Introduction
Uterine leiomyomas, commonly known as fibroids, are the most prevalent gynecologic and uterine neoplasms, affecting up to 80% of women by the age of 50 [1]. Although most women with uterine fibroids are asymptomatic, approximately 30% of women experience severe symptoms, including abnormal uterine bleeding, anemia, pelvic pain and pressure, back pain, urinary frequency, constipation, or infertility, necessitating clinical intervention [2‐4]. With the advancement of hysteroscopic and laparoscopic technologies, further refining the classification is needed to assess the impact of different types of uterine fibroids on patients and to guide the selection of treatment methods. Therefore, classification assessment is crucial in the pretreatment evaluation of uterine fibroids [5, 6].
The implementation of the Federation of Gynecology and Obstetrics (FIGO) classification system has facilitated more detailed treatment planning and response assessments [6, 7]. According to the FIGO classification system, types 0, 1, and 2 refer to submucosal uterine fibroids. Types 3 and 4 are intramural fibroids, whereas types 5, 6, and 7 are subserosal fibroids. Additionally, all fibroids located entirely outside the uterus are classified as type 8. Mixed fibroids typically refer to those with both intramural and submucosal components and are classified as types 2–5. Submucosal fibroids (types 0–2) are often treated with hysteroscopic resection, whereas intramural or subserosal types (types 3–7) may require laparoscopy or laparotomy [8]. Misclassifying a FIGO type 2 fibroid as type 3 or 4 could result in unnecessary invasive surgery, whereas underestimating submucosal involvement may result in incomplete resection, persistent symptoms, or complications such as uterine rupture in future pregnancies [9]. Thus, an accurate pretreatment evaluation of the fibroid FIGO classification is crucial.
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MRI allows for high-resolution, multiplanar visualization of fibroids, outperforming ultrasound (US) in depicting their size, location, shape, and relationship with the uterine cavity [10‐12]. According to the European Society of Urogenital Radiology (ESUR) guidelines for MR imaging of leiomyomas, a basic MRI examination protocol with at least two T2WI orthogonal planes of the uterus, including a sagittal sequence of the uterine corpus, is recommended [13]. In contrast, ESUR also recommends that an oblique sequence aligned along the long axis of the uterus is optional for uterine fibroids [13]. This could provide useful information for the anatomic localization of leiomyomas and display the relationship of the leiomyomas to the endometrial cavity.
Currently, owing to the lack of consensus on MR scanning for uterine fibroid patients, the scanning protocols vary across different centers. Body-axial T2WI is the main protocol used for uterine fibroids; however, organ-axial T2WI is relatively limited. However, interobserver variability is constrained by the FIGO classification system identified by MRI, especially in the staging of a large fibroid, which could result in distortion of the landmarks in the uterus [14]. Therefore, this study aimed to determine the reliability and accuracy of the FIGO system for classifying uterine fibroids via organ-axial T2WI. For further investigation, we evaluated the factors associated with uterine compression on organ-axial T2WI.
Methods
This prospective study was approved by the Ethics Review Committee of Peking University People’s Hospital (No. 2023PHB094-001), and informed consent was obtained from all the patients. The study was conducted in compliance with the Health Insurance Portability and Accountability Act (HIPAA) and the Declaration of Helsinki (revised in 2013).
From March 2023 to May 2024, 245 consecutive patients needed treatment for symptomatic uterine fibroids at our institution. The inclusion criteria were as follows: (1) pretreatment pelvic MRI was performed, (2) the interval between surgery and MRI examination was < 14 days, and (3) MR image quality was adequate for further analysis. The exclusion criteria were as follows: (1) previous fibroid treatment, (2) multiple fibroids (more than 10 fibroids), and (3) pathological diagnosis was not fibroid. Ultimately, 130 patients (mean age, 39.8 years ± 7.54; range, 21–58 years) were included in this study. The patient inclusion process is shown in Fig. 1.
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Fig. 1
Flowchart of the patent selection process
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MRI acquisition
MRI was performed via a 3.0T system (Ingenia, Philips Health care, Netherlands) with a 32-channel body coil. Patients were required to fast for 3–6 h to reduce bowel motion artifacts. Patients were also required to empty their bladders 1 h prior to examination to achieve a moderately filled bladder [13, 15]. Patients were placed in the supine position with the abdominal band compressed. MRI sequences included the basic protocol of body-axial T2WI (sagittal and axial) and the optimal protocol of organ-axial T2WI (high resolution with oblique coronal and double oblique axial), as recommended by ESUR [13] (Fig. 2). Detailed information regarding the sequence parameters is presented in Table 1.
Fig. 2
T2W protocol for generating body-axial images and organ-axial images of uterine fibroids. (a and b) are the two T2WI orthogonal planes of the pelvis. (a) shows the sagittal T2WI sequence of the pelvis; b shows the axial T2W sequence of the pelvis. (c and d) are the two optimal T2WI orthogonal planes of the uterus. (c) coronal T2WI obtained parallel to the long axis of the uterus; (d) oblique axial T2WI images obtained perpendicular to the long axis of the uterus. The solid line represents the scan plane for coronal images acquired parallel to the long axis of the uterine body, and the dashed lines represent the scan plane for axial images acquired perpendicular to the long axis of the uterine body
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Table 1
Detailed scan parameters for all sequences used
Sequences | Repetition time/Echo time (ms) | Voxel (mm2) | Field of view (mm3) | Slice thickness/Gap (mm) | Number of signal average | Plane | Scan time (minutes: seconds) |
|---|---|---|---|---|---|---|---|
Body-axial T2WI | 2500/70 | 360 × 280 | 0.625 × 0.625 | 4.0/1.0 | 1 | Sagittal | 2:46 |
Body-axial T2WI | 3400/85 | 360 × 70 | 0.625 × 0.625 | 4.0/1.0 | 1 | Axial | 1:17 |
Organ-axial T2WI | 5600/80 | 180 × 180 | 0.280 × 0.280 | 4.0/1.0 | 2 | Oblique Coronal | 1:22 |
Organ-axial T2WI | 5200/80 | 180 × 180 | 0.280 × 0.280 | 4.0/1.0 | 2 | Oblique Axial | 5:25 |
Imaging analysis
The radiologist (L.XY with 10 years of experience in gynecologic MRI), who was not involved in the FIGO classification judgment, selected every fibroid resected during surgery according to the surgery record from each patient. If the number of resected fibroids was greater than five, the largest five were selected for women with multiple fibroids. Every selected fibroid was labeled; “A” represents the first fibroid, with subsequent fibroids designated “B to E” as applicable. These images were stored on a picture archiving and communication system (PACS) at the plane of maximal diameter on the body-axial and organ-axial T2WI. These images were reviewed and the classification of labeled fibroids was checked by a radiologist (H.N.) and gynecologist (Z.R.), who were experts in the evaluation and treatment of uterine fibroids.
Two academic radiologists (W.K. and G.XY, with 1 and 2 years of experience in gynecologic MRI, respectively) who were blinded to the final FIGO classification and independently assessed the FIGO classification of uterine fibroids on both body-axial and organ-axial MR images were selected as observers. Prior to the commencement of the assessment, these radiologists underwent a two-week training program covering primarily the latest guidelines of the FIGO classification system and best practices in MR image interpretation (Fig. 3a). The classification assigned to each fibroid was then recorded. A FIGO staging evaluation was performed 2 weeks apart for body- and organ-axial T2WI. A third expert radiologist (C.J., with 19 years of experience in gynecologic disease) made the final decision if a different classification was made. Using surgical outcomes as the standard, we compared the accuracy of axial T2W imaging and organ-axial T2WI in the FIGO classification of uterine fibroids.
The diameter of each fibroid and parameters related to uterine cavity deformation were assessed and measured on organ-axial T2WI via PACS. The radiologists (L.XY and W.K.) assessed the parameters at different times. The diameter of the fibroids was measured in three perpendicular planes, and the mean diameter was calculated. The measurement of uterine cavity deformation is performed at the most prominent point of compression in the organ-axial T2WI. All the parameters were measured three times, and the average value was calculated. These parameters include compression base width (B), compression depth (D), depth of compression cavity width (C), and compression angle (A), which are critical for selecting the appropriate surgical approach (laparoscopy or hysteroscopy) and provide an indication of the degree of uterine cavity compression [16] (Fig. 3b). If the fibroid was located at the fundus, measurements were obtained in the high-resolution coronal plane.
Fig. 3
FIGO classification (0–8) of fibroids and measurements of uterus compression-related parameters caused by fibroids. (a) FIGO 0 is a pedunculated intracavitary fibroid; FIGO 1 is a submucosal fibroid that is < 50% intramural; FIGO 2 is a submucosal fibroid that is ≥ 50% intramural; FIGO 3 is a fibroid that is 100% intramural but in contact with the endometrium; FIGO 4 is an intramural fibroid; FIGO 5 is a subserosal fibroid that is ≥ 50% intramural; FIGO 6 is a subserosal fibroid that is < 50% intramural; FIGO 7 is a subserosal pedunculated fibroid; FIGO 8 is another (e.g., cervical and parasitic) fibroid; and FIGO 2–5 is a hybrid fibroid that is < 50% submucosal and < 50% subserosal. (b) The dark dotted line angle is the compression angle, which depicts the angle between the endometrium and the circumference of the fibroid on the same plane. B The red solid line represents the compression base width, which depicts the line joining the two myoma-endometrial edges of the myoma. C The red dotted line represents the compression cavity width, which represents the distance at the widest part of the uterine cavity. D The blue line represents the compression depth, which depicts the perpendicular distance from line B to the surface of the fibroids within the uterine cavity
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Surgical procedures
All patients underwent laparoscopic or hysteroscopic myomectomy, which is the gold standard. The FIGO classification of each resected fibroid was identified intraoperatively by a gynecologist (Z.R.). During surgery, gynecologists determine the International Federation of Gynecology and Obstetrics (FIGO) classification of fibroids on the basis of their location, size, and growth direction.
Statistical analysis
Statistical analysis was performed via SPSS software (version 26.0; SPSS, Chicago, IL, USA). The baseline characteristics were summarized via descriptive statistics. For continuous variables, summary statistics included the mean and median as appropriate. Categorical variables are presented as frequencies and percentages. The paired chi-square test was used to compare the accuracy of image assessments for classifying uterine fibroids on the basis of body axial-T2WI and organ axial-T2WI. Interobserver agreements for assessing the FIGO classification between the two radiologists and interagreements between the two protocols and operations were evaluated via kappa statistics. The degree of agreement was interpreted as follows: 0.01 ≤ k < 0.20 as poor; 0.20 ≤ k < 0.40 as fair; 0.40 ≤ k < 0.60 as moderate; 0.60 ≤ k < 0.80 as substantial; and 0.80 ≤ k < 1.00 as excellent. The differences in cavity deformation among the different FIGO classifications were compared via the Kruskal‒Wallis test. The correlation between FIGO type and uterine cavity deformation parameters was analyzed via Spearman’s rank correlation test.
Results
In total, 130 patients were included in the analysis: 99 patients had only one fibroid, 24 patients had two fibroids, 6 patients had three fibroids, and 1 patient had five fibroids, comprising a total sample of 170 fibroids. Among the 130 patients, 106 underwent laparoscopy, 17 underwent hysteroscopic surgery, and seven underwent combined laparoscopic and hysteroscopic procedures. Among the 170 fibroids, 4 were classified as type 0, 7 were classified as type 1, 7 were classified as type 2, 11 were classified as type 3, 36 were classified as type 4, 42 were classified as type 5, 41 were classified as type 6, 9 were classified as type 7, 8 were classified as type 8, and 5 were classified as types 2–5.
Compared with intraoperative findings, organ-axial T2WI showed better interobserver agreement and higher interrater rates, with kappa values of 0.877 and 0.932, respectively (Table 2). Using intraoperative classification as the gold standard, among the 170 fibroids, 158 lesions in the organ-axial T2WI image were concordant with the intraoperative classification, and 100 lesions in the body-axial T2WI image were concordant with the intraoperative classification, with accuracy rates of 92.9% (158/170) and 58.9%(90/170), respectively. The classification accuracy of organ-axial T2WI (92.9%) was significantly better than that of body-axial T2WI (58.9%) (P < 0.001). Only 12 (7.1%) patients had discrepancies between organ-axial MRI and surgical identification; however, this did not affect the choice of surgical approach (Table 3).
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Table 2
Interobserver agreements between the two radiologists and interagreements between the two protocols and operations for assessing the FIGO classification
Consistency | Kappa | 95% CI | P | |
|---|---|---|---|---|
Lower | Upper | |||
Body-axial MR ICC | 0.576 | 0.428 | 0.724 | 0.076 |
Organ- axial MR ICC | 0.877 | 0.800 | 0.955 | 0.040 |
Body-axial MR vs. Operation | 0.591 | 0.469 | 0.713 | 0.062 |
Organ- axial MR vs. Operation | 0.932 | 0.860 | 1.000 | 0.037 |
Table 3
FIGO classification and cavity deformation of fibroids
Operation FIGO | Organ-axial MR FIGO | Cavity deformation | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 2–5 | ||
0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2/2 (100%) |
1 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3/3 (100%) |
2 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2/2 (100%) |
3 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 7/7 (100%) |
4 | 0 | 0 | 0 | 0 | 13 | 0 | 0 | 0 | 0 | 0 | 6/13 (46.2%) |
5 | 0 | 0 | 0 | 1 | 0 | 18 | 1 | 0 | 0 | 0 | 9/11 (81.8%) |
6 | 0 | 0 | 0 | 0 | 0 | 1 | 19 | 0 | 0 | 0 | 3/20 (15.0%) |
7 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 7 | 0 | 0 | 0/7 (0%) |
8 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 6 | 0 | 0/6 (0%) |
2–5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 3/3 (100%) |
Thirty-two (38.1%) fibroids showed cavity deformation according to organ-axial MR images, including fibroids with FIGO types 0–7 and 2–5 (Table 3; Fig. 4). The imaging characteristics related to cavity deformation are shown in Table 4. There were significant differences among the different FIGO types of fibroids in terms of tumor diameter (S), depth of uterine cavity compression (D), ratio of the base width of the compressed uterine cavity to the maximum width of the same layer of the uterine cavity (B/C), ratio of compression depth to the base width of the compressed uterine cavity (D/B), and compression angle (A). S, B/C, and A were positively correlated with the FIGO classification, whereas D and D/B were negatively correlated with the FIGO classification (Table 4). The compression angle exhibited a linear correlation with FIGO type, with a correlation coefficient of 0.68 (P < 0.001) (Table 4).
Fig. 4
For organ-axial MR images, fibroids (white arrow) with different FIGO classifications showed cavity deformation (asterisk). (a) FIGO 0 fibroid (white arrow); the fibroid is located within the uterine cavity, causing compression and deformation of the endometrium. (b) FIGO 1 fibroid (white arrow); the leiomyoma protrudes into the uterine cavity by more than 50%, resulting in compression and deformation of the endometrium.(c) FIGO 2 fibroid (white arrow); the leiomyoma protrudes into the uterine cavity by less than 50%, causing compression and deformation of the endometrium.(d) FIGO 3 fibroid (white arrow); the fibroid is large and in contact with the endometrium, resulting in localized compression and deformation of the endometrium.(e) FIGO 4 fibroid (white arrow); the leiomyoma is located within the myometrium, and although it is not in contact with the endometrium, its large size can still result in compression and deformation of the endometrium.(f) FIGO 5 fibroid (white arrow); a larger subserosal leiomyoma is present, with localized deformation of the endometrium also observable.(g) FIGO 6 fibroid (white arrow); the fibroid is large and displaces the myometrium, resulting in localized compression and deformation of the endometrium.(h) FIGO 2–5 fibroid (white arrow); a larger hybrid fibroid causes compression and deformation of the endometrium
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Table 4
Cavity deformation associated parameters with FIGO classification
Imaging feature | Median according to operation FIGO | Kruskal-wallis | Spearman | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 | 1 | 2 | 3 | 4 | 5 | 6 | 2–5 | F | P | r | P | |
Size of fibroid (S, mm) | 29.00 | 27.00 | 27.50 | 63.00 | 31.00 | 64.00 | 74.00 | 80.00 | 17.51 | 0.014 | 0.32 | 0.062 |
Base width (B, mm) | 9.00 | 15.00 | 16.00 | 21.00 | 31.00 | 19.00 | 23.00 | 33.00 | 14.61 | 0.041 | 0.25 | 0.126 |
Depth of compression (D, mm) | 26.00 | 17.00 | 4.90 | 4.00 | 4.25 | 3.00 | 2.00 | 3.50 | 14.35 | 0.042 | 0.26 | 0.331 |
D/B | 0.90 | 1.15 | 0.36 | 0.15 | 0.18 | 0.17 | 0.09 | 0.15 | 14.01 | 0.051 | -0.33 | 0.053 |
D/S | 0.31 | 0.68 | 0.26 | 0.06 | 0.16 | 0.04 | 0.03 | 0.06 | 18.02 | 0.012 | -0.35 | 0.041 |
Angle of compression (A) | 40.00 | 47.00 | 102.60 | 151.00 | 149.0 | 166.00 | 170.00 | 180.00 | 20.03 | 0.005 | 0.68 | 0.001 |
Discussion
The primary objective of this study was to evaluate the effectiveness of high-resolution organ-axial T2WI in increasing the accuracy and reliability of the FIGO classification of uterine fibroids. Organ-axial T2WI was more accurate than body-axial T2WI in the FIGO classification of uterine fibroids. In addition, organ-axial T2WI exhibited a high level of interobserver consistency and greater accuracy with surgical findings in the FIGO classification of uterine fibroids, significantly outperforming traditional body-axial T2WI. These findings suggest that organ-axial T2W imaging can be a reliable and consistent method for evaluating uterine fibroids, potentially improving diagnostic precision and clinical outcomes.
The FIGO classification system contributes to categorizing lesions, guiding patient management, and providing prognostic information [6, 10, 17]. The position of the uterus in the pelvis is variable, and adjusting the acquisition plane could overcome this issue. Organ-axial T2WI, which angles both the sagittal and the coronal planes, creates a “true axial oblique” plane that is correctly positioned along the true axis of the uterus [18, 19]. Our study revealed that the organ-axial T2WI protocol performed better than the body-axial T2WI protocol did in terms of the FIGO classification. These findings suggest that organ-axial T2WI may be superior to body-axial T2WI for fibroid classification. While there are no studies on the application of organ-axial images in terms of fibroids, our study confirmed that this technique increased the reliability and accuracy of FIGO classification, which is similar to that of endometrial cancer and cervical cancer [20, 21]. These results are consistent with the ESUR guidelines, which support the use of organ-axial T2WI [22].
In this study, the interobserver agreement for determining the FIGO classification of fibroids via organ-axial MRI achieved a kappa value of 0.877, indicating a high level of consistency among different observers. This finding may be because, in body-axial T2WI, partial volume effects result in discrepancies in the results, whereas organ-axial T2WI, which is determined along the true axis of the uterus, avoids the impact of partial volume effects, thereby generating greater interobserver agreement [12, 20]. Additionally, our study results confirmed that organ-axial T2WI has greater consistency with the operation. Furthermore, the organ-axial T2WI (k = 0.932) is more consistent with the operation than the body-axial T2WI (k = 0.591), which is consistent with previous literature, indicating that the consistency between readers regarding the FIGO classification of fibroids on the basis of body-axial T2WI is low and has poorer conformity with operation identification [14]. These findings suggest that organ-axial T2WI has potential value for fibroid classification and may be beneficial in surgical planning.
An understanding of the relationships among indices of uterine cavity deformation (such as compression pulse width, compression depth, and compression angle) is pivotal for a more accurate preoperative assessment of the uterine fibroid FIGO classification and surgical approach [23]. This understanding is crucial for guiding clinical decision-making and formulating treatment plans, facilitating optimized surgical strategies and improving patient outcomes. According to previous studies, distortion of the uterine cavity is typically attributed to submucosal fibroids with FIGO types 0, 1 and 2 and to intramural fibroids with FIGO types 2–5 [6, 12, 24]. Conversely, intramural fibroids, with FIGO types 3, 4, and 5; and subserosal fibroids, with FIGO types 6 and 7 [6, 12, 24], do not distort the uterine cavity. Nonetheless, our research revealed that patients with FIGO types 3–6 had different proportions of patients with signs of uterine cavity compression. In cases of types 0–6 and 2–5, which caused uterine cavity deformation, the compression angle was linearly correlated with the FIGO classification. This finding indicates that the deformation of the uterine cavity gradually transitions from tongue-like protruding to pushing from type 0 to types 6 and 2–5. Furthermore, fibroids cause physical compression, and deformation of the uterine cavity is an important mechanism related to infertility [24]. Our findings also imply that an increased number of fibroids may pose a potential risk of subfertility, requiring intervention to restore uterine cavity shape.
This study had several limitations. First, this study was conducted at a single center and multiple institutions, and a large sample size cohort is necessary to further validate the results of our present study. Second, due to the constraints of our study design and sample size, we were unable to conduct a detailed investigation into the relationship between uterine fibroids and infertility. This limitation highlights the need for further research with larger, more representative cohorts to better understand this complex relationship. Third, the two-week training program at study onset may have introduced bias, which we acknowledge as a limitation. To address this shortcoming, we implemented a standardized training protocol and a blinded assessment to minimize its impact. Future studies should expand the training period and sample size to further validate our findings. Fourth, organ-axial T2WI increases the additional scanning time, whereas 3D T2WI can help reduce the scanning time. In future studies, we will consider 3D scanning as a potential option, provided that image resolution is maintained.
Conclusion
In conclusion, organ-axial T2WI is essential for the precise FIGO classification of uterine fibroids because it offers detailed visualization of their size, location, and relationship with the endometrium, myometrium, and serosa. This advantage enables accurate classification, which is crucial for guiding individualized treatment strategies. As artificial intelligence advances, future research will likely focus on the automation of uterine cavity deformation assessment, providing a deeper understanding of how fibroids influence uterine cavity remodeling. These advancements will improve our ability to predict and manage the long-term effects of fibroids on uterine recovery and overall patient outcomes.
Declarations
Competing interests
The authors declare no competing interests
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