Unicameral bone cyst

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[edit] Discussion of Unicameral bone cyst

  • AKA Simple bone cyst
  • AKA Solitary bone cyst
  • Unicameral bone cyst is a common, benign, fluid-containing lesion, usually occurring in the metaphysis of long bones.
  • The pathogenesis of unicameral bone cysts is unknown.
  • On gross examination, the cyst expands the cortex of the bone and an intact periosteum covers this thin cortical shell.
  • The cyst usually contains clear serous fluid. Occasionally, blood products may be found within the fluid if a previous fracture has occurred.
  • Fibrous septa may form after a fracture and create a multilocular appearance.
  • Half of all simple bone cysts present as pathologic fractures.
  • Unicameral bone cysts occur more frequently in boys than in girls (ratio is 2:1).
  • Most cysts occur in the first and second decades of life, with most occurring in children aged 4-10 years.
  • Location of lesion depends on patient age
    • In patients younger than 20 years, unicameral bone cysts are found in the humerus in 55-65%, in the femur in 25-30%, and rarely in the tibia, fibula, radius, and ulna.
    • In patients older than 20 years, unicameral bone cysts are found more commonly in flat bones such as the iliac bone and calcaneus.
  • Within the long bones, most unicameral bone cysts are situated in the proximal metaphysis.

[edit] Imaging Findings for Unicameral bone cyst

[edit] Radiographs

  • Well-defined, geographic lesions with narrow transition zones.
  • A thin sclerotic margin is a typical finding.
  • Usually are situated in the intramedullary metaphyseal region immediately adjacent to the physis.
  • May cause expansion of the bone with thinning of the overlying cortex.
  • A pathologic fracture through a unicameral bone cyst is a common occurrence and may lead to the "fallen fragment" sign (migration of a fragment of bone to a dependent portion of the cyst).

[edit] MRI

  • MRI can confirm the presence of fluid within a simple bone cyst.
  • Uncomplicated unicameral bone cysts have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
  • Lesions that have a pathologic fracture have heterogeneous signal intensities on both T1- and T2-weighted images because of bleeding within the cyst.

[edit] Images

Patient #1: Radiographs and MR images demonstrate a unicameral bone cyst

[edit] See Also

[edit] External Links

[edit] References for Unicameral bone cyst