Transient osteoporosis is a rare condition in which a bone becomes temporarily thinned. Those most commonly affected are women during late pregnancy and middle-aged men.

Transient osteoporosis can occur after trauma. However, most often a specific cause cannot be identified. Treatment is conservative and includes pain relievers and staying off your feet. Your doctor will advise you on how to gradually increase weight bearing on the affected leg.

No other treatment is known to be effective, although some doctors recommend osteoporosis drugs (such as calcitonin or alendronate) or surgery (a procedure called core decompression). The overall success of these is uncertain.

Transient osteoporosis goes away on its own within three to 18 months. However, stress fractures can complicate this condition if the joint is not protected from full weight bearing.

I think it's important that the radiologist thought you "might" have transient osteoporosis. Since it's so rare, it's possible that this is not the cause of your hip pain. Tendonitis, bursitis, a cartilage injury or a muscle injury -- which may be related to inadequate rest between runs -- are more common causes of hip pain among long-distance runners.

If you have transient osteoporosis, a regular X-ray of the hip should show osteopenia (reduced bone density) in the femoral head. Repeat MRIs over several months (or a bone scan) can be helpful to verify the diagnosis.

"Bone marrow edema" is a common MRI finding. Trauma (such as a "bone bruise") could cause similar MRI findings. It's possible that long-distance running could cause MRI abnormalities. However, a small study published in 2004 found that MRIs performed before and after running a marathon showed no abnormalities.

I'd recommend reviewing the results of your MRI and any other tests you've had with your doctors to determine the likelihood of your having transient osteoporosis. Then you can decide on a treatment plan, including how long to rest the hip.