Uterine leiomyomas (uterine fibroids) are benign tumours of myometrial (smooth muscle) origin and are the most common solid benign uterine neoplasm.
They occur in ~25% of women of reproductive age 1 and are particularly common in the African population.
Fibroids are responsive to hormones (e.g stimulated by oestrogens). Being rare in prepubertal females, they commonly accelerate in growth during pregnancy and involute with menopause 1.
Often asymptomatic and discovered incidentally. Signs and symptoms associated with fibroids include:
- vaginal bleeding
- palpable masses
Leiomyomas are predominantly composed of smooth muscle cells with variable amounts of fibrous connective tissue. They are benign tumours that may be solitary or multiple (majority of cases ~85% 8) and range significantly in size. They may have a number of locations within or out of the uterus:
Within the uterus
- intra-mural leiomyoma (most common)
- sub-serosal leiomyoma
- sub-mucosal leiomyoma (least common, 10-15%)
Out of the uterus: see variants below.
Subserosal fibroids may be pedunculated and predominantly extra-uterine, simulating an adnexal mass. Any fibroid may undergo atrophy, internal haemorrhage, fibrosis, and calcification.
They can also undergo several types of degeneration
- hyaline degeneration: focal or generalized hyalinization: this is the most common type of degeneration (can occur in ~60% of cases) 6, 11
- cystic degeneration: ~4% 12
- myxoid degeneration: generally considered uncommon although reported as high a 50% by some authors 17
- red - carneous degeneration: due to haemorrhagic infarction, which can occur particularly during pregnancy, and may present with acute abdominal pain
Based on location
- extra uterine pelvic leiomyomas
- diffuse uterine leiomyomatosis
Based on histology
Popcorn calcification within the pelvis may suggest the diagnosis.
- ultrasound is used to diagnose the presence and monitor the growth of fibroids
- uncomplicated leiomyomas are usually hypoechoic, but can be isooechoic, or even hyperechoic compared to normal myometrium
- calcification is seen as echogenic foci with shadowing
- cystic areas of necrosis or degeneration may be seen
- on CT images, fibroids are usually of soft tissue density but may exhibit coarse peripheral or central calcification
- they may distort the usually smooth uterine contour
- enhancement pattern is variable
MRI is not generally required for diagnosis, except for complex or problem solving cases. It is however the most accurate modality for detecting, localizing and characterising fibroids. Size, location and signal intensity should be noted.
Signal characteristics are variable, and include 1-2
- non-degenerated fibroids and calcification appear as low to intermediate signal intensity compared with the normal myometrium
- characteristic high signal intensity on T1 weighted images/an irregular, T1 hyperintense rim around a centrally located myoma suggests red degeneration, which is caused by venous thrombosis 12-13
- non-degenerated fibroids and calcification appear as low signal intensity
- as they are usually hypervascular, flow voids are often observed around them 10
- fibroids that have undergone cystic degeneration/necrosis can have a variable appearance, usually appearing high signal on T2 sequences.
- hyaline degeneration is demonstrated as low T2 signal intensity
- cystic degeneration, which is an advanced stage of intratumoral edema, also shows high signal intensity on T2 weighted images and does not enhance 10
T1 C+ (Gd)
- variable enhancement is seen with contrast administration
- marked high signal intensity with gradual enhancement (albeit mild) suggests myxoid degeneration
MRI is of significant value in the symptomatic patient when surgery and uterine salvage therapy is considered. It is also of great value in differentiating a pedunculated fibroid from an adnexal mass 5.
- rarely invasion of adjacent venous channels leading to intravenous leiomyomatosis 18
- rarely (0.1-0.5%), they undergo malignant degeneration into leiomyosarcomas
- in extremely rare instances, lesions capable of metastasising without malignant transformation: benign metastasising leiomyoma 3
Treatment and prognosis
Common treatment options include:
- focal endometrial curettage
- hormone administration
- uterine artery embolisation (UAE)
General imaging differential considerations include
- malignant transformation into leiomyosarcoma is rare.
- unforutnately no imaging modality can reliably differentiate a benign leiomyoma from the rare leiomyosarcoma
- uterine smooth muscle tumours of uncertain malignant potential - rare
- uterine lipoleiomyoma: greater fat content (sometimes considered a variant of a leiomyoma)
- ovarian masses
- focal myometrial contraction (Braxton Hicks contraction): especially if seen during pregnancy
- focal adenomyosis 4
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- 9. Weinreb JC, Barkoff ND, Megibow A et-al. The value of MR imaging in distinguishing leiomyomas from other solid pelvic masses when sonography is indeterminate. AJR Am J Roentgenol. 1990;154 (2): 295-9. AJR Am J Roentgenol (abstract) - Pubmed citation
- 10. Okamoto Y, Tanaka YO, Nishida M et-al. MR imaging of the uterine cervix: imaging-pathologic correlation. Radiographics. 23 (2): 425-45. doi:10.1148/rg.232025065 - Pubmed citation
- 11. Eurorad teaching files : Case 7559 showing haemorrhagic degeneration
- 12. Eurorad teaching files : Case 8209 showing haemorrhage during pregnancy
- 13. Kawakami S, Togashi K, Konishi I et-al. Red degeneration of uterine leiomyoma: MR appearance. J Comput Assist Tomogr. 18 (6): 925-8. - Pubmed citation
- 14. Eurorad teaching files : Case 8056 showing haemorrhagic cellular leiomyoma
- 16. Hamm B, Baert AL, Beinder E( et-al. MRI and CT of the Female Pelvis. Springer Verlag. (2010) ISBN:3642060897. Read it at Google Books - Find it at Amazon
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- 18. Low G, Rouget AC, Crawley C. Case 188: Intravenous leiomyomatosis with intracaval and intracardiac involvement. Radiology. 2012;265 (3): 971-5. doi:10.1148/radiol.12111246 - Pubmed citation
- 19. Casillas J, Joseph RC, Guerra JJ. CT appearance of uterine leiomyomas. Radiographics. 1990;10 (6): 999-1007. doi:10.1148/radiographics.10.6.2259770 - Pubmed citation
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