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Ovarian Pathology and Trophoblastic Diseases

Pathologia ovariorum

For medical students2 min readUpdated 2026-10-10

The study of ovarian pathomorphology (cystic changes and neoplasms) is essential in gynecological practice. Accurate verification of follicular cysts, polycystic ovary syndrome, and tumors determines the prognosis and guides appropriate management.

Follicular cystDiagnostic criterion: the diameter of the atretic follicle exceeds 2.5–3 cm.

Mucinous tumorsAccount for approximately 10% of all primary epithelial ovarian neoplasms.

Mature teratomaThe most common type (up to 50% of all ovarian tumors), with a predominance of ectodermal tissue.

PCOSCorpora lutea and corpora albicantia are completely absent in the ovarian tissue in polycystic ovary syndrome.

Non-Neoplastic Lesions: Cysts and PCOS

Atresia of tertiary follicles can lead to their enlargement and cyst formation.

Follicular cyst: Macroscopically, it has a smooth, light-gray inner surface, and the lumen is filled with clear, pale fluid. Microscopically, the wall consists of granulosa and theca cells. Upon regression, it transforms into a corpus fibrosum.
Corpus luteum cyst: Characterized by a scalloped, bright-yellow rim (luteinized cells). Its regression results in a corpus albicans.

Polycystic ovary syndrome (PCOS) is characterized by numerous cystically dilated follicles. The condition develops against a background of elevated luteinizing hormone (LH), hyperandrogenemia, obesity, and hyperinsulinemia (with hyperprolactinemia in 25% of cases). Clinically, this manifests as infertility, anovulation, hirsutism, and acne. PCOS Morphology: Ovaries are enlarged 2-fold or more, with a whitish-gray surface. Microscopically, the cortex is fibrosed and thickened, with numerous atretic follicles visible. The key distinguishing feature is the absence of corpora lutea and corpora albicantia.

Stromal hyperplasia is the proliferation of stromal cells (often in peri- and postmenopausal women with obesity). When combined with luteinization of cells, the condition is termed stromal hyperthecosis (polygonal cells with vacuolated eosinophilic cytoplasm are identified).

Epithelial Ovarian Tumors

This group of neoplasms is characterized by a wide variety of histological structures.

Serous tumors: Characterized by fibrous tissue proliferation with small cysts. The malignant variant (serous cystadenocarcinoma) features papillary structures, pronounced cellular atypia, and deep invasion into the ovarian stroma. Psammoma bodies (lamellated calcifications) are frequently found in the tissue.
Mucinous tumors: Can reach giant sizes. Benign mucinous cystadenoma is a multilocular cyst containing clear mucus, lined by tall epithelium without cilia. Upon malignant transformation (cystadenocarcinoma), solid areas and hemorrhages appear, the epithelium becomes stratified, loses mucin, and invades the capsule. A specific complication is pseudomyxoma peritonei, in which gelatinous masses accumulate in the abdominal cavity, causing adhesive bowel obstruction. Its development does not depend on the grade of malignancy.
Endometrioid tumors: In most cases, they develop de novo from the surface epithelium (less frequently from foci of endometriosis). Usually malignant, they are microscopically identical to endometrial adenocarcinoma.
Clear cell tumors: Rare malignant neoplasms composed of large cells with abundant clear cytoplasm.
Brenner tumor: Features a dual-component structure—fibroma-like stroma and nests of transitional-type epithelium (resembling urothelium). The malignant variant contains transitional cell carcinoma structures.

Germ Cell Tumors

Germ cell tumors can consist of embryonic germ layer derivatives of varying degrees of maturity.

Mature teratoma (dermoid cyst): Develops from 2–3 germ layers, but ectoderm predominates. Occurs in patients aged 12–70 years. It is a unilocular cyst containing sebaceous material and hair, with a wall containing stratified squamous epithelium, teeth, cartilage, and bone.
Immature teratoma: A rare (3% of teratomas), aggressive tumor. Mean age is 18 years. Macroscopically, it is a solid, bosselated pinkish-gray nodule with foci of necrosis. Microscopically, it consists of immature tissues, among which neural tubes predominate. It is characterized by rapid growth and metastasis.
Monodermal teratomas: Struma ovarii (composed of normal thyroid tissue) and carcinoid (resembles GI tumors, may cause carcinoid syndrome, rarely malignant).
Dysgerminoma: A tumor composed of large cells rich in glycogen (resembling primordial follicle cells). The stroma is infiltrated by lymphocytes. Occurs at ages 20–40. Despite being malignant, it has a less aggressive clinical course, metastasizes late, and is radiosensitive.
Yolk sac tumor (endodermal sinus tumor): A malignant neoplasm derived from multipotent cells that forms extraembryonic structures.

Frequently asked questions

What are the histological types of epithelial ovarian tumors according to the WHO classification?

According to the WHO histological classification, the following types of epithelial tumors (surface epithelial-stromal tumors) are distinguished:

Serous tumors — simple, papillary, and papillary cystadenomas.
Mucinous tumors — pseudomucinous cystadenoma.
Endometrioid tumors — microscopically similar to endometrial adenocarcinoma.
Clear cell tumors — a rare variant of surface epithelial tumors.
Brenner tumors — feature a dual-component structure comprising stroma and transitional-type epithelium.
Ovarian carcinoma.

Which tumor markers are used for the differential diagnosis of ovarian germ cell tumors?

To differentially diagnose ovarian germ cell tumors, specific tumor marker levels are assessed:

Alpha-fetoprotein (AFP) — produced by yolk sac tumors; also elevated in embryonal carcinoma, polyembryoma, and approximately one-third of immature teratomas.
Beta-human chorionic gonadotropin (β-hCG) — characteristic of choriocarcinoma; also elevated in embryonal carcinoma and polyembryoma.
Lactate dehydrogenase (LDH) — elevations above reference ranges are characteristic of ovarian germ cell tumors.

Combined elevation of AFP and β-hCG is typical for embryonal carcinoma and polyembryoma. CA-125 and HE4 markers have no diagnostic value for germ cell tumors.

What are the forms of gestational trophoblastic disease?

Gestational trophoblastic disease includes benign and malignant forms:

Hydatidiform mole (complete or partial) — a benign form with malignant potential.
Invasive mole — a malignant trophoblastic tumor.
Choriocarcinoma — a malignant tumor developing from trophoblastic epithelium.
Placental site trophoblastic tumor — a malignant form.
Epithelioid trophoblastic tumor — a malignant form.

What are the microscopic differences between a complete and a partial hydatidiform mole?

Microscopic differences between complete and partial hydatidiform moles involve the extent of villous involvement, degree of trophoblast proliferation, and presence of fetal parts.

Feature	Complete Hydatidiform Mole	Partial Hydatidiform Mole
Chorionic involvement	Changes involve the entire chorion (the entire placental tissue is affected)	Changes involve only a portion of the chorion
Villous edema	Diffuse villous edema	Vesicular (edematous) villi are distributed focally
Trophoblast proliferation	Mild to severe	Local trophoblast proliferation is mild
Fetal parts	Completely absent	Must be present (among areas of normal placental tissue)

What is the main microscopic difference in the ovaries in PCOS?

Multiple cystic atretic follicles are found in the cortical layer, while corpora lutea and corpora albicantia are completely absent.

Why is the development of pseudomyxoma peritonei dangerous?

The accumulation of gelatinous masses causes mechanical disruption of organ function and the formation of severe adhesions, which can lead to acute bowel obstruction.

What is the prognosis for ovarian dysgerminoma?

Despite its malignant nature, the prognosis is relatively favorable because the tumor metastasizes late and responds well to radiotherapy.

Go deeper

Pathogenetic mechanisms of polycystic ovary syndrome
Histological differential diagnosis of epithelial carcinomas
Manifestations of carcinoid syndrome in specialized teratomas
Molecular and genetic features of immature teratomas