Fiona M. Lewis Vulval lesions are not well described in the early medical literature, but first appear in the writings of Severinus Pineus in the sixteenth century and van den Spieghel in the seventeenth century. The terms used to describe the anatomical structures are often related to their function. The word vulva is derived from the Latin word for ‘wrapping’. The vagina (sheath) and mons veneris (hill of Venus) are obvious descriptions. The clitoris is usually thought to come from the Greek kleitoris, meaning ‘key’ or ‘gatekeeper’. Hymen is derived from the Greek hymen, meaning membrane. The labia are probably so called because they surround the vaginal opening like lips (Latin labium – lip). There is a very wide variation in the appearance of the normal vulva, and this chapter looks at the normal anatomy, anatomical variants, and normal histological features at different sites. It is vital to understand the normal before the abnormal is diagnosed, thereby avoiding unnecessary treatment and worry for the patient. The vulva consists of seven main parts: the mons pubis, the labia majora and minora, the vestibule of the vagina, the hymen, the clitoris, and the external urethral orifice (Figure 2.1). All of these structures may vary in size and symmetry, but this is a subject that has been rather neglected. In a study of 59 textbooks, very little was included about this topic [1]. Patients often worry about normal variants and the quest for the ‘perfect’ vulva. Indeed, in a study of 33 women seeking labial reduction, all had labia minora within normal limits [2]. This incorrect perception was confirmed in another study of younger adolescent girls presenting for consideration of genital surgery. Again, none had documented abnormality [3]. Patients will also perceive an abnormality if the labia minora are visible, even though they are of normal size [4]. There has been more interest recently in the normal variation in appearance of the vulva in both popular culture and the scientific literature. The artist Jamie McCartney took plaster casts of 400 vulvas to create a sculpture which illustrates the wide range of appearance (www.greatwallofvagina.co.uk), and this has been used as both an artistic and educational resource. Several studies have addressed the normal vulval appearance in adults [5,6,7], prepubertal girls [8,9], and adolescents [10]. These studies include women of different ethnicities but the measurements are similar, and average measurements of the vulval structures in adults are shown in Table 2.1. It has been shown that genital dimensions have no effect on sexual function [11]. Figure 2.1 Anatomy of the normal vulva. The mons pubis (mons) in the adult female is a prominent pad of hair‐bearing skin and subcutaneous fat overlying the pubic symphysis. It forms an inverted triangle with the base being the anterior horizontal line of pubic hair growth. The average length of the base is 16 cm, and the height about 13 cm [12]. The character of pubic hair varies with ethnic background, as it is generally thicker in type 5 and 6 skin types. The normal hair density is 6–31 hairs/cm2, but this, together with the rate of hair growth, reduces with age. About a third of women over the age of 60 have progressive loss of pubic hair [13]. There is no change in the thickness of the hair with age. In contrast to hair growth in the axillae and on the scalp, pubic hair growth is not altered during pregnancy [14]. The labia majora are two cutaneous folds that form the lateral boundaries of the pudendal cleft. They originate from the mons pubis anteriorly and merge with the perineal body posteriorly (the posterior labial commissure). The subcutaneous fat is mainly deposited in the medial aspects, and so they tend to flatten out as they reach the perineal body. The lateral surfaces of the labia majora are adjacent to the medial surfaces of the thighs and are separated from them by a deep groove, the genitocrural or inguinal fold. The medial surfaces may be in contact with each other, but may be separated by the labia minora if they are large. The size of the labia majora varies considerably. The length of the labia majora and introitus has been shown to be positively correlated with body mass index but inversely correlated with age [5]. Table 2.1 Normal measurements of vulval structures The labia minora are two thin folds of keratinised skin that lie medial to the labia majora and lateral to the vestibule. They are separated from the labia majora by interlabial folds (sulci) in which the normal secretions from the adjacent skin surfaces may accumulate. Anteriorly, the labia minora divide into lateral and medial parts. The lateral parts join in a fold of skin over the glans to form the prepuce or hood of the clitoris, and the medial parts join under the clitoris to form its frenulum. Posteriorly, the labia minora fuse to form a transverse fold behind the vaginal opening, the fourchette. There is great variation in the size and symmetry of the labia minora (Figure 2.2a–d). In a study of 319 women, the length of the labia minora was associated with height and weight, and 23.8% of women had a 30% difference in the width of the labia minora on each side, confirming the asymmetry seen [7]. In 44 adolescents between the ages of 10 and 19, variation in length and width was again confirmed, with 43% showing asymmetry [10]. They can sometimes be bifid in their anterior insertion (Figure 2.2d). There is also wide variation in the texture of the labia minora. In a study of 50 women, the rims of the labia minora were smooth in 14, moderately rugose in 34, and markedly rugose in 2 [6]. Pigmentation of the rims is very common and was confirmed in 41 of the 50 patients. The whole of the inner surface of the labia minora may be covered with small sebaceous papules. These are a normal finding on the vulva, and the term Fordyce spots, which is often used, is not accurate as this refers to ectopic sebaceous glands, as found on the buccal mucosa. On the vulva, they are not ectopic but a part of the normal anatomy. They are very prominent in some women but can be seen more clearly if the labia are stretched (Figure 2.3). The clitoris is a complex structure, and our understanding of the anatomy has been helped by the use of MRI studies [15,16]. The clitoris has a wishbone like structure with the arms being the crura extending forwards as the corpora cavernosa and meeting in the midline to form the body of the clitoris (Figure 2.4). The tip of the body then bends anteriorly to form the glans clitoris, which is the only visible part, and is non‐erectile. The glans is covered by the clitoral hood, formed by the anterior fusion of the labia minora. The crura are attached to the pubic rami and covered by the ischiocavernosus muscle, and the clitoral body is attached to the pubic symphysis by a suspensory ligament. The clitoral bulbs lie between the crura and the urethra against the vaginal wall. They are covered by the bulbospongiosus muscles, which extend from the perineal body, around the vagina and urethra, to the glans clitoris. The whole of the clitoris is composed of similar erectile tissue with the exception of the glans [16]. Figure 2.2 Variation in appearance of normal labia minora. (a) Symmetrical labia minora with pigmentation on rim. (b) Labia minora protruding outside labia majora in a patient with lichen sclerosus. (c) Fimbriation and pigmentation on rims of labia minora. (d) Asymmetry of labia minora with bifid insertion on right side. The average clitoral width in children was measured at 3.8 mm, and this did not alter with age although the other vulval components increased with age [9]. This is important to exclude clitoral hypertrophy. In an adult study, the clitoral width was reported to increase with parity [17], but this has not been confirmed in larger studies. The vestibule extends from the clitoral frenulum to the fourchette and laterally from the hymenal ring to a variable position on the inner aspect of each labium minus. The vagina, urethra, ducts of Bartholin’s glands, and the minor vestibular glands all open into the vestibule. The area of the vestibule between the vaginal opening and the posterior union of the labia minora forms a shallow depression termed the vestibular fossa or fossa navicularis. Scars from obstetric tears can be seen on the anterior and posterior vestibule and sometimes pigment. Figure 2.3 Fordyce spots: yellow papules on inner labium majus. Figure 2.4 Anatomy of the clitoris. In some patients, there may be a very distinct line which represents the transition from the keratinised skin of the labium minus to the vestibular mucosa. This was first described by the Edinburgh gynaecologist David Berry Hart in his textbook of gynaecology in 1882 [18] and is termed ‘Hart’s line’. He wrote ‘a line running separates mucous membrane from skin – starting at the base of the inner aspect of the right labium minus, it passes down beside the base of the outer aspect of the hymen, up along the base of the inner aspect of the left labium minus, in beneath the prepuce of the clitoris and down to where it started from’. This is often very obvious, particularly in young women, and the normal mucosal surface medially is frequently mistaken for inflammation (Figure 2.5). Bartholin’s glands are situated deeply in the posterior labia majora. They lie just inferior and lateral to the bulbocavernosus muscle and are normally not palpable. The main duct of each Bartholin’s gland passes deep to the labium minus to open into the vestibule, and their openings are often seen at 5 and 7 o’clock. These can be very prominent in some patients with erythema around the glandular duct opening (Figure 2.6). Figure 2.5 Hart’s line, which demarcates the junction of the keratinised skin of the labia minora with the non‐keratinised mucosa of the vestibule. Figure 2.6 Openings of Bartholin’s ducts. The minor vestibular glands are small shallow glands usually less than 3 mm into the dermis and open directly to the surface. In postmortem studies, they vary in number from 1 to more than 100 [19]. Vestibular papillae are 1–5 mm thin projections that occur in the vestibule and inner labia minora, and are a normal variant (Figure 2.7). It is suggested that they are the female equivalent of the tiny symmetrical projections found around the coronal sulcus known as penile pearly papules of the penis [20]. Originally, it was thought that the lesions were induced by the human papillomavirus (HPV), but there is now good evidence to the contrary [21, 22]. The normal glycogenation of the cells at the vestibule is often mistaken for koilocytosis, which is another reason for good communication with the pathologist. Vestibular papillae can be distinguished from viral warts as they are soft and the same colour and texture as the surrounding mucosa. They are symmetrical in distribution and each papilla arises from a solitary base (Figure 2.8), whereas viral warts often coalesce into a single base. Dermoscopy has also been used to distinguish the two entities [23] where the single base of each papilla is again confirmed. The application of 5% acetic acid does not produce acetowhitening in vestibular papillomatosis. They are usually asymptomatic, and no treatment is needed. Figure 2.7 Vestibular papillae. Multiple filiform projections of the vestibular epithelium. Figure 2.8 Histology of vestibular papillomatosis. Low power showing papillary projections with normal epithelium each arising from individual base. The hymen is a thin membrane of connective tissue surrounding the inner edge of the vestibule and the opening of the vagina. The appearance is again varied and can be a ring or semi‐circular fold.
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The Normal Vulva
Normal vulval anatomy
Mons pubis
Labia majora
Mean (mm)
Range (mm)
Clitoris
Width
4.7
1–22
Length
10.0
5–35
Clitoris to urethra
25.0
3–65
Labia majora
Length
8.3
12–180
Labia minora
Length
50.0
5–100
Width
28.6
1–61
Perineum
25.7
3–55
Urethra
Length
40.0
19–45
Labia minora
Sebaceous glands (Fordyce spots)
The clitoris
The vestibule
Hart’s line
Bartholin’s glands
Minor vestibular glands
Vestibular papillomatosis
Hymen
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