Anatomic structures and boundaries
The female pelvis has particular and intricate anatomy. A three-layer model is suggested for a better understanding of the pelvic segmentation. The uterine cervix is located at the superior middle layer of the pelvis, delimited anteriorly by the vesicovaginal space and partially by the vesicouterine peritoneal reflection. The parametrium is the fibrous layer that separates the bladder and the supravaginal portion of the cervix[4]. Posteriorly it's limited by the rectovaginal septum and partially by the anterior peritoneal reflection(Fig. 3).
The uterine cervix can be divided into four zones: the innermost endocervical canal, which can be filled with gel or mucosal secretions, showing long T2; the endocervical glands and plicae palmatae, with intermediate T2; the inner fibrous stroma, with short T2; and the outer fibrous stroma with intermediate T2 [5,6](Fig. 4).
The cardinal ligament is formed at the base of the broad ligament, separate the vesicovaginal space anteriorly, from the rectovaginal fascia laterally. Ureters are located within the posterior to the middle segments as perform its anteroposterior rout on the pelvis[4].
The pelvic sidewalls contain the obturator internus and piriformis muscles, followed by their vessels, internal and external iliac arteries and veins, and the sciatic nerve posteriorly.
The external iliac vessels are located laterally to perivesical space in the anterior compartment(Fig. 5).
Pelvic nodal anatomy includes internal and external iliac nodes, lateral sacral and sacral promontory nodes[4,5].
Para-aortic and inguinal nodes are included on the external lymph node route(Fig. 6).
Technical key points
Cervical cancer MR imaging requires oblique planes, both orthogonal and parallel to the uterine cervix[6-8]. Diagnostic-quality imaging requires a system greater than or equal to 1.5 T and intravenous contrast material administration[2,3](Fig. 7).
Bowel peristalsis-related motion artifacts might limit the visualization and hinder detailing of anatomical structures. Fasting for 4 to 6 hours before the examination may reduce bowel peristalsis[4,6,8]. The persistence of motion artifacts might require the usage of spasmolytics[6,7].
Evaluation of vaginal extension can be challenging, especially in exophytic tumors. Overstaging can be avoided by vaginal gel instillation[7,8](Fig. 10).
Sagittal high-resolution T2WI with 5-mm thickness and large FOV is obtained initially, to be used as reference and landmark to define the true axial and coronal cervical planes[7,8].
A large FOV gradient-echo T1WI or echo-planar T2WI from the level of the renal hila through the pelvic floor should be obtained in the transverse plane to assess hydronephrosis and lymphadenopathy[7,8]. FIGO staging recommends that these should be routinely acquired if PET/CT or CT is not planned[2].
High-resolution oblique coronal and oblique axial T2WI (≤ 3 mm thickness and small FOV) are critical to evaluate lesion size and contour (Fig. 8).
Multiplanar fast spin-echo T2-WI help evaluate invasion into the parametria (stage IIB) and pelvic sidewall (stage IIIB).
Volumetric T1WI contrast-enhanced images are used to evaluate peritoneal, nodal, and bone metastases.
In patients with contraindications to gadolinium-based contrast media, diffusion-weighted imaging should be used to improve lesion detection[4,5,8]. We routinely include DWI with low and high b values (50-150 and 600-1000 s/mm2), but there is no standardization in the literature(Fig. 9).
What to look and expect
The majority of cervical cancer lesions show intermediate T2 and variable enhancement. Tumor morphology includes exophytic, infiltrating, or endocervical lesions[5,6,8]. In uterine cervical cancer, the center of the mass is located within the cervix and extends to the vagina or lower myometrium. In contrast, endometrial masses have their bulk centered in the uterine cavity and extends to the cervix[5](Fig. 10).
Large pelvic masses may simulate advanced cervical cancer.
Nabothian cysts and cervical polyps are common mimickers[5,6,8](Fig. 11).
The primary drainage of uterine cervical cancer is to the pelvic sidewall. The external iliac follows the lateral route, internal iliac nodes by hypogastric route, and lateral sacral and sacral promontory nodes by presacral route[2-5](Fig. 12).
Lungs, peritoneum, supraclavicular and thoracic lymph nodes, and bones represent the majority of other involved sites[2-5].
Staging
The hallmark of a sound staging system is the ability to define the anatomical extent of disease, define treatment options, and predict the outcome. The current FIGO staging system is depicted in Fig. 13, Fig. 14, Fig. 15, and Fig. 16 [2-5, 6,8].
The identification of microinvasive disease is one of the limitations of MRI. Contrast-enhanced and diffusion-weighted images improve lesion detection and might provide insight over suspicious areas[2,8]. However, for the determination of FIGO IA stages, the MRI has a supplementary role, given the possibility of false-negative results[2](Fig. 17 and Fig. 18).
FIGO classification states that extension to the uterine corpus should be disregarded in stage I disease [2]. However, this is a controversial issue, since uterine body involvement may contraindicate trachelectomy, an option for fertile women. Thus, radiologists should consider describing uterus corpus invasion in this group of patients[3].
Trachelectomy is a fertility-preserving treatment for cervical cancer which eligibility criteria include a cutoff size of 2 cm for the primary tumor (IB1 stage), absence of uterine body extension, and surgical N0 disease[2,3].
For stage I disease, lateral extent is no longer taken into consideration and does not need to be reported[2].
Lymph nodes should always be evaluated since involvement upstages the patient to IIIC. Lymphadenopathy at imaging is a major prognostic factor and an essential determinant in treatment planning. Besides nodal size, other morphological features related to metastatic involvement include shape, preservation of hilar fat, diffusion restriction and pattern of enhancement[5,6].
The vaginal invasion may be seen as a disruption of the short T2 vaginal wall by a long T2 area of thickening and/or an enhancing mass[3,5,7].
FIGO stages II are depicted in Fig. 19, Fig. 20 and Fig. 21[2,3,6,7].
FIGO stages III are depicted in Fig. 22, Fig. 23 and Fig. 24[2,3,6,7].
FIGO stages IV are depicted in Fig. 25, Fig. 26, Fig. 27 and Fig. 28[2,3,6,7].
Edema, recent biopsy, or large-sized tumors may result in overstaging.
Staging Post-treatment and recurrence
The differentiation between post-treatment changes and tumor recurrence may be challenging. Post-surgical scars and actinic fibrosis both show short T2 times[6,8]. Contrast-enhanced pulse sequences and PET/CT may improve the identification of residual/recurrent disease(Fig. 29).