As uterine artery embolization (UAE) gains ground as a mainstream treatment option, imaging specialists are staying one step ahead by investigating ways to assess post-UAE patients. Researchers have successfully turned to MRI to keep track of both UAE and uterine fibroid embolization (UFE) results up to six months after the procedure.
A group from Johns Hopkins Medical Institutes in Baltimore used echo-planar diffusion-weighted MR, along with apparent diffusion coefficient maps (ADC), to measure the response of fibroids to UFE. They found the modality was best suited for fibroids larger than 1 cm.
Guiding patient management
Diffusion-weighted echo-planar MRI was chosen by the Johns Hopkins team because of its ability to detect fibroid size reduction and enhancement treatment, said Dr. Ihab Kamel during a presentation at the 2003 RSNA conference in Chicago.
"Diffusion-weighted MR is based on the microscopic motion of water molecules. Therefore it detects membranous disruption and cellular permeability," he explained.
The inclusion criteria for this study were the diagnosis of uterine fibroids, treatment with UFE, and diffusion-weighted echo-planar MR results prior to, and six months after, UFE. The study population was made up of 32 lesions in 11 women (mean age 41).
Patients were scanned in a 1.5-tesla unit (Signa Horizon, GE Medical Systems, Waukesha, WI) with a phased-array torso coil. The protocol included T2-weighted FSE images, breathhold diffusion-weighted echo-planar images, as well as contrast-enhanced and non-contrast T1-weighted, fat-suppressed GRE images. The latter was done in the arterial (20 seconds) and venous (60 seconds) phases.
The ADC maps were generated from the diffusion-weighted images and included tumor size and degree of enhancement on the venous phase pre- and post-treatment. Statistical significance was set at p<0.05.
"Our embolization technique included selective catheterization of both internal iliac arteries and both uterine arteries," Kamel said. The mean duration between UFE and follow-up MR was six months.
According to the results, the mean tumor size before UFE was 5 cm. It decreased by 1 cm after UFE (p=0.018). The mean tumor enhancement was 82% before treatment, dropping to 11% after UFE (p<0.01).
On pre-treatment MR images, 28 fibroids had a decreased signal, while one had an increased signal relative to muscle, and three had an isointense signal. However, post-treatment, all 32 fibroids showed a decreased signal on post-treatment diffusion-weighted images. Finally, before treatment, the mean ADC value of fibroids was 1.74 E-3 mm2/sec, which decreased to 1.22 E-3 mm2/sec after treatment.
The group surmised that these types of MR and ADC maps could be used to predict fibroid necrosis. Even six months later, successfully treated lesions exhibited decreased signal strength and lower ADC values compared with untreated lesions. "These findings can be used to guide further management," Kamel concluded.
Kamel acknowledged that, for the moment, his patient population was still too small to make definitive statements about how the pre- and post-MR results might specifically impact patient symptoms and any subsequent pain management options.
However, the imaging protocol for UFE candidates at Hopkins now routinely includes diffusion-weighted MR imaging, Kamel wrote in an e-mail to AuntMinnie.com. "Diffusion gives us a better idea of tumor response at the cellular and molecular levels, as we have demonstrated in the liver with pathologic confirmation of the degree of tumor necrosis after TACE," he wrote, referring to another paper that he co-authored in the American Journal of Roentgenology (September 2003, Vol.181:3, pp. 708-710).
MR results and clinical outcome
U.K. researchers have also experienced success in using MRI to monitor UFE. In a 2002 paper, Dr. Nandita deSouza and Andreanna Williams set out to document "immediate or late changes in perfusion of the leiomyoma compared with the surrounding uterine muscle," they wrote in Radiology.
In the 11 consecutive patients who underwent bilateral UAE, MRI was used to monitor changes in uterine and leiomyoma perfusion and volume immediately after UAE as well as one and four months later.
One patient underwent imaging on a 1.5-tesla Eclipse system with a body coil; the remaining patients were scanned on a 0.5-tesla Apollo system with a pelvic phased-array coil (Marconi Medical Systems, now Philips Medical Systems, Andover, MA).
Embolization was performed with a femoral approach using a 5-French cobra catheter. Imaging was done before UAE and within 30 minutes after the procedure, then again at one month and four months. The imaging protocol included coronal and sagittal T1-weighted spin-echo sequences, obtained with and without contrast, as well as sagittal T1-weighted FSE sequences.
"Reduction in maximal enhancement above baseline at 90 seconds (ME90) after injection of the dominant leiomyoma immediately after embolization was correlated with its volume reduction at four months and with clinical response at 12 months," the authors explained (Radiology, February 2002, Vol. 222:2, pp. 367-374).
The final analysis included 45 leiomyomas, ranging in volume from 0.6 to 434 cm3. The authors reported the brisk enhancement of the myometrium (ME90 of 110%) before the procedure and an ME90 reduction to 26% immediately after UAE.
"After one and four months, perfusion of the myometrium recovered to normal levels, while leiomyoma perfusion remained extremely poor," they said. "Immediately following embolization, there was a 6% reduction in volume of the dominant leiomyoma. After one and four months, dominant leiomyoma volume was further reduced from the preprocedural values by 22.3% and 36.7%, respectively."
Immediately following UAE, an increase in signal intensity (SI) was seen within leiomyomas on T1-weighted images, the group said. However, at one and four months, there was a reduction in SI on T2-weighted images in 43 out of 45 cases. Also, leiomyomas that were initially high in signal intensity (SI) on T2-weighted images demonstrated a significantly greater volume reduction than those low in SI.
Based on the results of a patient questionnaire, a satisfactory clinical response was achieved post-UAE, with only one patient stating that she had no improvement in symptoms, such as menorrhagia. Williams and deSouza concluded that "dynamic MR imaging may be used to predict clinical response, while SI on T2-weighted images predicts volume reduction."
By Shalmali PalAuntMinnie.com staff writer
January 21, 2004
Related Reading
Focused ultrasound treatment of uterine leiomyomas is safe and effective, August 5, 2003
Adenomyosis made clear on ultrasound, July 18, 2003
Uterine fibroid embolization does not impair fertility, April 1, 2003
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