Bone cysts

Tumor	Age	Location	Clinical presentation	Pathology	Radiology	Treatment	Prognosis	DD
Unicameral (Simple) Bone Cyst (UBC)	5-15 yrs, M>F	proximal humerus (67%), proximal femur (15%),unusual sites (e.g. calcaneum, pelvis) in patients >17 years	Asymptomatic.Usually presents as a pathological fracture (~ 65%).Active cysts neargrowth plate, but move away with growth and become inactive (latent)	thin walled cavities filled with blood tinged fluid. lining cells are cuboidal, but are not an endothelium. endosteal osteoclastic activity and periosteal new bone formation.Aetiology- Unknown/Venous obstruction leading to a transudate of fluid/ Fluid contains high levels of IL-1 & IL-6, which stimulate osteoclasts	Well defined, central osteolytic area with a thin sclerotic margin.Metaphyseal in young - moves towards diaphysis with growth. fills and slightly expands the juxta epiphyseal metaphysis.CT not helpful unless the UBC is in the pelvis	goal is to minimise fracture risk until the cyst heals (but this can take years).Steroid inj. 60-80% success rate /Curettage and bone graft - 50% recurrence rate and possibility of damage to the growth plate .Bone marrow aspirate has recently been used
Aneurysmal Bone Cyst (ABC)	<20>M	any bone in the body.most common- metaphysis of the lower extremity long bones. vertebral bodies or arches of the spine. pelvis	Swelling, tenderness and pain. Limited ROM due to joint obstruction.Spinal lesions can cause cord compression.Pathological fractures are rare due to the eccentric location of the lesion	Macro- blood filled sponge with a thin periosteal membrane. Soft, fibrous walls separate spaces filled with friable blood clot.Micro- cystic spaces filled with blood. fibrous septa have immature woven bone trabeculae as well as macrophages filled with haemosiderin, fibroblasts, capillaries and giant cells.Aetiology- Unknown,/ a reactive process to trauma or vascular disturbance/ secondary to increased venous pressure that leads to haemorrhage which causes osteolysis. This osteolysis can in turn promote more haemorrhage causing amplification of the cyst/ secondary ABC-- common precursor GCT, (19-39%), osteoblastoma, angioma, and chondroblastoma. fibrous dysplasia,NOF,CMF, UBC, fibrous histiocytoma, eosinophilic granuloma, and osteosarcoma.	eccentrically in the metaphysis and appears osteolytic. periosteum is elevated and the cortex is eroded to a thin margin. expansile nature of the lesion is often reflected by a "blow-out" or "soap bubble" appearance .'Pencil-in-cup' appearance.CT scan can help delineate lesions in the pelvis or spine. can narrow theDDs by demonstrating multiple fluid-fluid levels within the cystic spaces.MRI can also confirm the multiple fluid-fluid levels	A slow growing, indolent ABC has been observed to regress spontaneously.Most lesions can be treated with curettage and application of a high-speed burr.Recurrence--Wide resection and limb-sparing reconstructions Curettage and bone graft can be complicated by profuse bleeding from the lesion.Radiation has been used in some cases where operative treatment is not possible, but this adds the additional risk of malignancy
GCT	20-30 yrs, F>M, after closure of physes	distal femur, proximal tibia and the distal radius.Most common tumour to occur in the distal phalanx.meta/epiphyseal.	Pain, swelling,Pathological fracture.Benign, usually solitary and locally aggressive.Egg shell crackling	Soft, friable tumour.Cut surface tan in colour, with areas of necrosis and haemorrhage.Numerous multinucleated giant cells. stromal cells are homogenous mononuclear round/ovoid with large nuclei. nuclei of the stromal cells are identical to the nuclei of the giant cells.Up to 50% have soft tissue extension but does not indicate malignancy	Usually well defined lesion in the epiphysis extending up to the joint surface without marginal sclerosis, cortex thinned and sometimes ballooned soap bubble appearance.Junction with normal bone poorly defined	Intralesional excision by "extended" curettage.Curettage alone has a high local recurrence rate (50%) and the curettage is "extended" into the bone by a few millimetres by either using a burr, liquid nitrogen or phenol. resulting cavity can be filled with bone graft or cement.En-bloc resection is possible if the bone is expendable e.g. proximal fibula, proximal radius.Amputation reserved for massive local recurrence, malignant change or infection.Radiotherapy reserved rare cases of unresectable tumours because of increased risk of secondary malignancy	Sarcomatous transformation in 5 - 10%.Recurrence following simple curettage 50%. Recurrence following simple curettage plus adjuvant treatment (cryo etc) 17%. Malignancy more common in recurrent GCT