Focal myositis of the iliopsoas muscle--a benign pseudotumour: ultrasound appearance in correlation with CT and MRI.

ABSTRACT

OBJECTIVE: Focal myositis of the iliopsoas muscle is a rare condition. A case is presented, emphasizing the value of ultrasound for detection, localisation, image-guided biopsy and follow-up in correlation with CT and MRI findings. MATERIAL AND METHODS: A 58-year-old woman was referred to our clinic with strong left sided inguinal pain, which radiated to the thigh and had lasted for four days. Ultrasound, CT and MRI were performed. Ultrasound-guided biopsy with histological correlation was obtained and US-follow-ups were available. RESULTS: CT showed an enlarged iliopsoas muscle on the left side without any focal pathology or enhancement. MRI revealed a sharpely delineated lesion, which was hypointense to muscle in fat-suppressed T1 w images with circumferential enhancement and showed a hyperintense appearance in T2 w images. Ultrasound displayed a polylobulated, inhomogeneous and hypoechoic tumour within the iliopsoas muscle. Ultrasound-guided biopsy was found to be compatible with myositis. After oral therapy with steroids, improvement could be documented by serial ultrasound follow-up as the size of the tumour was definitely regressing. CONCLUSION: Focal myositis of the iliopsoas muscle is a rare entity which may mimic a tumoural lesion. Imaging findings may not be conclusive, and US-guided biopsy is recommended to rule out a malignant mass. Ultrasound seems to be the most cost-effective method for diagnosis, image guided biopsy and follow-up.