and feet

spine

Question 21

ABC vs SBC

Answer 21

ABC: can deform bone, blood filled, fibrous septa with osteoid, fibroblasts and giant cells; may be USP6+

SBC: doesn’t deform bone, flat lining cells, serous fluid