Case of the Month, November 2010, Page 3

Most likely diagnosis?

Mature cystic teratoma

Findings

Single intrauterine pregnancy with last menstrual period gestational age matching gestational age calculated by crown rump length. Good fetal heart rate in the 160s.

Heterogeneous cystic masses are seen within the bilateral adnexal regions, measuring 6.5 cm on the right and 6 cm on the left. They contain focal hyperechoic components, likely representing fat, as well as regions exhibiting a “dot-dash” pattern, consistent with hair in fluid. There is no flow within the cystic lesions, and there is posterior acoustic enhancement, confirming their cystic nature. There is flow around these cystic masses, consistent with flow within the adjacent ovarian parenchyma.

Follow-Up

Patient was admitted for observation, and pain resolved overnight.

Two weeks later patient presented to the emergency department with similar symptoms. Patient was immediately taken to the operating room, where they saw large complex cystic masses bilaterally as well as 720-degree torsion of the right ovary. The cystic ovarian masses were removed and the right ovary untwisted, with preservation of both ovaries.

Pathology confirmed the diagnosis of bilateral mature cystic teratomas.

Discussion

Mature cystic teratomas (dermoids) contain at least two of the three germ cell layers: ectoderm (skin and neural tissue), mesoderm (fat, bone, cartilage, and muscle tissue), and endoderm (gastrointestinal, bronchial, and thyroid tissue).

They are commonly detected in the second and third decades of life in women. They are the most common benign ovarian tumor, constituting 20% of all ovarian tumors in adults and 50% of ovarian tumors in children. They are bilateral in approximately 10% of cases, and when unilateral occur more commonly on the right side (70%).

Most mature cystic teratomas are asymptomatic and are often incidentally discovered during routine pelvic exams. They may rarely present with pain or non-specific symptoms.

The most common complication of a mature cystic teratoma is ovarian torsion. Malignant degeneration occurs in less than 1-2% of cases, usually with squamous cell carcinoma arising from the squamous lining of the cyst. Another rare complication that occurs in less than 1% of cases is tumor rupture with spillage of sebaceous material into the peritoneum, causing a granulomatous peritonitis.

Imaging

Ultrasound is the most common imaging modality to assess ovarian masses.

The overall composition of a mature cystic teratoma can vary, leading to varying presentations on imaging. The classic appearance is a cystic lesion with a densely echogenic tubercle (representing sebaceous material or fat) projecting into the cystic lumen (termed a Rokitansky nodule). Well-defined areas of calcification with posterior acoustic shadowing may be seen in up to 30% of cases, representing teeth. “Thin band-like echoes” in a “dash-dot” pattern can also be seen, representing hair in fluid. Fat-fluid levels may also be seen, characterized by dependently layering hyperechogenic material.

Most Common Complication: Adnexal Torsion

Ovarian torsion occurs in 1 in 1800 pregnancies, and 25% of adnexal torsions occur in pregnant patients. Ovarian torsion most commonly occurs between 6 and 14 weeks gestation.

Ultrasound appearance of torsion can vary depending on the degree of ischemia and infarction. The classic appearance is of an enlarged, heterogeneous ovary with peripheral follicles and absent arterial flow. However, early in the process there may only be lymphatic and venous obstruction with preservation of arterial perfusion. Also, since the ovary has dual arterial supply, early on only one of the arteries may be occluded, and so a torsed ovary with all the other classic findings may still exhibit arterial flow. Technical factors may also lead to false positive studies.

Treatment

Most mature cystic teratomas can be managed conservatively in pregnant patients if less than 6 cm due to rate of slow growth.

Once greater than 6 cm, there is a greater risk for torsion. In these cases elective surgical removal is usually performed during the second trimester, unless there is evidence for torsion, in which case the patient will usually go to surgery immediately.

References

Outwater EK, Siegelman ES, Hunt JL.  Ovarian Teratomas:  Tumor Types and Imaging Characteristics.  Radiographics 2001; 21:475-490

Saba L, Guerriero S, Sulcis R, Virgilio B, Melis G, Mallarini G.  Mature and immature ovarian teratomas:  CT, US and MR imaging characteristics.  European Journal of Radiology 2009; 72:454-463

Walid MS and Boddy MG.  Bilateral dermoid cysts of the ovary in a pregnant woman: case report and review of the literature.  Arch Gynecol Obstet 2009; 279:105-108

Webb EM, Green GE, Scoutt LM.  Adnexal mass with pelvic pain.  Radiol Clin N Am 2004; 42:329-348

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