Vagina and Vulva

Contents

1    Introduction\

2    Embryonic Development

and Normal Anatomy\

3    Imaging Appearance

of the Normal Vagina and Vulva\

3.1  CT Appearance\

3.2  MRI Protocol\

3.3  MRI Appearance\

4    Congenital Anomalies

of the Vagina and Vulva\

4.1  Imperforate Hymen\

4.2  Congenital Vaginal Septa\

4.3  Vaginal Agenesis\

5    Benign Conditions

of the Vagina and Vulva\

5.1  Vaginal Cysts\

5.2  Inflammatory Conditions

of the Vagina and Vulva\

5.3  Vulvar Trauma\

5.4  Vaginal Fistula\

5.5  Post-Radiation Changes\

5.6  Benign Tumors\

6    Malignant Neoplasms

of the Vagina and Vulva\

6.1  Vaginal Malignancies\

6.2  Vulvar Malignancies\

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 360

A.C. Tsili

Department of Clinical Radiology, Medical School, University of Ioannina, University Campus,

Ioannina 45110, Greece

e-mail: a_tsili@yahoo.gr; atsili@cc.uoi.gr

2\ Embryonic Development

and Normal Anatomy

The paramesonephric ducts (Müllerian ducts) represent the precursors of the uterus, fallopian tubes, cervix, and upper vagina. The upper two-thirds of the vagina are formed by

the caudal end of the fused Müllerian ducts. Lateral fusion of the paramesonephric ducts occurs between the seventh and ninth weeks of gestation, when the lower segments of the paramesonephric ducts fuse. At this stage, a midline septum is present in the uterus, which usually regresses at about 20 weeks, although it may persist. Vertical fusion occurs in the eighth week, when the lower most fused paramesonephric ducts fuse with the ascending endoderm of the sinovaginal bulb. The lower third of the vagina is formed as the sinovaginal node (bulb) canalizes. The sinovaginal node inserts into the urogenital sinus at Müller’s tubercle. The hymen, a membrane separating the vagina from the urogenital sinus develops and is normally perforated by birth (Mann et al. 2012).

The external genitalia begin to display sexual differentiation during the tenth week, with complete differentiation occurring around the 12th week (Mann et al. 2012). The unfused parts of the genital swellings give rise to the labia majora, the folds fuse anteriorly to form the mons pubis and anterior labial commissure, and posteriorly the posterior labial commissure. The urethral folds fuse posteriorly to form the frenulum of the labia minora. The unfused urethral folds give rise to the labia minora. The unfused genital swellings enable the urogenital sinus to open into the anterior urethral part of the vagina and the vaginal vestibule. The genital tubercle becomes the clitoris by the 14th week (Mann et al. 2012).

The vagina is a 7–9-cm-long fibromuscular tube, extending from the vulvar vestibule to the uterus. It is attached to the levator ani at the level of the urogenital diaphragm, and is in close proximity to the urethra and neck-trigone area of the urinary bladder anteriorly, and to the anal canal and lower rectum posteriorly (Fig. 1) (Basmajian 1971; Siegelman et al. 1997; Walker et al. 2011; Hricak et al. 1988; Chang 2002; Griffin et al. 2010; Gardner et al. 2015). The vagina is anatomically divided into thirds, important for classifying tumor location

POSTERIOR

FORNIX

ANTERIOR

FORNIX

CLITORIS

Fig. 1  Anatomic draft of the normal female pelvis in sagittal orientation

and lymphatic drainage (Griffin et al. 2010; Gardner et al. 2015). The lower third is defined below the level of the bladder base, with the urethra anteriorly. The middle third corresponds to the level of the bladder base, and the upper third is at the level of the vaginal fornices (Fig. 2). The posterior vaginal wall is longer and ends in the posterior fornix, and the shorter anterior wall ends in the anterior fornix (Fig. 3). The vagina is lined with estrogen-sen- sitive stratified squamous epithelium. This epithelium lines a tunica propria, which has numerous transverse folds (rugae). Outside the tunica propria there is a thin muscular coat of longitudinal fibers and some interlacing circular ones and a thick fibro-areolar adventitious coat (Mann et al. 2012).

The vagina is supplied by a network of vessels formed by an anastomosis between the vaginal and uterine branches of the internal iliac artery. The middle rectal artery and internal pudendal artery provide additional blood supply to the mid and lower third of the vagina, respectively. Venous drainage is via the uterine and vaginal venous plexuses into the internal iliac veins. Posteriorly, this plexus forms the rectovaginal septum. Lymphatic drainage of the upper two-thirds of the vagina is into the internal and

Fig. 2  Normal anatomy of the vagina in a premenopausal woman. Sagittal T2WI shows the three anatomic divisions of the vagina

Fig. 3  Sagittal T2WI in a premenopausal woman delineates anterior and posterior vaginal fornices (long arrow)

external iliac lymph nodes. The lower third drains into the superficial inguinal nodes (Griffin et al. 2010).

The vulva is comprised of the mons pubis, the labia majora and minora, the clitoris, the ­vestibular bulb, the Bartholin glands, and the vestibule of the vagina. The mons pubis is composed of adipose tissue overlying the symphysis pubis and separating inferiorly into the

Clitoris

Labia

majora Urethra

Vagina

Labia minora

Anus

Fig. 4  The female external genitalia (vulva)

labia majora. The labia minora, the two thin skin folds lying between the labia majora, fuse at the level of the glans of the clitoris. The area between the labia minora is the vestibule of the vulva, containing the vaginal introitus and external urethral meatus. The Bartholin glands located posterolateral to the vaginal introitus secrete lubricant via ducts into the vestibule (Fig. 4) (Griffin et al. 2010; Hosseinzadeh et al. 2012; Lee et al. 2011). The vulva is supplied by branches of the external and internal pudendal arteries, with lymphatic drainage into the medial group of superficial inguinal nodes. Subsequent lymphatic flow is to the deep inguinal nodes, and then to the caudal external iliac nodes (Griffin et al. 2010; Lee et al. 2011).

3\ Imaging Appearance

of the Normal Vagina

and Vulva

3.1\ CT Appearance

CT is not considered the modality of choice for the evaluation of vaginal and vulvar diseases, due to its poor tissue characterization and the use of ionizing radiation. Based on the American College of Radiology Appropriateness Criteria, CT may be used to assess the local extent of vaginal cancer and to evaluate for nodal and distant metastases, although the sensitivity of the

Fig. 5  Transverse MPR (portal phase) in a young woman depicts normally enhancing vaginal mucosa (long arrow)

technique is modest compared to MRI (American College of Radiology 2013). However, CT is often the initial diagnostic examination in the emergency settings in patients presenting with abdominal pain and nonspecific clinical symptoms. In these cases, knowledge of the normal CT appearance of the vagina and vulva is useful to avoid misdiagnosis (Walker et al. 2011; Yitta et al. 2009). Multidetector CT with two-dimen- sional multiplanar reformatted (MPR) images has improved visualization of the normal anatomy and pathology of the female pelvis (Yitta et al. 2009). If vaginal pathology is suspected, a vaginal tampon or vaginal gel may be inserted to better define the vagina.

The normal vagina demonstrates intense central enhancement, which corresponds to the vaginal mucosa, and a poorly enhancing peripheral vaginal wall, in women of childbearing age (Fig. 5). In postmenopausal women, the vaginal mucosa has similar CT density to that of the vaginal wall and adjacent pelvic structures (Walker et al. 2011; Yitta et al. 2009). Vaginal pathology may be difficult to assess on CT due its similar density with the surrounding soft-tissue structures (Walker et al. 2011).

The vulva appears as a triangular soft-tissue structure within the perineum, bounded by the symphysis pubis anteriorly, the anal sphincter posteriorly, and the ischial tuberosities laterally (Griffin et al. 2010).

3.2\ MRI Protocol

Conventional MRI sequences obtained with a phased-array pelvic coil are usually diagnostic for the evaluation of the normal vaginal and vulvar anatomy and diseases (Walker et al. 2011; Griffin et al. 2010; Gardner et al. 2015; López et al. 2005). The use of a dry tampon or vaginal gel, although not included in routine practice provides better distension and visualization of the vagina, especially recommended in the assessment of vaginal malignancies (Gardner et al. 2015). The endoanal endoluminal coil can also be used to provide highresolution images of the rectum, anal canal, rectovaginal septum, and vagina, although the small field of view represents a limitation (Griffin et al. 2010). Axial T1-weighted (T1WI) and T2-weighted images (T2WI) and sagittal T2WI are included in the standard MRI protocol. Highresolution axial T2WI with thin slices and small field of view is useful in imaging vaginal and vulvar pathology and especially tumors. Coronal T2WI is used for the assessment of congenital anomalies, with a large field of view to include the kidneys. Fat-suppressed axial T1WI improves detection of hemorrhagic or proteinaceous lesions and distinguish them from fat. T2WI with fat suppression is useful for the assessment of vaginal fistulas (Walker et al. 2011; Griffin et al. 2010; Gardner et al. 2015; López et al. 2005). Threedimensional dynamic contrast-enhanced (DCE) images after intravenous administration of gadolinium are recommended in a sagittal orientation in cases of vaginal malignancies (Gardner et al. 2015). The role of diffusion-weighted imaging is currently unknown, but may be promising.

3.3\ MRI Appearance

At MRI, the vagina has uniform T1 signal, resembling that of skeletal muscles (Fig. 6a). The vaginal wall anatomy is best depicted on T2WI, similar to the zonal anatomy of the uterus. The mucosa along with any intraluminal secretions appears as a thin layer of bright T2 signal. Surrounding the vaginal mucosa is a submucosal layer of collagen and elastic fibers and a muscularis consisting of

Fig. 6  Normal vaginal anatomy at MRI in a 25-year-old woman. (a) Axial T1WI depicts normal vagina mainly isointense to the surrounding muscles. Note that the middle layer of the vagina has low signal intensity (arrow). T2WI in (b) transverse and (c) sagittal orientation depicting the zonal

anatomy of the vagina. The fibromuscular wall is of low signal intensity (arrowhead), surrounding a thin hyperintense layer, which corresponds to the vaginal mucosa and intraluminal mucus. External to the fibromuscular wall is a hyperintense layer containing a prominent venous plexus (arrow).

inner longitudinal and outer circular smooth muscle, exhibiting a low T2 signal. The outer connective tissue layer of the vaginal wall contains a prominent plexus of veins as well as the vaginal arteries and nerves. This layer appears hyperintense on T2WI, due to slow venous blood flow (Fig. 6b, c) (Siegelman et al. 1997; Walker et al. 2011; Griffin et al. 2010; Gardner et al. 2015; López et al. 2005; Taylor et al. 2007). Following intravenous administration of gadolinium, the vaginal mucosa enhances (Fig. 7). With the use of vaginal gel, the hyperintense mucosal layer is obscured by the hyperintense gel and only two layers are seen, the hypointense muscularis and the hyperintense adventitia (Gardner et al. 2015).

The MRI appearance of the normal vagina changes with patient age and phase of the men-

Fig. 7  Dynamic contrast-enhanced subtracted MR image (early phase) in sagittal orientation in a premenopausal woman shows normal enhancement of the vaginal mucosa (arrowhead)

Fig. 8  (a) Axial T1WI shows normal vulva (arrowhead) with intermediate signal intensity, similar to that of muscles. T2WI in (b) axial and (c) sagittal orientation depicts

vulva (arrowhead) with intermediate signal intensity, similar to that of normal myometrium (arrow)

strual cycle (Siegelman et al. 1997; Walker et al. 2011; Griffin et al. 2010; López et al. 2005; Taylor et al. 2007). Vaginal mucosa is relatively thin before menarche and after menopause. The vaginal wall and central mucus have the highest T2 signal and maximal thickness during the midsecretory phase of the menstrual cycle. Maximal T2 contrast between the vaginal wall and the surrounding pelvic fat is seen during the early proliferative or late secretory phase. In postmenopausal women who are undergoing hormone replacement therapy, the MRI appearance of the vagina is similar to that in premenopausal females (Walker et al. 2011).

At MRI, the vulva shows low to intermediate T1 signal and slightly high T2 signal (Fig. 8) (Griffin et al. 2010).

4\ Congenital Anomalies

of the Vagina and Vulva

Congenital anomalies of the vagina are associated with other Müllerian duct anomalies (MDAs) which result from non-development or fusion defects of the Müllerian ducts. The true incidence and prevalence of MDAs are difficult to assess. The close embryologic proximity of the Müllerian and Wolffian systems explains the association of MDAs with renal anomalies, the latter reported in 30–80% of cases. MRI is currently the modality of choice for the evaluation of patients with ambiguous genitalia and suspected MDAs, helping to demonstrate the presence or absence of the vagina, uterus, and ovaries, therefore, obviating unnecessary diagnostic ­laparoscopy.