Msk - Cystic Bone Lesions

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mnemonic for benign cystic bone lesions

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FEGNOMASHIC
Fibrous dysplasia
Enchodroma, E Gran
Giant Cell Tumor
Non-Ossifying FIbroma
Osteoblastoma
Mets, MM
ABC
Solitary Bone cyst
Hyper PTH
Infx
Chondroblastoma, Chodromyxoid

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distinguishing characteristic of fibrous dysplasia

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no periosteal rxn

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location of fibrous dysplasia

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pelvis (will almost always include ipsilateral prox femur)
prox femur (does not have to include pelvis)
ribs
skull
jaw

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appearance of fibrous dysplasia

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"ground glass" = "buzzword"
can be patchy, sclerotic, lucent, single or mutliple.
(basically can look like anything)

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mccune albright syndrome

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cafe au lait spots
precocious puberty
polyostotic fibrous dysplasia

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fibrous dysplasia appearance in ribs

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anterior is sclerotic
posterior is expansile/lytic

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adamantinoma

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malig lesion that resembles FD, seen in tibia and jaw

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characteristis of giant cell tumor

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only in pts with closed epiphysis
lesion must abut the articular surface with no margin of nml bone
eccentrically located
sharply defined ZOT that is NOT sclerotic

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who gets non-ossifying fibromas

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<30 yo

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location of NOF

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metaphysis of long bones most often
emanates from cortex

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where is NOF most common

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knee

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borders of NOF

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often has thin, sclerotic border that are scalloped (although this is not always seen) and slightly expansile

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T or F
NOF is a do not touch lesion

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T

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CT findings with regards to cortex of NOF

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cortex can be interrupted without cortical destruction, but rather cortical displacement by benign fibrous tissue

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periostitis in NOF

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only if h/o trauma

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pain in NOF

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no

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apperance of osteoblastoma

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can be bubbly and look like osteoid osteoma or simulate ABC with soap-bubble, expansile appearance

a rare lesion; should mention anytime ABC is in the differential.

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common location of osteoblastoma

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posterior elements of vertebral bodies

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DDX of expansile, lytic lesion sof posteiror elements of spine

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osteoblastoma
ABC
TB

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age descriminator to think of mets/MM

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>40 yo

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which bone mets are lytic?

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lytic:
renal, thyroid

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appearance of ABC
who gets it?

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aneurysmal/expansile
<30 yo

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presentation of ABC

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pain

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other names for solitary bone cyst

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simple bone cyst
unicameral bone cyst

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how to differentiate ABC from solitary bone cyst

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ABC - painful, expansile, <30 yo

SBC - painless, central, often has fallen fragment sign (<30 yo too)

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importance of sequestrum in osteomyelitis
what does sequestrum represent

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if present = devitalized bone with no blood supply, ,requires surgical intervention

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DDx sequestrum

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osteo
E gran
lymphoma
fibrosarcoma
osteoid osteoma (mimics sequestrum)

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location within bone for solitary bone cyst

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always CENTRAL in location

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most common location of SBC within body

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prox femur or humerus
inferior calcaneous

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presentation of SBC

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asx, unles fx'd (which is common)

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periostitis in SBC?

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no

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classic XR finding of SBC

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fallen fragment sign
(= a portion of cortical bone has broken off and falls in dependent portion of hte lesion --> fluid-fluid cystic lesion)
THIS FINDING IS PATHOGNOMONIC FOR SBC!!!!!

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growth pattern of SBC

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starts growing at physeal plate in ong bones and then grows into shaft

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what are brown tumors assoc with

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hyper PTH

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appearance of brown tumor

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subperiosteal bone resorption
if physes are open, there is cupping/fraying

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which bones are most affected by brown tumor

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radial aspect of middle phylanges (and other phylanges)
distal clavicle,
medial aspect of prox tibia
SI joint s

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where in bone does chondroblastoma occur

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only in epiphysis

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who gets chondroblastoma

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<30 yo

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DDx of young person with lytic lesion in epiphysis

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Infx
Chondroblastoma
giant cell tumor
subchondral cyst
geode

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dz associated with subchondral cysts

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DJD
RA
CPPD/Pseudogout
AVN

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apperance of a chondromyxoid fibroma

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resembles NOF except often extends into epiphyssi

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chondromyxoid fibroma - benign or malig?

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cartilagenous lesion that can progress to malignancy rarely

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presentation of chondromyxoid fibroma

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presents with pain (unlike NOF)

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difference between epiphysis and apophysis

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epiphysis contributes to the length of bone
apophysis = ligament attachment sites

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regardless of appearance of lytic lesion, what should be on every ddx if <30 yo

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E gran
infx

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regardless of appearance of lytic lesion, what should be on every ddx in >40 yo

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infx
metx
MM

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Lesions with no pain or periostitis

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Fibrous dysplasia
Enchondroma
NOF
SBC

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DDx for cystic rib lesion

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Fibrous dysplasia
ABC
Mets
MM
Enchondroma
E gran

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Epiphyseal lesions

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Infx
Giant Cell
Chondroblastoma
Subchondral cyst

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DDx for multiple cystic bone lesions

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FEEMHI
Fibrous dysplasia
E Gran
Enchondroma
Mets, MM
HyperPTH
Infx

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ollier disease

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multiple enchondromas, no incresaed rate of malignancy
not hereditary

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maffucci syndrome

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multiple enchondromas and hemangiomas
not hereditary, has increased risk of malig