Normal Image Findings of the 37

Normal Imaging Findings of the Uterus 3

Claudia Klüner and Bernd Hamm

CONTENTS the strong muscle coat forming the mass of the organ. The is mostly comprised of spindle- 3.1 Embryonic Development and shaped smooth muscle cells and additionally con- Normal Anatomy of the Uterus 37 tains reserve connective tissue cells, which give rise 3.2 Imaging Findings: Uterine Corpus 40 to additional myometrial cells in pregnancy through 3.3 Imaging Findings: Uterine 44 hyperplasia. The is only a thin cleft and References 47 is lined by (Fig. 3.2). Functionally, the endometrium consists of basal and functional layers. The isthmus of uterus (lower uterine segment), 3.1 together with the internal os, forms the junction be- Embryonic Development and tween the corpus and cervix. In nonpregnant wom- Normal Anatomy of the Uterus en the isthmus is only about 5 mm high and is less muscular than the corpus. Unlike the uterine cervix, During embryonal life, fusion of the two Müllerian the isthmus becomes overproportionally large in the ducts gives rise to the uterine corpus, isthmus, cervix, course of pregnancy and serves as a kind of reserve and the upper third of the . The Müllerian ducts for fetal development in addition to the uterine cor- are of mesodermal origin and arise in the 4th week pus. The endometrium of the isthmus consists of a of gestation. They course on both sides lateral to the single layer of columnar epithelium and only under- ducts of the mesonephros (Wolffi an ducts). The lower goes abortive cyclic transformation. two thirds of the vagina arise from the sinovaginal The uterine cervix consists of the supravaginal bulb, which develops from the posterior portion of the (endocervix) and the vaginal portion urogenital sinus. The arises from that projects into the vagina (Fig. 3.3). The wall of the the cellular lining of the urogenital sinus [1]. cervix is primarily made up of fi rm connective tis- The uterus is composed of three distinct anatomic sue. In contrast to the uterine corpus, the muscular regions, namely the corpus, the isthmus (or lower portion accounts for less than 10% of the cervical uterine segment), and the cervix. In women of re- wall and primarily consists of smooth muscle cells productive age, the uterus usually is 6–9 cm long and in circular arrangement. The cervical canal is coated weighs 40–60 g. The longitudinal axis is fl exed for- with mucus-producing columnar epithelium and ward (anteversion) with the corpus and cervix form- contains numerous gland-like units, the crypts. The ing a blunt angle (antefl ection) (Fig. 3.1a). The uterus squamocolumnar junction is the transition from the straightens with increasing bladder fi lling and the columnar epithelium of the endocervix to the non- anteversion angle becomes smaller (Fig. 3.1b). keratinizing squamous epithelium of the ectocervix The wall of the uterine corpus differs from that of and is situated at the level of the external os. the cervix in that it mostly consists of myometrium, The uterus is supplied with blood through the uterine and ovarian arteries. The uterine arteries C. Klüner, MD course to the organ through the cardinal Institut für Radiologie (Campus Mitte), Charité – Universitäts- and, at the level of the (internal os medizin Berlin, Charitéplatz 1, 10117 Berlin, Germany of the cervical canal), divide into an ascending and B. Hamm, MD a descending branch. Lymphatic drainage from the Professor and Chairman, Institut für Radiologie (Campus Mitte), Klinik für Strahlenheilkunde (Campus Virchow-Klini- corpus is through the broad into the para- kum und Campus Buch), Charité – Universitätsmedizin Berlin, aortic lymph nodes and from the cervix into parame- Charitéplatz 1, 10117 Berlin, Germany trial and iliac lymph nodes. 38 C. Klüner and B. Hamm

a b

Fig. 3.1a,b. T2-weighted TSE images of two different healthy premenopausal women in sagittal orientation

Below, the parametria extend to the cardinal liga- ment, which passes from the uterine cervix to the pel- vic sidewall and separates the from the paravaginal connective tissue (paracolpium). A total of eight ligaments contribute to the support of the uterus. Diagnostically, which primarily pertains to the evaluation of the local extent of cervical cancer, the vesicouterine and the sacrouterine ligaments are most important. The vesicouterine ligament extends from the cervix to the posterior wall of the and only has a minor role in supporting the uterus. The sacrouterine ligament has a more im- portant supportive function and originates on the anterior aspect of the sacral bone, arches around the rectum and attaches at the level of the uterine isth- mus. Most of the uterus is covered by peritoneum (Fig. 3.5). The peritoneum contributes only lit- Fig. 3.2. T2-weighted TSE image of a 40-year-old healthy wom- tle support but ensures adequate mobility of the an in coronal orientation. The uterine cavity is marked by the white arrow uterus relative to the urinary bladder and rectum, which is necessary to adjust to the variation in blad- der filling and especially during pregnancy. The Besides the pelvic fl oor, the normal topography peritoneum extends from the roof of the urinary of the uterus is primarily ensured by the parametria, bladder to the anterior uterine wall, forming the a kind of suspension system primarily consisting of vesicouterine pouch in between. Below this fold, connective tissue. In addition, the parametria contain there is the vesicouterine ligament. The posterior large amounts of fatty tissue, especially in their lateral peritoneal coat of the uterus extends downward to portions near the pelvic sidewall and a dense network form the rectouterine pouch (Douglas space) that of lymphatic and blood vessels. About 2 cm lateral to reaches to the level of the posterior the uterine cervix, both ureters course through the and from there extends to cover the anterior rectal parametria and cross the uterine arteries (Fig. 3.4). wall. Normal Image Findings of the Uterus 39

Parametria Isthmus Internal cervical os Parametria Uterine vessels Ureter Corpus uteri External cervical os

Internal cervical os Endocervix External cervical os

Vaginal cavity

from Hricak/Carrington (1991)

Fig. 3.3. Anatomic draft of the uterine cervix: coronal view and corre- sponding MRI

Broad ligament Parametria Round ligament

Fig. 3.4. Anatomic draft, which presents the strong relation Fig. 3.5. T2-TSE image in sagittal orientation. The extension of between uterine arteries and ureters (arrow) the peritoneum is marked by the grey line 40 C. Klüner and B. Hamm

density (Fig. 3.6). As with MRI, the endometrium 3.2 and junctional zone cannot be differentiated in most Imaging Findings: Uterine Corpus cases on the basis of their morphologic appearance on CT. In most cases, venous plexuses can be identi- The imaging appearance of the uterine corpus var- fi ed within the parametria on the basis of their strong ies widely with the age and hormonal status of the enhancement. However, reliable differentiation of patients examined [2–7]. myometrium from parametrial portions is usually On unenhanced CT scans, the layered anatomy of not possible while the peripheral fatty portions of the wall cannot be distinguished. After administra- the parametrium can be distinguished from the pel- tion of contrast medium, the myometrium can be vic wall with an adequate degree of accuracy. distinguished in most cases during the arterial phase Unenhanced T1-weighted MRI depicts the uterine as it shows early and strong enhancement while the corpus with a low and homogeneous signal intensity junctional zone/endometrium is of relatively low similar to that of skeletal muscle (Fig. 3.7a and b).

a b

c

Fig. 3.6a-d. CT of the female . a CT transversal unen- hanced. b CT transversal after CM and reformatted coronal (c) and sagittal CT images (d) d Normal Image Findings of the Uterus 41

Thus, it is not possible to differentiate the individual of progesterone becomes stronger (luteal phase), there layers. is hardly any further increase in thickness but primarily On the other hand, T2-weighted MR images in wom- a transformation of the mucosa with increased forma- en of reproductive age clearly depict the three layers of tion of glands and ingrowth of vessels. During menstru- the uterine corpus: the endometrium, the junctional ation, a blood clot may occasionally be present in the zone, and the myometrium (Fig. 3.7c and d) [8]. uterine cavity (Fig. 3.9), which must not be mistaken for The endometrium always has a high signal inten- a foreign body, polyp, or submucosal myoma. sity on T2-weighted images regardless of the hormonal The layer adjacent to the endometrium that can be state and age while its thickness clearly varies in the distinguished on MRI is the junctional zone, which course of the menstrual cycle [9]. The thickness ranges corresponds to the inner part of the myometrium and from 1–3 mm in the early proliferative phase (Fig. 3.7 is hypointense on T2-weighted images relative to the and 3.8) and 5–10 mm in the middle of the secretory outer portion of the myometrium. The lower signal phase (Fig. 3.9 and 3.10). The endometrium is thickest is primarily attributable to a lower water content, the under the effect of estradiol (follicular phase) on days 8 higher nucleus-to-cytoplasm ratio, and the smaller ex- through 16 of the cycle [10]. After day 16, when the effect tracellular space of the inner myometrium [11, 12].

b a

d

Fig. 3.7a-d. MRI of a 40-year-old healthy woman during early proliferative phase. T1-weighed TSE images in axial (a) and sagittal orientation (b). T2-weighted TSE images in axial (c) c and sagittal (d) plane of the same patient 42 C. Klüner and B. Hamm

a

Fig. 3.8a,b. MRI of a healthy woman during early proliferative phase (T2-weighted TSE in axial and sagittal plane) b

a Fig. 3.9a,b. MRI of a healthy woman during secretory phase. The T2-weighed TSE image (a) as well as the contrast-en- hanced T1-weighted TSE image (b), both in sagittal orienta- tion demonstrate a blood clot (arrow) in the uterine cavity b

Similar to the endometrium, the junctional zone also T2-weighted sequence a view minutes later, showing a varies over the menstrual cycle and is thickest around normal appearance of the former thickened junctional the 24th day. The mean thickness of the junctional zone in contrast to unchanged appearance of adeno- zone does not exceed 5 mm under normal conditions. myosis. By using cine MRI sequences (SSFSE: single- A focal thickness of over 12 mm of the junctional zone shot half-Fourier fast spin echo) it was furthermore can be interpreted as a sign of . However, shown that the junctional zone maintains cervicofun- a focal pathologic thickening of the junctional zone dal contractions that vary with the phase of the cycle has to be differentiated from uterine contractions. [13] and are assumed to have a role in transporting Uterine contractions may be diagnosed by a repeated sperm and in maintaining early pregnancy. Normal Image Findings of the Uterus 43

The normal outer myometrium is of an intermediate Long-term use of oral contraceptives is also associ- signal intensity on T2-weighted images. Its signal in- ated with marked thinning of the endometrium. In tensity is slightly higher during the secretory phase due women on GnRH analogues, the uterus is compara- to an increased fl uid content, which improves the dif- ble to the premenopausal uterus in terms of size and ferentiation from the junctional zone as compared with signal intensities with depiction of the endometrium other phases of the cycle (comparison of Figs. 3.7 and as a very thin stripe of high signal intensity that is 3.10). Vessels in the myometrium are also highly prom- clearly delineated from the low-intensity myome- inent during this phase of the cycle. Ultrasonography trium. The junctional zone is not seen or very dif- likewise depicts three uterine layers but the thickness fi cult to distinguish. Despite its anti-estrogen activity, of the junctional zone and of the endometrium deter- mined by ultrasound and MRI clearly differ, especially during the luteal phase [14]. This discrepancy is attrib- uted to the fact that ultrasound does not demonstrate the three layers in the same way as MRI [15]. Following intravenous administration of a para- magnetic contrast medium, the zonal anatomy of the uterus is also depicted on T1-weighted images (Fig. 3.9b). Both the endometrium and the outer myometrium are characterized by pronounced con- trast enhancement while the junctional zone is of low signal intensity. This is attributed to the denser tissue and smaller extracellular volume of distribution of the contrast medium [12, 16]. The uterus of newborns still shows good differ- entiation of the myometrium, junctional zone, and endometrium as a result of the effect of maternal es- trogen. Before the onset of menstruation, the endo- a metrium is merely seen as a very thin stripe of high signal intensity or not at all and the junctional zone is not distinguishable from the low-signal-intensity myometrium. The corpus is smaller than the cervix during this phase while in adult women the length ratio of the cervix to the corpus is 1:2. After menopause the uterine corpus as a whole is markedly smaller (Figs. 3.11 and 3.12) with a length ratio of nearly 1:1. On T2-weighted images the endo- metrium is seen as a thin central stripe of high signal intensity. The myometrium has a markedly lower sig- nal intensity as compared with women of reproductive age and is therefore diffi cult to distinguish from the junctional zone, which also has a low signal intensity. The endometrium decreases in thickness to about 3–5 mm. However, in women on external hormone re- placement therapy, the premenopausal signal pattern and zonal anatomy may be preserved. In this situation the endometrium may be up to 10 mm thick. Exogenous hormonal replacement may consid- erably alter the MRI appearance of the uterus and vagina. In premenopausal women taking oral con- b traceptives, the signal intensity of the myometrium is increased [17]. Moreover, the junctional zone ap- Fig. 3.10a,b. MRI of a healthy woman during secretory phase pears thinner and is more diffi cult to differentiate. (T2-weighted TSE) 44 C. Klüner and B. Hamm

Fig. 3.11. Reformatted sagittal CT image of a 55-year-old wom- Fig. 3.12. T2-weighted MRI of a healthy 58-year-old woman an, who underwent MSCT for polyp detection of the colon

tamoxifen treatment in postmenopausal women has er layer of intermediate signal intensity (Fig. 3.13c,d). an effect that is comparable to that of oral contracep- The inner layer of high signal intensity corresponds tives: There is a clear increase in the thickness of the to the endocervical mucosa. Sometimes an additional endometrium. Moreover, the endometrium becomes central area of very high signal intensity can be seen, increasingly heterogenous, which may be misinter- which corresponds to the mucous within the cervical preted as [18]. canal (Fig. 3.14). On high resolution T2-weighted images palmate folds of the cervical canal can be depicted as normal fi ndings (Fig. 3.15). Often, nabothian cysts are seen. These are benign 3.3 cysts of the uterine cervix that are assumed to result Imaging Findings: Uterine Cervix from obstruction of the cervical mucous glands [19]. The cysts are depicted on T2-weighted images as round In contrast to the uterine corpus, the uterine cervix to oval lesions with a smooth margin (Fig. 3.16). shows only little variation of its zonal anatomy as The low-signal-intensity middle layer corresponds depicted by MRI with age, phase of the menstrual to the cervical stroma and mostly consists of connec- cycle, hormone replacement therapy, or use of oral tive tissue. The outer layer has a signal intensity that contraceptives. is comparable to that of the myometrium and is char- On CT scans the individual layers of the wall of acterized by a more loose tissue structure [20] and the cervix cannot be distinguished. The same holds may not always be distinguishable from the parame- true for unenhanced T1-weighted MR images, which tria even on T2-weighted images. The mucosa in the depict the uterine cervix as a homogeneous cylin- cervical canal shows the strongest enhancement and der-shaped structure of intermediate signal intensity is thus clearly distinct from the less enhancing stro- without distinction of individual layers (Fig. 3.13a,b). mal layer. The outer stromal layer of the cervix and The orientation of the longitudinal axis of the cervix the portio also show contrast enhancement. is highly variable. The differentiation of the cervix versus the para- T2-weighted images depict three layers in most cervical tissue of the parametria is best on T2- cases: an inner layer of high signal intensity, a fairly weighted images compared to pre- or postcontrast wide middle layer of low signal intensity, and an out- T1-weighted images or CT scans. Normal Image Findings of the Uterus 45

a b

c d

Fig. 3.13a–d. T1-weighted and T2-weighted images of the cervix uteri of a 36-year-old woman 46 C. Klüner and B. Hamm

a

Fig. 3.15. MRI presenting palmate folds

b

Fig. 3.14a,b. T2-weighted TSE image detect the endocervical mucosa (white arrow) and cervical stroma (grey arrow) from the outer tissue

a b

Fig. 3.16a,b. Transversal and coronal MR images of a 40-year-old asymptomatic woman depicting Nabothian (cervical) cysts Normal Image Findings of the Uterus 47

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