What is ITOH?
This uncommon self-limited disease, also referred to as transient painful bone marrow edema, primarily affects middle-aged men as well as women in the third trimester of pregnancy. It is usually unilateral, resolves spontaneously in 6 to 8 months, and may recur in the same hip. Although the exact etiology is unknown, vascular causes, hormonal changes, and stress or insufficiency microfractures have been implicated. Patients typically present with severe hip pain without a history of trauma.
What are the imaging features of ITOH?
Radiographs are initially negative and may demonstrate osteopenia of the affected hip 3 to 6 weeks after the onset of pain, but MRI can demonstrate bone marrow edema as early as 48 hours after the onset of pain. Since the MRI appearance is similar to early AVN, it is important to make a correct diagnosis or at least to include ITOH in the differential diagnosis in order to institute appropriate conservative treatment.
Erroneous treatment for early AVN, such as core decompression, can increase the risk of fracture. Some more specific MRI signs that may help distinguish ITOH from other diseases are marrow sparing in the medial and lateral-most femoral head and greater trochanter, homogeneous well-marginated hyperintensity on fluid-sensitive sequences, signal intensity abnormalities extending from the femoral head to the intertrochanteric line, and a small to moderate associated hip joint effusion.
If intravenous contrast material is administered, there is prominent heterogeneous enhancement in the affected bone. MRI findings follow the clinical course and resolve with successful treatment.