Metal-on-metal pseudotumor

Case contributed by Jan Frank Gerstenmaier


Status post bilateral total hip replacement, currently right hip pain and restricted range of movement.

Patient Data

Age: 65 years
Gender: Male

Bilateral bipolar hip replacements in satisfactory postiion without evidence of stem loosening or failure on either side. No acute fracture or dislocation. Old right pubic rami fractures.


B-mode ultrasound demonstrates a large (10 cm) heterogeneous mass around the right THR. There is no internal color Doppler signal.

There is a small (<2 cm) fluid collection at the level of the acetabulum. 

No abnormality was seen at the left hip.

MARS (metal artifact reduction sequence)


An attempt was made to obtain post-contrast images, however, the patient was extremely claustrophobic and as a result these images were not obtained.

There is marked, lobular mass-like thickening of the synovium of the right hip.  Corresponding to the ultrasonographic findings, this extends over approximately 11 cm in the craniocaudal direction and approximately 7 cm in transverse diameter.  The synovium measures up to 1.8 cm in thickness.  It is predominantly of intermediate signal intensity on T1 and T2-weighted imaging, while its inner margin is of extremely low signal on all of the sequences.  A small amount of fluid remains in the synovial cavity.  

There is also a 1.8 x 1.2 cm fluid collection lateral to the hip, at the level of the acetabulum, as demonstrated on ultrasound.  There is complete fatty atrophy of the adductor muscles. The known right superior pubic ramus fracture is obscured by artifact from the cobalt acetabular component of the prosthesis. 

Incidental note is made of the presence of moderate sigmoid diverticulosis and of bilateral S2 Tarlov cysts.

Case Discussion

MR and US confirm the presence of a pseudotumor secondary to extensive, mass-like thickening of the synovium of the right hip.  The low signal returned from the deep aspect of the synovium is consistent with synovial metallosis.

A MARS (metal artifact reduction sequence) may be necessary to make the abnormality visible in cases of smaller pseudotumors.

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