Unicameral bone cyst
- Philips Australia, Paid speaker at Philips Spectral CT events (ongoing)
Updates to Article Attributes
Unicameral bone cysts (UBC), also known as simple bone cysts,(SBC) are common benign non-neoplastic lucent bony lesions that are seen mainly in childhood and typically remain asymptomatic. They account
SBC accounts for the S (simple bone cyst)FEGNOMASHIC, the commonly usedlyticlucent bone lesionsFEGNOMASHIC.
Epidemiology
UBCs are usually found in children in the 1st and 2nd decades (65% in teenagers) with the mean age at diagnosis being 9 years 8. They are more common in males (M:F ~ 2-3:1) 2,6. Active unicameral bone cysts occur most frequently between the ages of 1 and 10 years.
Diagnosis
Diagnostic criteria are 10:
essential: simple cyst lacking a true lining with typical imaging features
desirable: fibrin-like deposits +/- mineralisation forming cementum-like structures
Clinical presentation
These lesions are usually asymptomatic and found incidentally, although pain, swelling and stiffness of the adjacent joint also occur. The most frequent presentation is due to pathological fracture 1,2,6.
Pathology
The aetiology and pathogenesis are unknown 8,10. When uncomplicated by fracture the cysts contain clear serosanguineous fluid surrounded by a thin fibrous membranous lining.
During the active phase, the cyst remains adjacent to the growth plate. As the lesion becomes inactive it migrates away from the growth plate (normal bone is formed between it and the growth plate) and it gradually resolves 3,5.
Location
They are typically intramedullary and active cysts are found in the metaphysis of long bones, abutting the growth plate 1. Locations include 1,2,5:
proximal humerus: most common 50-60%
proximal femur: 30%
other long bones
-
occurrence elsewhere is relatively uncommon, and usually occurs in adults
As bone growth progresses the cyst loses its connection to the physis migrating into the diaphysis and subsequently healing. UBCs can be rarely seen in adults in unusual locations such as in the talus, calcaneus, or the iliac wing.
Radiographic features
Plain radiographs are the first-line imaging modality. CT and MRI add little to the diagnosis, however, can be helpful in eliminating other entities that can potentially mimic a simple bone cyst (see differential diagnosis below) 8.
Plain radiograph
Unicameral bone cysts are well defined geographic lucent lesions with a narrow zone of transition, mostly seen in skeletally immature patients, which are centrally located and show a thin sclerotic margin in the majority of cases with no periosteal reaction or soft tissue component. They sometimes expand the bone with thinning of the endosteum without any breach of the cortex unless there is a pathologic fracture. Prominent ridges of bone can appear as pseudotrabeculation on x-ray but in fact, UBC is usually unilocular. Rarely, they are truly multiloculated, which can occur after repeated fractures 3,10.
If there is a fracture through this lesion a dependent bony fragment may be seen, and this is known as the fallen fragment sign. The rising bubble sign is considered pathognomonic and occurs when a gas bubble is seen at the most non-dependent part of the UBC 8,10.
CT
Features on CT are similar to plain radiographs but CT has the advantage of characterising extent, detecting radiograph-occult fractures, and assessing internal density (usually between 10-15 HU) 8.
MRI
MR signal characteristics for an uncomplicated lesion include 8,10:
T1: low signal
T2: high signal
T1C+: peripheral enhancement
Fluid-fluid levels can be seen in the setting of fibrous septations, which can enhance 8. Internal signal heterogeneity, periosteal reaction and soft tissue oedema can be seen in the setting of fracture 8.
Nuclear medicine
Scintigraphy
Unicameral bone cyst on bone scintigraphy tends to appear as foci of photopenia (cold spot). This is referred to as the doughnut sign which results in increased uptake peripherally and a photopenic centre. However, a pathological fracture would cause an increased radioisotope activity.
Treatment and prognosis
Intervention is usually not required for an asymptomatic lesion. If large and threatening to fracture, or causing deformity then an intralesional steroid injection can be performed 3-5. If fractured the bone usually heals normally 5. In some instances, surgery with curettage and bone grafting is required. Local recurrence rates are ~15% (range 10-20%) 10.
History and etymology
Unicameral bone cysts were initially described by the German pathologist Rudolf Virchow in 1891 8,9.
Differential diagnosis
General imaging differential considerations include 8,10:
giant cell tumour of bone: usually older, extending to the articular surface
non-ossifying fibroma: eccentric, cortical base
haemophilic pseudotumour (intraosseous)
aneurysmal bone cyst (ABC): usually eccentric
See also
-<p><strong>Unicameral bone cysts (UBC)</strong>, also known as <strong>simple bone cysts</strong>, are common benign non-neoplastic lucent bony lesions that are seen mainly in childhood and typically remain asymptomatic. They account for the <strong>S</strong> (simple bone cyst) in <a href="/articles/lucentlytic-bone-lesion-differential-diagnosis-mnemonic-1">FEGNOMASHIC</a>, the commonly used mnemonic for lytic bone lesions. </p><h4>Epidemiology</h4><p>UBCs are usually found in children in the 1st and 2nd decades (65% in teenagers) with the mean age at diagnosis being 9 years <sup>8</sup>. They are more common in males (M:F ~ 2-3:1) <sup>2,6</sup>. Active unicameral bone cysts occur most frequently between the ages of 1 and 10 years.</p><h4>Diagnosis</h4><p>Diagnostic criteria are <sup>10</sup>:</p><ul>-<li>essential: simple cyst lacking a true lining with typical imaging features</li>-<li>desirable: fibrin-like deposits +/- mineralisation forming cementum-like structures</li>-</ul><h4>Clinical presentation</h4><p>These lesions are usually asymptomatic and found incidentally, although pain, swelling and stiffness of the adjacent joint also occur. The most frequent presentation is due to <a href="/articles/pathological-fracture">pathological fracture</a> <sup>1,2,6</sup>.</p><h4>Pathology</h4><p>The aetiology and pathogenesis are unknown <sup>8,10</sup>. When uncomplicated by fracture the cysts contain clear serosanguineous fluid surrounded by a thin fibrous membranous lining. </p><p>During the active phase, the cyst remains adjacent to the growth plate. As the lesion becomes inactive it migrates away from the growth plate (normal bone is formed between it and the growth plate) and it gradually resolves <sup>3,5</sup>.</p><h5>Location</h5><p>They are typically intramedullary and active cysts are found in the metaphysis of long bones, abutting the growth plate <sup>1</sup>. Locations include <sup>1,2,5</sup>:</p><ul>-<li>proximal <a href="/articles/humerus">humerus</a>: most common 50-60%</li>-<li>proximal <a href="/articles/femur">femur</a>: 30%</li>-<li>other long bones</li>-<li>occurrence elsewhere is relatively uncommon, and usually occurs in adults<ul>-<li>spine: usually posterior elements</li>-<li>-<a href="/articles/pelvis-1">pelvis</a>: only 2% of UBC <sup>1</sup>-</li>-<li><a href="/articles/calcaneus">calcaneus</a></li>-</ul>-</li>-</ul><p>As bone growth progresses the cyst loses its connection to the physis migrating into the diaphysis and subsequently healing. UBCs can be rarely seen in adults in unusual locations such as in the <a href="/articles/talus">talus</a>, <a href="/articles/calcaneus">calcaneus</a>, or the iliac wing.</p><h4>Radiographic features</h4><p>Plain radiographs are the first-line imaging modality. CT and MRI add little to the diagnosis, however, can be helpful in eliminating other entities that can potentially mimic a simple bone cyst (see differential diagnosis below) <sup>8</sup>.</p><h5>Plain radiograph</h5><p>Unicameral bone cysts are well defined geographic <a href="/articles/benign-lytic-bone-lesions">lucent lesions</a> with a narrow zone of transition, mostly seen in skeletally immature patients, which are centrally located and show a thin sclerotic margin in the majority of cases with no <a href="/articles/periosteal-reaction">periosteal reaction</a> or soft tissue component. They sometimes expand the bone with thinning of the endosteum without any breach of the cortex unless there is a pathologic fracture. Prominent ridges of bone can appear as pseudotrabeculation on x-ray but in fact, UBC is usually unilocular. Rarely, they are truly multiloculated, which can occur after repeated fractures <sup>3,10</sup>.</p><p>If there is a fracture through this lesion a dependent bony fragment may be seen, and this is known as the <a href="/articles/fallen-fragment-sign">fallen fragment sign</a>. The rising bubble sign is considered pathognomonic and occurs when a gas bubble is seen at the most non-dependent part of the UBC <sup>8,10</sup>.</p><h5>CT</h5><p>Features on CT are similar to plain radiographs but CT has the advantage of characterising extent, detecting radiograph-occult fractures, and assessing internal density (usually between 10-15 HU) <sup>8</sup>. </p><h5>MRI</h5><p>MR signal characteristics for an uncomplicated lesion include <sup>8,10</sup>:</p><ul>-<li>-<strong>T1</strong>: low signal</li>-<li>-<strong>T2</strong>: high signal</li>-<li>-<strong>T1C+</strong>: peripheral enhancement</li>-</ul><p><a href="/articles/fluid-fluid-level-containing-bone-lesions-2">Fluid-fluid levels</a> can be seen in the setting of fibrous septations, which can enhance <sup>8</sup>. Internal signal heterogeneity, <a href="/articles/periosteal-reaction">periosteal reaction</a> and soft tissue oedema can be seen in the setting of fracture <sup>8</sup>.</p><h5>Nuclear medicine</h5><h6>Scintigraphy</h6><p>Unicameral bone cyst on <a href="/articles/bone-scintigraphy-1">bone scintigraphy</a> tends to appear as foci of photopenia (cold spot). This is referred to as the <a href="/articles/doughnut-sign-on-bone-scinigraphy">doughnut sign</a> which results in increased uptake peripherally and a photopenic centre. However, a pathological fracture would cause an increased radioisotope activity.</p><h4>Treatment and prognosis</h4><p>Intervention is usually not required for an asymptomatic lesion. If large and threatening to fracture, or causing deformity then an intralesional steroid injection can be performed <sup>3-5</sup>. If fractured the bone usually heals normally <sup>5</sup>. In some instances, surgery with curettage and bone grafting is required. Local recurrence rates are ~15% (range 10-20%) <sup>10</sup>.</p><h4>History and etymology</h4><p>Unicameral bone cysts were initially described by the German pathologist Rudolf Virchow in 1891 <sup>8,9</sup>.</p><h4>Differential diagnosis</h4><p>General imaging differential considerations include <sup>8,10</sup>:</p><ul>-<li><a href="/articles/intraosseous-lipoma">intraosseous lipoma</a></li>-<li><a href="/articles/intraosseous-ganglion">intraosseous ganglion</a></li>-<li><a href="/articles/fibrous-dysplasia">fibrous dysplasia</a></li>-<li><a href="/articles/langerhans-cell-histiocytosis-skeletal-manifestations-1">eosinophilic granuloma (EG)</a></li>-<li>-<a href="/articles/giant-cell-tumour-of-bone">giant cell tumour of bone</a>: usually older, extending to the articular surface</li>-<li>-<a href="/articles/non-ossifying-fibroma-1">non-ossifying fibroma</a>: eccentric, cortical base</li>-<li>-<a href="/articles/haemophilic-pseudotumour">haemophilic pseudotumour</a> (intraosseous)</li>-<li>-<a href="/articles/aneurysmal-bone-cyst">aneurysmal bone cyst (ABC)</a>: usually eccentric </li>-</ul><h4>See also</h4><ul><li><a href="/articles/expansile-lytic-lesions-without-cortical-destruction-of-bone-differential">differential diagnosis of expansile lytic lesions without cortical destruction of bone</a></li></ul>- +<p><strong>Unicameral bone cysts (UBC)</strong>, also known as <strong>simple bone cysts</strong> <strong>(SBC)</strong> are common benign non-neoplastic lucent bony lesions that are seen mainly in childhood and typically remain asymptomatic. </p><p>SBC accounts for the 'S' in the popular mnemonic for lucent bone lesions <a href="/articles/lucentlytic-bone-lesion-differential-diagnosis-mnemonic-1">FEGNOMASHIC</a>.</p><h4>Epidemiology</h4><p>UBCs are usually found in children in the 1st and 2nd decades (65% in teenagers) with the mean age at diagnosis being 9 years <sup>8</sup>. They are more common in males (M:F ~ 2-3:1) <sup>2,6</sup>. Active unicameral bone cysts occur most frequently between the ages of 1 and 10 years.</p><h4>Diagnosis</h4><p>Diagnostic criteria are <sup>10</sup>:</p><ul>
- +<li><p>essential: simple cyst lacking a true lining with typical imaging features</p></li>
- +<li><p>desirable: fibrin-like deposits +/- mineralisation forming cementum-like structures</p></li>
- +</ul><h4>Clinical presentation</h4><p>These lesions are usually asymptomatic and found incidentally, although pain, swelling and stiffness of the adjacent joint also occur. The most frequent presentation is due to <a href="/articles/pathological-fracture">pathological fracture</a> <sup>1,2,6</sup>.</p><h4>Pathology</h4><p>The aetiology and pathogenesis are unknown <sup>8,10</sup>. When uncomplicated by fracture the cysts contain clear serosanguineous fluid surrounded by a thin fibrous membranous lining. </p><p>During the active phase, the cyst remains adjacent to the growth plate. As the lesion becomes inactive it migrates away from the growth plate (normal bone is formed between it and the growth plate) and it gradually resolves <sup>3,5</sup>.</p><h5>Location</h5><p>They are typically intramedullary and active cysts are found in the metaphysis of long bones, abutting the growth plate <sup>1</sup>. Locations include <sup>1,2,5</sup>:</p><ul>
- +<li><p>proximal <a href="/articles/humerus">humerus</a>: most common 50-60%</p></li>
- +<li><p>proximal <a href="/articles/femur">femur</a>: 30%</p></li>
- +<li><p>other long bones</p></li>
- +<li>
- +<p>occurrence elsewhere is relatively uncommon, and usually occurs in adults</p>
- +<ul>
- +<li><p>spine: usually posterior elements</p></li>
- +<li><p><a href="/articles/pelvis-1">pelvis</a>: only 2% of UBC <sup>1</sup></p></li>
- +<li><p><a href="/articles/calcaneus">calcaneus</a></p></li>
- +</ul>
- +</li>
- +</ul><p>As bone growth progresses the cyst loses its connection to the physis migrating into the diaphysis and subsequently healing. UBCs can be rarely seen in adults in unusual locations such as in the <a href="/articles/talus">talus</a>, <a href="/articles/calcaneus">calcaneus</a>, or the iliac wing.</p><h4>Radiographic features</h4><p>Plain radiographs are the first-line imaging modality. CT and MRI add little to the diagnosis, however, can be helpful in eliminating other entities that can potentially mimic a simple bone cyst (see differential diagnosis below) <sup>8</sup>.</p><h5>Plain radiograph</h5><p>Unicameral bone cysts are well defined geographic <a href="/articles/benign-lytic-bone-lesions">lucent lesions</a> with a narrow zone of transition, mostly seen in skeletally immature patients, which are centrally located and show a thin sclerotic margin in the majority of cases with no <a href="/articles/periosteal-reaction">periosteal reaction</a> or soft tissue component. They sometimes expand the bone with thinning of the endosteum without any breach of the cortex unless there is a pathologic fracture. Prominent ridges of bone can appear as pseudotrabeculation on x-ray but in fact, UBC is usually unilocular. Rarely, they are truly multiloculated, which can occur after repeated fractures <sup>3,10</sup>.</p><p>If there is a fracture through this lesion a dependent bony fragment may be seen, and this is known as the <a href="/articles/fallen-fragment-sign">fallen fragment sign</a>. The rising bubble sign is considered pathognomonic and occurs when a gas bubble is seen at the most non-dependent part of the UBC <sup>8,10</sup>.</p><h5>CT</h5><p>Features on CT are similar to plain radiographs but CT has the advantage of characterising extent, detecting radiograph-occult fractures, and assessing internal density (usually between 10-15 HU) <sup>8</sup>. </p><h5>MRI</h5><p>MR signal characteristics for an uncomplicated lesion include <sup>8,10</sup>:</p><ul>
- +<li><p><strong>T1</strong>: low signal</p></li>
- +<li><p><strong>T2</strong>: high signal</p></li>
- +<li><p><strong>T1C+</strong>: peripheral enhancement</p></li>
- +</ul><p><a href="/articles/fluid-fluid-level-containing-bone-lesions-2">Fluid-fluid levels</a> can be seen in the setting of fibrous septations, which can enhance <sup>8</sup>. Internal signal heterogeneity, <a href="/articles/periosteal-reaction">periosteal reaction</a> and soft tissue oedema can be seen in the setting of fracture <sup>8</sup>.</p><h5>Nuclear medicine</h5><h6>Scintigraphy</h6><p>Unicameral bone cyst on <a href="/articles/bone-scintigraphy-1">bone scintigraphy</a> tends to appear as foci of photopenia (cold spot). This is referred to as the <a href="/articles/doughnut-sign-on-bone-scinigraphy">doughnut sign</a> which results in increased uptake peripherally and a photopenic centre. However, a pathological fracture would cause an increased radioisotope activity.</p><h4>Treatment and prognosis</h4><p>Intervention is usually not required for an asymptomatic lesion. If large and threatening to fracture, or causing deformity then an intralesional steroid injection can be performed <sup>3-5</sup>. If fractured the bone usually heals normally <sup>5</sup>. In some instances, surgery with curettage and bone grafting is required. Local recurrence rates are ~15% (range 10-20%) <sup>10</sup>.</p><h4>History and etymology</h4><p>Unicameral bone cysts were initially described by the German pathologist Rudolf Virchow in 1891 <sup>8,9</sup>.</p><h4>Differential diagnosis</h4><p>General imaging differential considerations include <sup>8,10</sup>:</p><ul>
- +<li><p><a href="/articles/intraosseous-lipoma">intraosseous lipoma</a></p></li>
- +<li><p><a href="/articles/intraosseous-ganglion">intraosseous ganglion</a></p></li>
- +<li><p><a href="/articles/fibrous-dysplasia">fibrous dysplasia</a></p></li>
- +<li><p><a href="/articles/langerhans-cell-histiocytosis-skeletal-manifestations-1">eosinophilic granuloma (EG)</a></p></li>
- +<li><p><a href="/articles/giant-cell-tumour-of-bone">giant cell tumour of bone</a>: usually older, extending to the articular surface</p></li>
- +<li><p><a href="/articles/non-ossifying-fibroma-1">non-ossifying fibroma</a>: eccentric, cortical base</p></li>
- +<li><p><a href="/articles/haemophilic-pseudotumour">haemophilic pseudotumour</a> (intraosseous)</p></li>
- +<li><p><a href="/articles/aneurysmal-bone-cyst">aneurysmal bone cyst (ABC)</a>: usually eccentric </p></li>
- +</ul><h4>See also</h4><ul><li><p><a href="/articles/expansile-lytic-lesions-without-cortical-destruction-of-bone-differential">differential diagnosis of expansile lytic lesions without cortical destruction of bone</a></p></li></ul>
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