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Checkmark: A sign for the detection of iliopsoas pathology on MRI of the hip

Background: The iliopsoas compartment can be involved in many different disease processes with a wide variety of symptoms that may simulate avascular necrosis (AVN) of the femoral head. The psoas muscle merges with the iliacus to form a checkmark (√) shape in the coronal MRI plane, with normal muscle intensities, on both sides of the spine. Purpose: To evaluate whether abnormality of this checkmark shape (obliteration or abnormal intensity), the checkmark sign, can be used as a simple indicator of iliopsoas pathologies on MR examinations performed for suspected AVN of the hip. Material and Methods: A total of 75 hip MRI examinations performed during 2007 for suspected AVN (male:female ratio, 44:31; average age, 41 years) were retrospectively assessed. The iliopsoas compartment was assessed on the coronal T1 and T2 fat saturated sequences for the presence of the checkmark sign by a consensus of two readers. Results: Twenty-six patients had signs of AVN and 49 patients had either other hip findings or normal hips. A normal checkmark shape was observed in all but two examinations. Obliteration of the checkmark shape, a positive checkmark sign, in those two was due to psoas compartment pathology (infection and hematoma of the iliopsoas compartment). Conclusion: A positive checkmark sign (abnormal shape or intensity) can serve as a clue for unsuspected iliopsoas pathology when evaluating MRI of the hip in patients with suspected AVN.