Endometrial Dating

Endometrial dating refers to the determination of how closely the histologic characteristics of the endometrium match what is expected on the corresponding day of the menstrual cycle. In the past, this approach was one of the standard tests in an investigation of causes of infertility and pregnancy loss. However, the accuracy of this test has been questioned because abnormal results can be observed in cycles that eventually prove to result in a viable pregnancy.

Endometrial dating can be performed both before and after ovulation. Preovulatory phase (proliferative phase) endometrial dating is described as menstrual days, early follicular, midfollicular, and late follicular, but is not very precise. Postovulatory phase (secretory phase) endometrial dating has become the standard and is usually reported within a 2-day range, although the accuracy of this dating methodology is the subject of some debate.

For secretory phase endometrial dating, ovulation is used as the primary reference point. Originally, ovulation was assumed to occur on day 14 of the menstrual cycle and the days after ovulation numbered accordingly. Some pathologists refer to ovulation as “day 0” and report the postovulation day as the number of days after ovulation.

Most clinicians perform endometrial biopsy in the midluteal phase at about the time implantation is thought to occur. However, the original reports on secretory endometrial dating recommend a biopsy 3 days before the expected menses. Histologic criteria are then used to determine where the endometrial response would be in relation to ovulation (Table 8-1 and Figs. 8-1 and 8-2).

Table 8-1 Criteria for Histologic Dating

Figure 8-1 Midluteal phase endometrium has early spiral arteriolar formation (center) arising in edematous stroma. Endometrial glands are tortuous with basal nuclei, absence of mitotic activity, and intraluminal secretions.

Figure 8-2 Late luteal phase endometrium has large areas of coalescent predecidua and a conspicuous lymphoid infiltrate, giving the stroma a dimorphic appearance.

Several assumptions in the original concept of dating the endometrium besides the assumption of ovulation on day 14 increased the variation found with this method. For example, another assumption was that the length of the luteal phase is 14 days.¹ In reality, there is a normal variation in luteal phase length of several days. In addition, the original description fixed the time of ovulation with the onset of the period after the biopsy. The onset of ovulation can be more accurately determined using current modalities, such as determination of the midcycle urinary luteinizing hormone surge or ultrasonic identification of the collapse of a follicle. The accuracy of the former is approximately 85%; of the latter, 95%. Additional intrinsic inaccuracies of dating resulted from intraobserver and interobserver variation. This variation is typically about 2 days. For these reasons, a 2-day difference between the histologic estimation and the actual interval since ovulation is considered within normal limits.

Recently a detailed analysis on endometrial dating demonstrated that the histologic criteria used are not as temporally distinct as originally thought, and thus do not provide an accurate method to detect a luteal phase defect. In one study, approximately 20% of fertile couples had a delay of more than 2 days.² A between-cycle variation of more than 2 days was found in 30% to 60% of patients if the biopsy was performed between day 6 and day 13 after ovulation.

Endometrial Response to Exogenous Hormones

The endometrium responds to exogenous hormones with specific morphologic changes. With oral contraceptives, the progestin effect dominates because progestins decrease estrogen receptors. As a result, endometrial glands atrophy over time. The appearance of the stroma depends on the dose of progestin. Typically, a weak pseudodecidual response will occur (Fig. 8-3).

Figure 8-3 The microscopic appearance of the endometrium exposed to oral contraceptives varies, depending on the dose of progestin. Typically, stroma having a weak progestin effect surrounds simple, straight, widely spaced, and inactive-appearing endometrial glands.

Exposure to progestins only (e.g., medroxyprogesterone acetate) will show similar gland pattern but usually a more prominent stromal pseudodecidual response due to higher progestin dose. The selective estrogen receptor modulator tamoxifen is anti-estrogenic at some sites but has a weak estrogenic agonist effect on the endometrium. The endometrium usually atrophies, but variable hyperplasia and, rarely, adenocarcinoma can occur due to the weak estrogen agonist effect.

Endometritis

Chronic endometritis is sometimes demonstrated in endometrial biopsies for infertility or recurrent pregnancy loss. This is characterized by infiltration of plasma cells (Fig. 8-4). Chronic pelvic inflammatory disease, intrauterine devices, and postabortion complications are also associated with chronic endometritis. Although rare in the United States, endometrial tuberculosis may sometimes be found during a biopsy for infertility and is characterized by granulomas (Fig. 8-5).

Figure 8-4 The presence of plasma cells defines chronic endometritis. Typically, the endometrium resembles a proliferative-type endometrium. The stroma often has a spindled appearance.

Figure 8-5 Tuberculosis endometritis causes granulomatous inflammation. In reproductive age women, granulomas tend to be cellular but not markedly necrotic. The case illustrated here has a well-formed nonnecrotizing granuloma (right) adjacent to an endometrial gland. In postmenopausal patients, tuberculous endometritis causes striking necrotizing granulomatous endometritis.

Abnormal Uterine Bleeding

The biopsy of an endometrium for dysfunctional uterine bleeding in women may show a range of abnormalities of the endometrium (Fig. 8-6). In the reproductive age group organic lesions such as polyps and leiomyomas or a normal endometrium are often found. Pregnancy-related endometrial changes or premalignant or malignant changes may be found in this age group.

Figure 8-6 This endometrial biopsy specimen illustrates gland–stromal asynchrony. The endometrial glands have consistent and conspicuous subnuclear vacuoles corresponding to approximately postovulatory day 3 (cycle day 17). In contrast, the endometrial stroma has striking stromal edema corresponding to approximately postovulatory day 8 (cycle day 22). This appearance of gland–stromal asynchrony is the most common secretory phase morphologic abnormality.

In adolescent and perimenopausal age patients, anovulatory cycles are one of the most common causes of abnormal uterine bleeding. During anovulatory cycles, the endometrium is proliferative and may exhibit some breakdown. Thrombosis of vascular sinusoids also commonly occurs. Anovulatory cycles create a milieu of unopposed estrogen; therefore, hyperplasia and carcinoma can result.

Pregnancy-related Endometrial Changes

Early pregnancy, both intrauterine and ectopic, is characterized by hypersecretory endometrium (Fig. 8-7). However, hypersecretory endometrium is not specific for pregnancy, and similar changes can be seen with persistent corpus luteum cyst, double corpora lutea, or rarely as a drug effect. By the end of the first trimester, endometrial glands involute and the stroma shows a prominent decidual reaction (Fig. 8-8). Other histologic changes associated with gestation include the Arias-Stella reaction (Fig. 8-9) and optically clear nuclei (Fig. 8-10).

Figure 8-7 Hypersecretory endometrium has closely packed endometrial glands with marked intraglandular budding (ferning) and ongoing glandular secretions with secretory vacuoles. Hypersecretory endometrium characterizes early pregnancy; however, this change is not specific for gestation.

Figure 8-8 By the end of the first trimester, the hypersecretory glandular changes resolve. Subsequently, gestational endometrium has mostly simple widely spaced endometrial glands, separated by stroma with a prominent progestin effect (true decidual change), as seen in this example.

Figure 8-9 This photomicrograph illustrates the Arias-Stella reaction. The Arias-Stella reaction is a cellular and nuclear change characterized by nuclear enlargement and hyperchromatisma resulting from polyploidy. The enlarged hyperchromatic nuclei are typically arranged in an apical portion of the endometrial glandular cells. This nuclear change can be mistaken for malignancy; however, the Arias-Stella reaction, unlike adenocarcinoma, typically affects only scattered cells within the endometrial glands and mitotic figures are absent or at most infrequent.

Figure 8-10 This endometrial gland has the optically clear nuclear appearance seen with pregnancy (center top).

The Arias-Stella reaction refers to cytonuclear changes, including voluminous, vacuolated cytoplasms surrounding enlarged, hyperchromatic, polyploid nuclei that includes massively enlarged forms. The Arias-Stella reaction occurs almost exclusively in gestational endometrium associated with pregnancy or gestational trophoblastic disease; however, this reaction can rarely occur as a response to hormonal therapy in nonpregnant patients. The optically clear nuclei associated with gestation can resemble herpes virus inclusions.

Ectopic Pregnancy

Ectopic pregnancies can occur in several nonuterine locations. The most common site is the uterine tube. Hematosalpinx is the typical gross appearance. Trophoblastic tissue can grow predominantly intraluminally or invade the tubal wall (Fig. 8-24).

Figure 8-24 Hematosalpinx is the most consistent gross and microscopic feature of tubal pregnancy. In this example, chorionic villi are identified within the tubal lumen (center).

Morphologically, trophoblasts and chorionic villi are usually visible at the implantation site. However, the diagnostic tissue (products of conception) may be confined to the intraluminal blood clot. Thus, the blood clot should be carefully examined in these cases.

Ovarian ectopic pregnancies account for 3% of all ectopic gestations. An ectopic pregnancy found in the ovary is believed to be the result of an aborted tubal pregnancy in many cases. In 1878, Spiegelburg suggested four criteria to distinguish a primary ovarian pregnancy from a distal tubal pregnancy that has secondarily involved the ovary: (1) the fallopian tube with its fimbriae should be intact and separate from the ovary, (2) the gestational sac should occupy the normal position of the ovary, (3) the gestational sac should be connected to the uterus by the ovarian ligament, and (4) ovarian tissue must be present in the specimen attached to the gestational sac.

Tuberculosis Salpingitis

Tuberculosis can hematogeneously spread to the pelvic organs to cause chronic salpingitis. The majority of cases of tuberculosis of the uterine tubes simultaneously involve the endometrium. Other uncommon causes of granulomatous tubal inflammation are sarcoidosis and Crohn’s disease.

Functional Cysts

The most common cysts found in reproductive age women are functional cysts such as follicular or corpus luteum cysts. These cysts are most commonly lined with granulosa cells. Some functional cysts may cause disruption of the menstrual cycle or symptoms. However, most will spontaneously regress without surgical intervention. Occasionally a corpus luteum cyst may be confused grossly at the time of surgery with an endometriotic cyst. Microscopically, fibrosis and hemorrhage around the cyst can make it difficult to differentiate these cysts from endometriomas.

Gonadal Dysgenesis

Patients with gonadal dysgenesis usually have streak gonads (Fig. 8-25). Dysgenetic gonad (i.e., abnormally developed gonads) can harbor gonadoblastoma (Fig. 8-26). Gonadoblastomas are mixed germ cell-sex cord stromal tumors characterized by nests of immature sex cord cells surrounding germ cells. Gonadoblastomas almost always affect dysgenetic gonads in patients with a karyotype containing Y chromosome. Importantly, gonadoblastomas can give rise to invasive germ cell neoplasms, most commonly dysgerminoma (Fig. 8-27). Patients with genotypes that include a Y chromosome are at risk to develop a gonadoblastoma. In these patients the gonad should be removed.

Figure 8-25 The microscopic appearance of streak gonads varies over time. Disorganized germ cells, sex cord cells, and stroma, seen initially, give way to a nonspecific fibrous stroma. In this example of a streak gonad removed from an adult, a focus of lutein cells (top center) is surrounded by nonspecific fibrous stroma.

Figure 8-26 This gonadoblastoma is dominated by masses of dystrophic calcium associated with fibrosis. The constituent germ cells and sex cord cells are inconspicuous. Gonadoblastomas are tumors composed of nests of germ cells associated with sex cord cells. Calcification is a consistent feature. Gonadoblastomas almost always arise in dysgenetic gonads associated with a karyotype containing Y chromosome material. Gonadoblastomas can give rise to invasive malignant germ cell tumors, usually dysgerminoma.

Figure 8-27 Delicate fibrous septa containing lymphocytes separate nests of germinoma cells in this characteristic example of an ovarian dysgerminoma.

Pregnancy-related Cysts

Pregnancy causes prominent luteinization of the theca layer of atretic follicles. Multiple atretic follicles with theca luteinization are designated theca-lutein cysts. Theca-lutein cysts result from high levels of or increased sensitivity to human chorionic gonadotropin. This condition has been called hyperreactio luteinalis. Multiple theca-lutein cysts often occur with hydatidiform mole and choriocarcinoma but occasionally in other clinical settings, including normal single pregnancy. Grossly, the process is typically bilateral with greatly enlarged multicystic ovaries (Fig. 8-28). Pregnancy luteomas are non-neoplastic solid masses of lutein cells occurring in pregnant patients (Fig. 8-29).⁶ Multiple nodules occur in half of patients, and bilaterality occurs in at least one third of cases. The nodules spontaneously regress postpartum. Pregnancy luteomas are easily confused with sex cord neoplasms.

Figure 8-28 Cystic atretic follicles with luteinization of the theca characterize theca-lutein cysts. Theca-lutein cysts can result in massive cystic enlargement of the ovaries, as seen here. Theca-lutein cysts are associated with excessive levels of human chorionic gonadotropin. Therefore, typically, theca-lutein cysts are found with hydatidiform mole (in one third to one half of cases) and choriocarcinoma. However, theca-lutein cysts do occur with other gestations, including normal single pregnancies.

Figure 8-29 As illustrated here, pregnancy luteomas contain markedly luteinized cells having abundant, usually eosinophilic cytoplasm surrounding round nuclei with conspicuous nucleoli. A follicular space is identified (center).

Polycystic Ovaries

Polycystic ovary syndrome (PCOS) is an endocrine diagnosis rather than a pathologic one. The pathologic findings include characteristic gross and microscopic features. Grossly, the ovaries are referred to as sclerocystic (Fig. 8-30).

Figure 8-30 Sclerocystic ovaries result from chronic anovulation. Multiple cystic follicles underly thickened fibrotic superficial stroma. Note the absence of gross stigmata of prior ovulation, such as involuting corpora lutea.

Sclerocystic ovaries are enlarged with cysts underlying thickened fibrotic superficial stroma. Stigmata of prior ovulation are inconspicuous or absent. The cysts are relatively small, usually ranging in size from 0.5 to 1.5 cm. Histologically, luteinized follicular cells line the cysts.

Stromal Hyperthecosis

Stromal hyperthecosis is defined histologically as the presence of luteinized cells within the ovarian stroma. Stromal hyperthecosis can cause clinical signs of hyperandrogenism, and with peripheral conversion, hyperestrogenism. These patients are typically postmenopausal. Stromal hyperthecosis also occurs commonly in pregnancy. The ovaries are enlarged bilaterally with no clear appearance of cysts. Microscopically nests and individual lutein cells occur in the stroma (Fig. 8-31). The associated spindle cell ovarian stroma is typically hyperplastic, characterized by increased cellularity and a loss of the normal corticomedullary demarcation.

Figure 8-31 The presence of luteinized cells within the ovarian stroma, as illustrated here, defines stromal hyperthecosis. The luteinized stromal cells have abundant cytoplasm that might stain eososinophilic or clear and vacuolated, as seen in this example. Stromal hyperthecosis commonly affects postmenopausal and pregnant patients and also causes a virilizing syndrome in younger nonpregnant patients.

Sex Cord-Stromal Tumors

Sex cord-stromal tumors represent approximately 5% of ovarian neoplasms. They are usually unilateral and occur in all age groups but are more common in postmenopausal women. Sex cord-stromal tumors often secrete hormones and are thus often associated with endocrine-related symptoms (Table 8-5). Both Leydig and theca cells secrete androgens (Table 8-6). They should be considered as part of the differential diagnosis of severely hyperandrogenic patients. However, many of these tumors have no endocrine manifestations.

Table 8-5 Types of Sex Cord-Stromal Tumors of the Ovary

Table 8-6 Typical Clinical Features of Sex Cord-Stromal Tumors

The stroma of the embryonic gonad has the potential to differentiate into cell types that have specific endocrine functions in both the male (Sertoli and Leydig cells) and the female (granulosa and theca cells) gonad. The Sertoli and granulosa cells both secrete inhibin, which can be used as a tumor marker for these patients. Elevated inhibin levels usually precede clinical recurrence of disease by months to years.

Granulosa Cell Tumors

Granulosa cell tumors are mostly found in postmenopausal women. The symptoms are related to estrogen secretion and can include postmenopausal bleeding with endometrial pathology such as endometrial hyperplasia or carcinoma. The tumors also occur in prepubertal girls and may produce precocious sexual development. In some cases, androgen secretion results in symptoms of hyperandrogenism.

Granulosa cell tumors are usually unilateral and characteristically have both cystic and solid components (Fig. 8-32). Histologically, the tumor architecture varies, but the cells often have “coffee bean” nuclei described as pale, angular, and cleaved (Fig. 8-33).⁷

Figure 8-32 This adult-type granulosa cell tumor has a characteristic hemorrhagic cystic and solid gross appearance.

Figure 8-33 The pale angular grooved appearance of nuclei in adult-type granulosa cell tumors is the key diagnostic criterion.

Granulosa cell tumors in prepubertal girls and young adults often have microscopic features differing from adult-type granulosa cell tumors. The differences are sufficient to permit recognition of these tumors as a distinctive subset with different behavior that is designated juvenile granulosa cell tumor.^8,9

Thecomas

Thecomas are usually unilateral (>90%) and typically occur in postmenopausal women. Thecomas may be hormonally active tumors. Grossly, thecomas typically are yellow and have a solid uniform appearance. Histologically, plump vacuolated spindle cells predominate (Fig. 8-34).

Figure 8-34 Ovarian thecomas often have a distinctive gross color, often yellowish tan, as seen in this example. Also note the homogeneous appearance and sharp circumscription.

Fibromas

Fibromas are usually unilateral tumors. Large fibromas (>6 cm) may be associated with ascites (40% of cases) or hydrothorax (Meigs’ syndrome). Other ovarian tumors may also cause these clinical signs (pseudo-Meigs’ syndrome). Fibromas are also associated with basal cell nevus syndrome (Gorlin’s syndrome). Fibromas have a uniform, pale, tan, solid gross appearance (Fig. 8-35) and benign spindle cells microscopically.

Figure 8-35 In contrast to the typical yellow color of a thecoma, ovarian fibromas, as illustrated here, typically have a pale tan gross appearance.

Sertoli-Leydig Cell Tumors

Sertoli-Leydig cell tumors are hormonally active tumors that occur in reproductive age women. These tumors are mostly unilateral. These tumors are classically associated with severe masculinization, with hirsutism, balding, clitoral hypertrophy, and voice changes.

Sertoli-Leydig cell tumors have remarkably diverse histologic appearances.¹⁰ The fundamental components are a variable spindle cell stroma and variably immature tubules. Often, an alternating hypercellular and hypocellular zonation characterizes Sertoli-Leydig cell tumors. The presence of heterologous tissue contributes to the array of microscopic appearances. Histologic grading (well, intermediate, and poorly differentiated) correlates well with survival (Fig. 8-36). Other hormonally active tumors occur that have lipid-laden cells associated with hyperandrogenism and are variably referred to as steroid cell tumors.

Figure 8-36 Sertoli-Leydig cell tumors have a broad spectrum of microscopic appearances resulting in part from variable mixtures of Sertoli tubules and nonspecific cellular stroma. In this example, well-formed Sertoli tubules arise in a background of densely cellular tissue.