Age / Sex : 65 / F

Chief complaint: buttock swelling, left

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한개만 보내주시기 바라오며, 복수의 답안을 보내주시는 분은 정답이 포함되어 있더라도 부득이 semi-correct answer로 처리토록 하겠습니다.)

Courtesy:  황지영(Ji Young Hwang), 이화여대목동병원(Ewha Womans University School of Medicine Mokdong Hospital)

Ischial bursitis

Discussion

Findings: A well-defined soft tissue mass is located in posteroinferior aspect of left ischial tuberosity, compressing gluteus maximus muscle. The mass is lobulated and septated with thin septa. The signal intensity of the mass is low on T1WI and high on T2WI, and multiple fluid–fluid levels are seen within the mass. A small mural nodule which signal intensity is intermediate on both T1WI and T2WI is seen. After contrast enhancement, the wall of cystic mass and small mural nodule is enhanced. The common hamstring tendon is located lateral to the cystic mass.

Differential Diagnosis:  1. hematoma

2. epidermoid cyst

3. buttock abscess

Diagnosis:  Ischial bursitis

Discussion:

Inflammation of the ischial bursa (or ischiogluteal bursa) has been known to be common in people whose occupations are related with frequent irritation to the bursa, and this irritation can occur during long periods of time spent in the sitting position. When vibration is involved in working, such as with heavy powered sewing machine (weavers), tractor driving or road equipment machines or in debilitated persons, particularly for those patients with malignancies or paraplegia, the ischial bursa can become inflamed.

MRI and/or ultrasound is the first choice of modality. Ischial bursitis can be diagnosed with MRI, CT, and ultrasound by the characteristic anatomical location abutting to the medial aspect of the inferoposterior surface of the ischial tuberosity, and by its cystic appearance with a tendency for an intra-bursal blood-fluid level. The internal signal intensity of ischial bursitis is usually brighter than that of other bursitis observed elsewhere. The reason for this high signal intensity on the T1-weighted image of this affected bursal sac is due probably to the internal hemorrhage caused by the shearing force applied to the ischial tuberosisty area when sitting, and this hemorrhage is aggravated by frequent irritation. The heterogeneity on the T2-weighted and contrast studies is probably related to bleeding, synovial proliferation and the internal septation within the bursa. The wall and mural nodules of the bursa were enhanced after the intravenous administration of the contrast materials.

The typical location of ischial bursitis might be a very important diagnostic criterion for separating bursitis from the other cystic masses. The common hamstring tendon is typically located lateral to the inflamed ischial bursa.

References:

1. Kim SM, Shin MJ, Kim KS, Ahn JM, Cho KH, Chang JS, Lee SH, Chhem RK. Imaging features of ischial bursitis with an emphasis on ultrasonography. Skeletal Radiol 2002:31;631–636.

2. Cho KH, Lee SM, Lee YH, Suh KJ, Kim SM, Shin MJ, Jang HW. Non-infectious ischiogluteal bursitis: MRI findings. Korean J Radiol 2004;5:280-286.