Female - Fundus of Uterus

1. Overview

The fundus of the uterus is the broad, dome-shaped upper portion of the uterus, positioned above the openings of the fallopian tubes. It serves as a key anatomical landmark in gynecology and obstetrics and is involved in multiple reproductive functions, including menstruation, implantation, and pregnancy. The size and position of the fundus can change significantly depending on hormonal states and gestational age.

2. Location

The fundus is located at the superior-most aspect of the uterus. It lies above the uterine body and superior to the openings of the right and left fallopian tubes. In an anteverted uterus (the most common position), the fundus is tilted slightly forward over the bladder. It is situated deep within the pelvic cavity in non-pregnant females but may extend into the abdominal cavity during pregnancy.

3. Structure

Structurally, the fundus is part of the uterine wall and is composed of the same three layers as the rest of the uterus:

• Endometrium: The inner mucosal lining, which undergoes cyclic changes and supports implantation.

• Myometrium: The thick middle layer made of smooth muscle fibers that contract during menstruation and labor.

• Perimetrium: The outermost serous layer derived from peritoneum.

The fundus is richly vascularized by branches of the uterine and ovarian arteries and contains uterine glands and spiral arteries within the endometrial layer. It is shaped like a rounded dome and is continuous with the uterine body inferiorly.

4. Function

The fundus of the uterus has several important functions:

• Acts as a structural support and an anchoring site for the fallopian tubes

• Plays a role in the implantation of the fertilized egg, especially if implantation occurs in the upper part of the uterus

• Participates in coordinated uterine contractions during menstruation and labor

• Serves as a critical reference point for measuring uterine height during pregnancy

5. Physiological Role(s)

The fundus plays significant roles in the female reproductive cycle and pregnancy:

• Implantation and Gestation: In a typical pregnancy, implantation occurs in the upper posterior wall of the uterus near the fundus, where blood supply is richest and uterine wall thickness is optimal.

• Muscular Activity: The fundal region initiates strong, coordinated contractions during labor, helping to expel the fetus downward through the birth canal.

• Menstrual Function: During the menstrual cycle, the endometrium lining the fundus undergoes proliferative and secretory phases. If pregnancy does not occur, it is shed during menstruation.

• Pregnancy Monitoring: The fundal height (distance from pubic symphysis to fundus) is a useful clinical measure to estimate fetal growth and gestational age.

6. Clinical Significance

The fundus has various clinical implications in gynecology and obstetrics:

• Uterine Positioning: Changes in the orientation of the fundus (e.g., retroverted uterus) may affect fertility or menstrual flow but are usually benign.

• Fundal Height Measurement: During prenatal visits, measuring the height of the fundus helps assess fetal growth and detect abnormalities like intrauterine growth restriction (IUGR) or polyhydramnios.

• Placental Location: A fundal placenta is typically considered normal, while low-lying or previa placentas are clinically concerning.

• Uterine Fibroids: Fibroids located in the fundus (submucosal or intramural) may cause abnormal bleeding or affect fertility.

• Uterine Rupture: Rare but serious obstetric emergency that may occur at the fundus, particularly in women with previous uterine surgery like C-sections or myomectomy.

• Intrauterine Device (IUD) Placement: The ideal position for an IUD is within the uterine cavity, with the device seated near the fundus to ensure proper function and avoid expulsion.

Ultrasound imaging is commonly used to visualize the fundus and evaluate conditions such as fibroids, congenital uterine anomalies, or pregnancy complications.