Cysts are fluid filled spaces within the ovary. They are very common and could be physiological or pathological, benign or malignant. Functional or physiological cysts are either follicular or of corpus luteum origin. Follicular cysts form when a follicle fails to rupture at midcycle leading to its continuous enlargement. Usually these cysts are asymptomatic and disappear without any intervention within one or two months. Similarly a persistent corpus luteum might fail to disintegrate before menstruation and enlarge in size. As well it gives no symptoms in the majority of cases though it could lead to some alteration in menstruation. However both follicular and luteal cysts could become haemorrhagic if bleeding occured within them leading to rapid increase in size and severe pain. Otherwise they might cause severe pain only if they are large in size (>7 cm) and cause pressure symptoms or torsion of the whole ovary compromising blood flow when surgical intervention is indicated.
Certain women are more prone to develop such cysts than others. This is especially so after induction of ovulation with clomid (14%) and after using progestogens only pills, injections or implants for contraception. On the other hand using a combined oral contraceptive pill could reduce the overall risk of developing such functional cysts by preventing ovulation which is not necessarily true for the newer pills with low hormone concentration.
Different characteristics are used to differentiate benign from malignant cysts but the final diagnosis should always be histological. It is important to take the sonographic picture within a clinical context to narrow the spectrum of the diagnostic options. This is especially so as more than 30 different ovarian tumours subypes have been recognised and there are no corresponding diagnostic ultrasound parameters to match them. The clinical factors to be taken into consideration should include the patient's age, presenting sympotms, personal and family history of ovarian, breast or colon cancers.
Despite these restrictions certain ovarian cysts / masses have
characteristics ultrasonic pictures which make the diagnosis most probable. Examples of such tumours include:
which are characterised by:
Thin smooth wall
no or only few septa
distal acoustic enhancement
A simple ovarian cyst on the right side of the uterus fulfilling all the characteristics mentioned before
Other commonly seen benign cysts are haemorrhagic cysts, endometriomas and dermoid cysts.
Haemorrhagic ovarian cysts
Bleeding could occur within the confines of any simple or complex ovarian cyst. The ensuing haemorrhagic cyst could show the following patterns on transvaginal scan examination:
A reticular pattern formed by fibrin deposits is the most common appearance of haemorrhagic cysts. It could simulate the presence of septa but as they are made of fibrin they would show no vascular markings on colour Doppler mapping. This pattern could be mistaken for mucinous cystadenomas
The second most common appearance is a retracted triangular or curvilinear clot with the rest of the cyst being anechoic reflecting the sequestered serum. It could be mistaken for a papillary cystadenoma with a neoplastic mural nodule.
A bright or echogenic solid look of a fresh blood clot could be seen when scanning is done within a short time after bleeding. This pattern on the other hand could look like a solid ovarian mass.
The most common haemorrhagic cyst is the corpus luteum. Because of the variety of its imaging appearances it could be mistaken for endometriomas, serous and mucinous cystadenomas and dermoid cysts. A corpus luteum usually changes texture and disappears within a short period of time while other pathological cysts maintain their shape and texture on repeated examinations.
A haemorrhagic cysts could be a chance finding during transvaginal scan examination but pelvic pain is the most common presentation. This is usually midcycle lower abdominal pain after ovulation. It could be due to stretching of the ovarian capsule by the increase in cyst size by blood, leakage of blood into the pelvis causing peritoneal irritation or partial twisting and untwisting of the enlarged ovary. The cyst could attain a large size and free echogenic fluid could be seen in the pelvis during transvaginal scan examination. It should not be mixed up with an ectopic pregnancy which could give similar ultrasound findings. In this case a positive pregnancy test and a short period of amenorrhoea would be useful clues.
A haemorrhagic cyst [corpus luteum] with a large blood clot occupying most of the cyst. Haemolysis started at the periphery as shown by dark areas of sequestered serum.
Haemorrhagic cyst [corpus luteum] with a retracted blood clot and fibrin trabeculae shown as bright strands within the sequested serum
A haemorrhagic cyst [corpus luteum] with a retracted blood clot showing retricular inner pattern within the clot indicating haemolysis of the red blood cells.
An endometrioma which looks like a haemorrhagic cyst. The fluid level is made by a retracted blood clot or debris on one side and free serum on the other side
Vaginal scanning could show an endometriotic cyst in one or both ovaries as cystic mass with thick wall, homogeneous low level internal echoes and occasionally wall calcifications. However this pattern is seen in other adnexal masses including dermoid and haemorrhagic cysts, tubo-ovarian abscess and ectopic pregnancies.
Furthermore purely cystic or cysts with some internal debris or septae and solid-looking appearances have been described in histologically proven cases of endometriosis. This was thought to be due to the natural course of endometriomas which resembles the natural resolution course of any other haematoma.
It is important to remember that only 15-20% of women with endometriosis have ovarian endometriomas. Accordingly a diagnosis of endometriosis could not be excluded by the mere absence of ultrasonically visible ovarian involvement.
An endometriotic cyst occupying most of an ovary with some normal ovarian tissue seen toward the side [crescent sign].
The 3 pictures shown above reveal a different texture for different histologically confirmed endometriomas in different patients. Colour was used to enhance these differences. The first picture showed a fluid level occasionally seen in haemorrhagic cysts. Accordingly there is no appearance exclusively specific to an endometrioma and the clinical picture would help in the final interpretation of the result.This confirms the importance of pelvic scanning being conducted by gynaecologists who could use the scan probe to extend their clinical judgement for the benefit of that particular case. It could also be used to elicit site specific tenderness and to test for pelvic adhesions.
Normally pelvic organs move freely against each other and relative to the pelvic sidewall. This normal ‘sliding sign’could not be elicited when organs are stuck together with adhesions. However transvaginal scan or even MRI examinations might show no abnormality. This is especially so when only pelvic sidewall implants are present without any significant ovarian involvement.
Dermoid cysts or cystic teratomas are the most common benign cysts in young women. They contain all cell types in the body except gonadal tissue. They constitute up to 25% of all ovarian neoplasm and could be bilateral in 15-20% of cases. The risk of malignant transformation is 1-3%. They are often diagnosed incidentally during pelvic scan examinations but could present with pain or pressure symptoms. Occasionally they might produce different chemicals and hormones which could dictate their presentation mode. They could show different echo-patterns during transvaginal scanning which is a reflection of the different types of tissues they harbour. The inner layer might have single or multiple protuberances (Rokitansky) containing bone, teeth or hair which are strong reflectors of ultrasound causing distal shadowing. Highly differentiated monodermal teratomas could be seen. A good example is the epidermoid mass with an inner lining entirely composed of stratified squamous epithelial cells with no evidence of any hair, bone or a Rokitansky tubercle. Hyper-reflective keratin would be the imposing texture on transvaginal scan examination. However the most frequent finding is the presence of hair strands which gives a characteristic ultrasound pattern. All these characteristics could be summarised into the following patterns which could be suggestive of the diagnosis:
An echo-poor cystic structure with an echogenic mass inside
Echogenic particles within a low echogenicity fluid giving a mesh-like appearance
Fat-fluid interface within the cyst.
Dermoid cysts usually grow 1.8 mm in diameter every year in premenopausal women. An increase in size of >2.0 cm every year and a size of >6.0 cm are usually used to indicate surgery because of the known complications of malignancy changes and torsion in such circumstances. On the other hand benign dermoid cysts virtually do no increase in size at all in postmenopausal women.
A semi solid mass seen in the right ovary which proved to be a dermoid cyst. The other ovary was polycystic and harboured a mature follicle
A small dermoid cyst showing a distinct fat-fluid interface.
Abdominal scan showing a cyst with typical hair shadows at the centre and Rokitansky nodule at the top
An epidermoid mass in the left ovary with echogenic but homogeneous keratin texture. No Rokitansky nodule, bone or hair shadows were seen. A vascular corpus luteum is seen in the right ovary
Other benign ovarian cysts
Mucinous cystadenomas make 20% of all benign ovarian tumours and tend to occur more often in middle age women. They could reach large size of 20 - 30 cm before being discovered. Small cysts with different echogenicity could be found along the thickened wall of the large cyst. They are all filled with mucous which has low echogenicity and could show layering with the more reflective layer at the back of the large cyst. As well papillary projections are occasionally found on the inner wall of the larger cyst. In most cysts blood vessels could be seen within the thickened wall making Doppler studies less diagnostic of malignant changes.
Serous cystadenomas make 30% of benign ovarian tumours and are usually much smaller than the mucinous ones. They could be bilateral in up to 30% of the cases. They are multilocular with clear fluid and multiple small papillae projecting into the cyst from the inner cyst wall. Doppler studies usually show no blood flow within the cyst wall but would be of high impedance if at all detectable. They are more liable to change malignant than the mucinous type to form serous adenocarcinoma which make about 70% of all ovarian carcinomas.
Solid ovarian masses
This group include fibromas which are the most common type, granulosa cell tumour and Brenner tumours. They all tend to have the same ultrasound appearance of uniform echotexture which is more echogenic compared to the neighbouring normal ovarian tissues. With granulosa cell tumour the endometrium would show excessive oestrogen stimulation and the patient would give history of recurrent episodes of uterine bleeding.
In young adolescent girls they are most probably germ cell tumours including dysgerminomas, immature teratomas and endometrial sinus tumour. Tumour markers including hCG, alpha fetoprotein and lactate dehydrogenase should be checked. In this young age group unilateral oophorectomy is the most likely line of management with adjuvant chemotherapy.
A solid or partially solid ovarian mass in postmenopausal women should be treated surgically.
The life time risk of malignancy is 1.8% which is reduced to 0.8% after using an oral contraceptive pill for 5 years. On the other hand this risk is increased to 6.7% if a first degree relative has already been inflicted and to 40% in families with a genetic syndrome. Other factors including the patient’s age and the size of the cyst should be taken into consideration when making a provisional diagnosis of the nature of an adnexal mass. The life time risk of malignancy at the age of 60-69 years is 12 times more than at the age of 20-29 years. On the size side, masses > 10 cm in diameter are more likely to be malignant.
The ultrasonic characteristic usually seen with ovarian malignancy include:
They have thick wall > 3 mm with irregular outline and frequent papillary projections into the cyst itself.
They are multilocular with multiple thick and irregular septae
The cyst fluid has mixed echogenicity which could resemble haemorrhagic cysts
They have increased blood flow with bizarre arrangement of blood vessels. 3D power Doppler mapping is best in showing this pattern.
They could be bilateral
Ascites could be seen.
On the other hand the presence of healthy ovarian tissue on the side of a cyst or a mass [crescent sign] is suggestive of a benign nature. absence of such a sign had a sensitivity of 96% and specificity of 76% in diagnosing ovarian carcinoma. However, it is not very helpful in differentiating benign and borderline masses.
The importance of these characteristics in differentiating benign from malignant cysts is especially important in 10-15% of postmenopausal women who still show ovarian cysts at different times. Purely cystic masses less than 5 cm in diameter with no septae or solid components are most unlikely to be malignant. With a normal CA 125 test the patient should be scanned after 3, 6. 9, 12 months and annually afterwards. Surgical intervention would be indicated if the patient became symptomatic or the cyst changed texture or increased in size. On the other hand a high CA 125 level in a postmenopausal woman with an ovarian mass has a positive predictive value of 70% for diagnosing a malignancy.
Presence of fluid in the pelvis is an important sign to look for especially in postmenopausal women. Normally little if any fluid could be seen in the pouch of Douglas in postmenopausal women ranging between <2 ml - 5.5 ml as reported by different authours. Accordinlgy moderate amount of fluid should raise the suspicion of the gynaecologist to the possibility of ovarian malignancy or hepatic disease.
The above two pictures show respectively:
A large left ovarian cyst with multiple septae seen in a 60 year old patient who presented with postmenopausal bleeding. The cyst proved to be malignant.
A complex mass in the right ovary showing solid and cystic areas in the same patient. It also proved to be malignant.
Though different scoring systems are used to differentiate malignant from benign ovarian cysts and masses, histological diagnosis remains to be the most reliable method.
Role of Doppler Ultrasound
Doppler studies did not fulfil the great expectations raised initially in helping with the diagnosis of ovarian malignancy. The initial plethora of articles documenting particular cut off figures of PI and RI has been replaced by non-numerical criteria for that purpose. With ovarian malignancy penetrating vessels with bizzare arrangements into the mass, along the septae or into papillary excrescences is more suggestive of malignancy than peripheral arrangement of blood vessels around the cyst which is mostly seen with benign tumours.
Pelvic masses of non-ovarian origin should always be kept in mind. Examples of such lesions include broad ligament fibroids, pedunculated uterine fibroids, tubo-ovarian inflammatory lesions and diverticular abscesses.