Anatomy and dimensions of the uterus

Age-related evolution of size and structure

The development of the organ goes through several physiological stages that are clearly monitored by ultrasound:

• Neonatal period: Immediately after birth, the uterus appears enlarged and thickened, with its length ranging from 2 to 4.5 cm. During this period, the endometrium is clearly visualized. This pattern is due to the intrauterine effect of maternal estrogens.
• Prepubertal age (by 1 year): As maternal hormone levels decline, the organ decreases in size and acquires a characteristic tubular shape. The uterine fundus and cervix become equal in size, and the endometrium is no longer detectable upon visualization.
• Pubertal period: Active hormone-dependent growth begins. The uterine fundus enlarges, becoming up to three times larger than the cervix. The total length of the organ reaches 5–7 cm, and it assumes the typical pear shape characteristic of an adult woman. The appearance of the endometrium begins to change regularly depending on the current phase of the menstrual cycle.

Congenital anomalies of shape and structure

The normal anatomy of the organ depends on the proper development and fusion of the Müllerian ducts (Müllerian ducts). Disruption of these processes leads to the formation of various malformations:

1. Unicornuate uterus: Characterized by a specific "banana-shaped" configuration. Often accompanied by the presence of a rudimentary horn. If this horn is functional (contains endometrium) but does not communicate with the main cavity, blood breakdown products accumulate within it. This leads to the formation of haematometra (haematometra) and significantly increases the risk of endometriosis (endometriosis).
2. Uterus didelphys (Uterus Didelphys): Occurs due to complete non-fusion of the ducts. Two isolated uterine horns of normal size and two separate cervices are formed. At the same time, the normal thickness of the myometrium and endometrium is preserved.
3. Bicornuate uterus (Bicornuate Uterus): The result of incomplete fusion of the cranial parts of the ducts. The uterine horns communicate with each other, and the fundus has a concave shape.
4. Septate uterus (Septate Uterus): The most common anomaly, arising from incomplete resorption of fibrous tissue between the horns. The septum may be partial or reach the external os of the cervix.
5. Arcuate uterus (Arcuate Uterus): Considered a variant of normal. Manifests as a smooth, broad depression of the cavity fundus with an absolutely normal outer contour. It does not affect fertility or pregnancy maintenance.
6. Diethylstilbestrol-related anomalies: Intrauterine exposure to this synthetic estrogen leads to organ hypoplasia, formation of a T-shaped cavity, irregular constrictions, and intraluminal filling defects.

Diagnostic imaging and differential signs

Ultrasound, hysterosalpingography (HSG), and MRI are used to assess uterine anatomy. Magnetic resonance imaging (especially T2-weighted images in the oblique coronal plane) is critical for the differential diagnosis of malformations.

A key MRI sign to distinguish a bicornuate uterus from a septate uterus is the evaluation of the outer myometrial contour of the fundus. In a bicornuate uterus, a cleft measuring $\ge$ 1 cm is identified. In a septate uterus, the outer contour remains convex, flat, or has a concavity of $\le$ 1 cm. Accurate measurement of the septum size is necessary for planning surgical treatment (hysteroscopic metroplasty).

Topographic changes in adjacent pathologies

The anatomical position of the uterus can change significantly in vaginal malformations. For example, with an imperforate hymen or a transverse vaginal septum, the outflow of menstrual blood is impaired.

The accumulation of blood leads to the formation of haematocolpos. The distended vagina presents as a large, elastic mass whose upper pole can reach the umbilicus. Meanwhile, the uterus is displaced high above the pelvic inlet. During a rectoabdominal examination, pressure on the haematocolpos is transmitted to the uterus and felt upon suprapubic palpation, which helps distinguish this condition from an ovarian cyst.

Class and exam questions

What else to study on this topic

• Imaging diagnostics of Müllerian duct anomalies (MRI, HSG, 3D Ultrasound).
• Pathogenesis and complications of vaginal atresia (formation of haematocolpos and pyocolpos).
• Effect of diethylstilbestrol on the intrauterine development of the reproductive system.
• Surgical treatment of septate uterus (hysteroscopic metroplasty).
• Differential diagnosis of pelvic masses in adolescents.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.