Corpus Luteum and Hemorrhagic Cyst
Synonyms/Description
Functional cyst (corpus luteum)
No synonym for hemorrhagic cyst
Etiology
The corpus luteum (CL) is a transient structure formed as a result of ovulation, due to the midcycle luteinizing hormone surge from the pituitary gland. The CL is responsible for the production of progesterone, hence the term “functional cyst.” It is necessary for regulating menses and for maintaining a pregnancy until it develops the ability to make its own progesterone. If a pregnancy does not occur, the CL breaks down. It can, on occasion, undergo internal hemorrhage and develop into a hemorrhagic cyst. When such a cyst continues producing progesterone, it is a hemorrhagic corpus luteum. If progesterone synthesis ceases, but the cyst persists, then it is considered a hemorrhagic cyst. Hemorrhagic cysts can enlarge up to 5 cm or more, causing pain, and may occasionally rupture, resulting in a hemoperitoneum. The pain typically resolves within a few days, whereas the cyst may take 1 to 3 months to regress. Patients with symptomatic hemorrhagic cysts typically present with acute unilateral pelvic pain and have a complex-appearing lesion on ultrasound evaluation. Often they are asymptomatic and can be an incidental finding. The nonspecific and confusing sonographic appearance of the hemorrhagic corpus luteum and hemorrhagic cyst often results in misdiagnosis and unnecessary surgery.
Ultrasound Findings
The CL is an ovarian cystic structure, typically 2 to 3 cm in size. Gray scale ultrasound characteristics include an irregular thick wall, unilocular cyst, often with internal debris or echogenic material. The most constant and specific feature of the CL is the “ring of fire” pattern of color Doppler, showing intense and abundant circumferential blood flow. The hemorrhagic CL often has a fine reticular or fishnet-like internal pattern and/or a solid area consistent with a retracting clot. Color Doppler reveals circumferential flow but no internal blood flow. The specific diagnosis is often possible sonographically, but because the CL is a mimicker of adnexal pathologies, a follow-up scan may be helpful when uncertain of the diagnosis, as discussed in clinical recommendations. A hemorrhagic cyst will have the same appearance as a hemorrhagic corpus luteum but without color flow. If internal hemorrhage occurs with cyst rupture or partial rupture, then complex fluid may be seen in the cul-de-sac or higher, or surrounding the ovary.
Differential Diagnosis
The correct diagnosis is often challenging because of variations in size, irregularity of the cyst wall, and internal solid areas (clot), all of which are nonspecific sonographic findings mimicking pathology. Knowing the menstrual cycle day is very helpful, although not always possible, in patients with irregular bleeding or menses.
In the setting of a patient presenting with pelvic pain and a tender, cystic adnexal mass, the differential diagnosis is vast and includes most commonly ectopic pregnancy, pelvic inflammatory disease (PID), adnexal torsion, and neoplasm in addition to a functional or hemorrhagic cyst. In a patient with a positive pregnancy test, the adnexal ring of an ectopic pregnancy can have a similar appearance to a CL, including the “ring of fire” Doppler pattern. Useful sonographic discriminators between these two entities are the location of the cyst and the appearance. An ectopic pregnancy typically has a more echogenic rim than a corpus luteum, and most (although not all) ectopics are extraovarian, whereas functional cysts are always in the ovary. The circumferential Doppler pattern of a corpus luteum (ring of fire) is easily distinguishable from a torsed ovary, which would typically have a paucity of flow. Doppler pattern is also a key factor in distinguishing a CL from a neoplasm. Sometimes, the retracting blood clot of a CL may have a nodular shape resembling a mural nodule. An ovarian malignant tumor will typically have blood flow visible in the internal solid area, whereas the CL only has circumferential flow with no internal Doppler signal. If the CL has undergone acute hemorrhage, the internal clot will be transiently echogenic and may be confused with a dermoid cyst. A follow-up ultrasound will be helpful because a hemorrhagic cyst will resolve, whereas the dermoid will not. Patients with PID are often clinically ill (e.g., fever, elevated white blood cell count), and the mass is typically more tubular than an ovarian cyst, often involving the fallopian tube.
Clinical Aspects and Recommendations
It is important to understand that the CL is a normal, short-lived, functional cyst found in premenopausal and pregnant women. Its function is essential, and if the corpus luteum is surgically removed in early pregnancy an abortion will ensue. Occasionally, the development of a corpus luteum may cause acute pain, even without internal hemorrhage, known as Mittelschmerz. Hemorrhage may develop within a functional cyst, resulting in acute pain, although not all hemorrhagic cysts are symptomatic. Hemorrhagic cysts will resolve over 1 to 3 months, depending on their size, as the clot is broken down and reabsorbed. If the pain and cystic mass do not resolve, the diagnosis may not be a hemorrhagic cyst (see Differential Diagnosis, earlier). It is essential to know the menstrual history, if the patient is pregnant, or if there is associated fever indicating an infection. Follow-up scans are particularly useful to track progress toward spontaneous resolution of the lesion.
Figures
Figure C3-4 Two different cases of hemorrhagic cysts with retracting clot. A, The typical reticular or fishnet internal structure consistent with a retracting clot. B, A more solid internal structure of the cyst. Note that the solid areas are retracting toward the periphery of the cyst rather than growing into the center, as would a neoplasm. No flow was seen within the clot.
Suggested Reading
Guerriero S., Ajossa S., Melis G.B. Luteal dynamics during the human menstrual cycle: new insight from imaging. Ultrasound Obstet Gynecol. 2005;25:425–427.
Jain K.A. Sonographic spectrum of hemorrhagic ovarian cysts. J Ultrasound Med. 2002;21:879–886.
Parsons A.K. Imaging the human corpus luteum. J Ultrasound Med. 2001;20:811–819.
Stein M.W., Ricci Z.J., Novak L., Roberts J.H., Koenigsberg M. Sonographic comparison of the tubal ring of ectopic pregnancy with the corpus luteum. J Ultrasound Med. 2004;23:57–62.
Swire M.N., Castro-Aragon I., Levine D. Various sonographic appearances of the hemorrhagic corpus luteum cyst. Ultrasound Q. 2004;20:45–58.
