Cyst, Follicular, Ovarium

Synonyms

Corpus luteum cysts; Follicle cysts; Follicular cysts; Luteal cysts; Physiologic ovarian cysts; Simple ovarian cysts

Definitions

Physiologic cysts including follicular and luteal cysts constitute the vast majority of cystic ovarian lesions. They typically result from failure during folliculogenesis, most often from rupture or regression of the ovarian follicles. They may also result from continued hemorrhage in a corpus luteum. Follicle cysts are usually larger than the mature graafian follicle and range from 3 to 5 cm in size; however, they may attain a diameter of 8–12 cm. Physiologic ovarian cysts are an extremely common incidental finding during the reproductive ages. However, they may be found in all age groups, particularly in adolescents and in the early postmenopausal period. Functional ovarian cysts may also develop due to irregularities of pituitary gonadotropin hormone release or due to external hormonal replacement therapy.

Pathology/Histopathology

In women who do not take birth control pills, numerous small, thin‐walled cystic follicles and a dominant follicle are seen within the ovarian peripheral stroma. At midcycle the latter attains a size of 15–25 mm and can be identified partially protruding from the ovarian surface ( 1). After ovulation the rupture stigma is sealed by a mass of coagulated follicular fluid, fibrin, and connective tissue ( 1). The normal corpus luteum demonstrates a convoluted yellow lining and usually measures 1.5–2 cm in diameter. If it is larger than 3 cm, it is defined as a corpus luteum cyst ( 1).

Microscopically, follicle cysts are lined by an inner layer of granulosa cells and an outer layer of theca interna cells ( 1). They may be luteinized in both layers. Corpus luteum cysts demonstrate a convoluted inner lining consisting of large luteinized granulosa cells and an outer lining of luteinized theca interna cells ( 1). Capillaries from the theca interna penetrate the granulosa layer to reach the central cavity ( 1). The contents of follicle and luteal cysts vary from serous to serosanguinous to clotted blood.

Follicles may persist for several years after menopause and give rise to sporadic ovulations or cyst development. Solitary follicular cysts are a different entity from follicular cysts that occur during the reproductive age ( 1). They tend to be larger and are most commonly found during menarche and menopause, but may also be seen in the fetus. Cysts related to anomalies in the release of anterior pituitary hormones tend to recur and manifest as multiple large cysts in both ovaries ( 1).

Clinical Presentation

Most functional cysts are asymptomatic and not hormonally active. Vague abdominal or pelvic pain, pelvic pressure, and lower back pain may be caused by larger functional cysts. Corpus luteum cysts may be hormonally active and become clinically apparent by menstrual disorders and prolonged hemorrhage. Complications of functional cysts include rupture, hemorrhage, and torsion. Intraperitoneal hemorrhage following rupture is characterized by an acute onset of pelvic pain. Similarly, patients with ovarian torsion most commonly experience abrupt onset of severe lower abdominal pain. Follicle cysts in precocious puberty are manifestation of McCune–Albright syndrome ( 1).

Imaging

Ovarian cysts are a common incidental finding in ovarian imaging.

Transabdominal in combination with endovaginal sonography is the primary imaging modality in assessing the ovaries. If physiological cysts do not exceed a size of more than 3 cm they cannot be differentiated from normal follicular derivates in women of reproductive age.

Other imaging modalities for assessing cystic ovarian lesions include computed tomography (CT) and magnetic resonance imaging (MRI). They are infrequently used for further characterization of sonographically detected cystic lesions. More often, functional cysts are incidental findings in pelvic imaging studies for other indications.

Due to partial volume average and proteinaceous contents, follicles are often missed in CT. Furthermore, CT usually does not allow differentiation between hemorrhagic functional cysts and hemorrhagic cysts in endometriosis. Hemorrhagic cysts may also mimic solid ovarian lesions in CT. This problem can be overcome by performing a noncontrast series before application of intravenous contrast media. This technique and thin‐slice multispiral CT also improve the detection of smaller ovarian cysts. In cystic ovarian lesions, contrast‐enhanced images provide better detail of the internal morphology of cystic lesions. They also assist in the differential diagnosis between simple ovarian cysts and other cystic ovarian lesions, for example, cystadenomas, hydrosalpinx, and cystic ovarian cancer.

In MRI imaging, sequences for assessing cystic ovarian lesions include T1‐weighted imaging (WI), T2‐WI, and contrast‐enhanced imaging. If lesions display high signal intensity (SI) on T1‐WI, fat saturation techniques are useful to differentiate between proteinaceous or hemorrhagic contents and fat that is pathognomonic for dermoid cysts.

Nuclear Medicine

Nuclear medicine usually does not contribute to the diagnosis of functional ovarian cysts.

Diagnosis

Sonography, particularly endovaginal sonography, is the modality of choice in monitoring follicles and ovarian follicle cysts (Fig. 1).

Figure 1

Color Doppler sonography of a normal ovary at midcycle in a 25‐year‐old female patient. Transvaginal sonography demonstrates a normal ovary which is located medial of the iliac vessels. Within the ovarian parenchyma, ovarian vessels and small follicles are demonstrated. The graafian follicle presents the largest cystic lesion and measures 15 mm in diameter. (Courtesy of R. Gruber, Salzburg)

Ovarian cysts larger than 3 cm in diameter are regarded as follicular cysts ( 2). Follicle cysts are thin‐walled ovarian lesions most commonly filled with watery contents. Compared with follicle cysts, corpus luteum cysts have thicker, well‐vascularized walls. The internal echoes depend on the quality of the contents. Bleeding in an unruptured cyst causes a spectrum of sonographic findings related to the temporal sequence of clot formation ( 3). Corpus luteum cysts often display mildly echogenic echoes, most likely presenting partially solid clots ( 3). They may also present as cystic lesions with irregular walls due to an adherent clot or may contain internal debris that is not vascularized. Recent hemorrhage frequently appears as an irregular echogenic mass ( 3) (Fig. 2). A complex mass with internal echoes enhanced through transmission is also a common finding of hemorrhagic functional cysts ( 3).

Figure 2

Hemorrhage in a physiologic cyst. In a 29‐year‐old female patient with acute pain, a 6‐cm right ovarian lesion is demonstrated. It is well delineated and is composed of a solid area with irregular borders surrounded by liquid. The sonographic follow‐up showed continuous decrease in size and change in morphology of the internal clot. (Courtesy of R. Gruber, Salzburg)

Echogenic free fluid in the cul‐de‐sac is a typical finding of cyst rupture into the peritoneal cavity. However, in women of reproductive age, a pregnancy test is mandatory for differentiation of hemorrhagic functional cysts and ectopic pregnancy.

The clue for establishing the diagnosis of functional cysts with watery contents or hemorrhage and for their differentiation from cystadenomas is the decrease in size and change of the internal architecture during a sonographic follow‐up. The vast majority of functional cysts will regress within a 2‐month observation period ( 2).

MRI is usually performed complementary to sonography in indeterminate cases. It is particularly helpful for differentiating functional cysts with a complex pattern from hemorrhagic ovarian lesions of other etiologies and teratomas.

Simple ovarian cysts display well‐defined, thin walls (<3 mm). Most ovarian cysts have a low to intermediate signal on T1‐WI and very high SI on T2‐WI due to the presence of simple fluid ( 2). Cyst walls are usually clearly identified on T2‐WI, they display low SI, and enhance mildly following contrast media application. Hemorrhagic and corpus luteum cysts display high to intermediate signal on T1‐WI and intermediate to high SI on T2‐WI ( 2). Their appearance varies according to the quantity and age of their hemorrhagic and proteinaceous contents (Fig. 3). Corpus luteum cysts tend to have thicker walls that display smooth distinct contrast enhancement ( 2). Internal debris is often present, but does not enhance. Enhancement is a sign of solid internal contents, and is highly suggestive of malignancy. Low‐signal intensity on T2‐WI presenting shading is due to repetitive hemorrhage and allows the diagnosis of endometriomas ( 2). The diagnostic feature of benign teratomas is demonstration of intralesional fat, which can be diagnosed by fat‐suppression techniques.

Figure 3

Follicle cyst in a 31‐year‐old female patient. Transaxial T1‐weighted imaging (WI) (a) and T2‐WI (b) show a 6‐cm right adnexal lesion. It is cystic and displays higher signal than water on T1‐WI (a) due to proteinaceous contents. Thin walls and no evidence of mural thickening or solid areas are demonstrated on T2‐WI. Small amounts of ascites in the cul‐de‐sac are a physiologic finding in this age. The differential diagnosis from unilocular cystoma was only possible by a follow‐up.

If an ovarian cyst does not decrease in size, unilocular cystoma, which can present with the same imaging features as functional cysts, is the most important differential diagnosis ( 2). Mesothelial and tubal inclusion cysts occur in the same age group and can also display similar imaging findings to simple ovarian cysts. They can only be differentiated from physiologic ovarian cysts when they are visualized separate from the ipsilateral ovary.