Abstract
Pelvic ultrasound remains the single most effective method for detection and characterization of adnexal masses . While transvaginal ultrasound provides optimal visualization, it has limited field of view; larger masses, which extend up into the abdomen, are best assessed by both transvaginal and transabdominal scan. Colour or power Doppler is useful in detecting flow in apparent solid areas and septations. The majority of adnexal masses are benign, particularly in premenopausal women. The vast majority of benign adnexal masses have characteristic ultrasound features to allow correct diagnosis in 90 per cent of women . Ultrasound assessment of the morphological and vascular features of a mass has been shown to be highly effective for predicting whether a mass is benign or malignant. Accurate characterization of adnexal masses is essential for optimal patient management.
Pelvic ultrasound remains the single most effective method for detection and characterization of adnexal masses [1]. While transvaginal ultrasound provides optimal visualization, it has limited field of view; larger masses, which extend up into the abdomen, are best assessed by both transvaginal and transabdominal scan. Colour or power Doppler is useful in detecting flow in apparent solid areas and septations. The majority of adnexal masses are benign, particularly in premenopausal women. The vast majority of benign adnexal masses have characteristic ultrasound features to allow correct diagnosis in 90 per cent of women [2]. Ultrasound assessment of the morphological and vascular features of a mass has been shown to be highly effective for predicting whether a mass is benign or malignant. Accurate characterization of adnexal masses is essential for optimal patient management. Correctly identifying a benign mass enables the patient to be discharged or treated accordingly in general gynaecology departments, whereas patients with suspected malignancy should be referred appropriately to subspecialist gynaecology oncology units, which has been shown to optimize care and improve survival [3].
Ovarian Masses that Can Usually be Diagnosed on Ultrasound
Simple Cyst
These are usually hormone-dependent functional cysts.
Ultrasound features. Criteria for a simple cyst are: well circumscribed, anechoic with smooth, thin walls and posterior acoustic enhancement. No septations or solid elements are seen and there is no internal blood flow (Figure 8.1). They are usually less than 5 cm in size. Simple cysts less than 5 cm in premenopausal and less than 1 cm in postmenopausal women do not require a follow-up ultrasound scan [4]. A cyst that is otherwise simple but has a single thin septation or a small calcification in the wall is almost always benign and should be followed in a similar fashion as a simple cyst [4].
Clinical significance. It is a common incidental finding in premenopausal women and most are follicular cysts, which regress spontaneously in one or two cycles. Rarely, simple ovarian cysts, particularly the larger ones or those in older women, are serous cystadenomas. In a study of postmenopausal women, no cancers were detected in 3259 simple cysts smaller than 10 cm, estimating the risk of malignancy in simple cysts as 0.1 per cent [5].
Ovarian Inclusion Cyst
These occur due to invagination of the ovarian cortical surface, resulting in cyst formation.
Ultrasound features. These are small, less than 10 mm simple cysts most commonly seen in postmenopausal women (Figure 8.2). In premenopausal women these cannot be differentiated from a follicle. They are typically located immediately beneath or within 1–2 mm of the ovarian surface. No internal blood flow is seen.
Clinical significance. Common incidental finding with no clinical significance. They typically remain stable or involute and require no follow-up. The presence of ovarian inclusion cysts has no significance in identifying patients with increased risk of malignancy.
Corpus Luteum
Corpus luteum is a physiological structure that develops after ovulation and is a normal finding on ultrasound.
Ultrasound features. These are unilocular cysts typically less than 3 cm which can be simple/anechoic or haemorrhagic. They have a thick, crenellated wall. Haemorrhage may produce internal echoes or mimic a solid mass [6]. There is no internal blood flow, but prominent vascular flow is noted in the cyst wall, described as a ‘ring of fire’ [7] (Figure 8.3).
Clinical significance. The majority regress spontaneously within two months. Mostly asymptomatic although can present with acute pelvic pain.
Haemorrhagic Cyst
This is a functional cyst with internal haemorrhage. Haemorrhage usually occurs during ovulation secondary to rupture of germinal epithelium. These are seen in premenopausal women or sometimes in early postmenopausal women due to occasional ovulation.
Ultrasound findings. A complex cystic mass with reticular pattern of internal echoes due to fibrin strands creating a net- or mesh-like appearance described as: lace-like, fishnet or cobweb (Figure 8.4). The clot can be seen as a solid-appearing area usually with concave margins, showing no internal blood flow (Figure 8.5). An echogenic, retracting clot may be confused as a solid mural nodule. Fluid–fluid levels may sometimes be seen, with echogenic blood products layered at the bottom [8] (Figure 8.6). A haemorrhagic cyst may overlap with endometrioma if imaged acutely before the fibrin strands or clot develop (Figure 8.7). If the cyst ruptures, echogenic free fluid in the pelvis may be seen.
(b) Transvaginal scan of a haemorrhagic cyst with fluid–fluid level (arrow). Note that the level is almost horizontal on the abdominal scan and vertical on the transvaginal scan (the left of the screen is anterior, the right is posterior).
Tips and Tricks
Fibrin strands are thin, weakly echogenic and do not extend completely across the cyst, unlike true septations.
Clinical significance. Haemorrhagic cysts may be asymptomatic or present with acute pelvic pain. When large, these may serve as a lead point for ovarian torsion. No follow-up is necessary in asymptomatic women with cysts less than 5 cm. If more than 5 cm, a short-term follow-up in 6–12 weeks is recommended as they usually disappear or reduce significantly in size in 6–8 weeks. Ideally, the follow-up scan should be done in the follicular phase (day 3–10) of the menstrual cycle.
Endometrioma
Endometriomas are formed by extra-uterine functional endometrial tissue involving the ovary. Repeated bleeding every month in response to hormonal stimulation produces thick, concentrated and degraded blood products.
Ultrasound findings. Endometriomas show diffuse, homogeneous low- to medium-level internal echoes giving a ground glass appearance [9] (Figure 8.8). This may appear solid but posterior acoustic enhancement differentiates it from solid masses (Figure 8.9). They are usually unilocular but can be multilocular and may have a thick, fibrous wall. There may be tiny, echogenic foci or small solid areas along the cyst wall (Figure 8.9) [10,11]. These should not be confused with mural nodules of malignancy. There is no internal vascular flow. Unlike haemorrhagic cysts they do not involute or disappear on follow-up scans. A small percentage (less than 15 per cent) have a less typical appearance, such as anechoic fluid, fluid–fluid level, heterogeneity or calcification [10–12]. Decidualized endometriomas are also uncommon and are characterized by the presence of hyperechoic foci within an otherwise homogeneous cyst, mainly observed in the luteal phase of the menstrual cycle (Figure 8.9b). Doppler signal may be present within these islands. Comparison with previous imaging confirming the presence of an endometrioma and a subsequent scan showing resolution of these changes aids in diagnosis.
(b) An endometrioma in a different patient, measured in three orthogonal planes. The content is homogeneous, but more hypoechoic in the posterior aspect of the cyst due to attenuation of ultrasound waves (arrows).
(b) Luteal phase scan; an endometrioma (callipers) with hyperechoic nodules on the periphery (arrows). Vascularity was present on Doppler and comparisons with earlier and subsequent imaging confirmed it was decidualization of the ectopic endometrium.
Tips and Tricks
Diffuse internal echoes can sometimes be seen in dermoids, haemorrhagic cysts and some ovarian carcinomas [13]. Other features, such as a dermoid plug or solid component, will suggest different diagnoses. An endometrioma is very likely if there are diffuse internal echoes in a cystic mass with no other ultrasound features [10].
Rarely malignancy (endometrioid or clear cell carcinomas) may develop in endometriomas (1 per cent), likely in those larger than 9 cm and in women older than 45 years [14]. Development of a significant solid component with flow on Doppler should raise concern for malignancy.
Clinical significance. Usual presentation is with dysmenorrhoea, dyspareunia and infertility. Treatment is usually by hormonal suppression or surgery.
Dermoid (Mature Cystic Teratoma)
Benign germ cell tumour of the ovary, which occurs during reproductive years, is the most common benign ovarian tumour in women less than 45 years old. It is composed of well-differentiated derivatives of all three germ layers and may be composed of adipose tissue, hair, bone, teeth, cutaneous, bronchial and gastrointestinal tissues. Fat is present in about two-thirds of cases. It is bilateral in 20 per cent of cases.
Ultrasound features. Ultrasound appearance is variable, depending upon histological composition. Demonstration of fat clinches the diagnosis. Characteristic ultrasound appearance is cystic adnexal mass containing a highly echogenic mural nodule with distal acoustic shadowing (Rokitansky nodule or dermoid plug) (Figure 8.10) [15,16]. The echogenic focus consists of adipose tissue, hair and calcium, which cause posterior acoustic shadowing. Very echogenic focus casting a sharp acoustic shadow is due to the presence of bone or teeth (Figure 8.11).
Figure 8.11 Dermoid in a 20-year-old patient. The right ovary shows a well-defined hyperechoic component (long arrow), which did not show any vascular flow. Calcification seen within this mass (short arrow) is even brighter and shows distinct shadowing. Normal ovary is seen (curved arrow) at the periphery.
Other common appearances are:
Diffusely or partially echogenic mass with distal acoustic shadowing (Figure 8.11). Shadowing may be so marked that only the superficial part of the cyst is seen, called the ‘tip of iceberg’ sign (Figure 8.12).
Dermoid mesh: multiple thin echogenic lines and dots caused by hair in the cyst cavity [15,16] (Figure 8.12).
Floating echogenic globules [17]: multiple echogenic floating globules are present in the cyst cavity, which change position with change in the patient’s position (Figure 8.13).
Fluid–fluid level: more echogenic fluid (sebum) layered on the top of serous fluid [18]. This is opposite to the haemorrhagic cyst, where echogenic blood products are layered at the bottom.
Rarely, a dermoid will have none of these characteristic features [9] (Figure 8.14) and cannot be diagnosed on ultrasound appearance.
Tips and Tricks
Highly reflective area with distal shadowing in a cystic mass is highly predictive of a dermoid. Blood clot in haemorrhagic cyst and solid elements in a complex ovarian cyst can appear echogenic, but these tend to be less echogenic than the fatty component of a dermoid cyst and do not cause shadowing (Figure 8.15). If there is any doubt, CT and MRI can confirm the presence or absence of fat.
Clinical significance. Usually asymptomatic and managed non-surgically if dermoid measures less than 6 cm. Dermoids larger than 7 cm can cause torsion or rupture. Torsion is most common during pregnancy. Surgery involves excision of the dermoid with conservation of ovarian tissue. Malignant transformation is rare and usually occurs in the sixth or seventh decade of life with tumours larger than 10 cm [19]. Squamous cell carcinoma is the most common associated cancer.
Ovarian Fibroma/Fibrothecoma
A benign solid ovarian neoplasm classified as sex cord-stromal tumour. The spectrum includes fibroma, thecoma and fibrothecoma. These lesions are composed of fibrous tissue and theca cells, which are responsible for the oestrogenic effects of these tumours. They are usually asymptomatic and found incidentally.
Ultrasound features. Well-defined round or oval low-echo solid mass, usually homogeneous with acoustic shadowing (Figure 8.16). Marked acoustic shadowing is a predictive feature that occurs in 18–52 per cent of fibromas [20,21]. With fibromas, shadowing does not arise from an area of increased echogenicity such as dermoid plug or calcification, but due to attenuation of the sound by the mass itself. Calcification can be present. Larger lesion shows cystic change. Generally hypovascular, although may show increased vascularity. Differential diagnosis is pedunculated uterine leiomyoma where a separate ovary is often seen and a pedicle extending to the uterus may be seen. A minority of ovarian fibromas grow exophytically from the ovary [22] and may be difficult to distinguish from a pedunculated uterine fibroid.
Tips and Tricks
A completely solid mass, particularly in a premenopausal woman, is usually a fibroma.
Clinical significance. Always benign. Excision of affected ovary by laparoscopy for larger lesions. Ovarian thecoma may be associated with endometrial thickening if it secretes oestrogen. One per cent of ovarian fibromas are associated with Meigs syndrome, which consists of ovarian fibroma, ascites and pleural effusion, both of which disappear with excision of the tumour. In Gorlin–Goltz syndrome (rare autosomal dominant syndrome with craniofacial anomalies and multiple basal cell carcinomas of the skin), 25 per cent of women develop ovarian fibromas which tend to be bilateral, multiple and calcified.
Extra-Ovarian Masses that Can Usually be Diagnosed on Ultrasound
Paraovarian Cyst
Separate from the ovary, it usually arises from peritoneal mesothelium of the broad ligament.
Ultrasound features. Simple unilocular adnexal cyst separate from the ovary. It is thin-walled with no septations or solid elements (Figures 8.17 and 8.18). If the extra-ovarian location is not obvious, the ovary may be separated from the cyst by gentle pressure from the transvaginal probe or the examiner’s hand on the lower abdomen.
Figure 8.18 Paraovarian cyst in a 29-year-old patient. Simple cyst (callipers) seen separate to the ovary (arrow).
Clinical significance. Can be symptomatic if large. Almost always benign and no follow-up is required in the vast majority [4].
Hydrosalpinx
A dilated, fluid-filled fallopian tube usually forms owing to obstruction of its ampullary segment. The most common cause is adhesions from pelvic inflammatory disease (PID). It usually contains clear serous fluid. Fluid may be haemorrhagic (haematosalpinx), usually as a result of endometriosis, or purulent (pyosalpinx) as a complication of PID.
Ultrasound features. A normal fallopian tube is usually not visible on an ultrasound. Hydrosalpinx is seen as a tubular, thin-walled, fluid-filled structure with a C or S shape, interposed between the uterus and ovary (Figure 8.19). Incomplete septations within the tubular cystic structure represent partially effaced mucosal or submucosal plicae, a finding specific to a hydrosalpinx (Figure 8.20). Thickened endosalpingeal folds can give a ‘beads on a string’ appearance that consists of small 2–3 mm hyperechoic, short, round projections along the tubal wall [23] (Figure 8.21). The ‘waist sign’ constitutes indentations of the tube wall directly opposite each other (Figure 8.22), forming a waist [23]. Presence of the ‘waist sign’ or ‘beads on string’ sign in a tubular cystic structure is highly predictive of hydrosalpinx [23].
