MR imaging in malignant and benign neoplastic
pathologies of uterus
Dr.P. Goswami, Dr N Medhi , Dr P K Sarma, Dr H .S. Das, Dr P Hazarika Dr B J Sarma
Primus, GS Road, Guwahati –
Although ultrasound remains the initial modality for evaluating clinically suspected masses in female pelvis, ultrasound is limited in its ability to clearly differentiate between many pelvic pathologies. MR imaging is exceptionally well suited for study of female pelvis. MR imaging provides an excellent noninvasive means of evaluating uterine zonal anatomy. The superior contrast resolution of MRI and the capability for direct multiplanar imaging has made it a valuable tool in the evaluation of benign and malignant uterine tumors and staging of pelvic malignancies.
Clinical indications : MRI is often indicated in the patients in whom ultrasound findings are suboptimal. MRI is also indicated in the patients in whom the origin of the pelvic mass can not be determined by ultrasound, patients in whom further lesion characterization is required and in patients with pelvic malignancies.
Cervical diseases :
Carcinoma of cervix :
Carcinoma of cervix is the most common gynaecologic malignancy in woman under the age of 50. Widespread screening was made possible following introduction of papanicolau smear. Improved early detection of noninvasive cancer has led to an overall decrease in mortality over the past three decades. Unfortunately, there has been no significant change in the mortality of invasive cervical carcinoma over the same period, despite improved treatment. Carcinoma cervix can occur at any age from menarche onwards. The peak incidence is prenemopausal. The two major symptoms of cervical carcinoma are vaginal bleeding and discharge. However upto 20% of patients with invasive carcinoma are asymptomatic at the time of diagnosis. The majority of noninvasive or early stage disease is most likely to be discovered in asymptomatic females with abnormal cervical cytology. Approximately 90% of cervical malignancies are squamous cell carcinomas. The remaining 10% of cervical cancers consists of adenocarcinoma and sarcomas. The prognosis is determined primarily by the tumor stage, histological grade, size, location within the cervix, depth of stromal invasion, adjacent tissue extension and presence of lymphnode metastases. Stage of disease is one parameter influencing the choice of therapy. For stage l and limited stage lla disease the options are surgery, radiation therapy, or both. In the majority of the patients with more advanced disease (stage ll a or greater ) treatment consists of radiation only. Therefore accuracy of staging is important not only for prognosis but also for choice of optimal therapy. The clinical staging in a patient of cervical carcinoma is not very accurate because of limitations in assessment of tumor extension in the pelvis.
MRI plays a crucial role in the evaluation and staging of cervical carcinoma. On T2 weighted images, cervical carcinoma most often appears as a mass of high signal intensity, distinct from the normal lower signal intensity cervical stroma, with distortion or disruption of the normal zonal anatomy of the cervix (Fig : 1). There may be broadening of the central uterine high intensity zone caused by uterine secretions retained within the enlarged uterine cavity due to cervical stenosis. On T1 weighted images, the cervical mass is isointense with normal cervix and uterus and only gross parametrial or adnexal extension causing contoural abnormality can be seen. Although administration of intravenous Gd allows distinction between viable tumor and areas of necrosis, it has not been shown to increase diagnostic accuracy in tumor depiction. For the local staging of cervical carcinoma, MRI is superior to other available modalities. In evaluating stage of disease MRI has an accuracy of 90% compared with 65% for CT. MRI is more accurate than CT (94% versus 76%) in assessing parametrial infiltration. MRI assessment is useful for placement of radiation ports. CT can not evaluate the tumor size or stromal invasion because it can not distinguish cancer from surrounding normal cervical tissue due to similar densities. MRI can accurately determine the tumor size. Tumor staging based on MRI follows FIGO staging criteria. Cervical carcinoma in situ is considered as stage O. Cervical carcinoma is considered stage l, when the tumour is strictly confined to the cervix. Stage l carcinoma is again subdivided to (a) stage la – microinvasive carcinoma and (b) stage l b – all other cases of stage l. MRI is not applicable in stage O and stage la disease. Stage ll disease indicates extension of tumor beyond the cervix. This stage is further subdivided to (a) stage ll a – tumor extension into the upper two thirds of the vagina and there is no obvious parametrial involvement. On T2 weighted images there is loss of low signal intensity from the normal vaginal wall (b) stage ll b – obvious parametrial involvement. Parametrial involvement is diagnosed when, in addition to loss of the normal low signal intensity cervical stroma, there is irregularity of the lateral cervical margin on T1 weighted images and presence of parametrial soft tissue mass. On T2 weighted images, there is diffuse or localized abnormal signal intensity within the paracervical region. Encasement of uterine vessels is another important finding in diagnosing parametrial invasion. Disruption of the fibrous stroma is the earliest finding of parametrial invasion. The presence of an intact ring has a high true negative rate for absence of parametrial infiltration. A tumor is considered as stage lll when it involves the lower third of vagina. Stage lll disease is subdivided to (a) stage lll a – no extension to the pelvic side wall (b) stage lll b – extension to the pelvic side wall and /or hydronephrosis or nonfunctioning kidney. Stage IV disease indicates extension of the tumor beyond the true pelvis or involvement of the mucosa of the bladder or rectum. This stage is further subdivided to (a) stage lV a – spread to bladder or bowel wall, which appears on T2 weighted images as loss of the normal low signal intensity of the wall of the organ (b) stage lV b – spread to distant organs. Cervical carcinoma spreads to parametrial nodes, followed by obturator nodes and then the internal iliac and external iliac chain. MRI can accurately detect adenopathy when an axial diameter of greater than 1 cm is used as an indicator of lymphadenopathy.
Nabothian cysts :
Nabothian cysts are small nodules on the surface of the cervix caused by distension of the endocervical glands. They are often associated with healing chronic cervicitis. When small they are rarely symptomatic and require no treatment.
MR Findings :
A nabothian cyst demonstrates high signal intensity on T2 weighted images (Fig : 2). On T1 weighted images they exhibit medium to high signal intensity. The small size and well defined margins differentiate them from other cervical neoplasms.
Uterine tumors :
Endometrial Carcinoma :
Endometrial carcinoma is the most common invasive malignancy of the female genital tract. Approximately 70% of endometrial cancers are adenocarcinoma, 15% are adenoacanthoma, and 15% are adenosquamous carcinoma. Uterine sarcomas are rare. Patient most frequently present with postmenopausal bleeding. Tumors may be localized or diffuse. Localized tumors are polypoidal or exophytic in nature, with only superficial attachment to the endometrium. Diffuse tumors often demonstrate extensive invasion of entire endometrium. Intitial tumor spread through myometrium to involve both corpus and cervix, is followed by spread outside the uterus and then involvement of adjacent organs. The lymphatic spread is to pelvic, paraaortic and inguinal nodes. Distant metastases occur frequently in the peritoneum, lung, liver and supraclavicular nodes. The prognosis depends on the stage of the disease, tumor location, size, depth of myometrial involvement, lymphnode involvement, histological grade, cell type and age of the patient.
MR findings :
Endometrial carcinoma has a variable MRI appearance. On T1 weighted images, most endometrial carcinoma will be isointense to the uterus unless they contain haemorrhagic areas. On T2 weighted images, tumor nodules ranging from a few millimeters to a few centimeters in size can be identified within the endometrial cavity. They usually have a signal intensity intermediate between that of normal endometrium and that of myometrium. In some patient with endometrial carcinoma, MRI will show only show expansion of the central high signal intensity area of the uterus without discrete nodules (Fig :3). Because endometrial carcinoma occurs predominantly in postmenopausal woman, and because normal post menopausal uteri have a very thin central high signal intensity zone (< 5mm), expansion of the central high signal intensity zone in this age group should raise the suspicion of uterine malignancy. The appearance of endometrial carcinoma after intravenous administration of Gd is variable. Most tumors enhance less than myometrium on both dynamic and delayed post contrast images. However some may show early enhancement compared to the myometrium, and others may appear isointense or hyperintense to myometrium on delayed images. Although MR appearance of endometrial carcinoma is nonspecific, MRI can accurately stage the disease in histologically documented endometrial carcinoma. In stage l endometrial carcinoma the tumor is confined to uterine corpus. Stage l tumors are further subdivided depending on degree of myometrial penetration. – (a) Stage l A , tumor confined to the endometrium (b) Stage l B, invasion confined to the inner half of myometrium and (c) Stage l C, invasion of outer half of myometruim. Stage ll endometrial cancer indicates involvement of the cervix but does not extend beyond uterus. Stage ll tumors are subdivided to (a) stage ll A – cervical stroma not invaded (b) stage ll B – cervical stoma invaded. Endometrial carcinoma is stage lll when tumor extends outside uterus. Stage lll endometrial carcinomas are subdivided to (a) stage lll A – tumors invades serosa and / or adnexa. (b) stage lll B – vaginal metastases, (c) stage lll C regional lymphnode larger than 1 cm in diameter. Stage IV endometrial carcinoma indicates tumor extension outside true pelvis or involvement of bladder or rectal mucosa. This stage is further subdivided to (a) stage IV a – tumor involves bladder or rectum, (b) stage IV B – tumor extends outside true pelvis (distant metastases). MRI can not distinguish malignant from hyperplastic nodes.
Gestational Trophoblastic Neoplasia :
Gestational trophoblastic neoplasia (GTN) represents a spectrum of tumors ranging from the benign hydatidiform mole, to the invasive mole, to the highly malignant choriocarcinoma. Choriocarcinoma is a very aggressive tumour, growing rapidly and metastasizing to the lung, liver and the brain. With the development of combination chemotherapy, complete and permanent remission can be achieved in more than 90% of the patients.
MR Findings :
Uterine GTN appears on MR images as a heterogeneous hypervascular mass that obliterates uterine zonal anatomy. The distortion of uterine zonal anatomy and the presence of a mass are detected on T2 weighted images. On T1 weighted images tumor may demonstrate a signal intensity similar to that of myometrium or they may demonstrate a high signal intensity within the tumour. Intratumoral haemorrhage and necrosis are frequently findings in GTN and they produce high signal intensity within the tumour in MR images. Tortuous vessels are frequently seen traversing the tumour and through adjacent myometrium and adnexa. Engorgement of internal iliac vessels are often seen, exceeding the diameters of corresponding external iliac vessels. Prominence of main uterine arteries may also be seen. Associated adnexal cysts (theca lutein cysts) may exhibit medium to high signal intensity on T1 weighted images. Contrast enhanced scans show enhancement of the involved myometrium and identification of the vesicles suggest the diagnosis of molar pregnancy. MRI findings in persistent GTN, incomplete abortion and ectopic pregnancy are relatively nonspecific. In the setting of documented GTN, however MRI can diagnose invasive disease that may alter therapeutic management. MRI sensitivity in detecting GTN within the uterus is specially useful when the tumour deeply infiltrates the myometrium but does not extend to the endometrial surface, because uterine curettage specimen will be non diagnostic. MR imaging may play an important role in excluding a uterine source for elevated HCG in patient with extrauterine germ cell tumour or gestational, mammary, hepatic or pulmonary malignancies.
Leiomyomas are the most common tumor in women of reproductive age. They may be solitary or multiple and most are found in submucosa, intramural or subserosal locations. Submucosal leiomyomas most often come to clinical attention because of infertility, recurrent abortion or hypermenorrhoea. Intramural leiomyomas may also be associated with infertility. Subserosal leiomyoma may undergo torsion causing acute abdominal pain. MRI accuracy for diagnosis of leiomyoma can have a significant clinical impact.
MR findings :
Most leiomyomas are round or oval, have clear margin and do not infiltrate the myometrium. The nondegenerative leiomyomas have intermediate signal intensity on T1 weighted images, and low signal intensity on T2 weighted images (Fig: 4). Calcified leiomyomas have low signal intensity on both T1 and T2 weighted images. Degenerative ( hyaline, myxomatous, fatty and cystic) leiomyomas show variable signal intensities. They may have medium or high signal intensity on T1 weighted images, and on T2 weighted images they demonstrate heterogeneous high signal intensities. Red degeneration leiomyomas demonstrate variable signal intensity on both T1 and T2 weighted images. There is no further benefit in the detection and chraracterization of leiomyomas after intravenous contrast. There is yet no reliable MRI feature for detecting malignant degeneration within a benign leiomyoma.
Adenomyosis is defined as the presence of endometrial glands and stroma within the myometrium, at least 2.5 mm from the basal endometrial layer. Patient frequently present with hypermenorrhoea, anaemia, dysmenorrhoea, perimenstrual pelvic pain and enlarged uterus.
MR findings :
There are two types of adenomyosis, a diffuse and a focal type. In diffuse adenomyosis the fundus and body of uterus show diffuse enlargement. The thickness of low signal intensity junctional zone is increased on MR images (> 12 mm ). Tiny foci of high signal, which probably represent islands of endometrium, can be seen within the myometrium on T2 weighted images. When these high signal intensity foci are seen on both T1 and T2 weighted images, they possibly represent haemorrhage. Focal adenomyosis is seen as a mass of low signal intensity which may
appears similar to a leiomyoma. Distinction between focal adenomyosis and leiomyoma is of primary clinical importance. The interface between focal ademyosis and adjacent myometrium is ill defined, whereas leiomyomas are sharply defined. In extensive adenomyosis there may be distortion of endometrial canal. There may be multiple dilated veins accompanying a leiomyoma, which are not seen with adenomyosis.
Endometrial polyps :
Endometrial polyps are sessile or pedunculated hyperplastic endometrial projections. They arise in the fundus or cornual regions of the uterus. Malignant change is only rarely identified within endometrial polyp. Patient usually present with intramenstrual or post menopausal bleeding.
MR findings :
On T1 weighted images endometrial polyps show medium signal intensity similar to that of normal endometrium. On T2 weighted images, polyps demonstrate signal intensity similar to or slightly lower than that of endometrium. They may also cause apparent expansion of the endometrial cavity. Non contrast scans may not be able to detect them because of their similar signal intensity with the normal ebdometrium. Endometrial polyps show enhancement after Gd contrast, facilitating their detection. Polyps may degenerate and become heterogeneous in appearance.