Aneurysmal bone cyst

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rohan A. Bhimani, M.B.B.S., D.N.B., M.Ch.[2]

Overview

Aneurysmal bone cyst (ABC) accounts for 1% to 2% of all primary bone tumors. The incidence of aneurysmal bone cyst is approximately 0.14 per 100,000 individuals worldwide. Adolescents and children are most affected by aneurysmal bone cyst. The age distribution of aneurysmal bone cyst is between 1.5-25 years. The mean age of the patients with aneurysmal bone cyst is 16 years. Women are more commonly affected than men, with a 1:0.84 ratio. In 1942, Jaffe and Lichtenstein first described aneurysmal bone cyst. Aneurysmal bone cyst can be classified based on mechanism of origin into primary and secondary. The true causes of aneurysmal bone cyst are not known. ABCs usually present in the long bones such as the humerus, femur, tibia and fibula. About 25% of ABC's are seen in posterior element of spine. ABC's typically occur in the metaphysis of the long bones. The hallmark of ABC is Pain, swelling and pathological fracture. The mainstay of treatment for ABC is surgery in form of curettage and bone grafting.

Historical Perspective

• In 1942, Jaffe and Lichtenstein first described aneurysmal bone cyst.
• In 1940, Ewing propoosed that aneurysmal bone cyst was caused by increased venous pressure.
• In 1956, Cruz and Coley also supported Ewing's hypothesis.
• In 1956, Barnes hypothesized that aneurysmal bone cyst was due to an abnormal response to injury.
• In 1956, Otterdoom after a thorough pathological study, concluded that aneurysmal bone cyst was an angioma of bone.

Classification

• Aneurysmal bone cyst(ABC) can be classified based on imaging findings and on mechanism of origin.

Mechanism of Origin

Based on mechanism of origin, aneurysmal bone cyst can be classified into:

Primary Aneurysmal Bone Cyst(ABC)

• When ABC arises de novo, it is called primary ABC.
• About 70% of ABC's are primary in origin.

Secondary Aneurysmal Bone Cyst(ABC)

• When ABC coexist with other bone lesions, it is termed as secondary ABC's.
• About 30% of ABC's are secondary in origin.
• Commonly associated bone lesions include:
  • Unicameral bone cyst
  • Osteoblastoma
  • Giant cell tumor
  • Enchondroma
  • Chondroblastoma
  • Fibrous dysplasia
  • Chondromyxoid fibroma
  • Nonossifying fibroma

Enneking (MSTS) Staging System

• The Enneking surgical staging system (also known as the MSTS system) for benign musculoskeletal tumors based on radiographic characteristics of the tumor host margin.
• It is widely accepted and routinely used classification.

Stages	Description
1	Latent: Well demarcated borders
2	Active: Indistinct borders
3	Aggressive: Indistinct borders

Pathophysiology

• The exact pathogenesis of aneurysmal bone cyst is not fully understood.
• Various theories have been proposed concerning the pathogenesis of aneurysmal bone cyst:
  • Local alteration in hemodynamics resulting in markedly increased venous pressure and development of a dilated vascular bed within the involved bone.
  • Primary ABCs demonstrate a t(16;17)(q22;p13) fusion of the TRE17/CDH11-USP6 oncogene leading to increased cellular cadherin-11 activity which arrests osteoblastic maturation in a more primitive state.
• ABCs usually present in the long bones such as the humerus, femur, tibia; and fibula.
• About 25% of ABC's are seen in posterior element of spine.
• ABC's typically occur in the metaphysis of the long bones.

Causes

• The true causes of aneurysmal bone cyst(ABC) are not known.
• Commonly proposed theories are as follows:
  • ABCs may be caused by a reaction secondary to another bony lesions such as giant cell tumor, chondroblastoma, fibrous dysplasia, osteosarcoma and chondrosarcoma.
  • ABCs may arise de novo.
  • ABCs may arise secondary to previous trauma.

Differentiating Aneurysmal Bone Cyst from Other Diseases

Aneurysmal bone cyst must be differentiated from following bone disorders:

Disease	Bubbly lytic lesion on x-ray	Lakes of Blood on histology	Diagnosis	Treatment is curretage and bone grafting
Aneurysmal bone cyst	+	+	Radiology and biopsy	+
Unicameral bone cyst	+	-	Radiology and biopsy	-
Non ossifying fibroma	+	-	Radiology and biopsy	-
Giant cell tumor	-	-	Radiology and Biopsy	+
Chondroblastoma	-	-	Biopsy	+
Chondromyxoid Fibroma	-	-	Radiology and biopsy	+
Osteoblastoma	-	-	Radiology and biopsy	+
Telangiectatic osteosarcoma	-	+	Radiology and biopsy	-

Epidemiology and Demographics

• ABC accounts for 1% to 2% of all primary bone tumors.
• The incidence of aneurysmal bone cyst is approximately 0.14 per 100,000 individuals worldwide.
• Adolescents and children are most affected by aneurysmal bone cyst.
• The age distribution of aneurysmal bone cyst is between 1.5-25 years.
• The mean age of the patients with aneurysmal bone cyst is 16 years.
• Women are more commonly affected than men, with a 1:0.84 ratio.
• There is no racial predilection to aneurysmal bone cyst.

Risk Factors

There are no established risk factors for aneurysmal bone cyst.

Screening

There is insufficient evidence to recommend routine screening for aneurysmal bone cyst.

Natural History, Complications, and Prognosis

• Common complications of aneurysmal bone cyst include:
  • Pathological fracture
  • Premature epiphyseal closure
    • Limb-length discrepancy
    • Angular deformity
  • Malignant transformations to form malignant osteosarcoma.
• Prognosis is generally excellent for aneurysmal bone cyst.
• Factors that influence the outcome of the aneurysmal bone cyst include:
  • Young age
  • Open growth plates
  • Metaphyseal location

Diagnosis

Diagnostic Study of Choice

Histology of Aneurysmal Bone Cyst.Source: Case courtesy of RMH Neuropathology, Radiopaedia.org, rID: 29294

• Biopsy is the diagnostic study of choice for the diagnosis of aneurysmal bone cyst.
• Gross appearance of aneurysmal bone cyst include:
  • Blood-soaked sponge.
  • A thin subperiosteal shell of new bone surrounds the structure
  • Cystic blood-filled cavities.
  • The tissue within shows brownish intertwining septa.
  • The stroma contains proliferative fibroblasts, spindle cells, areas of osteoid formation, and an uneven distribution of multinucleated giant cells that tend to surround the fluid-filled cavities in a pigs at the trough formation.
• HIstological appearance includes:
  • Cavernous space
  • Blood-filled spaces without endothelial lining
  • Cavity lining with numerous benign giant cells and spindle cells with thin strands of woven bone present

History and Symptoms

• The majority of patients with aneurysmal bone cyst have a positive history of:
  • Pain
  • Swelling
  • Pathological fracture
  • Neurologic conditions occur often due to compression of either the spinal cord or nerve roots, and may lead to paralysis and spinal stiffness

Physical Examination

X-ray showing aneurysmal bone cyst of left proximal femur.Source: Case courtesy of Dr Lawrence Chia Wei Oh, Radiopaedia.org, rID: 28998

• Common physical examination findings of aneurysmal bone cyst include:
  • Deformity
  • Decreased range of motion, weakness, or stiffness
  • Torticollis
  • Occasionally, bruit over the affected area
  • Warmth over the affected area

Laboratory Findings

There are no diagnostic laboratory findings associated with aneurysmal bone cyst.

Electrocardiogram

There are no ECG findings associated with aneurysmal bone cyst.

X-ray

• An x-ray may be helpful in the diagnosis of aneurysmal bone cyst.
• Findings on an x-ray suggestive of aneurysmal bone cyst include include:
  • Expansile, eccentric and lytic lesion with bony septae giving it a soap bubble appearance.
  • Involves the metaphyseal area of the bone
  • Thin rim of periosteal new bone surrounding lesion
  • No matrix mineralization

CT scan showing aneurysmal bone cyst of posterior element of spine.Source: Case courtesy of RMH Neuropathology, Radiopaedia.org, rID: 29294

• Radiologically aneurysmal bone cyst can be stratified into 4 phases:
  • Initial phase 1 – Small, lytic lesion without evidence of lifting off of the periosteum.
  • Phase 2 - Rapidly enlarging demonstrating a characteristic blowout appearance.
  • Phase 3 - Growth slows or stops after some sort of intervention.
  • Phase 4 - Healing with progressive ossification and calcification of the cavity.

Echocardiography or Ultrasound

There are no echocardiography/ultrasound findings associated with aneurysmal bone cyst.

CT scan

• CT scan confirms the x-ray findings.
• In addition, CT demonstrates internal septation such as calcified rim, giving an eggshell appearance, which may be completely or partially intact.
• Fluid-fluid levels can also be seen.

MRI

• Magnetic resonance imaging (MRI) are similar to those from CT scan.
• However, MRI can more specifically reveal blood within the lesion as well as extension into the soft tissues.

MRI showing aneurysmal bone cyst of left proximal femur.Source: Case courtesy of Dr Lawrence Chia Wei Oh, Radiopaedia.org, rID: 28998

Bone Scan

• Increased uptake is observed around the lesion of aneurysmal bone cyst.
• Findings often demonstrate a halo effect of increased radionuclide uptake surrounding an area of little uptake.

Angiography

• Angiography demonstrates a hypervascular area around the aneurysmal bone cyst.
• An intense diffuse area of persistent contrast accumulation may be visualized without main afferent or efferent vessels observed.
• It can be helpful to plan selective arterial embolization as the primary treatment or as a preoperative method to help control intraoperative blood loss.

Treatment

Medical Therapy

There is no treatment for aneurysmal bone cyst, the mainstay of therapy is surgery.

Surgery

• Surgery is the mainstay of treatment for aneurysmal bone cyst.

Aggressive curettage with adjuvant and bone grafting

Indications

• Symptomatic aneurysmal bone cyst without acute fracture

Technique

• Possible adjuvants
  • Phenol
  • Argon beam
  • Liquid nitrogen

Recurrence

• Local recurrence in up to 25% and more common in children with open ephyses.

Primary Prevention

There are no established measures for the primary prevention of aneurysmal bone cyst.

Secondary Prevention

There are no established measures for the secondary prevention of aneurysmal bone cyst.

References

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