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"Dermoid Cyst"

Mature Cystic Teratoma


Adnexal mass typical of a mature cystic teratoma. Hair within the cystic mass, slightly attenuates the sound beam

Findings:

The image demonstrates the typical features of a 'dermoid cyst' (mature cystic teratoma). A cystic mass in the adnexa is identified containing hair both loosely and in a clump. The conglomeration of hair is responsible for slight acoustic shadowing.

Discussion:

Dermoid cysts or mature cystic teratomas are the most common benign germ cell tumor and the most common neoplasm of the ovary. It is also one of the most commonly described ovarian neoplasms in the sonographic literature. This discussion will focus on the pathology, sonographic appearance and management of patients with mature cystic teratomas.

Pathology

While the term 'dermoid' or 'dermoid cyst' is commonly used it is incorrect and probably obsolete. The more appropriate term 'mature cystic teratomas of the ovary' describes well-differentiated derivatives of the three germ cell layers (ectoderm, mesoderm and endoderm). They have been divided into three major categories: mature (benign), immature (malignant) and highly specialized (monodermal). Another classification suggested by Peterson et al and often used pathologically divides these lesions into: 'benign cystic teratoma' - a benign cyst containing derivatives of two or more germ cell layers with differentiation and maturity of tissue elements; 2) 'malignant teratoma' - a predominantly solid tumor frequently containing cystic structures and 3) carcinoma- sarcoma arising in a benign cystic teratoma. An additional category described by Matz et al includes a group of tumors that are solid but histologically benign. Mature cystic teratomas derive from the ectodermal differentiation of totipotential cells. Thus ectoderm elements are present in 100% of mature cystic teratomas.

Pathologically, mature cystic teratomas are often globular or cystic structures which possess a smooth glistening capsule that is milky-white in color unless there is an accumulation of fat or hair beneath the capsule within the cyst cavity. At body temperature the contents of the cyst are in a liquid state. Most cysts are unilocular. The inner lining of every mature cystic teratoma contains single or multiple white shiny masses projecting from the wall toward the center of the cysts. When hair, other dermal appendages, bone and teeth are present, they usually arise from this protuberance. This protuberance is referred to as the Rokitansky protuberance. The Rokitansky protuberance is a common site of malignant transformation.

Rokitansky protuberance containing predominantly sebum

Rokitansky protuberance containing hair and sebum

Characteristically they are unilocular. 8%-15% of mature cystic teratomas are bilateral. The incidence of malignant transformation is said to be between 1-2.8%. Malignacies either represent transformation of a pre-existing benign element or a coexisting lesion. The most common malignancy associated with teratomas are squamous cell carcinomas. Mature cystic teratomas constitute 5%-25% of all ovarian neoplasms and are usually encountered in the reproductive years (85% of mature cystic teratomas occur in women ages 16-55 years). They are often discovered as an incidental finding on physical examination, at the time of ultrasonography or abdominal or pelvic surgery. Most patients are asymptomatic. The most common complication associated with mature cystic teratomas is torsion. The reported rate of torsion ranges from 3.2-16%. Torsion is more common in tumors of intermediate size than in small or extremely large tumors. They may be associated with pregnancy (in one series teratomas constituted 22%-40% of all tumors complicating pregnancy). A report by Peterson et al found that the complication rate associated with teratomas increased with pregnancy, although a more recent study by Caruso et al found the incidence of complications (torsion, hemorrhage or rupture) were not increased in gravid patients.

The rate of spontaneous rupture of mature cystic teratomas is low, ranging from 1.2-3.8%. This has been ascribed to the thick capsule surrounding this lesion. An interesting feature of these lesions is the appearance of thyroid tissue, which may be seen in 5-20% of cases. When the tumors are comprised either entirely or predominantly of thyroid tissue, the 'term struma ovarii' is used. Approximately 5% of ovarian struma ovarii cases produce thyrotoxicosis and 5-10% of these lesions may develop carcinoma.

An interesting analysis of the features of mature cystic teratomas was reported by Comerci et al in 1994. Comerci et al reviewed their data of 573 mature cystic teratomas removed from 517 patients over a 14 year period. The patient's ages ranged from 10-90 years with a median and mean o 30 and 32 years respectively. The mean tumor size was 6.4 cm. Fifty-six patients (10.8%) had cystic teratomas present bilaterally. Three hundred ten patients (60%) were asymptomatic. Of the symptomatic patients, 77.6% presented with abdominal or pelvic pain, 6.6% with dysmenorrhea. Twenty seven tumors (4.7%) were diagnosed during pregnancy. There was no significant difference in the size of tumors between and non-pregnant women. Torsion occurred in 18 patients (3.5%). Tumors undergoing torsion were larger with a mean diameter of 10.8 cm compared to tumors that did not undergo torsion 6.3 cm.

A number of theories exist attempting to explain the histogenesis of mature cystic teratomas. The most widely accepted theory is that they originate from primordial germ cells. This theory is supported by the anatomical distrubution of tumors alon the line of migration of the primordial germ cell from the yolk sac to the primitive gonad. In addition, studies have demonstrated that all benign ovarian teratomas have a 46, XX karyotype.

Imaging of Mature Cystic Teratomas

Clearly, ultrasound has been the main imaging modality utilized for the detection of these lesions. Imaging has come a long way since the first descriptions of the difficulty in detecting this lesion with such findings as the 'tip of the iceberg sign'. While numerous reports exist documenting the accuracy in detecting mature cystic teratomas, two of the more recent are those of Mais et al and Patel et al. In the study by Mais et al using transvaginal ultrasonography the sensitivity was 57.9% and positive predictive value was 84.6%. In this study, more than 30% of cystic teratomas were not apparent on ultrasound, even if the ovaries are identified. This may either be due to the intrinsic nature of the teratomas or to the presence of associated pelvic abnormalities. These authors concluded that the use of transvaginal sonography as a screening test for cystic teratomas cannot be recommended. This study did find a high specificity (98.1%) in differentiating cystic teratomas from other ovarian masses.

The study of Patel et al attempted to assess the diagnostic accuracy of the numerous signs that have been described with this lesion. The sonographic features often ascribed to mature cystic teratomas include: the presence of a shadowing echodensity, hyperechoic lines and dots, regional diffuse bright echoes and a 'hair/fluid level'. In their study, they found 74 benign cystic teratomas in a group of 252 adnexal masses. The single feature which most commonly defined an ovarian mass as a cystic teratoma was the observation of focal or diffuse high amplitute echoes which attenuated the sound (shadowing echodensity). Sixty-four (86%) of the 74 cystic teratomas contained a shadowing echodensity compared to 3 of 178 non-dermoid masses. The tissues most responsible for generating these high-amplitude echoes are: calcified structures such as bone and teeth, clumps of hair in a cystic cavity, and fat in a Rokitansky protuberance. Acoustic shadowing was the sole manifestation of a cystic teratoma in only 16% of patients. Diffuse or regional high amplitude echoes was seen in cystic teratomas without shadowing in 4% of their cases, presumably due to echogenic sebum. The sonographic finding of hyperechogenic lines and dots within the cyst cavity is thought to be due to hair. In their study this sonographic finding had the highest positive predictive value of any individual finding (98%) and was seen in association with at least one other finding in 44/45 cases (98%). Only 1% of dermoids exhibited hyperechoic lines and dots with no other dermoid features. As the sole manifestation of a dermoid, a mass containing hyperechoic lines and dots has a 50% chance of being a cystic teratoma, because fibrinous strands from a hemorrhagic cyst can mimic this appearance.

Hair within the cyst particularly when loosely distributed, produces a 'dot-dash' appearance. When clumped together (arrowhead) with sebum, it may often be quite echogenic and attenuate the sound.

An interesting observation in their study was that cystic teratomas are often not very "cystic" appearing lesions on sonograms (42% characterized as having no cystic features). When a mature teratoma is predominantly solid it may lead to the erroneous conclusion that it is a solid neoplasm and thus suspicious for ovarian carcinoma. Fluid-fluid levels within a dermoid are presumably due to sebum layered on serous fluid. This sonographic feature had prognostic significance only when identified in combination with at least one additional sonographic feature associated with cystic teratomas. As an isolated finding, a fluid-fluid level within an adnexal mass has no diagnostic value in discriminating cystic teratomas from other adnexal masses.

Fluid-fluid level, likely due to sebum layered on serous fluid

Solid-appearing echogenic nodules from a cystic teratoma may simulate other pathology

While the report by Patel et al is encouraging, there are still numerous instances where the definitive diagnosis of a benign cystic teratoma may be quite difficult. An interesting pictorial review of the pitfalls in diagnosis was reported by Hertzberg and Kliewer. In their report, pitfalls were divided into two major categories.

Pelvic disorders that can simulate a benign cystic teratoma

Acute hemorrhage in a pelvic mass
Exophytic lipomatous uterine mass
Uterus obstructed by endometrial carcinoma
Perforated appendicitis with an appendicolith

Appearances of 'Dermoid Plugs' that can go unrecognized

Cystic teratoma mistaken for a distended urinary bladder
Mass missed because a 'dermoid plug' is mistaken for bowel
Cystic teratomas, high in the pelvis, not identified by transvaginal imaging
Discovery in a misleading clinical context

Hertzberg BS, Kliewer MA. Sonography of benign cystic teratoma of the ovary: Pitfalls in diagnosis Amer J Roentgenol 167:1127-1133, 1996

While sonography is often the first imaging modality that is called upon to detect this abnormality, the diagnosis can be aided in difficult cases with the addition of either computed tomography or magnetic resonance imaging. Computed tomography often demonstrates the calcification and low attenuating fat within these lesions. Magnetic resonance imaging (MRI) may also demonstrate blood and lipid within these tumors. The use of fat and water suppression techniques may help differentiate them from endometriomas.

Coronal plane of section MRI scan in a patient with a cystic teratoma. T1 image demonstrates high-intensity lesions.

Coronal plane of section MRI scan from the same patient using fat-supression technique. The low intensity sebaceous component of the cystic teratoma is confirmed. This is helpful in differentiating this lesion from an endometrioma.

Management

As was mentioned above, many cystic teratomas are discovered fortuitously at the time of abdominal or pelvic surgery for other conditions. Initially these lesions were treated by oophorectomy and biopsy of the contralateral ovary. In the report by Comerci Jr et al, they found that over the 14 year period of their study the number of cystectomies increased significantly and the nuber of oophorectomies decreased markedly. In addition, by the end of their study period in 1989, the biopsy rate of the contralateral ovary was less than 1%. Teratomas that are solid are rare and is comprised of tissue derived from all three germ cell layers. They behave in a benign manner and are adequately treated with simple surgical excision. Occasionally, the solid mature teratomas may be associated with peritoneal implants. Pathologically, these are composed entirely of mature glial tissue. The prognosis in these cases is excellent. Most of the malignant teratomas arise in prepubertal adolescents and young women. They grow rapidly with early penetration of the capsule, followed by contiguous spread or distant metastasis. The survival rate is poor due to the fact that patients often present late, with advanced tumors. When they are confined to the ovary at presentation, the survival is good.

Ovarian Cystic Teratomas and Pregnancy

An interesting recent report appearing discussing the outcome of ovarian cystic teratomas diagnosed both prior to and during pregnancy and their managment by Caspi et al. The authors presented an analysis of their data of forty-nine women with sonographically diagnosed ovarian cystic teratomas < 6 cm. managed conservatively during pregnancy and labor. Serial sonographic examinations prior to pregnancy, during pregnancy, and after delivery were performed to detect changes in the size of the cystic teratoma. In a group of 49 women with dermoid cysts (mean age, 30 years), 68 pregnancies resulted. Of the 68 pregnancies, 4 ended in miscarriages, 1 was electively terminated, and in the remaining 63 pregnancies, a total of 64 healthy infants were delivered. Five patients needed treatment with assisted reproductive techniques. Fifty-five pregnancies ended in normal vaginal deliveries and 8 were delivered by cesarean (cesarean delivery rate of 16%). None of the classical complications attributed to dermoid cysts such as torsion, dystocia, or rupture occurred in the study group. In a follow-up of 56 dermoid cysts throughout pregnancy, cyst size remained unchanged. The decision to operate during pregnancy to remove ovarian cystic teratomas is undoubtedly due to some reports of poor outcome if left untreated. A study by Peterson in 1955 reported that pregnancy increased the complication rate associated with dermoid cysts. In that study torsion occurred in 19.3%, rupture in 17% and malignancy in 5% of cases. It should be noted that in 87% of their cases the size of the cystic teratomas was greater than 5 cm. The authors of this study concluded that ovarian dermoid cysts < 6 cm are not expected to grow during pregnancy or to cause complications in pregnancy and labor.

 

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Hertzberg BS, Kliewer MA. Sonography of benign cystic teratoma of the ovary: Pitfalls in diagnosis Amer J Roentgenol 167:1127-1133, 1996

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California