The Acute Female Nongravid Pelvis: A Review of Appropriate Clinical Applications of Sonography,Computed Tomography,and Magnetic Resonance Imaging

Abstract

Objective:

The objective of this literature review was to provide a summary of the primary concerns in evaluating ovarian cysts and compare the diagnostic roles of each imaging technique, in an emergent setting.

Materials and Methods:

A literature review of the imaging evaluation of functional ovarian cysts, emergent complications, and relevant case studies was performed using peer-reviewed articles. The literature search was conducted using PubMed, The Wiley Online Library, and Google Scholar search engines.

Results:

Sonography, computed tomography (CT), and magnetic resonance imaging (MRI) demonstrate comparable accuracy in the diagnosis of functional ovarian cysts and ovarian torsion. While sonography is the preferred method of imaging the female pelvis, CT and MRI demonstrate similar diagnostic capabilities.

Conclusion:

Functional ovarian cyst rupture/hemorrhage and ovarian torsion can be accurately demonstrated using sonography, CT, and MRI.

Acute pelvic pain is a common presenting complaint in nongravid female patients of reproductive age. Although the cause of pelvic pain may be difficult to determine in some cases, functional ovarian cysts are the most common lesion in female patients of menstrual age. ¹ The exact rate of occurrence is unknown due to a limited amount of published research. Studies indicate an asymptomatic occurrence of 6.6% to 7%^2,3 with other outlying studies showing rates of 0.9% ⁴ and 13.7%. ¹ Most asymptomatic functional cysts resolve spontaneously within 3 menstrual cycles, which further hinders accurate statistical reporting.^1–3 Patients who present to acute care are commonly found to have rupture or hemorrhage of the cysts. Ovarian torsion, a rare emergent complication, occurs in 3% of surgical patients ⁵ and is more commonly seen in patients with ovarian masses greater than 5 cm.^5,6

Abdominal pain is the most common presenting complaint in the emergency department (ED), ⁷ leaving a wide range of possible gastrointestinal and genitourinary pathologies for the acute care physician to rule out. Governing and regulatory bodies such as The Joint Commission endorse faster turnaround times from ED admission to discharge or inpatient admission. ⁸ The rationale for this, as stated on The Joint Commission website, is to “improve access to treatment and increase quality of care. Reducing this time potentially improves access to care specific to the patient condition and increases the capability to provide additional treatment.” ⁸ Thus, acute care providers are tasked with efficiently and quickly diagnosing each patient; laboratory values and medical imaging results are crucial to this process. Thorough knowledge of each imaging technique and the ability to correlate with the patient’s relevant clinical presentation and laboratory values is essential for ED physicians to provide effective acute care while avoiding unnecessary testing that contributes to low-value care and delayed patient discharge.

Materials and Methods

Research was conducted utilizing Google Scholar, PubMed, and The Wiley Online Library search engines. Search criteria included peer-reviewed literature regarding the anatomy and pathophysiology of functional ovarian cysts and associated complications, and the search was performed using the following search terms: ovarian cysts in women, functional ovarian cyst, follicular cyst, corpus luteal cyst, cyst rupture, cyst hemorrhage, ovarian torsion, and acute female pelvis. Thorough reviews of specific imaging findings were obtained utilizing these search terms cross-referenced with the terms “computed tomography” (CT), “magnetic resonance imaging” (MRI) and “ultrasound/sonography.” Current imaging criteria for acute female pelvic pain and guidelines for appropriate use of ultrasound, CT, and MRI of the female pelvis were reviewed utilizing published guidelines set forth by the American College of Radiology.

Results

Functional Ovarian Cysts

In women of reproductive age, functional ovarian cysts develop during the normal cycle in response to the menstrual hormone cascades. The two types of functional ovarian cysts are follicular cysts and corpus luteal cysts.

At the start of each menstrual cycle, multiple ovarian follicles begin to mature under the influence of follicle-stimulating hormone (FSH). Over the course of the follicular phase of the menstrual cycle, the ovary produces multiple follicles that develop until one matures to become the dominant follicle. Once the dominant follicle produces enough estrogen to prompt a surge of luteinizing hormone (LH), ovulation is triggered and the follicle ruptures to release the oocyte; the remnant of the ruptured dominant follicle remains as the corpus luteum. Progesterone production from the corpus luteum suppresses FSH and LH production until its decline in the absence of fertilization, which then allows FSH and LH to rise, precipitating the next menstrual cycle.

Functional cysts occur when the dominant follicle fails to rupture during ovulation or when the cycle is anovulatory due to a disruption to the normal FSH/LH cycle. Functional cysts are differentiated from the dominant follicle when they reach a diameter greater than 25 mm. They are thin-walled, fluid-filled, unilocular sacs. Corpus luteal cysts are present when the corpus luteum fails to dissolve after its usual 14-day life span; these cysts are thick-walled, fluid-filled, unilocular sacs. Both follicular cysts and corpus luteal cysts can contain simple fluid, or they may contain blood products due to internal hemorrhage.

Clinical signs of symptomatic functional ovarian cysts are unilateral pelvic pain and/or pressure of varying quality and degree. Adnexal masses are sometimes palpated by physical examination. Bimanual examination can be of limited diagnostic value, however, depending upon patient’s pain level, anatomy, and body habitus as well as the experience level of the provider performing the examination.

Complications of Ovarian Cysts: Cyst Rupture and Cyst Hemorrhage

A common complication of ovarian cysts is rupture and/or hemorrhage. Rupture of functional ovarian cysts usually occurs due to increasing size. The fluid contained within the sac spills into the pelvic cavity, which can cause diffuse pelvic pain resulting from irritation of the peritoneal lining and pressure on surrounding pelvic structures. The intensity of pain can vary depending on the volume of free pelvic fluid. Hemorrhagic cysts are usually found postovulation. Bleeding within the cavity of the cyst from the internal wall usually occurs due to the increased vascular flow of the corpus luteum. ⁹

Treatment for ruptured and hemorrhagic cysts depends upon the severity. Patients who experience significant blood loss require hospital admission for surgical evacuation of hemoperitoneum and/or blood transfusion. Hemodynamically stable patients can be discharged to home once their pain is sufficiently managed.

Complications of Ovarian Cysts: Ovarian Torsion

In some instances, large ovarian cysts and other masses can cause ovarian torsion, an emergent condition in which the ovary, the supporting ligaments, and sometimes the ipsilateral fallopian tube are twisted, resulting in loss of vascular flow and subsequent tissue ischemia and necrosis if surgical intervention is delayed. Torsion is a rare finding, with studies showing a rate of occurrence ranging from 2.7% to 3%.^5,6,10,11 Lesions measuring greater than 5 cm are of the most concern as they are widely cited to be most likely to cause ovarian torsion.^5,6 Benign ovarian masses are more likely to cause torsion than malignant masses. Less than 2% of torsion cases were reported to be caused by malignancy. ⁶

Clinically, patients with ovarian torsion present with acute unilateral lower abdominal pain accompanied by nausea with or without vomiting and low-grade fever. While symptoms and imaging results can be highly indicative of torsion, the only method of confirming and treating torsion is surgery—detorsion, cystectomy, oophorectomy, or salpingoophorectomy if there is fallopian tube involvement.

Because symptoms due to complications of ovarian cysts are nonspecific, there are quite a few differential diagnoses that providers must consider. As torsion is a surgical emergency, diagnosis must be made quickly to preserve ovarian function. It is difficult to differentiate ovarian torsion from cyst rupture or hemorrhage due to the similarities in clinical presentation. A 5-year retrospective study on patients with either confirmed ovarian torsion or cyst rupture confirmed no difference in clinical presentation between the two. ¹² As differentials include lower gastrointestinal and urinary tract pathology in addition to possible gynecologic cause, a thorough triage assessment and laboratory evaluation can help determine the best course of diagnostic imaging. Most notably, urine pregnancy testing and/or serum beta-hCG should be obtained to exclude emergent obstetric complications with similar presentation, such as ectopic pregnancy.

Imaging Evaluation: Sonography

In patients with high clinical suspicion for gynecologic pathology, sonography should be the initial modality due to its accessibility and ability to efficiently evaluate the pelvic anatomy for ovarian torsion, ovarian cyst rupture, or hemorrhagic ovarian cyst. Indications specific to ovarian cause include recent diagnosis of pelvic mass, palpable pelvic mass by physical examination, and/or recent history of fertility treatments to stimulate follicular development.

Transabdominal (TAS) and transvaginal (TVS) sonographic protocols include evaluation of the uterus, endometrial canal, and bilateral ovaries and adnexa. Sonographically, benign simple cysts appear as unilocular, well-defined anechoic structures with thin walls and posterior enhancement contained within or at the periphery of the ovary. ¹

Hemorrhagic cysts may have a variable appearance depending on the age of the blood products; the presence of posterior enhancement can help to differentiate complex echo patterns from retracting clot from heterogeneous solid masses. Other findings include fluid-fluid levels, irregular appearance of cyst walls due to retracting clot, or fine lace-like septations.^1,13 Hemorrhagic corpus luteal cysts may have more complex appearance, with thick walls that have a scalloped appearance, and can be isoechoic or hypoechoic to the ovary. The central component is generally hypoechoic due to blood products or has the same appearance of resolving clot as hemorrhagic follicular cysts. Peripheral vascular flow in the cyst walls, or the textbook “ring of fire,” may be present on color Doppler. ⁹

In patients with cystic rupture, the cyst itself will likely have a complex or hemorrhagic appearance accompanied by free fluid in the pelvic cavity. ¹³ Free fluid can accumulate in any location throughout the pelvis but is commonly found in the rectouterine pouch or in the ipsilateral adnexa. Echogenic free fluid is an indicator of blood products due to hemoperitoneum. In patients with severe bleeding, hemoperitoneum can extend to the upper abdomen and collect in Morison’s pouch or the splenorenal space. ⁹

The most common findings in ovarian torsion are unilateral ovarian enlargement and ovarian mass/cyst. Additional indicators of torsion include an abnormally rounded contour in comparison with the contralateral ovary and an overall heterogeneous appearance due to edema from lymph and venous congestion. Abnormal situs is an indicator; an enlarged ovary found outside of the usual adnexal location is highly suggestive of torsion. ⁵ While the absence of flow on color and spectral Doppler is diagnostic for torsion, it is important to note that the presence of arterial flow does not exclude torsion.^5,10 The ovary receives a dual blood supply from the ovarian artery and uterine artery collaterals; arterial signals may still be present due to the alternate blood supply or intermittent torsion. The presence of the whirlpool sign, or a swirling snail-shell type appearance of the twisted vascular pedicle, is another finding that studies suggest may be more sensitive for torsion than color Doppler. ⁶

Limitations to sonographic evaluation include patient body habitus, skill of the performing sonographer, and patient’s clinical condition. Findings may be equivocal or nondiagnostic in patients with increased acoustic attenuation of soft tissue precluding adequate penetration, in those who are unable to tolerate the examination due to severe pain, or in cases where ovaries cannot be visualized due to technical factors such as bowel gas. In cases such as these, if there is high clinical suspicion of ovarian torsion, then advanced imaging may be warranted if immediate surgical intervention is not indicated.

Sonography is the preferred imaging modality for gynecologic imaging due to its high diagnostic accuracy and is considered the gold standard in imaging hemorrhagic ovarian cysts. ⁹ A large, multicenter review demonstrated an overall specificity of pelvic ultrasound for all diagnoses ranging from 94% to 100%; however, the ability to distinguish between benign and malignant lesions was inconsistent. ¹⁴ The same study reported a low sensitivity for functional cysts, however, at only 17%. ¹⁴ Torsion remains a challenge to diagnose, with studies reporting a wide range in diagnostic accuracy. Ghulmiyyah et al. ⁵ report a sensitivity ranging from 40% to 90% and a specificity ranging from 44% to 70%, each depending on the number of sonographic indicators used.

Imaging Evaluation: CT

When gastrointestinal or urinary tract cause is suspected, CT is the most appropriate diagnostic imaging technique for initial evaluation. ¹⁵ As it is not the preferred modality for gynecologic imaging, most ovarian findings are incidental; however, it is still possible for an abdominopelvic CT to provide adequate diagnostic information to diagnose ruptured ovarian cysts, hemorrhagic cysts, and ovarian torsion.

Ovaries are identified on CT as low-attenuation soft tissue structures in the bilateral pelvic cavity. Follicles can be identified on contrast-enhanced images. Functional ovarian cysts present on CT much the same as sonography: well-defined, thin- or thick-walled unilocular lesions. ¹⁶ Hemorrhagic follicular cysts and corpus luteal cysts have similar appearance on CT; however, there is a lack of data on the correlation between sonographic and CT findings for complex lesions. ¹⁷ They appear complex with a mixed pattern of internal increased attenuation, demonstrating blood products. Ruptured cysts have a collapsed, complex appearance with associated pelvic free fluid. While blood flow cannot be assessed using CT other indicators of ovarian torsion are consistent with suspicious sonographic findings: prominent peripheral follicles, ovarian enlargement, abnormal morphology, abnormal situs, free fluid, and twisted pedicle.^18–20 Additional CT findings that may not be appreciated on ultrasound are deviation of the uterus to the affected side due to mass effect,^18,20 ovarian hemorrhage, and edema of the adjacent pelvic fat and the ipsilateral fallopian tube.^19,20

Limitations of CT include radiation exposure and contrast can be contraindicated in some patients. Adequate evaluation of the pelvis using CT can be further limited due to inconsistent diagnostic criteria. As CT is not the preferred method of gynecologic imaging, pelvic anatomy is not described in-depth or detail in many instances, resulting in a paucity of data regarding its diagnostic accuracy. A single-center study performed by Harringa et al. ²¹ demonstrated a sensitivity of 66.7% and a specificity of 98.3% for the five most common acute pathologies of the female pelvis, including ovarian cyst rupture/hemorrhage and ovarian torsion. The corresponding ultrasound sensitivity and specificity of this study are 64.3% and 97.7%, ²¹ respectively.

Imaging Evaluation: MRI

Owing to the higher cost, longer examination times, and limited availability of the MRI equipment systems, it is rarely performed in an emergent setting. Owing to the excellent soft tissue resolution without the need for contrast and the ability to accurately characterize fluid components using signal intensity, it is utilized in an acute setting, mainly for advanced evaluation in cases of indeterminate sonographic findings or for abdominopelvic evaluation of pregnant patients when clinically indicated. ²⁰

When performed, pelvic MRI images are obtained utilizing nonenhanced T1 and T2 weighted sequences, diffusion weighted imaging (DWI), and dynamic contrast-enhanced imaging. Rapid imaging protocols can be helpful in patients with severe pain who have difficulty remaining immobile. ²²

The internal composition of a cyst is easily determined due to the different signal characteristics of fluid and blood. Areas of edema, fat, free fluid, air, blood, and soft tissue can be readily identified due to the superior soft tissue resolution. ²³ The MRI findings for torsion are like those of ultrasound and CT: ovarian enlargement, pelvic ascites, abnormal enhancement, ipsilateral uterine deviation, abnormal ovarian situs, and twisted pedicle. ²⁰ Possible additional findings of central ovarian edema or hemorrhage, edema of the fallopian tube, and congested vessels in the region of the twisted vascular pedicle may be appreciated on MRI. ²⁰

The most significant limitations to MRI are metallic implants and allergy or other contraindication to contrast agents. In addition, motion artifact, resulting from severe pain or discomfort, may limit the examination. Although MRI consistently demonstrates accurate soft tissue imaging, there is limited information available on the accuracy of MRI in diagnosing ovarian cysts, possibly due to the lack of widespread usage for this purpose. The previously referenced study by Harringa et al. ²¹ reported an overall MRI sensitivity of 57.1% and specificity of 97.2% for the common acute pelvic pathologies. Despite its superior resolution, cost and availability constraints preclude the routine use of MRI for acute gynecologic imaging.

Discussion

Sonography provides excellent characterization of ovarian cysts and is easily accessible in an acute setting when ovarian torsion, ovarian cyst rupture, or hemorrhagic cyst is of clinical concern. Patients with significant clinical concern for gynecologic pathology, such as ovarian cyst complications or ovarian torsion, should receive initial assessment using emergent sonography.

Although not generally preferred for gynecologic imaging, CT is adequately diagnostic for ovarian cysts and possible complications that are of immediate concern in an emergency room setting. In patients with nonspecific abdominopelvic symptoms, particularly when nephroureterolithiasis or appendicitis is included in the differentials, CT provides a more thorough and efficient evaluation with a wider field of view and examination focus. In cases where CT findings are diagnostic for functional ovarian cysts and possible complications, additional imaging is not indicated to confirm these findings. A study performed by The Royal College of Radiologists found that additional imaging using pelvic sonography in patients with normal CT examinations adds no diagnostic information relevant in the course of care; however, the additional imaging contributed an average of approximately 3 additional hours spent in the ED. ¹⁵ If CT findings are highly suggestive of torsion, further imaging confirmation may only serve to delay surgical intervention, as well as contribute to excess medical costs and patient anxiety.

The MRI of the pelvis provides excellent characterization of pelvic anatomy; unless the examination is nondiagnostic due to limiting factors, there is no additional imaging necessary for confirmation of findings. In patients with complex ovarian pathology, MRI is preferred for more in-depth assessment of pelvic anatomy outside of the emergent setting.

Conclusion

Owing to the high prevalence of functional ovarian cysts, patients with female reproductive organs are extremely likely to experience acute pelvic pain due to functional ovarian cysts at some point in their reproductive years. Although diagnostic imaging is determined based on the most likely differential diagnoses, a review of current literature indicates the diagnostic capabilities of CT and MRI to be similar to that of sonography in the diagnosis of emergent complications of ovarian cysts. To facilitate more efficient and effective evaluation and treatment of patients presenting with acute pelvic pain, it is important for both the ordering provider and the interpreting radiologist to correlate the patient’s clinical presentation with imaging findings to ensure appropriate use of diagnostic imaging for high-value patient care.