What are the causes of an enlarged uterus?

Causes of an Enlarged Uterus

The most common causes of an enlarged uterus are uterine leiomyomas (fibroids), adenomyosis, pregnancy, and endometrial or myometrial malignancies. 1 Each of these conditions has distinct characteristics that can be identified through appropriate imaging techniques.

Common Causes

1. Uterine Leiomyomas (Fibroids)

• Most common cause of uterine enlargement, especially in cases of significant enlargement (≥280g) 2
• Characteristics:
  • Well-circumscribed masses within the myometrium
  • Can be classified as:
    • Subserosal (projecting outward from the uterus)
    • Intramural (within the myometrial wall)
    • Submucosal (projecting into the endometrial cavity)
  • May cause abnormal uterine bleeding, particularly with submucosal location
  • On imaging: appear as well-defined masses with variable signal intensity on MRI 3

2. Adenomyosis

• More commonly associated with smaller uterine enlargement (<280g) 2
• Characterized by the presence of ectopic endometrial glands and stroma within the myometrium
• Features:
  • Diffuse or focal thickening of the myometrium
  • Heterogeneous myometrium with blurred endometrial-myometrial junction
  • On imaging: appears as ill-defined, relatively homogeneous low-signal-intensity areas with high-intensity spots on T2-weighted MRI 3
  • Transvaginal ultrasound shows echogenic nodules/striations radiating from endometrium into myometrium 4

3. Pregnancy

• Normal physiological cause of uterine enlargement
• Enlarging uterus compresses the inferior vena cava and can elevate the diaphragm 1
• In pregnancy, the uterus enlarges progressively, beginning at approximately 12 weeks of gestational age

4. Endometrial Pathologies

• Endometrial hyperplasia
• Endometrial polyps
• Endometrial cancer (particularly in postmenopausal women) 1
  • Type 1 (endometrioid) - associated with excess estrogen exposure
  • Type 2 (non-endometrioid) - typically more aggressive, estrogen-independent

5. Uterine Malignancies

• Endometrial carcinoma - most common gynecologic malignancy
• Uterine sarcomas (including leiomyosarcoma) - rare but should be suspected in postmenopausal women with rapidly growing fibroids 5
• Gestational trophoblastic neoplasia (including hydatidiform mole, invasive mole, choriocarcinoma) 1

6. Other Causes

• Hydronephrosis during pregnancy (can cause mechanical compression from enlarged uterus) 1
• Adenomyotic cysts
• Hematometra (collection of blood in the uterine cavity)

Diagnostic Approach

Initial Imaging

1. Transvaginal ultrasound (TVUS) - first-line imaging modality 1

   • Combined with transabdominal ultrasound for significantly enlarged uterus
   • Doppler imaging should be included to evaluate vascularity
   • Sensitivity of 90-99% for detecting uterine fibroids 1

2. MRI - when ultrasound is inconclusive or further characterization is needed 1

   • Superior for differentiating between adenomyosis and leiomyomas
   • Excellent for mapping fibroids and assessing their number, size, and location
   • Should include diffusion-weighted imaging to help distinguish between benign and malignant pathologies

Key Distinguishing Features

• Fibroids: Well-circumscribed masses with variable signal intensity on MRI; on ultrasound appear as hypoechoic masses with shadowing 1
• Adenomyosis: Ill-defined areas with heterogeneous myometrium and high-intensity spots on MRI; on ultrasound shows myometrial cysts and heterogeneous myometrium 4
• Endometrial cancer: Thickened endometrium (≥5mm in postmenopausal women) with possible myometrial invasion 1

Clinical Implications

• Symptoms vary based on the cause but may include:

  • Abnormal uterine bleeding
  • Pelvic pressure or pain
  • Low abdominal pressure (more common with larger uterine size) 2
  • Urinary or bowel symptoms due to compression

• The relationship between uterine size and symptoms is not always direct; smaller uteri with adenomyosis may cause significant symptoms, while larger fibroid uteri may sometimes be asymptomatic 2

• Management depends on the specific cause, patient age, desire for future fertility, and symptom severity

Important Considerations

• Postmenopausal women with enlarging uterus require thorough evaluation to rule out malignancy
• Pregnancy should always be excluded before invasive diagnostic procedures
• Coexistence of multiple pathologies (e.g., fibroids with adenomyosis) is common and may complicate diagnosis 2

Understanding the specific cause of uterine enlargement is crucial for appropriate management and treatment planning.