Unicameral Bone Cyst

Author: Deborah Allen

Topic updated on 12/03/12 8:54am

Introduction

Also referred to as a simple bone cyst
A non-neoplastic, serous fluid-filled bone lesion thought to result from temporary failure of medullary bone formation near the physis
Age & location
- age
  - usually found in patients <20 years of age
- location
  - usually found in the proximal humerus of young patients
  - can be found in other locations including proximal femur, distal tibia, ilium, calcaneus, and occasionally metacarpals, phalanges, or distal radius
  - arises in the metaphysis adjacent to physis and progresses toward the diaphysis with bone growth
Prognosis
- as a patient approaches skeletal maturity, a UBC will often decrease in size and may heal after growth is complete
- fracture healing usually does not lead to cyst resolution
- requires close follow up while in active phase due to recurrence and risk of fracture or growth arrest

Classification

Classification is important as it impacts treatment
- active
  - if cyst is adjacent to the physis
- latent
  - if normal bone separates cyst from physis

Presentation

Symptoms
- most asymptomatic unless fracture occurs (usually with minor trauma)
- presents with pain from a pathologic fracture in ~50%

Imaging

Radiographs
- central, lytic, well-demarcated metaphyseal lesion (2-3% cross physis)
- cystic expansion with symmetric thinning of cortices
- "fallen leaf" sign (pathologic fracture with fallen cortical fragment in base of empty cyst is pathognomonic)
- trabeculated appearance after multiple fractures
MRI
- very dark on T1
- very bright on T2
- gadolinium shows classic rim enhancement of a cystic lesion
Bone scan
- is variable, but usually warm

Histology

Characteristic findings
- cyst with thin fibrous lining containing fibrous tissue, giant cells, and hemosiderin pigment
- chronic inflammatory cells may be found in small numbers
- cementum spherules (calcified eosinophilic fibrinous material) in 10%
- uniform population of spindle cells without nuclear atypia
Biopsy usually indicated for questionable diagnosis

Differential

ABC
- is more expansive than UBC (UBC lesion usually not wider than physis)
Telangiectatic osteosarcoma

Treatment

Nonoperative
- immobilization alone
  - indications
    - proximal humerus lesions with pathologic fracture (15% of lesions fill in with native bone after acute fracture)
- aspiration/methylprednisolone acetate injection
  - indications
    - active cysts (communicates with physis) in the proximal humerus
  - technique
    - usually requires several injections, especially in very young children
    - bone marrow injections have recently been reported to be effective
Operative
- curettage and bone grafting +/- internal fixation based on tumor location
  - indications
    - symptomatic latent cysts that have not responded to steroid injections
    - latent cysts in the proximal femur that are a structural concern and at risk for fracture and osteonecrosis
    - proximal femoral lesions with a pathologic fracture have a high rate of refracture and malunion when treated nonoperatively therefore, internal fixation is recommended
  - contraindications
    - avoid in active lesions as communication with physis may lead to growth arrest

Differentials & Groups

	"Bubbly" lytic lesion on xray	Treatment is USAULLY Aspiration and Injection	Treatment is OCCASIONALLY curettage and bone grafting.
UBC	•	•	•
ABC	•
NOF	•		•
Enchondroma			•

Ibank

	Location	Xray	Xray	CT	B. Scan	MRI	MRI	Histo(1)
Case A	femur
Case A	humerus
Case A	humerus
(1) - histology does not always correspond to clinical case

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Qbank (5 Questions)

TAG

(SBQ07.38) An 8-year-old boy complains of left shoulder pain after a collision with his younger brother. He was asymptomatic prior to the incident. Which of the following treatments is most appropriate at this time? Topic

Review Topic

FIGURES: A

1. Aspiration and injection of methylprednisolone acetate
2. Open reduction, internal fixation
3. Initiation of radiation and chemotherapy
4. Immobilization in sling
5. Radiofrequency ablation

PREFERRED RESPONSE ▶

DISCUSSION: The clinical presentation and radiograph are consistent with a pathologic fracture through a likely unicameral bone cyst. Appropriate initial management includes immobilization in a sling until the fracture has healed. Since the lesion is benign in appearance, biopsy is not indicated at this time.

Unicameral bone cysts (UBC), or simple cysts, are serous fluid-filled bone lesions usually found in patients younger than 20 years of age. Radiographically, they present as central, lytic lesions that rarely cross the physis. Approximately 50-75% of patients with a UBC present with a pathological fracture. Initial treatment focuses on immobilizing the fracture with a sling for 4-6 weeks. Once the fracture is healed, intervention should be considered for those lesions that remain symptomatic, active (abutting the growth plate), or have increased in size. Options for intervention include injection with steroid or bone marrow, curettage and bone grafting, and internal fixation.

Rougraff et al treated 23 patients with "active" unicameral bone cysts with trephination and injection of allogeneic demineralized bone matrix and autogenous bone marrow. They found pain relief and prevention of pathologic fracture in 78% of patients after one injection, and 100% of patients after two injections. They conclude that percutaneous injection of a combination of allogeneic demineralized bone matrix and autogenous bone marrow is an effective treatment for active unicameral bone cysts.

Roposch et al treated 32 patients with unicameral bone cysts in either the proximal humerus, proximal femur, or distal radius with flexible intramedullary nailing. 30 of these patients had already sustained a pathological fracture. 30 of the 32 lesions had healed within 36 months. They conclude that flexible IM nailing is an effective treatment for unicameral bone cysts in long bones.

Figure A shows a central, well marginated, radiolucent defect in the metaphysis of the proximal humerus with associated pathologic fracture. Illustration A shows another example of a pathologic fracture through a unicameral bone cyst with the arrow pointing to the "fallen leaf" sign. This is caused by the cortical fracture fragment displacing centrally into the fluid-filled cyst.

Incorrect Answers:
Answer 1: Aspiration and injection of steroid may be indicated when the fracture has healed, but is not the appropriate initial management for a UBC with a pathologic fracture.
Answer 2: Internal fixation is considered if conservative management fails.
Answer 3: Given the benign appearance of the lesion, radiation and chemotherapy are not indicated.
Answer 5: Radiofrequency ablation is the appropriate management for osteoid osteoma, not a pathologic fracture through a UBC.

Illustrations: A

REFERENCES:

1. Rougraff BT, Kling TJ. Treatment of active unicameral bone cysts with percutaneous injection of demineralized bone matrix and autogenous bone marrow. J Bone Joint Surg Am. 2002 Jun;84-A(6):921-9. PMID:12063325 (Link to Abstract)

2. Roposch A, Saraph V, Linhart WE. Flexible intramedullary nailing for the treatment of unicameral bone cysts in long bones. J Bone Joint Surg Am. 2000 Oct;82-A(10):1447-53. PMID:11057473 (Link to Abstract)

Question Authors:

Mark Karadsheh MD, Jan Szatkowski MD, Michael Hughes MD,

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(SBQ06.1) A 14-year-old boy is brought to the emergency department after falling onto his right shoulder. Radiographs are shown in Figure A. Which of the following is most likely to occur with curettage and bone grafting of this lesion? Topic

Review Topic

FIGURES: A

1. Metastases to the lungs
2. Recurrence of the lesion
3. Limb-length discrepancy of the affected side compared to the contralateral side
4. Continued pain in the affected extremity
5. Paraneoplastic disease

PREFERRED RESPONSE ▶

DISCUSSION: Figure A shows an unicameral bone cyst in the proximal humerus of a skeletally immature person. These cysts are commonly found in the proximal humerus and are often associated with a fracture. There is no ‘gold standard’ treatment for these lesions and they often recur no matter what treatment is chosen.

Sung et al reviewed 167 patients 20 years or younger who had unicameral bone cysts treated with either steroid injection, curettage and bone grafting or a combination of steroids, demineralized bone matrix and bone marrow aspirate. The recurrence rate for each treatment was 84%, 76% and 63%, respectively after the initial treatment.

Canavese et al reviewed 46 children with unicameral bone cysts treated with either autologous bone marrow injection, methylprednisolone acetate injection or percutaneous curettage alone. At the 2 year follow up mark, there was unsatisfactory healing in 30% of the percutaneous curettage group, 79% of the autologous bone marrow injection group and 59% of the methylprednisolone acetate injection group.

Incorrect Answers:
Answer 1: Metastases to the lungs: Unicameral bone cysts do not metastasize.
Answer 3: Limb-length discrepancy of the affected side compared to the contralateral side: This is not a common complication reported during the operative treatment of unicameral bone cysts.
Answer 4: Continued pain in the affected extremity: Unicameral bone cysts are usually painless (unless fractured).
Answer 5: Paraneoplastic disease: Unicameral bone cysts are not associated with paraneoplastic diseases.

REFERENCES:

1. Canavese F, Wright JG, Cole WG, Hopyan S. Unicameral bone cysts: comparison of percutaneous curettage, steroid, and autologous bone marrow injections. J Pediatr Orthop. 2011 Jan-Feb;31(1):50-5. PMID:21150732 (Link to Abstract)

2. Sung AD, Anderson ME, Zurakowski D, Hornicek FJ, Gebhardt MC.Unicameral bone cyst: a retrospective study of three surgical treatmentsClin Orthop Relat Res. 2008 Oct;466(10):2519-26 PMID:18679761 (Link to Abstract)

Question Authors:

Chad Krueger, Jan Szatkowski MD, Michael Hughes MD,

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(OBQ11.268) An 11-year-old boy presents with acute right arm pain after throwing a baseball. He is otherwise healthy and has no other complaints. Radiograph and CT scan of the lesion are shown in Figures A and B. What is the most appropriate treatment? Topic

Review Topic

FIGURES: A

1. Biopsy
2. Immobilization
3. Intramedullary nailing and chemotherapy
4. Wide resection and radiation therapy
5. Amputation

PREFERRED RESPONSE ▶

DISCUSSION: The history and radiographs are consistent with a pathological fracture through a unicameral bone cyst (UBC) in the child's humerus. The radiograph shows a lytic, expansile lesion with well-defined borders, no soft tissue mass, no significant matrix, and no periosteal reaction. The CT scan confirms this lesion is benign appearing with sharp sclerotic borders. Given the benign appearance, location, and history, biopsy is not required as a diagnosis of UBC can be made with the information provided.

The initial treatment of a pathological fracture through a benign bone cyst includes immobilization while the fracture heals. If this same lesion were present in a weight bearing bone, such as the proximal femur, then the treatment choice becomes more problematic and internal fixation needs to be considered to allow the child to mobilize. While many adjuvants have been tried in the treatment of UBCs, none have shown to be advantageous.

Dormans and Pill review the treatment of pathological fractures through bone cysts. They focus on the crucial identification of the specific diagnosis as the treatment of pathological fracture through a benign cyst is much different than the same fracture through a malignant neoplasm.

Wilkins reviews unicameral bone cysts in his JAAOS article. With appropriate imaging and patient history, a diagnosis of UBC can often be identified without advanced studies or surgical biopsy. As most UBCs will heal spontaneously, treatment includes immobilization and observation, except in tumors which occur in weight bearing bones or in situations where pathological fracture is preventable.

Incorrect answers
1) Biopsy - as discussed above, biopsy is not necessary given the benign appearance, location, and history.
3,4,5) Adjuvant therapy or aggressive surgical resection is not indicated for a benign bone tumor.

REFERENCES:

1. Dormans JP, Pill SG. Fractures through bone cysts: unicameral bone cysts, aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas. Instr Course Lect. 2002;51:457-67. Review. PMID:12064135 (Link to Abstract)

2. Wilkins RM. Unicameral bone cysts. J Am Acad Orthop Surg. 2000 Jul-Aug;8(4):217-24. Review. PMID:10951110 (Link to Abstract)

Question Authors:

Patrick O'Donnell MD/PhD, Dave Marcu MD, John Badylak MD,

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(OBQ08.63) A 9-year-old child presents to your office after he felt a painful snap in his arm while throwing a baseball. He is otherwise in good health and has no family history of disease. A radiograph of his arm is shown in Figure A. What is the next step in your management? Topic

Review Topic

FIGURES: A

1. Sling for comfort
2. Tumor staging
3. Biopsy
4. Open reduction with internal fixation
5. Intramedullary nailing

PREFERRED RESPONSE ▶

DISCUSSION: Pathologic fractures through benign appearing bone cysts are a difficult problem in orthopaedic surgery. The history and imaging suggest a benign lesion, likely a unicameral bone cyst, with a pathologic fracture.

Betsy et al discuss in their Level 5 review article that because the fracture alignment is acceptable, and the lesion is benign, conservative management is appropriate. After healing, if the lesion continues to grow or cause problems, curettage and grafting may be necessary. If the lesion were more aggressive appearing then staging and biopsy are indicated. ORIF and intramedullary nailing are not indicated for this child.

REFERENCES:

1. Dormons JP, Flynn JM: Pathologic fractures associated with tumors and unique conditions of the musculoskeletal system, in Beaty JH, Kasser JR (eds): Rockwood & Wilkins Fractures in Children, ed 5. Philadelphia, PA, Lippincott Williams & Wilkins, 2001, pp 142-168

2. Betsy M, Kupersmith LM, Springfield DS. Metaphyseal fibrous defects. J Am Acad Orthop Surg. 2004 Mar-Apr;12(2):89-95. Review. PMID:15089082 (Link to Abstract)

Question Authors:

Patrick O'Donnell MD/PhD, Michael Hughes MD,

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(OBQ07.51) An 8 year-old boy injures his arm pulling open a car door. A radiograph is shown in Figure A. Which of the following is the most likely diagnosis and preferred initial treatment? Topic

Review Topic

FIGURES: A

1. Telangietic osteosarcoma, Open biopsy with wide excision
2. Unicameral bone cyst, Aspiration of fluid and injection of bone cement
3. Non-Ossifying Fibroma, Radiation
4. Unicameral bone cyst, Sling and swath
5. Telangietic osteosarcoma, Chemotherapy

PREFERRED RESPONSE ▶

DISCUSSION: The pathologic fracture shown in Figure A is most likely through a unicameral bone cyst (UBC), and initial treatment should be conservative for fracture healing. UBCs occur most commonly in the proximal humerus and are characterized by cystic, symmetric expansion with thinning of the cortex. Pathologic fractures thru UBCs characteristically have a “fallen leaf” sign when a piece of bone fractures off and is captured within the basin of the cyst floor. Distal tibia and proximal femur are also common sites. Patients generally present with pain, usually after fracture resulting from minor trauma. Treatment of UCB begins with fracture healing, then advanced imaging and aspiration to confirm the diagnosis if there is any question. Margau et al reviewed MRI characteristics of UBCs and found they frequently appear complicated, with heterogeneous fluid signals and regions of nodular and thick peripheral enhancement related to previous pathologic fracture and early healing. Some lesions decease in size or heal by skeletal maturity without treatment. For recalcitrant UBCs that continue to be symptomatic or are in high-stress locations then either a steroid injection or curettage with bone grafting has been recommended.

REFERENCES:

1. Margau R, Babyn P, Cole W, Smith C, Lee F. MR imaging of simple bone cysts in children: not so simple. Pediatr Radiol. 2000 Aug;30(8):551-7. PMID:10993540 (Link to Abstract)

Question Authors:

Charles Jobin MD,

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(OBQ05.144) A 7-year old boy experienced severe right hip pain following ice-skating. He previously had no hip pain and is otherwise healthy. Radiographs are shown in figures A and B. What is the recommended treatment ? Topic

Review Topic

FIGURES: A

1. Open biopsy and pathological staging without fracture fixation
2. Open reduction and internal fixation with bone grafting of the bone cyst
3. Bedrest for 4 weeks followed by progressive weigh-bearing as tolerated
4. Immediate hip spica casting
5. Tibial traction pin with 4 weeks of skeletal traction followed by open biopsy

PREFERRED RESPONSE ▶

DISCUSSION: A pathological fracture is one that occurs through abnormal bone because the bone lacks its normal biomechanical properties. Benign tumors of bone that are associated with pediatric pathological fractures commonly include unicameral bone cyst, nonossifying fibroma, fibrous dysplasia, and aneurysmal bone cyst. With bone cysts, there is a high risk of fracture recurrence because of cyst persistence and the recommended treatment is ORIF with bone grafting.

Dormans et al have proposed grouping the treatment of pathologic fractures. The four types of fracture treatments include: 1) no treatment-the fracture and lesion may heal spontaneously; 2) treating the fracture first and then the lesion; 3) treating the fracture and lesion simultaneously; and 4) treating only the underlying process-the fracture can heal with treatment of the underlying process.

Ortiz reviews general principles of diagnosis, management, and treatment of pathological fractures in children. He emphasizes making the correct diagnosis prior to instituting any form of treatment with lesions that are not diagnostic based on preoperative imaging.

REFERENCES:

1. Ortiz EJ, Isler MH, Navia JE, Canosa R. Pathologic fractures in children. Clin Orthop Relat Res. 2005 Mar;(432):116-26. PMID:15738811 (Link to Abstract)

2. Dormans JP, Flynn JM: Pathologic fractures associated with tumors and unique conditions of the musculoskeletal system. In Bucholz RW, Heckman JD, Beaty JH, Kasser JR (eds): Rockwood, Green and Wilkin’s Fractures. Ed 5. Philadelphia, Lippincott Williams & Wilkins 139-240, 2001

Question Authors:

Patrick O'Donnell MD/PhD, Derek Moore, John Badylak MD,

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(OBQ04.54) A 15-year-old boy twists his ankle and is brought to the emergency room. Radiographs are shown in Figure A. What is the most likely progression of the this lesion as the child reaches skeletal maturity? Topic

Review Topic

FIGURES: A

1. Increase in size and involve the entire bone
2. Decrease in size and may disappear altogether
3. Turn into a malignant tumor
4. Remain unchanged
5. Lead to deformity of the affected bone

PREFERRED RESPONSE ▶

DISCUSSION: The lesion depicted in Figure A is unicameral bone cyst (UBC), a benign tumor typically seen in the ends of long bones(Illustration A) in the skeletally immature. UBCs can also occur in the tarsal bones of the foot. The cyst usually progressively shrinks as the patient approaches skeletal maturity and may heal spontaneously after growth is completed.

Smith and Smith reviewed 20 cases of pediatric calcaneal UBCs over 20 years. Half were treated operatively with curretage and bone grafting. The non-operative group did well and after 20 years most of the UBCs healed completely. Those that didn't heal did not progress.

Illustrations: A

REFERENCES:

1. Smith RW, Smith CF. Solitary unicameral bone cyst of the calcaneus. A review of twenty cases. JBJS Am 1974, Jan;56(1):49-56. PMID:4149588 (Link to Abstract)

Question Authors:

Patrick O'Donnell MD/PhD, Ben Taylor MD, Michael Hughes MD,

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Cases

http://upload.orthobullets.com/cases/1332/bone cyst.jpg

http://upload.orthobullets.com/cases/1332/bon cyst23.jpg

bone cyst (C1332)

Pathology - Treatment Consult - Unicameral Bone Cyst

HPI - Incidental finding on xray a day ago,done by GP

observation or intervention.role of mri to do or not

11/24/2012

115 responses

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Groups

ABOS II: Unicameral Bone Cyst

General - Oral Boards Review

7/29/2011

0 responses

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Evidence & References Show References

Level of Evidence 4 (Case Series)

Rougraff BT, Kling TJ. Treatment of active unicameral bone cysts with percutaneous injection of demineralized bone matrix and autogenous bone marrow. J Bone Joint Surg Am. 2002 Jun;84-A(6):921-9. PMID:12063325 (Link to Abstract)
Roposch A, Saraph V, Linhart WE. Flexible intramedullary nailing for the treatment of unicameral bone cysts in long bones. J Bone Joint Surg Am. 2000 Oct;82-A(10):1447-53. PMID:11057473 (Link to Abstract)
Canavese F, Wright JG, Cole WG, Hopyan S. Unicameral bone cysts: comparison of percutaneous curettage, steroid, and autologous bone marrow injections. J Pediatr Orthop. 2011 Jan-Feb;31(1):50-5. PMID:21150732 (Link to Abstract)
Sung AD, Anderson ME, Zurakowski D, Hornicek FJ, Gebhardt MC.Unicameral bone cyst: a retrospective study of three surgical treatmentsClin Orthop Relat Res. 2008 Oct;466(10):2519-26 PMID:18679761 (Link to Abstract)
Margau R, Babyn P, Cole W, Smith C, Lee F. MR imaging of simple bone cysts in children: not so simple. Pediatr Radiol. 2000 Aug;30(8):551-7. PMID:10993540 (Link to Abstract)
Smith RW, Smith CF. Solitary unicameral bone cyst of the calcaneus. A review of twenty cases. JBJS Am 1974, Jan;56(1):49-56. PMID:4149588 (Link to Abstract)

Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions, Personal Observations, and Biomechanic Studies)

Dormans JP, Pill SG. Fractures through bone cysts: unicameral bone cysts, aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas. Instr Course Lect. 2002;51:457-67. Review. PMID:12064135 (Link to Abstract)
Wilkins RM. Unicameral bone cysts. J Am Acad Orthop Surg. 2000 Jul-Aug;8(4):217-24. Review. PMID:10951110 (Link to Abstract)
Betsy M, Kupersmith LM, Springfield DS. Metaphyseal fibrous defects. J Am Acad Orthop Surg. 2004 Mar-Apr;12(2):89-95. Review. PMID:15089082 (Link to Abstract)
Ortiz EJ, Isler MH, Navia JE, Canosa R. Pathologic fractures in children. Clin Orthop Relat Res. 2005 Mar;(432):116-26. PMID:15738811 (Link to Abstract)

Textbooks

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Dormons JP, Flynn JM: Pathologic fractures associated with tumors and unique conditions of the musculoskeletal system, in Beaty JH, Kasser JR (eds): Rockwood & Wilkins Fractures in Children, ed 5. Philadelphia, PA, Lippincott Williams & Wilkins, 2001, pp 142-168
Dormans JP, Flynn JM: Pathologic fractures associated with tumors and unique conditions of the musculoskeletal system. In Bucholz RW, Heckman JD, Beaty JH, Kasser JR (eds): Rockwood, Green and Wilkin’s Fractures. Ed 5. Philadelphia, Lippincott Williams & Wilkins 139-240, 2001

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Unicameral Bone Cyst

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