Introduction

Uterine arteriovenous malformation (UAVM) is an abnormal connection between the arteries and the veins of the uterine myometrium without an intervening capillary bed. They were first reported by Dubreil and Loubat in 1926.

They can be congenital or acquired.

Clinical presentation

Even though UAVMs have varied presentation, uterine bleeding is the most common one. They often follow a pregnancy event. Episodic or occasionally torrential vaginal bleeding can occur. Congestive heart failure secondary to vascular steal can be a rare presentation due to a large UAVM.

Causes and risk factors

UAVM is most commonly an acquired condition. Pregnancy has a significant role in their pathogenesis. It is most commonly observed in reproductive age group. UAVMs are frequently observed in the postpartum period, few months after spontaneous miscarriage, surgical evacuation of uterus for miscarriage or medical termination of pregnancy. Infection, inflammation, retained products of conception (RPOC), gestational trophoblastic disease (GTD), gynaecologic malignancies, pelvic trauma and exposure to diethylstilboestrol can also lead to UAVMs. Few cases are also reported in young adolescent and postmenopausal females.

UAVMs rarely are congenital and may be also associated with AVMs in other locations.

Pathophysiology

Congenital AVMs

Congenital AVMs have a central nidus with multiple feeding arteries and draining veins. In this condition, there is extension of the lesion beyond that uterus and multiple pelvic vessels other than uterine vessels draining into them. That cause of congenital AVMs are thought to be due to failure of embryological differentiation. With the progression of pregnancy, these vessels have the propensity to invade surrounding structures.

Iatrogenic Acquired AVMs

When the venous sinuses are incorporated into the scars of myometrium after the necrosis of chorionic villi, acquired malformations may arise. In contradiction to congenital AVMs, acquired AVMs multiple fistulous communication between the intramural arteries and the venous plexus. These AVMs may have either dual blood supply or a single supply from the uterine arteries and presents without nidus.

Vaginal bleeding caused by pregnancy-related causes must be differentiated from UAVMs. Surgery/evacuation is the appropriate management for the former and the same is contraindicated in the UAVMs and hence an accurate definitive diagnosis is important.

Radiological features

Colour doppler

On colour Doppler, within the myometrium, a region of increased vascularity and most commonly with aliasing is seen. A group of vessels traversing the myometrium running perpendicular to and into the endometrium, from the arcuate vessels, can be seen. It is not specific, as they are also observed in RPOC, GTD, placental polyp and vascular endometrial neoplasm.

Differential diagnosis

With elevated serum beta-HCG

Gestational Trophoblastic Disease

RPOC: Presence of endometrial pathology rather than myometrial origin.

Introduction

Leiomyomas, also known as fibroids or myomas, are the most common gynaecologic neoplasms, occurring in 20%–30% of women of reproductive age. Symptomatic uterine fibroid accounts for about 30% of hysterectomies performed for women older than 18 years of age and 41% of hysterectomies performed for women from 44 to 64 years of age.

Prevalence and incidence

Histopathologic features

Leiomyomas are the benign neoplasms made up of whorled fascicles of smooth muscle and fibrous connective attached to the uterine muscular wall. Even in the absence of true capsule, leiomyomas are well circumscribed and contains a pseudocapsule. Its size is variable, ranging from tiny microscopic to large tumours filling the abdomen.

Classification

Most commonly, the uterine leiomyomas are seen in the myometrium of uterine corpus. However, it is also seen in the cervix (<5% of cases). On the basis of the location, uterine fibroids are classified as submucosal, intramural or subserosal. This classification is of clinical significance because the symptoms and treatment vary among these subtypes of leiomyomas. Submucosal myomas are further subclassified as 0, I and II depending on the percentage within the endometrial cavity. The first two categories can be removed hysteroscopically (Table 11.15.3.1). Pedunculated leiomyomas are attached to the uterus by a stalk and may be either intracavitary or exophytic (narrower than 50% of diameter of myoma). Rarely, a submucosal fibroid may grow pedunculated and extends into the cervical canal or vaginal canal and its prevalence is about 2.5%. Pedunculated subserosal leiomyomas may undergo torsion, resulting in infarction accompanied by pain. Lateral growth into broad ligament leads to intraligamentous leiomyoma (Table 11.15.3.1). Rarely, a pedunculated leiomyoma may become detached from the uterus (parasitic leiomyoma).

Symptoms

Depending on the location, size and number of uterine fibroids, it has varied presentation. Symptoms caused by leiomyomas are classified into three different categories such as abnormal uterine bleeding, pelvic pressure and pain and reproductive dysfunction.

Bleeding

Submucosal leiomyomas and intramural leiomyomas are often associated with menorrhagia (Table 11.15.3.1).

Pressure on adjacent organs and pain

Because of leiomyoma, uterus may be irregularly shaped and causes symptoms based on their locations. Anterior leiomyomas cause urinary symptoms, whereas the posterior leiomyomas cause constipation. Ureter may be compressed by broad ligament leiomyomas and presents as hydroureter or hydronephrosis. In case of degeneration or torsion of a pedunculated leiomyoma, acute pain may be the presentation.

Reproductive dysfunction

Leiomyomas are an infrequent primary cause of infertility. Malpresentation, pregnancy failures and dystocia are reported.

Imaging

Ultrasound is the first-line imaging modality because it is a cost-effective portable real-time examination that provides good anatomic detail. Leiomyomas appear as a well-defined round or oval hypoechoic solid mass. It is mostly associated with posterior shadowing possibly due to calcifications or interface of the margins of the leiomyoma with the normal myometrium.

Degeneration or lipoleiomyoma can be suggested when there is internal echo-poor or hyperechoic foci, respectively. The presence of hypervascularity in a large solitary uterine mass can identify suspicious masses, such as a leiomyosarcoma (LMS). Another study found that there is an increased detection rate of uterine sarcomas while using a cut-off value of 41 cm/s. In the assessment of a uterus enlarged with multiple leiomyomas, ultrasound has FOV limitations. Likewise, it has limited role in the assessment of retroverted uteri, pedunculated subserosal myomas and concomitant adnexal processes. Little has been reported regarding sonographic changes after MR HIFU and uterine fibroid embolization (UFE). Differential diagnosis has been discussed in Table 11.15.3.2.

CT

Enlarged uterus and a deformed contour are the most common computed tomography (CT) findings. Even though CT is the primary modality for the staging of cancers, it has limitation of reduced contrast resolution for the assessment of focal myometrial masses, and associated with risk of ionizing radiation. Also, in delineating the zonal anatomy for accurate localization of leiomyomas and LMSs, CT is inferior to magnetic resonance imaging (MRI). More often dense or amorphous calcification is seen. Almost exclusively, on plain radiography or CT, these patterns of calcification favours the diagnosis of leiomyoma. Ring-like calcification at the margins of a leiomyoma is a rarely observed pattern, which represents the thrombosed veins.

Positron emission tomography (PET)/CT is an ideal modality for the confirmation of malignancy and also helps in detection of metastasis and recurrence. In a small study of patients with histopathologically confirmed uterine sarcoma found that on comparing with the findings of MRI and ultrasound with power Doppler imaging, the results of fluorodeoxyglucose (FDG) PET examinations were 100% positive. However, it has limitations such as increased false-positive rate and reduced widespread availability.

MRI appearance of leiomyomas: MRI is considered as the most accurate imaging technique for the detection and localization of leiomyomas. In determining the presence and location of leiomyomas in infertile women before myomectomy, MRI has been shown to be more accurate and sensitive than US or hysterosalpingography.

Nondegenerated uterine leiomyomas usually has a typical MRI appearance of (Table 11.15.3.4) well-circumscribed masses with homogeneously decreased T2-weighted signal intensity.

TABLE 11.15.3.3

Established Characteristics of Usual Leiomyomas on Multiparametric MRI

Characteristics	Findings
Margins	Well defined
Shape	Round or oval
SI on T1-weighted images	Homogeneously isointense
SI on T2-weighted images	Homogeneously hypointense
Enhancement on gadolinium contrast-enhanced images	Yes (can be variable); enhancement indicates viability
SI on DW images (high b value)	Hypointense compared with normal smooth muscle (blackout phenomenon)
SI on ADC map	Hypointense compared with normal smooth muscle (blackout phenomenon)

Note: SI, signal intensity; ADC, apparent diffusion coefficient.

Compared with that of normal smooth muscle myometrium.

Degenerated leiomyomas have varied imaging appearances on T1-weighted, T2-weighted and contrast-enhanced images as described in Tables 11.15.3.4 and 11.15.3.5.

TABLE 11.15.3.4

Variant and Subcategory

• Ordinary Leiomyoma’s benign Nondegenerated Degenerated Cystic Haemorrhagic (carneous) Fatty (lipoleiomyoma) Hyaline Myxoid • Leiomyoma variants Mitotically active Cellular Atypical Smooth muscle tumours of uncertain malignant potential (STUMP) • Leiomyosarcoma – malignant

TABLE 11.15.3.5

Features of Degenerating Leiomyomas on Multiparametric MRI

Leiomyoma Degeneration Type	Overall Shape	SI on T1-Weighted Images	SI on T2-Weighted Images	Early Enhancement	Restriction on DW Images and ADC Maps
Hyaline	Round or oval	Hypointense or isointense	Hypointense	Minimal or non	No
Oedema *Common *50% cases *Usually peripheral	May show speckled pattern	Hypointense	Hyperintense	Marked enhancement	—
Cystic	Round or oval	Hypointense	Hyperintense	None	No
Myxoid	Round or oval	Hypointense	Markedly hyperintense	Progressive	No
Carneous, red, or UAE associated	Round or oval	Peripheral or diffuse hyperintensity	Peripheral or diffuse hyperintensity	None	No
Calcific	Amorphous, central or peripheral	Hypointense	Hypointense	None	No

Leiomyoma variants (Tables 11.15.3.4 and 11.15.3.6): There are several, such as mitotically active, cellular and atypical leiomyomas, as well as smooth muscle tumours of uncertain malignant potential (STUMP). On histopathological examination, the nondegenerated fibroids are made up of goals of uniform smooth muscles with varied amounts of collagen. Cellular leiomyomas, which are composed of compact smooth muscles cells only with no collagen, will demonstrate increased T2-weighted signal intensity and homogeneous enhancement. There is a greater risk of recurrence in case of atypical leiomyomas and uterine STUMP. The patients who had undergone myomectomy and were found to have atypical leiomyoma, must be under surveillance with an annual pelvic ultrasound or MRI. Since the recurrences may presents as pelvic or abdominal masses or as pulmonary metastases, for all the patients with STUMP lesions, routine physical examinations, including pelvic examinations and the baseline CT of the chest, abdomen and the pelvis are recommended for every 6 months for 5 years and then annually thereafter. In addition, prompt re-exploration and staging is recommended for patients with STUMP who have undergone a morcellation myomectomy. An aggressive imaging surveillance is considered, when the disease is present. Atypical leiomyomas and STUMPs routinely express progestin receptors; however, because of the low recurrence rates, there is no role for adjuvant hormonal therapy. Atypical uterine masses can be treated surgically with hysterectomy or myomectomy.

TABLE 11.15.3.6

Features of Leiomyoma Histologic Subtypes on Multiparametric MRI

Leiomyoma Degeneration Type or Histologic Subtype	Overall Shape	SI on T1-Weighted Images	SI on T2-Weighted Images	Early Enhancement	Restriction on DW Images and ADC Maps	Follow-Up
Histologic subtype Cellular leiomyoma	Round or oval Single large lesion with absence of coexistent adenomyosis	Variable	Diffusely hyperintense	Marked	Yes	Responds to GnRH analogues Cured with surgery No need for follow-up
Lipoleiomyoma	Well defined: round or oval	Heterogeneous (hyperintense with loss of SI on fat-saturated sequences) with amorphous bands of hypointensity	Heterogeneous, amorphous bands of hypointensity coursing through fat components	Marked enhancement of amorphous bands	Unknown
STUMP	Round or oval	Heterogeneous with hyperintense areas	Heterogeneous with hyperintense areas	Variable	Unknown/yes at high b values	Intense surveillance

Note: SI, signal intensity; ADC, apparent diffusion coefficient; UAE, uterine artery embolization; STUMP, smooth muscle tumours of uncertain malignant potential.

Unusual growth patterns

Being a benign neoplasm, fibroids usually have a pushing border and rounded edges. But, specific types of fibroids represent growth pattern variations, such as intravenous leiomyomatosis, metastasizing leiomyoma, diffuse leiomyomatosis and peritoneal disseminated leiomyomatosis. Retroperitoneal growth and parasitic growth are the other atypical growth patterns. Even cervical and vaginal leiomyomas may show growth pattern.

Differential diagnosis

It is important to note that adenomyosis and focal myometrial contraction can coexist and distinction is important at preprocedure imaging (Table 11.15.3.7).

TABLE 11.15.3.7

Differential Diagnosis Based on MRI Features

Differential Diagnosis on Ultrasound	Lesion	Features on MRI
Intramural	Adenomyosis (the low signal intensity due to smooth muscle hypertrophy) small foci of high signal due to endometrial glands)	Thickened (12 mm) junctional zone The low signal intensity of adenomyosis with small foci of high signal intensity
	Focal myometrial contraction	Transient hypointense T2-weighted lesion Involves the inner myometrial wall
Subserosal	Ovarian fibromas and Brenner tumours	Signal intensity similar to myomas surrounded by ovarian stroma and follicles
Vaginal leiomyoma	Fibroepithelial polyp	Rare benign asymptomatic lesion Has a fibrovascular stalk

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