Female Pelvis

Vaginal Agenesis.

Partial or complete vaginal agenesis occurs in 1 in 5000 women and should be suspected with a clinical history of primary amenorrhea. This may be isolated or associated with agenesis or hypoplasia of the uterus. The most common cause of vaginal agenesis is Mayer-Rokitansky-Küster-Hauser syndrome, which is characterized by congenital aplasia of the uterus and upper two thirds of the vagina in women showing normal development of secondary sexual characteristics with a normal 46,XX karyotype. Other causes of vaginal agenesis include conditions associated with ambiguous genitalia, such as gonadal dysgenesis (Turner's syndrome, 45,XO), male pseudohermaphroditism, and testicular feminization syndrome.

Vaginal Septum.

Congenital vaginal septa may present as either a transverse or longitudinal septum and may be complete or incomplete. A transverse vaginal septum can occur anywhere along the vagina, although it is most commonly seen at the junction of the upper and middle thirds. It can appear as a thin T2-hypointense band that is composed of fibrous connective tissue with vascular and muscular components. It may present as primary amenorrhea or hematometrocolpos, with resulting complications of hematosalpinx and endometriosis. MRI is useful in defining the location and thickness of a vaginal septum for preoperative planning, as well as identifying other potential causes of hematocolpos such as hymenal atresia ( Fig. 57-2 ). Longitudinal vaginal septa are usually asymptomatic and may arise either as a failure of lateral fusion of the müllerian ducts (resulting in duplication of the uterus, cervix, and vagina) or as a result of incomplete resorption of the vaginal septum. They are best visualized on T2-weighted imaging in either the coronal or axial plane and appear as thin low-signal-intensity structures.

Congenital Vaginal Cysts.

Congenital vaginal cysts are often incidentally found on pelvic MRI and include both müllerian (paramesonephric) and Gartner's duct (mesonephric) cysts, which cannot be distinguished from each other on imaging. Both lesions typically appear as T1-hypointense, T2-hyperintense cystic structures within the vaginal anterolateral wall anywhere from the cervix to the introitus ( Fig. 57-3 ). Lesions may contain intermediate to high T1 signal if proteinaceous or hemorrhagic contents are present. The majority of lesions are small and asymptomatic and do not require intervention.

Noncongenital Cysts.

Noncongenital cystic lesions of the vagina include retention cysts of the vestibulum and epidermal inclusion cysts. Inclusion cysts are usually asymptomatic and often found within the lower posterior or lateral vaginal wall. They typically occur after trauma and are due to buried epithelial fragments, appearing as a complex cystic lesion on MRI. Although CT and US can be used to make the diagnosis, MRI is the modality of choice for assessment of vaginal cysts because MRI is often useful in excluding other etiologies in the differential diagnosis, such as vaginal prolapse, tumors, and ischiorectal fossa lesions.

Vaginal Fistula.

Several different types of fistulas can develop, including vesicovaginal, colovaginal, or recto- or anovaginal fistulas. These typically develop after gynecologic surgery or radiation therapy, although other causes include Crohn's disease, diverticulitis, malignancy, chronic infection, or trauma. Fistulous tracts appear as high-signal tracts extending from the vagina to adjacent structures, best visualized on T2-weighted sequencing and short tau inversion recovery (STIR) imaging ( Fig. 57-4 ). Gadolinium-enhanced T1-weighted images with fat suppression will often show parallel fistulous wall enhancement.

Radiation Change.

The vagina may demonstrate significant changes after receiving radiation. Within the first 6 months post radiation, the vaginal wall shows T2-hyperintense signal primarily due to mucosal and intramuscular edema. Typically this is followed by vaginal atrophy, where the vaginal wall shows T2-hypointense signal. Additional findings can include narrowing, foreshortening, and/or stenosis of the vaginal canal. Severe radiation injury can result in vaginal ulceration, necrosis, and secondary fistula formation.

Endometriosis.

Endometriosis is defined by the presence of functional endometrial glands and stroma outside the uterine cavity. The most common site of endometriosis is the ovary, but endometrial deposits may be found in any pelvic organ or other distant sites, including the vagina. Vaginal endometrial implants usually occur in the posterior aspect of the upper vagina and demonstrate intense enhancement on postcontrast images. Lesions are typically T1 hyperintense, best visualized on fat suppression images, with intermediate to high signal intensity on T2-weighted imaging. In addition, areas of fibrosis and adhesions due to a resulting inflammatory response may be seen, which is typically characterized by T2-hypointense fat stranding or spiculation. MRI has a sensitivity and specificity of 80% and 93%, respectively, for the diagnosis of vaginal endometriosis. Endometriosis is further discussed later under “Ovaries.”

Vaginal Leiomyomas.

These are rare solid, well-defined benign tumors ranging from 1 to 5 cm that typically arise within the anterior midline vaginal wall and less likely the posterior or lateral walls. Leiomyomas arising from the anterior wall are associated with urinary tract symptoms (e.g., increased frequency, dysuria, urgency). Similar to uterine leiomyomas, vaginal leiomyomas may be intramural or pedunculated and demonstrate homogenous T1- and T2-hypointense signal with homogenous enhancement on postcontrast images. Hyaline degeneration results in low T2 signal intensity, whereas myxoid and cystic degeneration demonstrates high T2 signal intensity. Hemorrhagic degeneration demonstrates high signal intensity on both T1- and T2-weighted imaging. Differential diagnosis includes a fibroepithelial polyp of the vagina, which is an uncommon benign asymptomatic lesion characterized by a squamous epithelial surface with a fibrovascular stalk.

Vaginal Cancer.

Primary carcinoma of the vagina comprises approximately 1% to 2% of all gynecologic malignancies, with 90% composed of squamous cell carcinomas, usually occurring in elderly women. Risk factors for development of vaginal cancer include chronic human papillomavirus (HPV) infection, multiple sexual partners, immunosuppression, prior radiation, and smoking. It commonly arises from the posterior wall of the proximal third of the vagina and tends to demonstrate early involvement of adjacent structures, including the parametrium, cervix, vulva, and rectovaginal and vesicovaginal septae. Lymph node involvement typically involves the iliac chain nodes from the upper third of the vagina and spreads to the inguinal lymph nodes from the lower two thirds of the vagina. MRI is helpful in defining the local extent of vaginal carcinoma and lymph node status.

Tumor typically appears isointense on T1, and on T2 shows intermediate to high signal intensity relative to normal vaginal tissue, with enhancement on postcontrast images. Management depends upon the size, location, and tumor-node-metastasis (TNM) staging of the tumor. Stage I tumors are limited to the vagina, with the paravaginal fat retaining its normal high signal intensity on T1-weighted images. Stage II tumors extend into the paravaginal fat, disrupting the normal low signal intensity of the vaginal wall and replacing the paravaginal fat with abnormal low signal intensity on T1-weighted images. In stage III tumors, the carcinoma extends to the pelvic sidewall, with disruption of the normal low signal intensity of the pelvic sidewall muscles on T2-weighted imaging. Stage IV tumors extend beyond the true pelvis or invade the rectum or bladder, with resultant loss of the normal low-signal-intensity rectal or bladder wall on T2-weighted imaging.

Additional vaginal cancers include vaginal adenocarcinoma, which is typically associated with in utero exposure to diethylstilbestrol (DES), and a T-shaped uterus. Very rarely, primary vaginal melanoma, lymphoma, and leiomyosarcoma can also occur.

Secondary Vaginal Involvement.

Most tumors affecting the vagina (up to 90%) are due to direct extension from primary cervical, vulvar, bladder, or rectal neoplasms. The overall accuracy of MRI for all metastatic tumors involving the vagina has been reported as 92%. Metastatic tumors demonstrate similar imaging characteristics to primary tumors, with low to intermediate signal intensity on T1-weighted imaging and high to intermediate signal intensity on T2-weighted imaging, with enhancement on postcontrast imaging sequences.

Bartholin's Cysts.

Bartholin's cysts are the most common vulvar cyst and are of urogenital sinus origin, arising from the Bartholin's glands. They are commonly seen in women of reproductive age, range in size from 1 to 4 cm, and are typically located at the lateral introitus adjacent to the labia minora. Lesions are typically T2 hyperintense, with variable signal on T1 depending on the proteinaceous content ( Fig. 57-5 ). Thickening and enhancement of the wall can be seen with inflammation. Rarely, solid or nodular mural lesions can be indicative of the extremely rare Bartholin's gland carcinoma.

Solid Lesions.

Rarely, vulvar fibromas, lipomas, and leiomyomas can occur. Fibromas demonstrate areas of marked hypointensity consistent with fibrosis on T1- and T2-weighted MRI. Vulvar lipomas demonstrate signal intensity that follows fat sequences on MRI. Vulvar leiomyomas typically arise from the labia majora, are homogenously T1 and T2 hypointense, and may demonstrate changes of cystic degeneration.

Vulvar Infection.

The vulva is susceptible to community-acquired infections such as community-acquired methicillin-resistant Staphylococcus aureus (MRSA) colonization, which can lead to vulvar abscesses, necrotizing fasciitis, or Fournier's gangrene. Common risk factors include obesity and diabetes mellitus.

Vulvar Thrombophlebitis.

Rarely, vulvar edema and varicose veins may develop during pregnancy as a result of compression from the gravid uterus. Thrombophlebitis can subsequently occur in these varicose veins either during pregnancy or in the postpartum period. Occasionally tamoxifen use for breast cancer has also been associated with superficial thrombophlebitis, presumably owing to the effect of a hypercoagulable state.

Primary Vulvar Carcinoma.

Vulvar cancer is a rare malignancy that tends to affect elderly women, although a bimodal distribution exists. Approximately 90% of all vulvar carcinomas are squamous cell carcinomas. HPV-positive tumors (associated with HPV types 16, 18, and 33) occur in a younger age group, may be multifocal, and show an association with vulvar intraepithelial neoplasia. Other histologic types include sarcoma, basal cell carcinoma, adenocarcinomas, and extramammary Paget's disease. Vulvar carcinoma usually involves the labia in two thirds of cases and demonstrates local invasion before lymph node involvement ( Fig. 57-6 ). The most important prognostic factors for determining survival are tumor size, depth of invasion, and presence of inguinofemoral lymph node metastases.

Imaging does not play a significant role in assessment of the primary tumor, inasmuch as this is readily assessed on clinical exam. However, imaging does play an important role in assessment of any regional adenopathy and in surgical planning. Enlarged superficial inguinal lymph nodes measuring greater than 10 mm in short-axis diameter and deep inguinal nodes measuring greater than 8 mm in short-axis diameter have been shown to demonstrate a high specificity for malignant involvement (97%-100%). Additional vulvar malignancies may rarely include vulvar lymphoma, melanoma, leiomyosarcoma, and aggressive angiomyxoma.

Urethral Diverticula.

Urethral diverticula are protrusions of the urethra into the periurethral fascia. The epithelial lining of a diverticulum is identical to the urethral mucosa, and communication with the urethral lumen is maintained. Some diverticula may be congenital, but the vast majority are felt to arise from acquired causes. The most widely accepted theory involves rupture of a chronically obstructed and infected periurethral gland into the urethral lumen. Most patients present with nonspecific symptoms including urinary frequency, urgency, pelvic pain, urinary tract infections, incontinence, and urine retention. Urethral diverticula are classically most conspicuous on T2-weighted images, with the fluid-containing cystic cavity being T2 hyperintense relative to the surrounding soft tissues. They typically arise from the posterolateral wall of the midurethra at the level of the pubic symphysis and demonstrate various degrees of extension around the circumference of the urethra ( Fig. 57-7 ). Occasionally the diverticula can become infected with Escherichia coli and less often, gonococci and Chlamydia species. Inflamed urethral diverticula may demonstrate heterogeneous signal intensity on T1-weighted images and a possible fluid-fluid level. Additional complications include calculus formation, which occurs in approximately 10%. Rarely, neoplasm can develop within the diverticulum, with the majority being adenocarcinoma.

Skene's Gland Cyst.

Ductal obstruction secondary to infection or trauma leads to formation of Skene's duct cysts, which are located at the floor of the distal urethra and are bilateral. Most of these cysts are clinically insignificant, but cysts larger than 2 cm often cause urinary symptoms such as dysuria or obstructive voiding symptoms. Differential diagnosis includes a urethral diverticulum, although MRI findings such as distal location, teardrop shape, and paired structures are more suggestive of Skene's cysts.

Urethral Leiomyoma.

Urethral leiomyomas are extremely rare benign smooth muscle tumors that may grow during pregnancy and result in dysuria. They frequently involve the proximal segment of the urethra and may be confined to the urethra, extend into the paraurethral region, or protrude through the urethral meatus. On MRI, lesions typically demonstrate intermediate T1 signal intensity, variable signal on T2-weighted images, and contrast enhancement.

Urethral Caruncle.

Urethral caruncles are small benign lesions of the posterior margin of the external urethral meatus that are caused by distal urethral prolapse in hypoestrogenic postmenopausal women. Although most women are asymptomatic, urethral caruncles can occasionally cause pain and hematuria. On MRI a caruncle may appear as a T2-hyperintense mound of tissue surrounding the external urethral meatus.

Urethral Fistulas.

Urethral fistulas are divided into urethrovaginal, rectourethral, and urethroperineal subtypes. Urethrovaginal fistulas are typically sequelae of Crohn's disease, Behçet's disease, or postsurgical complications. Rectourethral fistulas are typically congenital, whereas urethroperineal fistulas are thought to be acquired fistulas from chronic decubitus ulcers or abscesses in the perineal region. These fistulas appear as T2-hyperintense tracts extending from the urethra to the vagina, rectum, or perineum.