High Yield Topics

Aneurysmal Bone Cyst

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Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
> Table of Contents > Aneurysmal Bone Cyst

Aneurysmal Bone Cyst
Frank J. Frassica MD
Basics
Description
  • Destructive, painful, lytic bone lesions occurring in young patients
  • May occur primarily in bone (de novo) or develop within another benign bone lesion
  • Can be locally aggressive and can cause a bone to “balloon” as a result of aneurysmal cystic expansion
  • Occurs most often at the proximal ends of long bones and 2nd most commonly in the vertebral column
  • In general, considered benign active or aggressive lesions
  • Children with open physes are much more prone to local recurrence (up to 50%) (1,2).
Epidemiology
  • Can occur in any decade of adult life, but nearly 80% occur in the 2nd decade (2).
  • Occurs equally in males and females (1)
Incidence
Rare
Risk Factors
May develop within other benign bone tumors
Pathophysiology
  • Appears to be hemorrhagic and consists of a combination of “fleshy” tissue and unclotted blood
  • Often brown soft tissue because of hemosiderin deposition
  • Normally, at the periphery of the lesion is an eggshell-like layer of periosteal bone around the lesion.
  • Microscopically, there appear to be cavernous spaces filled with blood.
  • The walls of the spaces contain fibroblastic cells, multinucleated giant cells, and strands of bone.
Etiology
  • No known causes
  • However, nearly 1/2 are seen to occur in
    conjunction with another benign tumor and may represent a breakdown in
    the body’s reaction to the other tumor.
Associated Conditions
  • May occur in other benign bone tumors or processes:
    • Giant cell tumor
    • Chondroblastoma
    • Osteoblastoma
    • Fibrous dysplasia
    • NOF
Diagnosis
Signs and Symptoms
  • Pain (usually mild and intermittent) is the most common symptom.
  • The involved area may swell.
    • Swelling will tend to increase until the lesion is treated.
  • If the lesion is located in the vertebral
    column, it may cause signs and symptoms of spinal cord compression (leg
    weakness, bowel or bladder dysfunction).
Physical Exam
  • Check the affected area for tenderness to palpation and the presence of swelling.
  • Quantify ROM.
  • Check for neurologic deficits.
Tests
Imaging
  • Radiography:
    • Plain radiographs show a “ballooned” expansion of the affected bone.
    • No matrix mineralization is present in the lesion.
    • Lesions most commonly are seen in the
      metaphyseal regions of the femur and tibia, as well as in the posterior
      elements of the vertebra.
    • One often can see a sclerotic rim or a fine shell of periosteal bone surrounding the lesion.
  • CT:
    • Can be used to assess lesions of the pelvis or vertebral column more precisely than radiography
    • Often allows the physician to assess carefully the presence of the periosteal rim of bone around a lesion
    • Often shows a fluid level in the lesion
  • MRI:
    • Allows more accurate assessment than CT or radiography of the extent of an aneurysmal bone cyst
    • Allows quantification of soft-tissue expansion and minor involvement by the lesion that points away from the lesion
    • On T2-weighted images, the lesions have high signal levels, and layering in the blood (fluid-fluid levels) often can be seen.
Differential Diagnosis
  • Depending on the location of the tumor, a widely varying differential diagnosis is possible, based on symptoms.
  • Based on radiographs, the differential diagnosis includes:
    • Unicameral bone cyst
    • Giant cell tumor
    • Osteosarcoma (telangiectatic type)
    • Osteoblastoma
    • Fibrous dysplasia
  • Based on histologic features, the differential diagnosis includes:
    • Giant cell tumor
    • Giant cell reparative granuloma
    • Simple bone cyst
    • Telangiectatic osteosarcoma
Treatment
General Measures
  • After appropriate evaluation of the
    lesion with radiologic studies, a needle or open biopsy may be
    performed, followed by excision, curettage, and bone grafting.
  • Once the bony defect is healed, patients return to normal function.
  • Lesions can recur locally; the treatment is repeat surgical excision.
Activity
  • Most patients need to limit weightbearing activity on the involved region while bony healing occurs.
  • Once the bone has healed, no limitations on activity are necessary.
Special Therapy
Physical Therapy
Physical therapy may be needed to regain joint motion or to assist in gait training after surgery.
Surgery
  • Treatment of aneurysmal bone cysts
    involves excision of the ballooned cortex, curettage with hand and
    power instruments, chemical cauterization of the cyst walls, and bone
    grafting (2).
  • If the cyst is in an expendable bone (rib or fibula), resection of the lesion may be performed.
  • Radiation therapy should be used only when no surgical option exists.
  • Embolization may be effective as an
    adjunct to control bleeding or control the lesion in difficult sites
    such as the pelvis, sacrum, or vertebral bodies.

P.15


Follow-up
Radiotherapy should be reserved for progressing or untreatable lesions.
Prognosis
  • With modern treatment, 95% of patients can be expected to be cured of these lesions (1).
  • An aneurysmal bone cyst should not be expected to metastasize unless rare malignant transformation occurs.
  • If a patient does have a local recurrence, repeat surgical excision can be performed.
Complications
  • Complications of surgical treatment vary
    greatly, but the most common problem after appropriate treatment is
    local recurrence of the tumor.
  • Other surgical complications, such as infection and neurologic or vascular injury, occur with a low frequency.
Patient Monitoring
After surgical treatment, regular follow-up is required
for several years to evaluate bony healing and to look for local
recurrence of the tumor.
References
1. Dorfman HD, Czerniak B. Cystic lesions. In: Bone Tumors. St. Louis: Mosby, Inc, 1998:855–912.
2. McCarthy
EF, Frassica FJ. Bone cysts. In: Pathology of Bone and Joint Disorders:
With Clinical and Radiographic Correlation. Philadelphia: WB Saunders,
1998:277–289.
Additional Reading
Bruckner JD, Conrad EU, III. Musculoskeletal neoplasms. In: Kasser JR, ed. Orthopaedic Knowledge Update 5: Home Study Syllabus. Rosemont, IL: American Academy of Orthopaedic Surgeons, 1996:133–148.
Wold LE, McLeod RA, Sim FH, et al. Aneurysmal bone cyst. In: Atlas of Orthopedic Pathology. Philadelphia: WB Saunders, 1990:232–237.
Miscellaneous
Codes
ICD9-CM
213.9 Aneurysmal bone cyst
Patient Teaching
Patients must be educated to look for signs and symptoms
of local recurrence of the tumor, including onset of pain or localized
swelling in the area of a previous lesion.
FAQ
Q: Can aneurysmal bone cysts be confused with other bone conditions?
A:
The pathologist must study the histologic specimens carefully to
exclude an underlying condition. Telangiectatic osteosarcoma, a highly
malignant tumor, can be confused with an aneurysmal bone cyst.
Q: Is aneurysmal bone cyst a neoplasm?
A:
Probably not. Most clinicians believe they are benign reactive
conditions, occurring in the presence of a disturbance of the vascular
system.
Q: Can patients with aneurysmal bone cysts be observed to see if this bone lesion will resolve?
A:
Aneurysmal bone cysts can grow quickly and destroy large areas of the
bone. Curettage and grafting rather than observation should be the
treatment of choice.

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