This case report describes an unusual case of an enchondroma with secondary aneurysmal bone cyst formation in the proximal femur of a 13-year-old male. Imaging showed a septated lytic lesion in the intertrochanteric region. Histology revealed lobulated cartilaginous proliferation without atypia surrounded by bone and blood-filled cystic spaces, consistent with a secondary aneurysmal bone cyst arising from the enchondroma. This is a rare occurrence, as cystic changes are not usually seen in enchondromas. The patient will need monitoring due to the higher recurrence risk of aneurysmal bone cysts compared to typical enchondromas.

1. Case
Report:
Enchondroma
in
Secondary
Aneurysmal
Bone
Cyst
Skeletal
Radiol.
2011
Nov;41(11):1475-­‐8.
Epub
2012
May
26

2. Introduc:on
• Enchondroma
are
common
benign
car:laginous
tumors
• Most
common
in
metaphyseal
regions
• Most
common
sites:
Metacarpals,
Metatarsals,
Phalanges,
Proximal
humerus,
and
Femur
• X-­‐Ray:
well-­‐defined
ly:c
lesions,
punctate
intralesional
lesions
(giant
cell
tumor
of
bone,
fibrous
dysplasia,
chondrosarcoma,
and
osteonecrosis
• Histology:
lobulated
tumor
composed
of
hyaline
car:lage
that
lacks
significant
cellularity
and
atypia,
lamellar
bones
surround
the
lobules
Cys:c
change
in
enchondroma
is
unusual
case

3. Clinical
History
Male,
13
years
old
Medical
Evalua:on
Antalgic
gait
Exacerbated
on
daily
exercises
training
Right
groin
pain
radiated
down
the
front
of
thigh

4. AP
and
lateral
views
of
the
right
hip
demonstra:ng
a
ly:c
lesion
with
peripheral
sclerosis
of
the
right
proximal
femur

5. Axial
and
coronal
CT
demonstrates
septated,
ly:c
lesion
in
the
intertrochanteric
region
with
significant
thinning
of
the
posterior
cortex

6. T1-­‐weighted,
T2-­‐weighted,
T1
fat-­‐satura:on
post-­‐contrast
MRI
studies
demonstrates
a
septated
mass
with
low
T1
signal,
increased
T2
signal,
and
rim
enhancement
within
the
intertrochanteric
region
of
the
right
femur

7. WORKUP
Non-­‐aggresive,
mildly
expansile,
radioluscent
Mul:lobulated,
Thinning
of
septated
mass
lesion
with
cortex
intralesional
without
with
low
T1,
Fibrous
density
and
obvious
increase
signal
Dysplasia
peripheral
fracture
T2,
rim
enhancement
sclerosis
in
intertrochanteri
c
region
of
right
femur

8. Opera:on
Benign
car:laginous
lesion
with
significant
cys:c
fibroosseus
component

9. Lobular
car:laginous
prolifera:on
without
significant
atypia
encircled
by
a
rim
of
bone.
Blood-­‐filled
cys:c
spaces
lined
by
benign
spindle
cells,
giant
cells,
woven
bone,
and
hemosiderin.
Focal
area
with
eosinophilic
“cementum-­‐like”
fibrin
reminiscent.

10. Discussion
 Aneurysmal
cys:c
changes
occur
secondary
to
number
of
pathologic
lesions
à
never
been
reported
in
Enchondroma

11. Fibrous
Dysplasia
 Radiographic
in
this
case:
Fibrous
Dysplasia
 X-­‐Ray:
Radiolucent
lesion
with
‘ground-­‐glass’
opacifica:on
 Histology:
prolifera:ng
fibroblasts
with
osteoid
trabeculae
 FD
with
massive
chondroid
differen:a:on
à
Fibrocar:laginous
Dysplasia
(FCD)
 Rare
occasions:
Calcifica:on
may
be
so
extensive
à
mimicking
Enchondroma
or
Chondrosarcoma

12. Aneurysmal
Bone
Cyst
 Aneurysmal
Bone
Cyst
(ABC)
are
benign
osteoly:c
lesions
 Blood-­‐filled
spaces
separated
by
connec:ve
:ssue
septae
 Common
sites:
Long
bones
of
lower
extremity,
and
posterior
of
spine
 Primary
and
secondary
ABC

13. Pathophysiology
of
Secondary
ABC
(Jaffe
et
al.,
1942)
Primary
lesion
ini6ates
an
intraosseus
AVM
Hemorrhagic
“blow-­‐out”
in
the
preexis6ng
lesion
Secondary
reac6ve
lesion
of
bone
The
cyst
may
obliterate
the
original
morphology
and
obscure
the
true
nature
of
the
preceding
lesion

14. Aneurysmal
Bone
Cyst
 Recurrence
rate
of
Enchondroma
with
treated
intralesional
cure`age
is
extremely
low
(<1%)
 Recurrence
rate
of
ABC
is
more
aggressive
and
have
higher
rate
(
<40%),
 Recurencees
within
2
years
from
surgery
à
monitored
for
at
least
2
years

15. Thank You

21. BUBBLY
LYTIC
BONE
LESIONS
• F
:
Fibrous
Dysplasia
or
Fibrous
Cor:cal
Defect
• O:
Osteoblastoma
• G
:
Giant
cell
tumour
(GCT)
• M
:
Metastases
• A
:
Aneurysmal
Bone
Cyst
(ABC)
• C
:
Chondroblastoma
or
Chondromyxoid
fibroma
• H
:Hyperparathyroidism
(Brown
Tumor)
• I
:
infec:on
(Osteomyeli:s)
• N
:
Non-­‐ossifying
Fibroma
• E
:Enchondroma
or
Eosinophilic
Granuloma
• S
:
Simple
Bone
Cyst
AJR
August
2009
vol
193
no.
2
W79-­‐W94

22. Distribu:on
of
Lesions
Enchondroma
Fibrous
Dysplasia
ABC
GCT
Layout
and
distribuLon:
Frank
Gaillard
2009,
Line
drawing
of
skeleton:
Patrick
Lynch
2006,
CreaLve
Common
NC-­‐SA-­‐BY

23. Enchondroma
 Benign
medullary
car:laginous
neoplasm
 Childhood
to
early
adulthood
(10-­‐30
y.o)
 Arise
from
chondrocytes
composed
of
mature
hyaline
car:lage
 X-­‐Ray
and
CT:
1-­‐2
cm
non-­‐aggressive
ly:c
lesions,
endosteal
scalloping,
chondroid
calcifica:on,
periosteal
reac:on
(-­‐),sof
:ssue
mass
(-­‐)
 MRI:
Intermediate-­‐low
signal
T1WI,
high
signal
T2WI
 Treatment
and
Prognosis:
No
treatment
à
cure`age
and
bone
grafing

27. Fibrous
Dysplasia
• Benign
tumour-­‐like
congenital
process
• Defect
in
osteoblas:c
differen:a:on
and
matura:on,
with
progressive
replacement
of
normal
bone
with
immature
woven
bone
• Children
and
yound
adults,
<
30
y.o
• X-­‐Ray
and
CT:
Well
circumscribed
cys:c
or
sclero:c
lesion,
Ground-­‐glass
opacity,
Endosteal
scalloping,
intact
bone
• MRI:
Heterogenous
Intermediate
signal
T1WI,
heterogenous
low
signal
T2WI
• Treatment:
no
treatment
à
surgical
decompression

28. FIBROUS
DYSPLASIA

31. Aneurysmal
Bone
Cyst
• Benign
expansile
tumor-­‐like
bone
lesion,
contain
numerous
blood
filled
channels
• Children
and
adolescents
(<20
y.o)
• X-­‐Ray
:
sharply
defined,
expansile
osteoly:c
lesions,
with
thin
sclero:c
margins
• CT:
fluid
fluid
levels
• MRI:
low
signal
of
T1
and
T2,
• Treatment
:Opera:ve
(Bone
curretage
and
Grafing)

37. Giant
Cell
Tumor
 Benign,
metaepiphysis
of
long
bones
 Early
adulthood
(
20-­‐
50
y.o)
 Single
lesions
(knee,
distal
radius,
sacrum)
 X-­‐Ray
and
CT
:
occurs
only
with
a
closed
epiphyseal
plate,
ar:cular
surface,
well
defined
with
non-­‐
sclero:c
margin,
periosteal
reac:on
(10-­‐30%
cases),
no
calcifica:on
 MRI:
low
signal
in
T1WI
and
T2WI
 Angiography:
hypervascular
tumor
with
the
rest
being
hipo/avascular

39. ENCHONDROMA
VS
LOW
GRADE
CHONDROSARCOMA

41. Unicameral
(Simple)
Bone
Cyst
Fallen-­‐Fragment
sign