Normal Imaging Findings of the Uterus 3

Normal Image Findings of the Uterus 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 myometrium 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 Cervix 44 hyperplasia. The uterine cavity is only a thin cleft and References 47 is lined by endometrium (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 vagina. 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 cervical canal (endocervix) and the vaginal portion urogenital sinus. The vaginal epithelium 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 ligaments Institut für Radiologie (Campus Mitte), Charité – Universitäts- and, at the level of the uterine isthmus (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 ligament 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 ligament, which passes from the uterine cervix to the pelvic sidewall and separates the parametrium 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 urinary bladder and only has a minor role in supporting the uterus. The sacrouterine ligament has a more important supportive function and originates on the anterior aspect of the sacral bone, arches around the rectum and attaches at the level of the uterine isthmus. 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 bladder 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 vaginal fornix 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 pelvis. a CT transversal unenhanced. 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.

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