(1)
Department of Fetal Medicine and Obstetric & Gynecological Ultrasound, Manipal Hospital, Bangalore, Karnataka, India
The vagina is a structure that is generally overlooked during the ultrasound imaging of the female pelvis done for the detection of gynecological disease.
On a transabdominal ultrasound (TS) in the midsagittal plane, the normal vagina is seen below the uterus as a hypoechoic elongated structure with a central bright linear echo (which represents the collapsed vaginal lumen betweenopposing vaginal walls). On TAS, only the upper half of the vagina can be seen, as the lower part is obscured by shadowing from the pubic symphysis.
On a transvaginal scan, evaluating the vagina is possible, though often considered suboptimal because of the proximity of the vagina to the probe and the collapsed nature of the vaginal walls. MRI has therefore been commonly used in the diagnostic evaluation of the vagina. Transrectal examination may help when TVS is not possible or there is local bleeding. Gel sonovaginography (GSV) has been used by the author for evaluating suspected or known vaginal pathology as it provides better resolution and spatial orientation.
For ultrasound (TVS) evaluation, it is important that the probe, once introduced into the vagina, is gradually moved upwards, while simultaneously evaluating the anterior and posterior vaginal walls. The vagina is limited on its outer surface by the hyperechoic visceral facia. The posterior vaginal wall is in close proximity to the anterior muscularis of the anus and rectum, and the anterior vaginal wall is in close proximity to the urethra and the base of the bladder. The space between the hyperechoic outer margin of the vagina and the rectum is called the rectovaginal space, while that between the outer margin of the vagina and the bladder is called the vesicovaginal space. Both of these spaces are comprised of areolar tissue.
The common vaginal pathologies encountered are congenital vaginal anomalies, vaginal cysts, vaginal masses and deep infiltrating endometriosis.
6.1 Normal Vagina (Fig. 6.1)
The vagina is a collapsed fibromuscular tubular sheath extending from the vulva to the uterus with the cervix projecting into its upper end. The average length of the vagina is generally 7–9 cm, with the posterior wall being longer than the anterior wall. The vaginal fornices are the upper part of the vagina, and based on their relation to the cervix, they are arbitrarily divided into the anterior, the posterior and the two lateral fornices. The vaginal wall is made up of three layers – the inner mucosa (stratified squamous epithelium), the muscularis (connective tissue and smooth muscle fibres) and the adventitia (endopelvic visceral fascia surrounding the vagina). A small amount of urine within the vaginal lumen in girls of the paediatric age group could be a normal finding.
Fig. 6.1
Normal vagina (a) TAS – the lumen of the upper vagina is seen as a hyperechoic line (arrow) extending down from the lower end of the cervix. The lower vagina cannot be seen due to shadowing by the pubic bones. (b) TVS – the vagina is not clearly visualised because of its collapsed lumen (arrow showing the lumen of the distal vagina). (c) GSV – corresponding to the image in (b). Here the vaginal walls are seen apart because of the intervening gel (arrow), which facilitates optimal visualisation of the vaginal walls and its lumen
6.2 Congenital Vaginal Anomalies
The upper two-third of the vagina develops from paired Mullerian ducts (from which the uterus and cervix also develop), and the lower one-third develops from paired sinovaginal bulbs. The paired Mullerian and sinovaginal components are solid to begin with. Later, they get canalised. They fuse together with that of the contralateral side to form a common canal. In addition, the Mullerian and sinovaginal components also fuse together to form a single common vagina. A persistent transverse septum can result from incomplete canalisation at various levels of the vagina. If the lateral fusion or resorption of the paired Mullerian ducts is abnormal, a longitudinal septum will result (which is common in association with anomalies of the uterus and cervix like a septate uterus or a bicornuate uterus). Longitudinal and transverse vaginal septa are dealt with in the chapter on ‘Uterine Anomalies’.
Imperforate hymen is a common congenital abnormality of the female genital tract with a prevalence of about 0.1 %. This has also been dealt with in the chapter on ‘Uterine Anomalies’ (Chapter 12).
6.3 Vaginal Cysts (Figs. 6.2, 6.3, 6.4, 6.5, 6.6, 6.7)
Vaginal cysts are most often incidental findings seen on ultrasound or MRI. Common vaginal cysts are Gartner duct cysts, Mullerian cysts and Bartholin gland cysts. Periurethral cysts (like Skene gland cysts) may also be seen adjoining the vaginal wall.
Other less common vaginal cysts are endometriotic cysts (in association with DIE), inclusion cysts (area of previous surgery), dermoid cysts, etc.
6.3.1 Gartner Duct Cysts and Mullerian Cysts
These cysts result from incomplete regression of the Wolffian (mesonephric) duct or Mullerian (paramesonephric) duct, respectively. It is not possible to differentiate these on ultrasound, and clinically their distinction is of little importance. They are usually asymptomatic unless they are infected, at which time they could cause pain and discomfort.
These cysts are typically seen along the anterolateral wall of the upper vagina, but they may be present anywhere along the lateral aspect of the vagina. The location of the cyst can be found out by observing their relationship to the TVS probe. As the probe is gradually moved upwards, the cyst slides to one side of the probe which lets us know on which side of the vaginal wall the cyst is located.
They are seen as unilocular well-defined cysts, varying in size from 1 to 7 cm, with an average of about 2 cm.
Their contents may be anechoic but may appear hypoechoic when they have turbid contents.
They are non-tender.
If infected, they may show turbid contents with thick and vascular walls.
Fig. 6.2
Vaginal cyst. (a) A large anechoic cyst is seen in the anterolateral vaginal wall. (b) Normal cervix and vagina is seen below the cyst. The lower end of the cyst was some distance away from the introitus. This could either be a Gartner duct cyst or a Mullerian cyst
Fig. 6.3
Vaginal cyst. Unilocular turbid cyst in the anterolateral wall of the upper vagina. This could either be a Gartner duct cyst or a Mullerian cyst
6.3.2 Bartholin Gland Cysts
Bartholin glands are mucin-secreting glands that could develop into retention cysts because of the obstruction of their duct, by trauma or infection. These are usually asymptomatic but may get infected and undergo abscess formation, at which time they may be very painful and tender. The patient may complain of a mass at the introitus. The treatment of Bartholin gland cysts appears simple but recurrence is known. These cysts can rarely be malignant.
These cysts are seen located posterolateral to the vaginal introitus (medial to labia minora).
They are seen as unilocular well-defined cysts, usually 1–4 cm in size.
Their contents often show internal echoes because of the mucin content or due to infection.
They are non-tender, unless infected.
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