Myometrium

29.1 Fibroids (Leiomyomas) and Leiomyosarcomas

Description and Clinical Features

Fibroids, or uterine leiomyomas, are commonly occurring benign myometrial tumors composed of smooth muscle and fibrous tissue. They are found in approximately 20% of women over the age of 35 and are more common in women of African than European origin. They often enlarge during pregnancy and may shrink after menopause. Most are located in the uterine body and fundus, but they can also occur in the cervix. Fibroids are classified as:

Intramural: confined to the myometrium
Submucosal: projecting into the endometrium
Subserosal: projecting from the serosal surface of the uterus

Fibroids can cause various symptoms, including pain and abnormal vaginal bleeding. A large fibroid uterus can cause ureteral compression, leading to hydronephrosis. During pregnancy, fibroids can cause several complications, including miscarriage, pain, obstruction of vaginal delivery (if the fibroid is large and in the lower segment or cervix), and placental abruption (if the placenta is implanted on a fibroid).

Lipoleiomyoma is a rare variant of a fibroid that contains fat cells in addition to smooth muscle and fibrous tissue. It is a benign tumor whose clinical presentation is similar to that of a conventional fibroid.

Leiomyosarcoma is a rare malignant tumor of the myometrium, occurring most often after menopause. These tumors generally enlarge over time, unlike fibroids, which generally remain stable or regress in postmenopausal women.

Sonography

The appearance of fibroids on ultrasound is variable. In some cases, ultrasound demonstrates a single or multiple discrete, heterogeneous, highly attenuating masses in the myometrium. In others, the entire uterus is enlarged and heterogeneous, often with a nodular external contour. The latter appearance can be difficult to distinguish from uterine adenomyosis (see Section 29.2).

A discrete fibroid may be intramural (Figure 29.1.1), submucosal (Figure 29.1.2), or subserosal (Figure 29.1.3). Fibroids are usually located in the uterine body or fundus but occasionally originate in the cervix (Figure 29.1.4). Submucosal fibroids may develop a stalk and protrude far enough into the uterine cavity to prolapse into the cervix (Figure 29.1.5). Subserosal fibroids may extend from the uterus on a narrow pedicle, which carries its blood supply from the uterus (Figure 29.1.6). Fibroids tend to be quite vascular on color Doppler

(Figure 29.1.1). They may calcify (Figure 29.1.7). Cystic areas are occasionally seen within fibroids, a finding that may indicate necrosis or degeneration (Figure 29.1.8).

Figure 29.1.1 Intramural fibroid. A: Sagittal (SAG UT) and (B) coronal (COR UT) transvaginal views of the uterus demonstrate a large fibroid (calipers) within the body of the uterus. C: Color Doppler image in coronal plane demonstrates considerable blood flow at the periphery and within the fibroid, indicating that it is highly vascular.

Figure 29.1.2 Submucosal fibroid. Sagittal view of the uterus demonstrates a submucosal fibroid (FB) indenting the endometrium (arrowheads).

Figure 29.1.3 Subserosal fibroids. Sagittal transvaginal views of the uterus in two patients demonstrating (A) a large subserosal fibroid (calipers) extending outward from the posterior wall of the uterus and (B) a small subserosal fibroid (arrowheads), surrounded by free fluid (*) in the pelvis, extending outward from the anterior fundal aspect of the uterus.

Figure 29.1.4 Cervical fibroid. Sagittal view of the cervix (SAG CX) demonstrates a large cervical fibroid (arrowheads) located caudal to the uterine body (Body).

Figure 29.1.5 Fibroid prolapsing into the cervix. A: Sagittal midline view of the cervix (SAG ML CVX) demonstrating a hypoechoic mass (arrows) within the cervix. B: Sagittal midline view of the uterus shows that the cervical mass (arrows) extends from the body of the uterus via a stalk (arrowheads). C and D: Color Doppler documents the stalk carrying blood to the prolapsed fibroid from the mid uterus.

While conventional 2D sonography is generally sufficient for diagnosis of fibroids, the diagnosis and characterization of submucosal fibroids are aided, in some cases, by the use of more specialized sonographic techniques. In particular, sonohysterography (Figure 29.1.9) and 3D ultrasound (Figure 29.1.10) can confirm that a fibroid is submucosal and assess its degree of projection into the endometrial cavity. This information is useful in preoperative planning, before surgical excision of a submucosal fibroid.

Lipoleiomyomas appear as echogenic masses within the uterus (Figure 29.1.11). The echogenic appearance is due to the adipose tissue in the mass.

Leiomyosarcomas have a sonographic appearance similar to that of fibroids. Because they are much less common than fibroids, they are not generally diagnosed preoperatively. If a mass in a postmenopausal woman has the sonographic characteristics of a fibroid but it enlarges on serial sonograms, the diagnosis of leiomyosarcoma should be suspected (Figure 29.1.12).

Figure 29.1.6 Pedunculated fibroid in a pregnant patient. A: Transverse image of the uterus (Uterus) and a solid mass (arrows) with sonographic characteristics of a fibroid lateral to it. A hypoechoic stalk (arrowheads) is seen extending from the uterus to the mass. A gestational sac (*’s) is seen in the uterus. B: Color Doppler images showing blood flow in the stalk (arrowheads) extending from the uterus (Uterus) to the pedunculated fibroid (arrows).

Figure 29.1.7 Calcified fibroid. (A) Sagittal (SAG UT) and (B) coronal (COR UT) transvaginal views of the uterus demonstrate a rim of calcification (arrows) with posterior acoustic shadowing, representing calcification in the wall of a fibroid.

Figure 29.1.8 Degenerated fibroid. Image of left pedunculated (LT PED) subserosal fibroid (calipers) that is complex and contains several cystic areas as well as solid components. The cysts are areas of degeneration within the fibroid.

Figure 29.1.9 Saline infusion sonohysterogram of a submucosal fibroid. A: Sagittal transvaginal view of the uterus demonstrates a fibroid (arrows) abutting the endometrium (arrowheads). B: After instillation of saline, the fibroid (arrows) is seen projecting into the fluid-filled (F) uterine cavity.

Figure 29.1.10 3D ultrasound of a submucosal fibroid. A: Transverse transvaginal view of the uterus demonstrates a fibroid (calipers) indenting the endometrium (arrowheads). B: Coronal image of uterus reconstructed from 3D volume shows that the fibroid (arrows) is submucosal, projecting into the endometrium. The 3D image demonstrates the location of the fibroid with respect to the endometrium more precisely than does the 2D image.

Figure 29.1.11 Lipoleiomyoma. A: Sagittal midline (SAG ML) view of the uterus demonstrates a large echogenic mass (arrows) in the body and fundus of the uterus. The echogenic nature of the mass indicates that it has a high fatty content consistent with lipoleiomyoma. B: Sagittal (SAG) and (C) transverse (TRV) views demonstrating the borders and full size of the lipoleiomyoma (calipers).

Figure 29.1.12 Leiomyosarcoma. (A) Sagittal (SAG) and (B) transverse (TRV) transabdominal views of the uterus in a postmenopausal woman demonstrate a hypoechoic mass (calipers) in the uterus. This was initially diagnosed as a fibroid. (C) Sagittal and (D) transverse views 5 months later show that the mass has grown substantially. In view of the increasing size of the mass in a postmenopausal woman, leiomyosarcoma was felt to be the likely diagnosis. Hysterectomy was performed, and the diagnosis of leiomyosarcoma was confirmed by pathology.

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