Unicameral Bone Cysts are fluid-filled bone lesions most common in children under 20. They form due to venous occlusion in the bone marrow and contain substances that cause bone resorption. Clinically, they present as swelling and pain after trauma in the femur or humerus. Radiographs show expanded thin bone with fractures. Treatment involves injections or surgery to curette the cyst membrane and fill the cavity to prevent fractures and recurrence.

1. Unicameral Bone Cysts

2. Introduction
Initially described by Jaffe and Lichtenstein in 1942
Common in first two decades of the life, the rarity of the
lesion in the adults suggests that spontaneous healing occurs.

3. Pathogenesis
Hypothesized that the cyst forms as a response to venous
occlusion in the intramedullary space
Considered them to be intraosseous synovial cysts
Dysplastic areas, which they believed developed in response
to trauma

4. Pathology
An area of fusiform expansion
Periosteum lifts away easily and underlying bone is egg-shell
thin, semitranslucent,bluish and easily penetrated.

5. Histologic examination
The cyst walls are
lined with a fibrous
membrane, with
occasional giant
cells

6. The fluid within the cyst has been
analyzed and shown to contain high
levels of oxygen-free-radical
scavengers, prostaglandins
(prostaglandin E2), interleukin-1, and
proteolytic enzymes

7. These substances, which cause bone resorption, may play a role
in the formation and growth of cysts.
The cyst fluid has a lower total protein content than serum but
higher levels of protein-bound hydroxyproline, lactate, and
alkaline phosphatase.

8. Vascular occlusion theory
The pressures within a cyst are elevated above venous
pressures
if radiopaque dye is injected into the cyst with enough
pressure, the dye can be extruded into the venous system of
the limb. Reestablishing these outflow channels may assist in
the involution of the cyst

9. simply lowering the interstitial pressure by multiple
perforations may cause cyst involution

10. Clinical Features
Age- younger patients
Sex- M:F 2:1
Most common site-the proximal femur, followed by the proximal
humerus
Many cysts are immediately adjacent to, and appear to involve,
the epiphyseal growth plate

11. The area is slightly warm and swollen
The symptoms of unicameral bone cysts are most often
brought on by trauma
When fractures do become evident, they rarely involve the
growth plate itself

12. Cysts progress from active to quiescent to an involutional
stage in the course of their natural history
The difficulty for the clinician is to assess the current stage of
the cyst at the time of diagnosis

13. Radiographs
Radiographs usually reveal a nondisplaced or minimally
displaced fracture through an area of very thin, expanded
cortical bone

14. Fallen leaf sign
Occasionally, a fragment of the cyst wall has fractured and
fallen into the fluid cavity

15. The cortical
fragment becomes
dislodged from the
margin at the time
of fracture and
literally floats to the
bottom of the cystic structure.

16. MRI
Magnetic resonance imaging most accurately delineates the
central fluid collection

17. D.D.
Aneurysmal bone cyst
Fibrous dysplasia
Enchondroma
Eosinophilic granuloma
GCT

18. Treatment
Difficult to decide whether the cyst is in the active, latent, or
involutional Stage
Unless there is a tremendous amount of cortical thinning,
there may not be a comparable decrease in strength as a cyst
expands the cortical margins

19. It may be reasonable to choose close observation rather than
a surgical procedure
If the cyst is active and obviously enlarging during
observation (3 to 6 months), treatment may be appropriate

20. Exception
large cyst involves the subtrochanteric region of the femur
Early treatment may be needed to avoid fracture

23. Injection Techniques
Injecting methylprednisolone into the cyst under fluoroscopic
control while using radiopaque dye to confirm entry into the cyst
Aspiration of the cyst is done prior to injection
The level of PGE2 in cyst fluid is reduced after injection of
methylprednisolone

24. Advantageous by decreasing the morbidity due to a major
surgical procedure
Recurrence rates of 15% to 88% after an average of three
injections

25. Surgical Techniques
Resection or curettage plus bone grafting has been employed
as the definitive treatment for unicameral bone cysts

26. Technique
A cortical window is made, which allows access to the entire
contents of the cavity
The clear fluid should be removed, and the fibrous membrane
curetted from the cyst wall

27. Autologous bone marrow, allograft, demineralized bone matrix
(DBM), and other bone substitute materials have been used
successfully
Thus sparing the patient the morbidity of an autograft harvesting
site
Allograft bone chips have proved effective in the treatment of
cysts

28. Calcium sulfate in the form of plaster of paris has been used
with a good success rate and a low recurrence rate

29. Demineralized
bone matrix,Bone marrow

30. Complications
Recurrence of the lesion after treatment
Development of a subsequent fracture

31. Recurrence
Recurrence is more when the patient is younger than 10
years,
When the lesion is in the upper humerus and closely adjacent
to the growth plate