(1)
Department of Fetal Medicine and Obstetric & Gynecological Ultrasound, Manipal Hospital, Bangalore, Karnataka, India
The cervix is the muscular lower end of the uterus. Its inner cervical canal is continuous with the endometrial cavity above at the internal os, and its muscular myometrium is continuous with the myometrium of the uterine body. The cervix is fusiform in shape and has a central cervical canal which extends from the internal os to the external os with its narrowest portion at the internal os. The portion of the cervix above the attachment of the vaginal vault is called the supravaginal cervix, and the lower cervix below the attachment of the vaginal vault that protrudes into the vagina is called the ‘portio vaginalis’. Cervical pathologies include nabothian cysts, polyps, fibroids, uterine anomalies, ectopic pregnancy, endometriosis and carcinoma. Fibroids, congenital anomalies and cervical ectopic are dealt with in their respective chapters. Congenital cervical anomalies are discussed in the chapter on uterine anomalies. Cervical fibroids are briefly discussed in this chapter.
5.1 Evaluation of the Cervix and Its Normal Appearance
Measurements
The length of the cervix, on an average, is 3–4 cm and the diameter is about 2–3 cm. The cervix is about half the size of the uterine body in the reproductive age group. In prepubertal girls, the cervix is prominent and almost similar in size to that of the uterus.
Appearance (Fig. 5.1)
The cervix is homogeneous in echotexture with echogenicity similar (i.e. isoechoic) to that of the myometrium of the uterine body.
The central canal is lined by cervical mucosa that usually appears hypoechoic and contains the endocervical glands. This cervical mucus makes it easy to identify the cervix and differentiate it from the uterine body above it.
The internal os can be identified by the fact that:
It is the narrowest part of the uterine cavity where the endometrial cavity is continuous with the cervical canal.
The cervical mucosa can be seen to taper off and end at the internal os.
The uterine arteries enter the uterus at the levelof the internal os.
This feature is especially helpful when the normal cervical architecture is distorted by pathological lesions.
The external os is small and round in a nulliparous woman but appears as a larger transverse slit in a woman who has had a normal vaginal delivery. The os can be seen on the transverse section of the cervix but is better seen on a 3D rendering of the external os, especially with GSV.
The cervical canal just prior to ovulation shows anechoic cervical mucus which improves visualisation of the cervical canal on ultrasound. This helps in the diagnosis of cases with cervical polyps and congenital anomalies of the cervix.
Doppler
The uterine arteries can be identified on both sides of the cervix at the level of the internal os.
The presence of an abnormal vessel in the cervical canal should raise a high suspicion of a feeder vessel of a polyp at the cervix, which may be originating either from the cervix or the endometrium above.
Cervical carcinoma is difficult to detect on 2D especially when it is small and isoechoic. On Doppler, these lesions are easier to pick up because most of them are highly vascular.
Tips to Improve Ultrasound Diagnosis of Cervical Lesions (Fig. 5.2)
The assessment of the cervix should be a part of all routine gynecological ultrasound examinations. Lesions of the cervix are often missed on ultrasound because most of the sonologists proceed directly to the uterine body and adnexa in search of gynecological pathology, leaving out the assessment of the cervix.
Since visualisation of the cervix on ultrasound is suboptimal at times, because of its proximity to the TVS probe, withdrawing the probe a little helps to evaluate the cervix. One may push on the cervix with the probe placed in one of the fornices to further antevert or retrovert the uterus so that the cervix lies more perpendicular to the ultrasound beam and is seen better. When cervical pathology is seen or suspected, gel sonovaginography (GSV) may be resorted to (dealt with in Chap. 2) for better visualisation of the pathology.
Doppler evaluation of the cervix should be done routinely in all patients to help detect cervical lesions like polyps and carcinomas, which may otherwise be missed on 2D greyscale (as the assessment of the cervix is relatively suboptimal on TVS).
Fig. 5.1
Uterus with cervix on TAS (a) and TVS (b). Long arrows show the internal os; short arrows show the external os
Fig. 5.2
When the USG beam is perpendicular to the cervical canal, the entire cervical mucosa and the posterior wall of the upper vagina (short arrows) abutting the external os of the cervix (long arrows) is well visualised. (a) The cervix in sepia mode, which is supposed to enhance perception by the human eye. (b) Greyscale image of the cervix corresponding to (a)
5.2 Nabothian Cysts
Nabothian cysts, also known as nabothian follicles, are common retention cysts seen in the cervix. They are formed as a result of the retention of mucoid secretions in the endocervical glands. They are a sequel to the healing process of chronic cervicitis, minor trauma of cervix or vaginal delivery. Being asymptomatic, they are generally picked up on ultrasound done for other pathologies. Their main significance lies in distinguishing them from other cervical lesions like DIE, which may also show cystic lesions in the cervix.
These are seen as discreet round or oval cystic spaces in the walls of the cervix, most often close to the mucosa.
They are usually multiple.
They are generally anechoic but may show turbid contents.
No increase in vascularity is noted around the cysts, on Doppler.
Fig. 5.3
Nabothian follicles seen in the cervix on (a) TAS and (b) TVS. These are seen as anechoic cystic areas in the cervix on either side of the cervical canal (arrow)
Fig. 5.4
Occasionally, nabothian follicles are many in number, giving the cervix a multicystic appearance: (a) on 2D and (b) on 3D
Fig. 5.5
Cervix with multiple (more than 10) nabothian cysts. (a) Nabothian cysts showing turbid contents. (b) Doppler evaluation done to help with differential diagnosis. HPE: chronic cervicitis
5.3 Cervical Polyps
Cervical polyps are solid circumscribed lesions seen at the cervix. They have a vascular connective tissue stroma and are covered with epithelium. Polyps in the cervix may be seen in the cervical canal or protruding out of the external os into the vagina. They may be sessile but most are pedunculated with a slender pedicle. These polyps may arise from the cervix or from the uterine cavity above. Malignancy is rarely found in polyps arising from the cervix, yet, if excised, they must be subjected to histological evaluation.
Cervical polyps are common in women in the reproductive age group, usually in their 40s. Most of these patients are asymptomatic. Symptomatic cases may present with intermenstrual bleeding, post-coital bleeding and vaginal discharge.
They are typically solid hyperechoic or isoechoic masses seen either in the cervical canal or protruding out through the external os. Rarely, they may show cystic areas within.
They are usually circumscribed, oval- or ‘tear drop’-shaped masses but may be irregular or frond-like in appearance.
Their margins are usually smooth, and very often these can be identified in the cervix because of the bright line formed at the interphase of the cervical mucosa with the smooth walls of the polyp.
They may be multiple.
They can often be identified as separate pedunculated masses by pushing with the TVS probe with consequential movement of the polyp within the cervical canal or vagina.
On Doppler, flow is seen within these polyps. By tracing the feeder vessel upwards (which may require some angulation of the probe), the site of origin of the polyp can be ascertained. Sometimes polyps in the cervical canal or protruding out of the cervical os may be originating from high up in the endometrial cavity. Very often, a polyp may be detected because of the suspicion raised by a feeder vessel in the cervical canal.
Larger fleshy polyps may show high vascularity because of the nature of the tissue or secondary infection. Very often, these fleshy polyps are adenomyomatous polyps (showing muscle and glandular tissue) arising from the endometrium.
Visualisation of cervical polyps is difficult due to the proximity of the cervix to the probe. At mid-cycle, when cervical mucus in the canal is present, these may be better visualised. In other cases, GSV may be used to evaluate these polyps. On GSV, these polyps (especially if they are soft and supple), due to slight pressure from instilled gel, are seen to abut the external os, obliterating it.
3D rendering of the cervix and external os, particularly with GSV, may also help to delineate the polyp.
Fig. 5.6
Cervical polyp arising from the anterior wall of the upper corpus of the uterus. (a) A feeder vessel is seen on TAS extending from upper corpus to the upper end of the polyp (P). (b) transverse section of feeder vessel at the internal os (determined by the uterine arteries entering the uterus at this level). (c) Feeder vessel of the polyp on TVS (RI-0.34). (d) polyp protruding out of external os. Arrows showing the splayed cervical lips. HPE: adenomyomatous polyp
Fig. 5.7
Polyp in the cervical canal which is protruding out from the cervical os. (a–d) Are images on regular TVS. The polyp is seen in the cervical canal (a) on 2D and (b) 3D. The lower margin of the polyp is seen protruding out of the external os. (c, d) On Doppler, there was a suspicion of two polyps (labelled as 1 and 2) because of the vascular pattern of flow with two vessels approaching the polyp (one venous and one arterial) from two different locations above the polyp. (e, f) Images on GSV. Single polyp is better seen and delineated on 2D and 3D with GSV
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