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 lesion (lytic).

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

Geodes are seen in a variety of disorders including:

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.

Geode is a term borrowed from geology, where it refers to rounded formations in igneous and sedimentary rocks.

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Article information

rID: 21095
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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