Unusual appearances of uterine leiomyomas: MR imaging findings and their histopathologic backgrounds

Typical appearances of uterine leiomyoma at magnetic resonance (MR) imaging are well established, and diagnosis is usually easy. However, cases that a re extremely difficult to differentiate from other conditions are occasiona lly encountered. To understand the wide spectrum of MR imaging findings, su ch unusual appearances can be classified into three categories: degeneratio n and other histopathologic findings, specific types of unusual leiomyomas, and unusual growth patterns. The common types of degeneration are hyaline (>60% of cases), cystic (similar to 4%), myxoid, and red. Edema is not a ph enomenon of degeneration but is a common histopathologic finding (similar t o 50% of cases). Hemorrhage, necrosis, and calcification (similar to 4% of cases) may also be observed. Specific types of unusual leiomyomas include l ipoleiomyoma and myxoid leiomyoma, which may have MR imaging features chara cteristic enough to allow differentiation from other gynecologic and nongyn ecologic diseases. Intravenous leiomyomatosis, metastasizing leiomyoma, dif fuse leiomyomatosis, and peritoneal disseminated leiomyomatosis represent u nusual growth patterns; other unusual growth patterns are retroperitoneal g rowth, parasitic growth, and the pattern that may occur in cervical leiomyo ma. Because leiomyomas are the most common gynecologic tumors and are exclu sively benign, it is important to be familiar with the variety of MR imagin g appearances of uterine leiomyomas to distinguish them from other signific ant diseases.