|ECR 2018 / C-3205|
|Uterine mass in pelvic MRI : the "atypical" myoma puzzle for the radiologist and the gynecologist.|
Findings and procedure details
TABLE OF CONTENTS :
Degenerative modifications in myomas are frequent and often associated (hyaline fibrosis or œdema > 50% of cases). They modify the MRI signal of the myoma +/- heterogeneity on T2-weighted images7,8. Table 3 Table 4
In this work, we revised the key imaging findings (morphological and functionnal MRI) with their histopathological correlation in :
- myomas and leiomyomas variants (cystic, œdematous, myxoid, hyaline, hemorrhagic, fatty, hypercellular, necrotic pseudo-invasive)
- endometrial stromal tumors : stromal nodule and endometrial stromal sarcoma (ESS of low to high grade),
- adnexal fibrous tumors and plurimyomatous uterus,
- pelvic lymphoma.
OVERVIEW OF THE LITERRATURE:
→ A significant difference of ADC value between sarcoma and myoma is described, but there is an overlap with ordinary myomas and hypercellular myomas9. A sensibility of 100% was observed in a study10 combined T2 signal and ADC value (cut-off at 1.05 x 10-3 mm2/s), thus differentiating 8 sarcomas from 95 myomas. For another one, highest ADC value of sarcoma was 1.095, combined with intermediate T2-weighted signal11.
A typical uterine sarcoma is characterized by 3 criteria malignancy12 :
- an intermediate or high T2-weighted signal
- a high b1000-weighted signal
- an ADC restriction (less than 1.23)
An accuracy of 92.4% (well-classified tumors on 51 lesions) is reported, with some reservations in the use of each MR sequence12 :
- some myomas have low ADC
- some sarcomas have low T2 signal or low b1000 signal
- but a given sarcoma is never hyposignal on these 2 sequences.
These data show the diagnostic benefit to combinate tumoral signal on T2-weighted images with DWI (b1000) and quantitative measurement of apparent diffusion coefficient (ADC). In addition, there is a good positive predictive value of the age of the patient (peri or post menopause) with malignancy in 71,8% after 44,8 years-old when a unique myometrial tumor is discovered12. Morphological features on nonenhanced and postcontrast MR sequences must also be take into account : invasive tumor with necrotic-haemorrhagic contingent and heterogeneity plead for malignancy. The use of perfusion sequences is alone not sufficiently discriminating to establish benignity or malignancy, but may sometimes be a complementary diagnostic tool.
- MYOMAS AND LEIOMYOMAS VARIANTS
TYPICAL MYOMA : is a round mass with circumscribed contours, but sometimes bumpy. Ordinary leiomyoma has a characteristic signal on MRI T2-weighted images (fibrosis low T2 signal). DWI and perfusion don't establish the diagnosis. Some secondary changes are easy to detect, for exemples : post menopausal atrophy, hyaline fibrosis, calcification, aseptic necrobiosis or "red degeneration", fatty-degeneration, homogeneous cystic degeneration.
OEDEMATOUS MYOMA : is frequently observed leading to a T2 intermediate signal of the myoma. It could be homogeneous or not, well enhanced after contrast similar to the myometrium (variable perfusion) and an hyperintensity on DWI is described without ADC significant restriction.
ASSOCIATION OF DEGENERATIVE MODIFICATIONS : it seems that each leiomyoma has its own unicellular origin (monoclonal), which explains that different myomas can evolve differently in a same uterus13. It is also common that within the same tumor, several types of secondary changes are observed in MRI, further accentuating the T2 signal changes of the myoma, as its heterogeneity. Heterogeneous necrosis, œdematous or cystic degeneration can mimic a suspicious necrotic aspect of sarcoma.
OTHER RARES MODIFICATIONS :
- Cellular myomas are mitotically active (that is histologically, beyond 5 mitoses / 10 fields). They appear with a T2 intermediate signal, hyperintensity on DWI with ADC moderate restriction. Their recurrence is more common after myomectomy. On T2-weighted images, these myomas are hyperintense compared to the adjacent myometrium with an early enhancement. The differential diagnosis with sarcomas is often difficult.
- Lipoleiomyoma and myxoid degeneration are extremly rare (respectively 0,2 and 0,8%).
LMS represent more than 50% of uterine sarcomas and most often, they have malignant MRI findings : large or irregular masses on T2-weighted images (opposite to the myoma), with heterogeneous signal and hypersignal areas. On T1-weighted, they are in isosignal or hyposignal compared to the signal of the myometrium, hypersignal areas are possible in case of hemorrhagic necrosis. Contrast-enhancement of tissular part is intense, with the arterial time of the injection and often heterogeneous. DW-images are suspicious : b1000 hyperintensity with significant ADC restriction.
The negative consequences of morcellate a uterine sarcoma discovered during a hysterectomy are incontestable. In case of R0 complete surgical resection with infracentimetric margins, risk of pelvic recurrence is estimated about 20%, passing respectively to 50% and 100% in case of R1 or R2 surgery14. Management of soft tissue sarcomas is recommended in a reference center.
- ENDOMETRIAL STROMAL TUMORS
ESS (endometrial stromal sarcomas) are rare malignant uterine tumors (15% of uterine sarcomas) with an histological gradation correlated with a decreasing prognosis : low or high grade and undifferenciated with a poor prognosis. It is a pathology of younger women (between 40-55 year-old) and some risk factors are described : tamoxifen, estrogen, polycystic ovary syndrome (PCOS).
Endometrial stromal nodule is a rare benign uterine tumor of the same histological group, but should be distinguished from ESS. Its diagnosis is histological and based on the absence of invasion of myometrium, lymphatic and vascular structures. Its morphological appearance is variable in MRI. Hysterectomy is required15.
Endometrial stromal tumors appear well limited in 50% of cases. Their MRI characteristics are a T1 hypointense similar to the myometrium and a T2 hypersignal greater than the myometrium. This hyperintesity on T2-weighted images may be similar or inferior to the endometrium. The presence of a T2 hyposignal band at the periphery of the tumor, all around the zone of invasion of the myometrium, is an argument in favor of a low-grade sarcoma, contrary to a diffuse infiltration and poorly limited myometrium observed in cases of high-grade sarcomas. Flow signal voids are sometimes visible within the myometrial invasion, reflecting the hypervascular nature of the lesion. After injection of gadolinium, early enhancement is observed to be superior to the myometrium, which is usually heterogeneous. Areas of necrosis and hemorrhage are more likely observed in cases of high-grade sarcoma. The main differential diagnosis of endometrial stromal tumors is endometrial adenocarcinoma.14,15
It is an extremely rare histological diagnosis corresponding to a group of uterine smooth muscle tumors that cannot be diagnosed decidedly as benign or malignant. Diagnosis, surgical management, and follow-up remain controversial17. Imaging features is poorly specific compared to LMS.
- ADNEXAL FIBROUS TUMORS AND POLYMYOMATOUS UTERUS
Distinction between uterine or adnexal origin of a pelvic mass discovered in MRI is the first step for the radiological approach. In case of voluminous pelvic mass possibly compressive on adjacent organs and occupying the entire pelvic cavity, identifying normal ovaries can orient the radiologist to the uterine origin, but some adnexal fibrous tumors or pedunculated subserosal uterine leiomyomas (type 7 of FIGO classification) are sources of MRI pitfalls.18
- PELVIC LYMPHOMA
It may rarely be a primitive or secondary uterine localization and its main differential diagnosis is sarcomatous pathology or other infiltrative tumors of pelvic cavity.
TAKE HOME MESSAGES :
MRI is the reference technique (as second line imaging after US) for :
− pre-therapeutic assessment of myomas (accurate lesions mapping : impact the choice of conservative therapeutic modality in 20%19)
− and characterisation of atypical myometrial tumors (particularly when the tumor is unique and large in a menopausal woman), but conventional MR sequences lack specificity to differentiate benign and malignant pathology. Correlation of morphological and functionnal imaging with clinical context may improve the diagnostic accuracy, according to 3 possibilities :
When T2-intermediate signal or hyperintensity of the tumor may be difficult for differenciate these 2 diagnoses, DW-images (b1000) with quantitative measurement of ADC and perfusion can be helpful. Full MRI pelvic protocol is so recommended, ie, sagittal and axial turbo spin-echo (TSE) T2-weighted sequences, axial gradient-echo T1-weighted sequences with and without fat-saturation (fat-sat), axial DWI/ADC, perfusion and 3D-isotropic gradient-echo T1-weighted sequence after gadolinium injection +/- axial lombo-aortic T2-weighted sequence. For exemple in our center, average total time for the exam is 17 minutes 55' (GE MR Discovery 750, 3 Tesla, Oscar Lambret Center-Lille/FR).
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