Leiomyomas are the most common myometrially-based benign tumors of the uterus occurring in 20% -40% of reproductive-age women and 70—80% of perimenopausal women while uterine sarcomas are rare malignant tumors.
Both types of tumors originate from smooth muscle (1).
Leiomyosarcomas (LMS), which represent <1% of uterine malignancies.
Uterine sarcomas constitute a group of cancers, and among them, leiomyosarcomas account for approximately 70% of cases, making them a major contributor to uterine cancer deaths (2).
Uterine sarcomas and leiomyomas share similar clinical presentations, which involve an increase in uterine size, abdominal pain, and vaginal bleeding; thus, cannot reliably be distinguished clinically (3).
Therefore, preoperative radiological differentiation is of paramount importance since uterine sarcomas should be diagnosed early and surgically removed with R0 resection, whereas conservative or minimally invasive intervention is usually sufficient for leiomyomas.
The distinction of leiomyosarcoma from the classical and the variant leiomyoma types (i.e., atypical imaging features) could be challenging.
On MR imaging, benign leiomyomas may present with varying appearances, including cystic or hemorrhagic degeneration or a highly cellular appearance.
The imaging features vary greatly, which in turn makes it quite challenging to distinguish and interpret them accurately.
Identifying an atypical leiomyoma as a malignant entity can result in extensive surgery with uterine loss, while a less extensive surgical procedure or a non-surgical approach may have been a viable option.
On the other hand, disregarding a potential sarcoma may cause a delay in diagnosis and inappropriate management, resulting in catastrophic consequences.
Due to the aggressive nature of these lesions to metastasize, there is a possibility of missing the opportunity for intervention at the time of uterine-limited disease.
In this educational poster, we aim to review the MR imaging spectrum of uterine leiomyosarcomas and atypical leiomyomas with emphasis on pearls and pitfalls in the distinction.
MR imaging of leiomyomas versus leiomyosarcoma The most effective imaging modality for evaluating the imaging features and differentiating leiomyomas from leiomyosarcomas is magnetic resonance imaging (MRI).
This is attributed to its ability to assess the signal intensity of soft tissues, which is especially useful for the diagnosis of fibroids that exhibit a characteristic appearance of a homogeneous, whorled, low T2 signal intensity lesion.
Indeed, such features have a very high negative predictive value for benign fibroids.
Characteristically, uterine leiomyomas appear as well-defined masses of variable size on magnetic resonance imaging, which can either present as single or multiple lesions, with low signal intensities detected on both T1-weighted images (T1-WI) and T2-weighted images (T2-WI) (Fig. 1) (4).
However, besides degeneration and edematous appearances, various spectrum of signal intensities may be seen in atypical leiomyomas.
Hyaline, cystic, myxoid, and hemorrhagic degeneration may occur in leiomyomas which are easily diagnosed on MRI.
Hyaline degeneration is the most prevalent type of degeneration, detected in up to 60% of leiomyomas.
On MRI, the appearance of hyaline-degenerated leiomyomas is usually comparable to non-degenerated fibroids.
Hyaline necrosis may at times present as scattered, thin, and ill-defined high T2WI signal intensity areas throughout the tumor.
Hyalinization leads to the reduction of extracellular space, thereby causing a decrease in the enhancement on dynamic contrast-enhanced MR scans (5).
Signal voids on MRI may indicate the presence of calcification (Fig. 2) (6).
The presence of cystic components of variable number and size within the leiomyomas is a characteristic of cystic degeneration.
This occurs due to extreme hyaline necrosis, resulting in liquefaction.
They are represented on MR imaging as well-defined internal areas exhibiting homogeneous fluid-like signal intensity and no enhancement after contrast administration (Fig 3) (5).
Myxoid degeneration is typically characterized by low or iso T1 signal intensity and markedly increased heterogeneous T2 signal intensity, and it may feature a characteristic laminated pattern either in T2WI or contrast-enhanced images (Fig 4) (7).
Hemorrhagic degeneration, also known as red or cavernous degeneration, is a result of coagulative necrosis caused by an acute obstruction of blood supply and tumor infarction.
Pregnancy and administration of oral contraceptives are factors associated with this condition.
Signs and symptoms may manifest as persistent acute abdominal pain, fever, and leukocytosis (5).
The high T1 signal intensity of red degenerated leiomyomas is usually due to the paramagnetic effect of methemoglobin.
Moreover, their T2 signal intensity changes with the progression of hemoglobin degradation through the natural aging process of blood (8).
The absence of enhancement may occur due to complete loss of blood flow to the affected component (Fig. 5) (9).
Lipoleiomyoma represents a rare form of leiomyoma that contains mature macroscopic fat.
The presence of high T1 signal intensity within the leiomyoma, which is suppressed on fat-suppressed sequences, is a characteristic feature (Fig. 6).
CT imaging can display fat attenuation (Fig.7) (10).
Cellular leiomyoma is a type of leiomyoma variant characterized by low T1 signal intensity, intermediate-to-high T2 signal intensity, and variable enhancement.
The hypercellularity of cellular leiomyoma is responsible for markedly restricted diffusion, which can be misleading and cause suspicion of malignancy (Fig. 8) (7).
On the other hand, leiomyosarcoma usually has some worrisome features such as irregular borders, areas of intralesional hemorrhage, necrosis, T2 dark areas, and early central enhancement in the soft tissue part of the tumor (Fig. 9).
Irregularly shaped or poorly defined tumor-myometrium interphase is a significant suspicious characteristic that occurs frequently in sarcomas.
Heterogeneous enhancement is typical for myometrially-based uterine sarcomas with central areas lacking contrast enhancement due to necrosis.
Extrauterine spread may occur in certain cases, which may include the presence of ascites and peritoneal deposits. (11).
Degenerating leiomyomas manifest areas without enhancement that are consistent with the locations of degeneration.
Therefore, it is paramount to compare the signal intensity in these areas to the standard T1-WI and T2-WI to distinguish areas with hyaline, cystic, or red cell degeneration that demonstrate typical signal intensities.
Moreover, it should be noted that uterine sarcomas exhibit distinct enhancement features when compared to leiomyomas.
Specifically, sarcomas present higher mean contrast enhancement and early enhancement ratios as opposed to leiomyomas (12).
Intralesional hemorrhage is highly sensitive and specific for LMS.
The identification of blood products within the lesion is hence a valuable aid in distinguishing sarcoma from fibroids and is an unusual finding in the latter (11).
Low signal intensity and dark areas may be observed in LMS due to flow voids or intralesional hemosiderin.
It is important to note that these characteristics are distinct from the regular low T2 signal observed in benign leiomyomas and, it would be useful to take into account their correlation with T1WI and enhancement pattern (11).
Besides, endometrial involvement is common in sarcomas, affecting up to half of cases and leading to endometrial stripe loss or irregularity (13).
In addition, sarcomas display high DWI signal intensity surpassing that of the endometrium and low ADC values (11).