Uterine leiomyomas, also known as uterine fibroids, are benign tumours of myometrial origin and are the most common solid benign uterine neoplasms. They are a common incidental finding on imaging and rarely cause diagnostic dilemma.

Epidemiology

They are clinically apparent in ~25% of women of reproductive age and over 70% of women by menopause ²¹. 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.

Risk factors

• 2-3x increased incidence in Black women than in White women ^20,21

• increasing incidence with age: 10x more common between 41-60 years of age compared to 21-30 years of age, reaching a peak at 50-60 years ^20,21

• 3x increased incidence with a family history of uterine fibroids ²¹

Clinical presentation

They are often asymptomatic and discovered incidentally. Signs and symptoms associated with fibroids include:

• abnormal vaginal bleeding

• pain

• infertility

• palpable masses

Pathology

Leiomyomas are benign monoclonal tumours ¹⁶ predominantly composed of smooth muscle cells with variable amounts of fibrous connective tissue. They are commonly multiple (~85% ⁸), and range significantly in size.

Any fibroid may undergo atrophy, internal haemorrhage, fibrosis, and calcification. They can also undergo several types of degeneration:

• hyaline degeneration: focal or generalised hyalinisation: this is the most common type of degeneration (can occur in ~60% of cases) ⁶

• cystic degeneration: ~5%

• myxoid degeneration: generally considered uncommon although reported as high as 50% by some authors ¹⁴

• red (carneous) degeneration: due to haemorrhagic infarction, which can occur particularly during pregnancy, and may present with acute abdominal pain

Location

Fibroids may have a number of locations within or external to the uterus:

• intrauterine

  • intramural leiomyoma: most common, centred within the myometrium

  • subserosal leiomyoma: projecting outwards from the uterus; may be pedunculated and predominantly extrauterine, simulating an adnexal mass

  • submucosal leiomyoma: least common (10-15%), projecting into the uterine cavity

• extrauterine

  • broad ligament leiomyoma

  • cervical leiomyoma

  • parasitic leiomyoma ⁷

• diffuse uterine leiomyomatosis

Subtypes

Histological subtypes include:

• uterine lipoleiomyoma

• myxoid uterine leiomyoma

Classification

• FIGO classification system for uterine fibroids

Radiographic features

Plain radiograph

Popcorn calcification within the pelvis may suggest the diagnosis.

Ultrasound

Ultrasound is used to diagnose the presence and monitor the growth of fibroids:

• uncomplicated leiomyomas are usually hypoechoic, but can be isoechoic, or even hyperechoic compared to normal myometrium

• calcification is seen as echogenic foci with shadowing

• cystic areas of necrosis or degeneration may be seen

• Venetian blind artifact may be seen but edge shadowing +/- dense posterior shadowing from calcification is also typically seen ¹⁷

CT

• fibroids are usually seen as soft tissue density lesions and may exhibit coarse peripheral or central calcification

• they may distort the usually smooth uterine contour

• enhancement pattern is variable

MRI

MRI is not generally required for diagnosis, except for complex or problem-solving cases. It is however more sensitive than ultrasound for detecting, localising, and characterising fibroids. Size, location, and signal intensity should be noted.

Signal characteristics are variable and include ^1,2:

• T1

  • non-degenerated fibroids and calcification appear as low to intermediate signal intensity compared with the normal myometrium

  • characteristic high T1 signal

  • an irregular, T1 hyperintense rim around a centrally located myoma suggests red degeneration, which is caused by venous thrombosis

• T2

  • 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 as high T2 signal

  • hyaline degeneration is demonstrated as low T2 signal

  • cystic degeneration, which is an advanced stage of intratumoural oedema, also shows high T2 signal and does not enhance ¹⁰

• T1 C+ (Gd)

  • variable enhancement is seen with contrast administration

  • the 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 are considered. It is also of great value in differentiating a pedunculated fibroid from an adnexal mass ⁵.

Treatment and prognosis

There are various medical, surgical, and interventional treatment options:

• myomectomy: recurrence rate of 40-55% at 5 years ²³

• focal endometrial curettage

• hormone administration

• hysterectomy

• uterine artery embolisation (UAE)

• high-intensity focussed ultrasound (HIFU)

Complications

• invasion of adjacent venous channels leading to intravenous leiomyomatosis: rare ¹⁵

• malignant degeneration into leiomyosarcomas: rare (0.1-0.5%)

• benign metastasising leiomyoma: extremely rare ³

• torsion of subserosal leiomyoma

• pyomyoma ¹⁹

• changes in pregnancy

  • around one-third of fibroids may grow in pregnancy (especially in the 1^st trimester ¹⁸)

  • pregnancy may cause fibroid growth by 30%

• intraperitoneal haemorrhage ^24,25

  • a rare complication from rupture of a fibroid

  • usually secondary to an increase in abdominal pressure, which causes rupture of superficial veins

  • less often, bleeding can be arterial and associated with hypertension

  • trauma causing avulsion of a fibroid, torsion of a pedunculated fibroid, and pregnancy causing venous congestion

Differential diagnosis

General imaging differential considerations include:

• uterine leiomyosarcoma

  • malignant transformation into leiomyosarcoma is rare.

  • unfortunately, 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)

• focal myometrial contraction (Braxton Hicks contraction): especially if seen during pregnancy

• focal adenomyosis: less well-defined; colour Doppler demonstrates tortuous vessels through the abnormality; no calcifications ^4,17

In occasional situations, it may be difficult to differentiate between uterine leiomyomas and:

• ovarian or adnexal masses (especially if the leiomyoma is pedunculated)

• endometrial carcinoma