Describe recent classification of Abnormal Uterine Bleeding (AUB). Briefly discuss the endometrial pattern in various types of Abnormal Uterine Bleeding.

The FIGO System for AUB (2018)

The FIGO system categorizes AUB into two main groups: PALM (Polyp, Adenomyosis, Leiomyoma, Malignancy and Hyperplasia) – structural causes, and COEIN (Coagulopathy, Ovulatory dysfunction, Endometrial, Iatrogenic, Not yet classified) – non-structural causes.

Endometrial Patterns in PALM Categories

1. Polyp (AUB-P)

Endometrial Pattern: Histologically, polyps are localized overgrowths of endometrial glands and stroma. They can be focal, smooth-muscle containing (fibroid polyp) or without smooth muscle. Microscopically, they exhibit varying degrees of glandular crowding, stromal edema, and may show cystic changes. Benign polyps are common, but atypical hyperplasia or malignancy can occur, particularly in postmenopausal women.

2. Adenomyosis (AUB-A)

Endometrial Pattern: Adenomyosis is characterized by the presence of endometrial tissue within the myometrium. Diagnosis often relies on imaging (MRI is preferred), but histological confirmation requires demonstrating endometrial glands and stroma within the uterine muscle. The endometrium itself may appear thickened and irregular. There is often associated myometrial hypertrophy and cystic changes.

3. Leiomyoma (AUB-L)

Endometrial Pattern: Leiomyomas (fibroids) themselves do not directly alter the endometrial pattern. However, their presence can cause secondary endometrial changes. Submucosal fibroids, in particular, can distort the endometrial cavity, leading to irregular bleeding and potentially endometrial hyperplasia due to prolonged estrogen exposure. The endometrium may show proliferative changes or, in some cases, atrophy.

4. Malignancy and Hyperplasia (AUB-M)

Endometrial Pattern: This category encompasses endometrial carcinoma and endometrial hyperplasia.

• Endometrial Hyperplasia without Atypia: Characterized by increased glandular density, irregular gland shape, and stromal cellularity, but without significant nuclear atypia.
• Endometrial Hyperplasia with Atypia: Shows similar features to hyperplasia without atypia, but with nuclear enlargement, hyperchromasia, and loss of nuclear polarity – indicating a higher risk of progression to cancer.
• Endometrial Carcinoma: Demonstrates malignant glandular cells with significant nuclear atypia, increased mitotic activity, and potential for myometrial invasion. Different histological subtypes exist (e.g., endometrioid, serous, clear cell).

Endometrial Patterns in COEIN Categories

1. Coagulopathy (AUB-C)

Endometrial Pattern: Endometrial patterns in AUB due to coagulopathy are often normal, but may show evidence of delayed shedding or irregular vascularization. The primary issue is impaired hemostasis, leading to prolonged or heavy bleeding, rather than intrinsic endometrial abnormalities.

2. Ovulatory Dysfunction (AUB-O)

Endometrial Pattern: This is a common cause of AUB. The endometrial pattern is often characterized by progesterone deficiency. This can manifest as:

• Proliferative Endometrium: Endometrium appears thick and shows continuous proliferation of glands and stroma, without secretory changes.
• Delayed Secretory Changes: Secretory changes are present but occur later than expected in the cycle.
• Out-of-Phase Endometrium: Secretory changes are observed at an inappropriate time in the cycle.

3. Endometrial (AUB-E)

Endometrial Pattern: This category includes primary endometrial causes of AUB, such as impaired local endometrial hemostasis. The endometrial pattern may be normal, but there may be evidence of increased vascularity or impaired decidualization. This is often a diagnosis of exclusion.

4. Iatrogenic (AUB-I)

Endometrial Pattern: The endometrial pattern depends on the iatrogenic cause (e.g., hormonal contraception, intrauterine devices). Hormonal contraception can lead to a thin, atrophic endometrium. IUDs can cause local inflammation and bleeding.

5. Not Yet Classified (AUB-N)

Endometrial Pattern: This category is reserved for causes of AUB that are not yet fully understood. The endometrial pattern will vary depending on the underlying cause.