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SIMPLE BONE CYST

Dr. Manmohan Bir ShresthaMD Resident, Phase-ADepartment of Radiology and ImagingBSMMU.

Simple Bone Cyst

Also known as Unicameral Bone Cyst.Are entirely benign lesion of unknown aetiology.Are always unilocular.

Age

Childhood and early adolescenseBefore the epiphyseal fusion occur.In adults, some lesions occur after skeletal maturation in such bones as the Calcaneus, Talus

Location

Typically Intramedullary.Most frequently found in the metaphysis.

Sites :Proximal humerusProximal femurOther long bonesCalcaneus, Talus.

Sex Prevalence

Male>Female (2:1)

Clinical Features

Asymptomatic and found incidentally.Only a few produce minor discomfort. May be pain, swelling and stiffness of adjacent joint.More than half present due to a pathological fracture.

Pathology

Cyst contains clear liquid unless there has been contamination by bleeding following a fracture .

Cyst is lined by a thin layer of connective tissue.

Investigations

Plain X-ray filmCT ScanMRIBone Scan.

Plain X-rayAn area of translucency centrally in the metadiaphysis is characteristic.The overlying cortex is often thinned and slightly expansed with no periosteal reaction unless a fracture has occurred.Sclerotic reaction is usually present around the margin.A serpiginous margin (by prominent ridges of bone) may cause the cyst to appear multilocular.

Fallen fragment sign

If there is fracture through this lesion, a dependent bony fragment may be seen, and this is known as the fallen fragment sign.

CT Scan

MRI

T1 -low signal intensity.

T2 -high signal intensity.

Bone scan

No abnormality develops in the blood-pool phase.

Treatment1)If small and low risk of fracture

Some cases resolve spontaneously with age.Intralesional Steroid An injection of Methylprednisolone Acetate into the lesion in several intervals for a time span of 6-12 months. Complications are infection, fracture or recurrence.

Cont.2)If risk of fracture or large lesion

CurettageBone grafting It is proceeded after curettage. The empty cavity is transplanted with donor bone tissue, bone chips or artificial material.

Differential diagnosis

Fibrous dysplasiaAneurysmal bone cystGiant cell tumorEosinophilic granulomaNon ossifying fibroma Chondroma.

Simple bone cystAneurysmal bone cystSiteMetadiaphysisTypically in the metaphysisBone scanNo abnormality developsRich increase in vessels and early venous fillingCT & MRI(fluid-fluid levels)AbsentAre the characteristicAssociationAbsentMay be with non-ossifying fibroma, fibrous dysplasia and chondromyxoid fibromaCystClear liquid and always unilocularContains blood with giant cells and multilocular.

Simple bone cystGiant cell tumorAge Before epiphyseal fusion . Childhood and early adolescentMajority between 20-40 yrs of age. Only 3% in immature skeleton.Anatomical distributionProximal humerus proximal femurOther long bones rarely calcaneumMajority occurs around knee and wristExtensionDo not extends to the articular surface and is centralExtension is subarticular and eccentric in nature.

Simple bone cystFibrous dysplasiaSitesProximal humerusProximal femurOther long bonesCalcaneusCommonly pelvis, femur, ribs. Often skullPlain filmAn area of translucency. Centrally in the metadiaphysis.Lesions may be lucent, dense or a mixture with small flecks of density due to ossificationPathologyCyst filled with clear fluidMedullary bone is replaced by well defined area of fibrous tissue and cysts containing blood or serous fluidEndocrine complicationsAbsentMay be associated with-Skin pigmentation,precocious puberty, acromegaly, hyperthyroidism, cushings syndrome.

SBC central and intramedullary

Non-ossifying fibroma- eccentric and cortical based.

Simple bone cyst Eosinophilic granulomaSiteProximal humerusProximal femurOther long bonesCalcaneusAny bone may be affected commonly skull - pelvis -femur.ClinicallyAsymptomatic often presents with pathological fracturePain, swelling and mild fever.HistologyCyst filled with clear liquidContains eosinophilic infiltration.

Simple bone cystChondromaAgeChildhood and early adolescence.AdultPlain filmArea of translucencyCentrally in metadiaphysisFlecks of calcification occur. As they become mature, may assume a pathognomic popcorn or annular configuration.

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