Purpose:To assess the possibility of differentiating between completely hyalinized leiomyomas and ordinary leiomyomas by using diffusion-weighted (DW) magnetic resonance imaging (MRI) (DWI) employing very small bfactors (b ϭ 1.51 and 55.3 seconds/mm 2 ) in comparison with three-phase dynamic MRI.
Materials and Methods:The subjects were 25 patients with 52 histopathologically confirmed uterine leiomyomas. All leiomyomas were divided into two histopathologic subtypes (5 completely hyalinized leiomyomas and 47 ordinary leiomyomas). For each leiomyoma, the enhancement index (EI) at three-phase dynamic MRI and apparent diffusion coefficient (ADC) were obtained and then compared.
Results:The EIs at second and third dynamic phases clearly differentiated the two types of leiomyomas without overlap of values. ADCs also clearly differentiated the two types of leiomyomas without overlap of values. Moreover, there were significant positive correlations between ADCs and EIs at all dynamic phases (r ϭ 0.41-0.50, P Ͻ 0.01).
Conclusion:Not only three-phase dynamic MRI but also DWI with very small b-factors could be useful for differentiating completely hyalinized leiomyomas from ordinary leiomyomas. UTERINE LEIOMYOMA IS a common pelvic tumor with an incidence of 20% to 50% in women older than 35 years (1). The role of magnetic resonance imaging (MRI) for diagnosing uterine leiomyomas has been established (2,3).The differentiation between completely hyalinized leiomyomas and ordinary leiomyomas is very important, not only because the leiomyomas effectively treated by gonadotropin-releasing hormone (Gn-RH) analogues or uterine artery embolization (UAE) fall into hyaline degeneration (4 -7), but also because successful medical treatment with Gn-RH analogues or UAE cannot be expected for completely hyalinized leiomyomas. Completely hyalinized leiomyomas have low signal intensities on T2-weighted images, with an appearance similar to those of ordinary leiomyomas (2,3). Using a gadolinium (Gd)-based contrast agent, we can differentiate these histopathologic subtypes of leiomyomas. To our knowledge, no attempts have been made to discriminate between completely hyalinized leiomyomas and ordinary leiomyomas by MRI without using contrast media.The recent advent of the ultrafast single-shot echoplanar technique has made possible diffusion-weighted MR imaging (DWI) of the abdomen (8 -16). Several authors have reported that DWI without using a Gd-based contrast agent can differentiate between malignant tumors and benign tumors (9,12,13). To our knowledge, application of DWI has not previously been reported in uterine leiomyomas. Hyalinization is likely to result in decreasing the apparent diffusion coefficient (ADC) because of restricting tissue perfusion and diffusion.
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