Half-moon sign (femoral neck)

Last revised by Dr Henry Knipe on 13 Jul 2022

The half-moon sign describes the morphology of bone marrow edema at the femoral neck on fluid-sensitive MRI sequences, which can be seen in osteoid osteoma or stress fractures 1-3

Differential diagnosis

  • intra-articular osteoid osteoma
    • in patients without history of overuse it is highly specific and sensitive for the diagnosis of osteoid osteoma 1-3
    • identification of the sign on MRI should prompt CT examination for the identification of a nidus 1
  • stress reaction/fracture of the femoral neck in cases with a history of lower limb overuse (e.g. athletes, armed forces member) 4,5

ADVERTISEMENT: Supporters see fewer/no ads

Updating… Please wait.

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

 Thank you for updating your details.