Surgical Anatomy of UterusCHAPTER 1

The uterus is hollow, muscular organ situated in the pelvis between the bladder in front and the rectum behind.

Its normal position is one of anteversion and anteflexion. The uterus usually inclines to the right (dextrorotation) so that the cervix is directed to the left (levorotation) (Figs 1.1A and B) and comes in close relation with the left ureter.^1,2

The uterus (Fig. 1.2) measures about 8 cm long, 5 cm wide at fundus and its walls are about 1.25 cm thick. Its weight varies from 50 to 80 gm. It has the following parts:^3–5

The body is further divided into fundus–the part which lies above the openings of the uterine tubes. The body proper is triangular and lies between the openings of the tubes and the isthmus. The superolateral angles of body of the uterus project outwards from the junction of fundus and body and are called the cornua of the uterus. The uterine tube, round ligament and ovarian ligament are attached to it.^1,3

Isthmus is a constricted part measuring about 0.5 cm situated between the body and the cervix. It is limited above by the anatomical internal os and below by the histological internal os.^2,6

Cervix is cylindrical in shape and measures about 2.5 cm.^{2, 3,6} It extends from the isthmus and ends at the external os which opens into the vagina after perforating its anterior wall. The part lying above the vagina is called supravaginal and that which lies within the vagina is called the vaginal part.

The uterine cavity is triangular on coronal section with the base above and the apex below. Its measures about 3.5 cm. The cervical canal is fusiform and measures about 2.5 cm. Thus, the normal length of the uterine cavity is usually 6.5 to 7 cm.^2,3

Anteriorly: Above the internal os, the body forms the posterior wall of the uterovesical pouch.^{1, 2,7} Below the internal os, it is separated from the base of bladder by loose areolar tissue.

Posteriorly: It is covered with peritoneum and forms the anterior wall of pouch of Douglas containing coils of intestine.^{6, 8,9}

Laterally: The double fold of peritoneum of the broad ligament are attached between which the uterine artery ascends up. Attachment of Mackenrodt's ligament extends from the internal os down to the supravaginal cervix and lateral vaginal wall. About 1.5 cm away at the level of internal os, the uterine artery crosses the ureter. The uterine artery crosses from above and in front of the ureter, soon the ureter enters the ureteric tunnel.^{4, 6,8}

The wall consists of three layers from outside inwards (Fig. 1.2):

Perimetrium: It is the serous coat which covers the entire organ except on lateral borders. The peritoneum is intimately adherent to the underlying muscles.^1,7

Myometrium: It consists of thick bundles of smooth muscle fibers held by connective tissues and are arranged in various directions. During pregnancy, three distinct layers can be identified–outer longitudinal, middle interlacing and the inner circular.^2,7

Endometrium: The mucous lining of the cavity is called endometrium. As there is no submucous layer, the endometrium is directly apposed to the muscle coat.¹ It consists of lamina propria and surface epithelium. The surface epithelium is a single layer of ciliated columnar epithelium. The lamina propria contains stromal cells, endometrial glands, vessels and nerves. The glands are simple tubular and lined by mucus secreting nonciliated columnar epithelium which penetrate the stroma.^1,2 The endometrium is changed to decidua during pregnancy.

The cervix is composed mainly of fibrous connective tissue. The smooth muscle fibers average 10 to 15 percent.^1,6 Only posterior surface has peritoneal covering. Mucous coat lining the endocervix is simple columnar and lining gland is nonciliated secretory columnar cells. The vaginal part of the cervix is lined by stratified squamous epithelium. The squamocolumnar junction is situated at the external os.

Peritoneum in relation to the uterus (Figs 1.4 and 1.5):^1–3,5,6 Anteriorly the peritoneum covering the superior surface of the bladder reflects over the anterior surface of the uterus at the level of the internal os. The pouch, so formed, is called uterovesical pouch. The peritoneum is firmly attached to the anterior and posterior walls of the uterus and upper one-third of the posterior vaginal wall where from it is reflected over the rectum. 5

The pouch, so formed, is called pouch of Douglas.

The blood supply is from the uterine artery one on each side. The artery arises directly from the anterior division of the internal iliac or in common with superior vesical artery. The other sources are ovarian and vaginal arteries to which the uterine arteries anastomose.^1,6

The venous channels correspond to the arterial course and drain into internal iliac veins.

From the fundus and upper part of the body of the uterus, the lymphatics drain into preaortic and lateral aortic groups of glands. The cornu drains to superficial inguinal glands along the round ligament.^1,66

Lower part of the body drains into external iliac groups.

On each side, the lymphatics drain into external iliac, obturator lymph nodes directly or through paracervical lymph nodes, internal iliac groups and sacral groups.^1,2

The nerve supply of the uterus is derived principally from the sympathetic system and partly from the parasympathetic system. Sympathetic components are from T5 and T6 (motor) and T10 to L1 spinal segments (sensory). The somatic distribution of uterine pain is that area of the abdomen supplied by T10 to L3. The parasympathetic system is represented on either side by the pelvic nerve which consists of both motor and sensory fibers from S2, S3, S4 and ends in the ganglia of Frankenhauser.^{1, 2,7}

Direct visual inspection of the cervical canal and uterine cavity through a rigid, flexible, or contact hysteroscope (Figs 1.7 and 1.8).^6,10

In embryos of 10 weeks, the female duct system (Müllerian or paramesonephric) is evident. The cranial segments of both ducts persist as uterine tubes.

Slanting middle segments of both ducts will soon merge and give rise to the fundus of the uterus. The caudal segments of the ducts, already fused, become the corpus cervix and much of the vagina. The caudal end of the now single tube presses against the urogenital subdivision of the cloaca, the joint membrane then representing the future hymen. The uterine epithelium buds off glands by the seventh prenatal month, and this establishes the endometrium; yet, they remain small until the child reaches puberty.12

A distinction between uterus and vagina becomes evident at the middle of the fourth month when the fornices appear. The muscular wall, or myometrium, of the uterus is indicated at 3 months by mesenchyme of the genital cord condensing into smooth muscle fibers that invest the endometrium. The parametrium differentiates from the exterior of the genital cord into a peritoneal covering (mesothelium and connective tissue).