Suzanne Denise LeBlang MD, Presenter: Nothing to Disclose

To determine the incidence and predisposing factors of anterior pelvic wall subcutaneous fat and muscle necrosis after MRgFUS treatment of uterine fibroids.

 118 MRgFUS procedures were performed from October 2004 through March 2008, and retrospectively evaluated to determine the incidence of anterior abdominal wall fat and muscle necrosis. The diagnosis was confirmed on the post contrast T1 fat saturation images obtained immediately after the MRgFUS procedure as evidenced by focal stranding and enhancement of the anterior pelvic wall subcutaneous fat and abnormal signal in the rectus muscle with peripheral enhancement and central hypoenhancing components. The T2 planning images for the procedure were evaluated and the anterior-posterior dimension of the subcutaneous fat at the level of the mid pelvis was measured. The images were also evaluated for the presence of subcutaneous scars, clacifications, or bowel loops anterior to the uterus.

5/118 (4%) patients experienced subcutaneous fat and/or muscle necrosis.  The average anterior-posterior width of these 5 patients' subcutaneous fat in the mid pelvis was 3.2 cm (ranging from 2.5 cm to 4.5cm) whereas the average dimension in the other 113 patients was 1.7 cm (ranging from 5mm to 2.5cm) (p<.001). After MRgFUS, the 5 patients with fat necrosis received an average non perfused fibroid volume of 30% versus the other 113 patients that received a non perfused volume of 55% (p<.005).  None of the T2 planning images revealed any scars, calcifications, or bowel loops along the beam path that could have resulted in reflection of the beam path causing heating in the near field. 

Patients with prominent pelvic abdominal wall subcutaneous fat measuring at least 2.5 cm in anterior-posterior diameter are at a higher risk of developing fat and/or muscle necrosis during MRgFUS treatments. As this occurs, there is less heat deposition in the fibroid that can result in a less than satisfactory non perfused volume and decrease the efficacy of the procedure. 

Prominent pelvic abdominal wall fat predisposes to fat and/or muscle necrosis during MRgFUS and may hinder the success of the ablation procedure.

LeBlang, S, The Incidence of Anterior Subcutaneous Pelvic Fat and Muscle Necrosis after MR Guided Focused Ultrasound (MrgFUS) Ablation of Uterine Fibroids.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6021397.html