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.


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.  


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.

Share article

Article information

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

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Case 1
    Drag here to reorder.
  • Drag
    Case 2: on knee MRI
    Drag here to reorder.
  • Updating… Please wait.

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.