Geode (or subchondral cyst) is a well-defined lytic lesion in the periarticular surfaces. A geode is one of the common differential diagnoses of an epiphyseal lesions (lytic). This is originally a geological term referring to rounded formations in igneous and sedimentary rocks.

Pathology

Presumably, one method of geode formation takes place when synovial fluid is forced into the subchondral bone, causing a cystic collection of joint fluid. Another aetiology is following a bone contusion, in which the contused bone forms a cyst.  

Associations

Geodes are seen in a variety of disorders including:

Treatment and prognosis

They rarely cause problems by themselves but are often misdiagnosed as something more sinister and an unnecessary biopsy of a geode might be performed on the basis of the differential of an epiphyseal lesion.

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Article Information

rID: 21095
Section: Pathology
Tags: geode, cases
Synonyms or Alternate Spellings:
  • Geodes
  • Subchondral cyst
  • Subchondral cysts
  • Geode formation

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Cases and Figures

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    Case 1
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    Case 2: on knee MRI
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