Age / Sex : 54 / F

Chief complaint : incidental finding on hip CT

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : So Young Park, Kyung Hee University Hospital at Gangdong

Discussion

Answer:  accessory sacroiliac joint (bilateral)

Findings:

Anteroposterior radiograph of the hip shows a calcified lesion adjacent to greater trochanter of right femur. Focal sclerosis is noted in the sacral side of the right sacroiliac joint.

Axial reformatted CT images of the hip show sclerosis and partial ankylosis at the posterosuperior portion of the right sacroiliac joint and osteophytes at the posterosuperior portion of the left sacroiliac joint.

Differential Diagnosis:

axial spondyloarthritis

infectious sacroiliitis

Discussion:

An accessory sacroiliac joint is the most common variant in the sacroiliac joints. The accessory sacroiliac joints are more commonly acquired fibrocartilaginous joints, increasing in prevalence with aging. It is located at the posterosuperior portion of the joint and may develop degenerative changes, thereby causing low back pain.

The articular facets on the sacrum are usually situated on the posterior surface just lateral to the second sacral foramen. The articular facets on the ilium are often situated at the medial surface of the posterior superior iliac spine, or less commonly as small osseous projections at the tuberosity of the ilium.

Familiarity with the accessory sacroiliac joint is important for correctly interpreting findings and avoiding misdiagnosis.

References:

1. Sacroiliitis Associated with Axial Spondyloarthropathy: New Concepts and Latest Trends. RadioGraphics 2013; 33:933–956


2. The Accessory Sacroiliac Joint: A Common Anatomic Variant. AJR 1988; 150:857-859