The Uterus Benign Conditions Leiomyoma

Leiomyomas are benign tumors of smooth muscle origin. They are the most common uterine tumors, with a prevalence of 20% in women over the age of 35. The prevalence is even higher in women of African descent. The tumors are estrogen-dependent and often regress with menopause.

Leiomyomas may be located intramurally (most common), submucosally or subserosally. They tend to be well-demarcated and may undergo some degree of degeneration (e.g., hyaline, cystic, fatty or carneous). Calcification is common in leiomyomas of older women. Rare complications include infection, torsion and sarco-matous degeneration (< 1%). Symptoms associated with leiomyomas include menorrhagia, dysmenorrhea, infertility (especially submucosal leiomyomas that may impede the implantation of fertilized ova) and bulk-related symptoms (mass effect on the bladder or bowel).

MRI can accurately diagnose leiomyomas [1-3]. It is also accurate for determining their size, number and location. This information is important to help match the appropriate patients with symptomatic leiomyomas with the different therapies available. For example, a patient with multiple intramural and/or submucosal hypervascu-lar leiomyomas is a good candidate for uterine artery em-bolization (UAE), whereas a patient with a pedunculated subserosal leiomyoma may be better served by myomec-tomy. Similarly, hysteroscopic resection may be the best therapeutic option in a patient with a single submucosal leiomyoma that does not significantly extend into the underlying myometrium. Detection of significant ovarian artery supply to the pre-UAE uterus may be a predictor of treatment failure or fibroid recurrence following UAE [4]. MRI can also be used to follow patients post-UAE and may help with imaging any complications [5].

T2-W images provide optimal contrast between leiomyomas and adjacent uterine tissue (Fig. 1). Most leiomyomas are well-circumscribed, low signal intensity (SI) masses. If there is associated degeneration, they may exhibit high SI components [6]. T1-W images provide information about the type of degeneration (e.g., high SI to

Fig. 1. Leiomyomas. Sagittal T2 SS FSE with multiple well-circumscribed low signal intensity intramural and subserosal leiomyomas

The symptoms of adenomyosis are non-specific and may mimic leiomyomas. However, it is important to establish the correct diagnosis pre-operatively, because uterine-conserving therapy is possible with leiomyomas, whereas hysterectomy is the definitive treatment for debilitating adenomyosis.

MRI is an accurate, non-invasive modality for the diagnosis of adenomyosis, differentiation of adenomyosis from other gynecologic disorders, and planning for appropriate therapy [10]. Several studies have found MRI to be very accurate in diagnosing adenomyosis, with a sensitivity and specificity ranging from 86-100% [11-13].

Adenomyosis is diagnosed when the junctional zone is greater than, or equal to, 12 mm (Fig. 2). Ancillary findings

Fig. 2. Adenomyosis. Sagittal (a) and coronal (b) T2 SS-FSE images with junctional widening, striations and the punctuate foci of adenomyosis diagnose hemorrhage). Additionally, T1-W sequences can aid in differentiating a pedunculated subserous leiomyoma from an ovarian mass. Contrast-enhanced T1-W sequences are optional, but do provide information about blood supply to, and viability of, a leiomyoma, which may be important for planning treatment and follow-up [7].

Prospectively differentiating a leiomyosarcoma from a degenerated benign leiomyoma is difficult. Reported MRI findings are variable and include lobulated mass of high SI on T2-W images, a sharply marginated mass of low SI on T2-W images, or a mass with focally infiltrative margins [8]. In a study of 12 patients (nine with leiomyosarcoma and three with smooth muscle tumors of uncertain malignant potential), the majority of malignant tumors had more than 50% high signal on T2-W images, the presence of many small high signal areas of T1-W images and well-demarcated, non-enhancing regions [9]. While these imaging characteristics are non-specific, any fibroid that demonstrates marked interval growth or change in appearance may suggest the possibility of leiomyosarcoma.

Adenomyosis

Adenomyosis is common uterine condition affecting up to one third of hysterectomy specimens. It is defined as the presence of ectopic endometrial glands and stroma within the myometrium. Adenomyosis is also associated with myometrial hyperplasia. Cyclic hemorrhage is unusual in adenomyosis because of the predomination of the zona basalis endometrial layer. This zone is relatively unresponsive to hormonal stimuli. Two types of adeno-myosis exist: diffuse adenomyosis and focal adenomyosis (adenomyoma). Diffuse adenomyosis is more common and typically affects the posterior uterine wall.

b include high SI foci on T1- and/or T2-W images. These may represent islands of ectopic glands, cystically dilated glands and/or hemorrhagic fluid. In some patients, linear high SI striations can be seen radiating from the endometrium into the myometrium. Following contrast, adenomyosis may have a 'swiss cheese' appearance, with foci of signal void that represent ectopic endometrial glands. Adenomyomas may be separate from the junctional zone and image as ill-defined, low SI masses on T2-W sequences.

Occasionally, the imaging appearance of submucous leiomyomas and adenomyosis overlap. Features favoring the diagnosis of adenomyosis include lesions that: (1) are poorly marginated; (2) elliptical lesions with minimal mass effect relative to their size; (3) have linear striations that originate in the endometrium and extend into the myometrium; and (4) do not have dilated vessels at their margins [10, 14, 15].

Congenital Anomalies

The incidence of congenital uterine anomalies among women of reproductive age ranges from 0.1-0.5%. The clinical significance of such anomalies is an increased likelihood of infertility, pregnancy wastage (e.g., recurrent miscarriage, premature labor, intrauterine growth retardation) and menstrual disorders.

The uterus, fallopian tubes and upper two thirds of the vagina originate from paired mullerian ducts. The ducts migrate caudally and then fuse. Subsequently, the intervening tissue (septum) resorbs to form the endometrial, endocervical and endovaginal canals. This process, which begins at approximately 10 weeks of gestation, may be interrupted at any stage in development. Failure of the paired ducts to develop results in various degrees of agenesis (or hypoplasia). Absent or incomplete fusion leads to didelphys or bicornuate uteri, respectively. Complete or partial failure of resorption following fusion results in a septate uterus. Congenital anomalies are classified according to the American Fertility Society classification, which divides anomalies into classes with similar features, prognoses and treatment options [16, 17]. It is important to note however, that congenital uterine anomalies are a spectrum of disorders and occasionally it may be impossible to assign a malformation to one particular class. This fact underscores the importance of imaging to highlight the affected anatomy. MRI is the most accurate modality for identifying uterine anomalies: it is more specific than ultrasound (US) or hysterosalpingography (HSG), and it is less invasive and less costly than laparoscopic evaluation [18]. In addition to depicting genital anomalies, MRI's large field of view allows the abdomen and pelvis to be surveyed for associated urinary tract anomalies (e.g., renal agenesis, ectopia).

Class I: Segmental Agenesis/Hypoplasia

This class of anomalies may affect just a portion of genital tract, or combined abnormalities may be present. Agenesis/hypoplasia may occur as part of a syndrome, as a result of chromosomal defects, or in isolation. Patients with vaginal agenesis but with patent endometrial and en-docervical canals are treated with vaginoplasty to allow egress of menses. Hysterectomy is reserved for patients without a cervix, as a neocervix or uterovaginal fistula is unable to successfully sustain a pregnancy, nor can it prevent retrograde menses and endometriosis.

Class II: Unicornuate Uterus

These anomalies result from the failure of one of both of the paired mullerian ducts. If no rudimentary horn is present, usually no further treatment is required. Similarly, no intervention is needed if there is a rudimentary horn that does not contain endometrium. However, if a rudimentary horn contains endometrium, regardless of whether it communicates with the main uterine cavity, surgical excision is recommended to prevent retrograde menses or ectopic pregnancy.

Class III: Uterus Didelphys

This anomaly results from failure of mullerian duct fusion, leading to two uteri and two cervices. In the majority of cases there is a transverse vaginal septum. If the septum is obstructive, hematocolpometra results. Resection of the septum establishes normal egress of menses via the vagina.

Class IV: Bicornuate Uterus

This class of anomalies results from incomplete fusion of the mullerian ducts. A fundal cleft of more than 1 cm distinguishes a bicornuate uterus from a septate uterus (see Class V). Bicornuate uteri rarely require surgery. However, if a patient is symptomatic, a transabdominal metroplasty can be performed.

Class V: Septate Uterus

This class of anomaly results from a failure of resorption of the central intervening tissue, septum, between the two endometrial canals. Complete and incomplete forms exist. In the former, the septum extends into the cervix (Fig. 3),

Fig.3. Complete Septate Uterus. Coronal T2 SS FSE of the uterus with fundal notch < 1 cm, and two endometrial and endocervical canals separated by a low signal intensity septum. Both ovaries are normal

Fig.3. Complete Septate Uterus. Coronal T2 SS FSE of the uterus with fundal notch < 1 cm, and two endometrial and endocervical canals separated by a low signal intensity septum. Both ovaries are normal whereas in the latter it is confined to the uterine body. Septate uteri have a flat, convex or minimally concave fundal contour. Septate uteri have the highest incidence of fetal wastage and can be successfully treated with hys-teroscopic removal of the septum.

Class VI: Arcuate Uterus

This anomaly is more appropriately termed a normal variant, as there is a slight fundal indentation. Patients are asymptomatic and do not require treatment.

Class VII: Diethystilbesterol (DES) Exposure in Utero

Approximately half of the women exposed to DES in utero have a congenital uterine anomaly. The most common abnormality is a T-shaped uterus, which often results in cervical incompetence. In these instances, pregnant women are treated with cervical cerclage.

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