Uterine leiomyomas, the most common solid tumor of the female genital tract, develops in 20-40% of women during their reproductive years.1 Degeneration of leiomyoma occurs secondary to a loss of blood supply and is usually attributable to rapid growth associated with pregnancy. It can cause severe pain not relieved by sedation as well as fever or leukocytosis. Degeneration of a leiomyoma is treated pain medication or surgical intervention. Uterine fibroid embolization (UFE) was established as an alternative to a hysterectomy for the treatment of symptomatic leiomyomas.2-5 However, patients with degenerated leiomyoma are more likely to have a poor response to UFE, and it is often difficult to differentiate symptoms and ultrasonographic findings in patients with degenerated leiomyoma from those in patients with non-degenerated leiomyomas.6,7 Therefore, being aware of any existing degenerated leiomyoma before performing UFE is mandatory. The aim of this study was to assess the incidence, imaging features and clinical characteristics of degenerated leiomyoma in patients who were referred for UFE.

The Institutional Review Board at Severance Hospital of Yonsei University approved this study. A retrospective analysis of 276 patients referred for UFE between 2008 and 2009 was performed. All patients underwent transvaginal or transabdominal ultrasound and uterine leiomyomas were primarily diagnosed by gynecologists. Patients ranged in age from 27 to 51 years (mean 38.0 years). The mean follow-up period was 9.7 months (range: 5-16 months).

Demographics and clinical characteristics of the patients of the patients are summarized in Table 1.

Among 276 patients who with MRI data, 14 (5.1%) showed degenerated leiomyomas. The size of the degenerated leiomyomas ranged from 5.2 cm to 15.5 cm (mean 7.7 cm). Nine patients had leiomyomas less than 8 cm in size while only three patients had leiomyomas larger than 10 cm.

The process of leiomyoma degeneration usually begins when the leiomyoma grows so large that the nearby blood vessels can no longer supply it with oxygen and nutrients. Degeneration of the leiomyoma results in a variable and often heterogeneous appearance, with minimal or irregular enhancement. Degeneration is categorized as hyaline, cystic, red or calcific. The most common type of degeneration is hyaline; it accounts for approximately 60% of all degeneration and produces a low SI on T2WI, without contrast enhancement.9,10 Cystic degeneration occurs in approximately 4% of leiomyomas and typically occurs after hyaline degeneration.10

Red degeneration is a hemorrhagic infarction of the uterine leiomyoma, which is a well known complication, especially during pregnancy. Red degeneration occurs in 8% of tumors complicating pregnancy, although the prevalence is about 3% of all uterine leiomyoma.11 Our data indicated that about 42.9% of patients had been pregnant in the previous two years. The mechanism of red degeneration is suggested to begin with venous obstruction at the periphery of the lesion, which induces hemorrhagic infarction and extensive necrosis that involves the entire lesion.

As leiomyoma enlarge, they may outgrow their blood supply, resulting in degeneration, thus degeneration occurs primarily in large leiomyomas. However, our study demonstrated that the majority of patients in whom degeneration was found had leiomyomas less than 8 cm in size; it was even detected in leiomyomas as small as 5.2 cm. One possible explanation seems to come from the widespread use of MRI, which allows an early, precise diagnosis of degenerated leiomyomas.

Pain is the most frequent sign of uterine leiomyoma degeneration. Pain is often severe and localized to the site of the leiomyoma. Severe pain associated with leiomyoma degeneration often lasts for two to four weeks. In addition to pelvic pain, degeneration may cause a low-grade fever and a temporary elevation in the white blood cell count. In some cases, a degenerating uterine leiomyoma may cause menorrhagia, which can also result in a drop in hemoglobin levels. Symptoms of patients with degenerated leiomyomas in our data were abdominal pain including acute onset of pain, menorrhagia, and bulk-related symptoms. These symptoms are similar to those of non-degenerated leiomyomas except acute onset of abdominal pain, which is unusual. A degenerating uterine leiomyoma is often misdiagnosed, frequently being confused with subacute salpingo-oophoritis. A pedunculated subserosal leiomyoma can undergo torsion ischemic necrosis, which is associated with pain similar to that of adnexal torsion.

Degenerating leiomyoma have various nonspecific MRI appearances ranging from medium to high SI on T1WI to a heterogeneous, mostly high SI in the area of degeneration on T2WI.9,12,13 Kawakami, et al.11 reported that red degeneration of uterine leiomyoma had a hyperintense rim on T1WI and a hypointense rim on T2WI. Microscopic examination revealed numerous dilated thrombosed vessels filled with red blood cells at the periphery and these red blood cells in the thrombosed vessels have abundant levels of intracellular methemoglobin, which is known to appear as a hyperintense signal on T1WI and a hypointense signal on T2WI.

The incidence of degeneration of leiomyoma in patients referred for UFE in our study was 5.1%, with the majority of them having undergone conservative treatment. Most patients were initially recommended to undergo surgery after consultation with gynecologists, but these patients wanted a minimally invasive surgery to preserve their uteri. Rest and sedation are recommended in most cases. The pain of red degeneration usually resolves within ten days and supportive treatment is required for this period only. Follow-up ultrasounds or MRIs in our data demonstrated spontaneous reductions in size of the leiomyoma with concurrent improvement of symptoms. Meanwhile, surgery may be needed in some patients with intractable pain. One patient in our study elected to undergo myomectomy for severe pain not controlled with medication, which lasted more than one week. Degenerated leiomyomas are known for their contraindication for UFE due to the likely poor response, as they may already have undergone hemorrhagic necrosis. However, a patient in our study underwent uterine artery embolization for bleeding because of concurrent adenomyosis. The patient's symptoms were significantly improved after embolization, but the volume of the degenerated leiomyoma demonstrated little change.

A limitation of the present study was the relatively small number of patients; therefore, and further studies are needed with larger study populations.

In summary, the incidence of degeneration of leiomyoma in patients referred for UFE was 5.1%. Patients presented with variable clinical symptoms with or without a history of pregnancy. MR imaging showed a high SI on T1WI and various SIs on T2WI without contrast enhancement. The majority of patients can be managed using conservative treatments; however, surgery or uterine artery embolization may be required in some patients. An understanding of the incidence and imaging features and clinical characteristics of the degeneration of leiomyoma is essential when considering UFE.