FNA of the ovary is often used for evaluation of small, incidental cystic masses that appear benign on sonographic or laparoscopic examination.1–3 Incidental ovarian cysts are often discovered in women with infertility or during pregnancy.⁴ Aspiration cytology, in combination with a benign ultrasound appearance, is used to reassure the patient that an oopherectomy is not necessary.⁵ In some laboratories, estradiol (E2) levels in the fluid are also measured, as these are usually elevated in follicle-derived cysts but not in epithelial lesions.^6,7 Thus, ultrasound, cytology, and E2 levels can form an effective “triple test” for distinguishing benign from malignant ovarian cysts.

Ultrasound features of a benign ovarian cyst

• small

• thin-walled

• no septations

• no papillarity

• no solid areas

• low echogenicity (sonolucency)

In part because of this preselection, a majority of ovarian FNAs are benign.⁸ The diagnosis of endometriosis is sometimes established by this means as an unsuspected cause of infertility.⁴

If imaging features suggest a malignancy, the clinician will often forego aspiration and recommend surgery. Because borderline and malignant ovarian tumors are treated by surgical resection, FNA is perceived as unnecessary in many such circumstances. Aspiration of suspicious ovarian masses is therefore uncommon, although it is used to confirm malignancy in patients with inoperable or metastatic disease.3,9 Nevertheless, on the basis of their positive experience, some authors advocate cytologic assessment for suspicious, potentially early stage ovarian lesions.¹⁰

Obtaining the Specimen

The aspiration can be carried out transrectally, transvaginally, percutaneously, intraoperatively,¹¹ or during laparoscopy. The method used depends on the size of the lesion, its location, and the resources available to the aspirator. Percutaneous transabdominal aspiration can be performed by palpation¹² or, more commonly, with imaging guidance. Transvaginal and transrectal aspiration can be done by palpation using the Franzen needle guide,¹² originally developed for FNA of the prostate. Transvaginal aspiration under ultrasound guidance, with the probe placed in the vagina, can be performed in the outpatient setting with only intravenous sedation.^4,8 Depending on the trajectory of the needle, the cyst fluid may be contaminated with squamous cells, mesothelial cells, urothelial cells, or intestinal epithelium. Therefore, knowledge of the route taken is important in evaluating the specimen.^8,13–15 Aspirations are also performed when cysts are discovered during laparoscopy and laparotomy.

Complications are uncommon. Two decades ago, a pair of authors argued that aspiration of a malignant ovarian tumor causes seeding of the peritoneal cavity,¹⁶ but their evidence consisted of only two cases, both with ambiguous circumstances. Since then, there has been no documentation of tumor seeding; on the contrary, practitioners with considerable experience have reported no such cases.^17,18 The risk of peritoneal seeding, therefore, is unknown but probably very low.¹⁸ Severe pelvic infection after transvaginal and transrectal FNA is seen in 1.3% of cases, however.¹⁷ Acute abdominal or pelvic pain is a contraindication to FNA, because it may delay treatment of a serious condition such as torsion of a cyst.¹

Preparing the Specimen and Reporting Results

Specimens are usually cyst fluids. Standard methods are used in the preparation of direct smears, cytocentrifuge preparations, thinlayer preparations, and/or cell block sections. A portion of the fresh fluid can be submitted to the clinical laboratory to measure the level of E2 or tumor-associated antigens CA-125, carcinoembryonic antigen (CEA), and alpha-fetoprotein. Elevated levels are typical of some ovarian lesions and can be a useful adjunct to cytologic examination.17,19

Specimens that are virtually acellular or uninterpretable for other reasons are reported as nondiagnostic.20,21 The percentage of FNAs of the ovary that are nondiagnostic ranges widely, from a low of 13% to a high of 72%.^{1,4,13,14,20–22} This variation is likely related to the type of lesion selected for aspiration and the definition of a nondiagnostic specimen. The cytology report should state that malignant cells are either absent (“no malignant cells identified”) or present (“positive for malignant cells”). If the findings are equivocal, the report should state that atypical or suspicious cells are present. If sufficient benign lesional cells (granulosa cells, epithelial cells) are seen, descriptive terms can further categorize the cyst as a follicular, simple, serous, benign mucinous, endometriotic, or dermoid cyst.³ Benign ovarian FNA results fall into two broad categories: (1) follicular/lutein cysts and (2) epithelial cysts. This has significant clinical relevance, because surgery is unnecessary for follicle-derived cysts, which usually regress over time. Surgery may be indicated, however, for a benign-appearing epithelial cyst, particularly if the sonographic findings are worrisome. The lining of an epithelial cyst can vary from one area to another, and some cysts contain benign, borderline, and frankly malignant foci; sampling is not always representative of this heterogeneity. For this reason, an explanatory note accompanying the diagnosis of a benign epithelial cyst is helpful (e.g., “clinical correlation is advised to ensure that the sample is representative of the underlying lesion”).²³

Accuracy

Reported sensitivities for malignancy of 84% and 93% are inflated because borderline tumors were excluded from analysis.13,17 In fact, FNA of a borderline tumor often yields a false-negative result.^4,17,24,25 Much of the lesion is acellular cyst fluid, and neoplastic epithelium may not be sampled. When borderline tumors are included, sensitivity is low, ranging from 26% to 40%.^24–26 Low sensitivity is another argument against the aspiration of clinically suspicious ovarian masses.

False-positive results have been reported.13,26 Follicle cysts are a notorious cause of false positives, because they can yield a cellular and highly mitotic specimen.^9,27,28 Familiarity with the laparoscopic and sonographic findings should be taken into account when making a diagnosis. Knowing that a lesion appears benign clinically can help avoid a false-positive interpretation.

FNA of the ovary, therefore, has its limitations. Not only is there a high false-negative rate, particularly for borderline tumors, but the method cannot reliably distinguish between borderline tumors and carcinomas.20,29,30 (Because both lesions are treated by surgical resection, the inadequacy of FNA in this instance is not very significant.) Furthermore, benign lesions cannot always be histologically categorized by cytologic evaluation.^19,29 Although in some cases FNA can establish a specific diagnosis such as endometriosis,⁸ at present it is most valuable for confirming a clinical impression that an ovarian cyst is benign, thus sparing the patient unnecessary surgery.^1,20,31

Benign Tumorlike Lesions of the Ovary

Non-Neoplastic Cysts

Benign ovarian cysts are common. Most are discovered incidentally by ultrasonography, laparoscopy, or laparotomy. They fall into two major categories: The most common are the so-called “functional cysts” (i.e., cysts of follicular origin—follicle and corpus luteum cysts). The rest are nonfunctional cysts derived from ovarian surface epithelium or endometriosis. Precise classification by cytologic examination is not always possible, particularly when only cyst contents (fluid and macrophages) are obtained.³²

Cystic Follicle and Follicle Cyst

These two lesions have a similar histogenesis and are distinguished only on the basis of size. The arbitrary size cut-off is variably given as 2 cm, 2.5 cm, and 3 cm. If the size cut-off is exceeded, a cystic follicle is called a follicle cyst. One of the most common, if not the most common, cystic lesions of the ovary, they arise from an ovarian follicle and are physiologic, not neoplastic. Ovarian follicles follow a predictable development from primordial follicle (oocyte surrounded by a flattened layer of granulosa cells), to primary follicle (increased size and mitotic activity of granulosa cells), to secondary follicle (stratification of granulosa cells), to the graafian follicle (characterized by a distinct zone of fluid, an antrum for the oocyte, and proliferation of surrounding theca cells). Cystic follicles and follicle cysts occur when a graafian follicle does not rupture but rather persists for a variable period of time. The remainder of this discussion focuses on the follicle cyst which, because of its size, is more likely to manifest clinically.

Follicle cysts can be solitary or multiple, and they range in size up to 8 cm or more in diameter. They look benign on sonographic and laparoscopic examination. They are unilocular, smooth-surfaced, translucent, and thin-walled. Most regress spontaneously within a few months. Multiple follicle cysts are common in juvenile hypothyroidism, ovarian hyperstimulation syndrome, and polycystic ovary disease.

Histologically, a follicle cyst is lined by an inner layer of attenuated or stratified granulosa cells and an outer layer of theca cells (Fig. 16.1). Both may show luteinization. Fluid is clear or hemorrhagic. It may be sparsely cellular, containing only histiocytes and blood, or markedly cellular (sometimes alarmingly so), with numerous granulosa cells that are isolated and in large clusters.

Figure 16.1 Follicle cyst.
In this histologic section, the follicle cyst is collapsed and the cavity slitlike. Follicle cysts are lined by one or several layers of granulosa cells. Mitotic activity (arrow) is common (hematoxylin-eosin [H & E] stain).

Because follicle cysts appear benign sonographically and laparoscopically, they are managed conservatively to preserve the ovary. FNA is commonly used as a minimally invasive method to confirm the diagnosis.

Cytomorphology of follicle cyst

• sparsely or highly cellular

• isolated cells and clusters

• coarsely granular chromatin

• mix of viable and pyknotic nuclei

• foamy cytoplasm

• mitoses

FNA specimens range from sparsely to highly cellular. The highly cellular cases are termed cellular follicle cysts and account for between 23% and 76% of all follicle cysts.20,33 The granulosa cells can be isolated, but they have a tendency to cluster haphazardly in loose spherical aggregates (Fig. 16.2). They have a round nucleus with coarsely granular chromatin and one or two small nucleoli. Nuclear grooves are not usually seen.²⁷ Some nuclei are dark, pyknotic, and eccentrically placed, whereas others are round and vesicular with a prominent nucleolus. Mitotic figures can be absent or numerous (Fig. 16.3). Luteinized granulosa cells have foamy cytoplasm that may contain yellow pigment. Theca interna cells have an eccentrically placed ovoid nucleus and a moderate amount of cytoplasm. Theca externa cells are indistinguishable from spindle-shaped ovarian stromal cells.³⁴

Figure 16.2 Follicle cyst.
Granulosa cells are clustered in loose aggregates (Papanicolaou stain).

Figure 16.3 Follicle cyst.
Granulosa cells have round nuclei and a moderate amount of granular cytoplasm. Degenerated granulosa cells with pyknotic nuclei are a common finding, as are mitoses (arrow) (Papanicolaou stain).

Differential diagnosis of follicle cyst

• granulosa cell tumor

• carcinoma

Follicle cysts can be a challenge to distinguish from epithelial cysts. When ciliated or mucinous epithelium is identified, the cyst is of surface epithelial origin and not a follicle cyst. Immunostaining for α-inhibin, epithelial membrane antigen (EMA), and CK7 can be very helpful. Granulosa cells are often immunoreactive for inhibin and negative for EMA and CK7; the reverse is true of epithelial cysts.³⁵ E2 levels in cyst fluid are also helpful. Elevated concentrations correlate strongly with cysts of follicular origin^1,6,7,17: 81% to 90% of follicle cysts have an E2 content greater than 20 nmol/L as measured by radioimmunoassay, and in 97% to 99% of nonfollicular cysts it is less than 20 nmol/L. Also helpful are fluid CEA and CA-125 levels, which are low in follicle cysts; one or more of these is usually elevated in serous, mucinous, and endometriotic cysts.^19,31 The differential diagnosis also includes a cystic granulosa cell tumor. Fluid from this lesion is usually highly cellular.³⁶ Unlike the cells of a follicle cyst, those of a granulosa cell tumor have nuclei with pale, finely dispersed chromatin. Cellular follicle cysts represent a potential diagnostic pitfall: Because of their cellularity and conspicuous mitotic activity, they may raise the possibility of a granulosa cell tumor or carcinoma.^9,27,28 Knowledge of the invariably benign sonographic and laparoscopic findings of follicle cysts, including the cellular variant, is reassuring and diagnostically helpful.

Corpus Luteum Cyst

Corpus luteum cysts are unilocular and histologically similar to follicle cysts except that the wall is composed of large luteinized granulosa and theca interna cells.

Cytomorphology of corpus luteum cyst

• isolated very large cells

• abundant foamy cytoplasm

• intact or pyknotic nuclei

• macrophages

• hyaline bodies, calcification (pregnancy)

The fluid may be hemorrhagic and composed of numerous, predominantly isolated luteinized granulosa cells with round or pyknotic nuclei. The cytoplasm is abundant and finely vacuolated and contains lipid (Fig. 16.4). Macrophages with hemosiderin or the yellow hematoidin pigment and smaller luteinized theca interna cells are also seen.³⁷ Cysts associated with pregnancy contain hyaline bodies and calcifications.²⁰ Fluid from a hemorrhagic corpus luteum cannot always be distinguished cytologically from that of other benign cysts, including endometriotic cysts.

Figure 16.4 Corpus luteum cyst.
These cysts are lined by very large cells that have a small nucleus and abundant finely vacuolated cytoplasm (Papanicolaou stain).

Endometriotic Cyst

Endometriosis affects women of reproductive age and is often associated with infertility. It can result in a cystic tumorlike mass of the ovary, known as an endometriotic cyst or endometrioma. As many as one half of ovarian endometriomas are bilateral. For an unequivocal diagnosis, identification of two of the following features is required: endometrial glands, endometrial stroma, and hemosiderin.

Cytomorphology of endometriotic cyst

• hemosiderin-laden macrophages

• endometrial glandular cells

• endometrial stromal cells

The aspirated cyst fluid contains hemolyzed old blood the color of chocolate (“chocolate cyst”). Hemosiderin-laden macrophages are numerous (Fig. 16.5A). Endometrial epithelial cells are usually arranged in clusters or sheets. The cells are small and have indistinct borders; nuclei are round or oval; nucleoli are inconspicuous; and cytoplasm is scant and sometimes vacuolated. Nuclear molding may be seen. Stromal cells with oval nuclei and scant cytoplasm may also be present. Epithelial and stromal cells are best appreciated as such on cell block preparations (Fig. 16.5B).