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Solitary Bone Cyst
(Traumatic Bone Cyst, Unicameral Bone Cyst, Progressive Bone
Cavity, Extravasation Cyst, Hæmorrhagic Bone Cyst,
Unilateral Bone Cyst & Progressive Bone Cavity)
Simple Bone Cysts (SBC's) are benign cysts that develop in children in their first two
decades.  Whilst normally found in the within the
medulla of long bones, 10% occur in the
jaws; 75% of these being in the
body of the mandible (lower jaw).

SBC’s are predominantly seen in the mandible, more frequently involving the posterior region
and less common in the
anterior mandible (front of the lower jaw) / mandibular symphysis
(midline lower jaw).  They are more frequently seen during the 2nd decade of life and sex
distribution is quite even.

The cyst is known by several other names, including Traumatic Bone Cyst, Unicameral Bone Cyst, Progressive
Bone Cavity
, Extravasation Cyst, Hæmorrhagic Bone Cyst, Unilateral Bone Cyst & Progressive Bone Cavity.

It is relatively uncommon with a reported incidence of 0.6% (from a study of 3353 bone cysts) and tends to occur
more frequently in males, presenting in the second and third decades.
What are Solitary Bone Cysts (SBC's)?

Simple Bone Cysts (SBC's) are benign cysts that develop in children in their first two decades.  Whilst normally
found in the "long" bones, 10% occur in the jaws.  The vast majority of these are in the
mandible (lower jaw).  They
are more frequently seen during the 2nd decade of life and sex distribution is quite even.


What are the signs & symptoms?

Lesions are generally asymptomatic, however, a few authors have reported symptoms including pain, tooth
sensitivity,
paræsthesia and delayed displacement of the Inferior Dental Canal.

SBC's are predominantly seen in the mandible, more frequently involving the posterior region and less common in
the
anterior mandible.


What are the causes of Solitary Bone Cysts (SBC's)?

It has been speculated that SBC's arise as a result of occlusal trauma, causing intra-medullary bleeding and
aberrant healing with
cavity formation (liquefactive necrosis or resorption of blood clot following intra-medullary
hæmorrhage
due to trauma results in the destruction of the surrounding bone by enzymatic activity, thereby causing
enlargement of the bone cavity).

This theory explains why
traumatic bone cysts occur more often in young individuals (an age at which trauma occurs
more often) and also explain the presence of blood within the cavity at the time of surgical exploration.  Reports of
trauma at the site of lesions and the presence of blood in the cavities, however, are uncommon.

The content of the cavity depends on the length of the time that the
cyst has existed.  In the early stages, the cyst
usually contains blood or sero-sanguineous fluid that lessens with the age of the lesion and eventually becomes
empty.  Since material for histological examination may be scant or non-existent, it is very often difficult for a
definite histological diagnosis to be achieved.  Indeed, the diagnosis of
SBC can be established only after surgical
exploration of the bone cavity.

Other theories include:

•        
cystic degeneration of fibro-osseous lesions / existing bone tumour
•        intra-osseous vascular anomalies (loss of blood supply to a hæmangioma / lymphoma)
•        alteration of
bony metabolism (faulty calcium metabolism as a result of systemic disease such as para-
thyroid diseases)
•        low-grade infection
•        infection of bone marrow
•        
ischaemic necrosis of the fatty bone marrow
•        changes and reduction in the osteo-genic activity
•        imbalance between the osteo-clastic & osteo-blastic activity due to trauma
•        failure of
mesenchymal tissue to form bone & cartilage & instead becomes immature as multiple bursa-like
synovial cavities
•        developmental defect


How are they diagnosed?

On radiological examination, between 61 - 79% of SBC’s are radio-lucent.  However, 21% have radio-opaque foci
& 7% may show “cloudiness”.

The border of the
SBC, although irregular, can vary from well-defined to a complete absence of cortical outline.

It is usually detected incidentally during routine radiographic examination, which can be attributed to the
asymptomatic nature of the lesion.  Radiographically,
SBC's usually appears as an uni-locular radiolucent area with
an irregular, well-defined / partly well-defined outline and with / without a sclerotic lining around the periphery of the
lesion.

Projection of the lesion into the
inter-radicular bone spaces produces a scalloping effect around the roots of the
associated teeth.  
Scalloping /  inter-digitation between the roots of teeth was a common feature in 44 -  68% of
the cases.

Root resorption is rather uncommon and the surrounding teeth are vital.  The bone cavity may either be empty or
present a thin connective tissue layer with a scant liquid content.

Loss of
lamina dura is predominantly in patients over 30 years of age and there is minimal involvement in younger
people.

Displacement of teeth and root resorption are rare although in one series they were reported in 9 and 22% of the
cases, respectively.

The definite diagnosis of
SBC is invariably achieved at surgery when an empty bone cavity without epithelial lining
is observed, leaving very little except normal bone and occasional fibrous tissue curetted from the cavity wall for the
histo-pathologist.

Sometimes, the cavity contains a straw-colored fluid / bright blood.  Most of the histologic findings reveal fibrous
connective tissue and normal bone.  There is never any evidence of an epithelial lining.  The lesion may exhibit areas
of vascularity, fibrin, erythrocytes and occasional giant cells adjacent to the bone surface


How are they treated?

The widely recommended treatment for SBC is surgical exploration followed by curettage of the bony walls.  The
surgical exploration serves as both a diagnostic manoeuvre and as definitive therapy by producing bleeding in the
cavity.

Resolution usually takes about 6 months or longer, depending on the size of the lesion.  The prognosis is usually
good and recurrence is rare.

Other alternative treatments include use of
allogenic materials like lyophilised bone, hydroxyl-apatite or gel foam
to fill the bone cavity in cases where conventional management fails and
dental implant rehabilitation is required.


Differential Diagnosis:




Useful Websites:

Radiopaedia.org

Dr G's Toothpix


Useful Articles:

J Ind Acad Oral Med Radiol 2010.  Solitary Bone Cyst.  A Case Report & Review of the Literature

J Pharmaceut Biomed Sci 2011.  Solitary Bone Cyst of Mandible

BMJ Case Rep 2014.  Case Report.  Solitary Bone Cyst of the Mandible.  A Case Report & Brief Review of
Literature

J Oral Maxillofac Pathol 2014.  Case Report.  Solitary Bone Cysts.  A Rare Occurrence with Bilaterally Symmetrical
Presentation

Dent Update 2015.  Case Report.  An Unusual Finding of a Solitary Bone Cyst in a Patient with a Fractured
Mandible

Ann Maxillofac Surg 2016.  Simple Bone Cyst of the Mandibular Condyle

BMC Musculoskeletal Disorders 2016.  Solitary Bone Cyst.  A Comparison of Treatment Options with Special
Reference to their Long-Term Outcome

Revista Odontológica Mexicana 2018.  Maxillary & Mandibular Solitary Bone Cyst.  Case Report & Literature
Review

J IMAB. 2020.  Case Report.  Traumatic Bone Cyst of the Mandible
Last Updated 13th November 2020
X-Rays of Solitary Bone Cysts