Müllerian Anomalies: Revisited

Abstract

The Müllerian structures are developed from paired embryologic ducts that undergo fusion and resorption in utero to form the uterus, fallopian tubes, cervix, and upper two-thirds of the vagina. Any disruption of the normal embryological development of the Müllerian structure results in Müllerian anomalies. Müllerian anomalies are a complex spectrum of abnormalities that are usually associated with primary amenorrhea, infertility, and obstetric complications. Obstructed anomalies can be associated with endometriosis due to retrograde menstruation and sometimes endometriosis. Frequently, Müllerian anomalies are associated with renal anomalies; therefore, identification of both kidneys is important. Ovaries are normal in patients with Müllerian anomalies. Hysterosalpingography is routinely used in the evaluation of infertility and can demonstrate Müllerian anomalies, but has its limitations in characterizing the external fundal contour, which is a key component in categorizing the Müllerian anomaly. Two-dimensional ultrasound is the first-line modality for evaluating the uterus and adnexa. Three-dimensional ultrasound or magnetic resonance imaging may help to visualize the external uterine fundal contour and internal indentation of the endometrial cavity, which are two morphologic characteristics that are keys to the diagnosis of congenital uterine anomalies. Three-dimensional ultrasound can be used to evaluate uterine morphology and endometrial cavity configuration. The American Society for Reproductive Medicine (ASRM) and European Society of Human Reproduction and Embryology classifications are commonly used to categorize the Müllerian anomaly. The New ASRM classification is more practical as it appears simpler and more user-friendly, as it uses drawings with clear descriptions rather than symbols, and gives us a whole view of the anomaly. Correct diagnosis of Müllerian anomalies and their classification is critical for surgical and clinical management.

 

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Keywords

ASRM classification - infertility - Müllerian anomalies - primary amenorrhea

Introduction

Müllerian anomalies are congenital disorders that occur due to the abnormal development of the Müllerian duct during embryogenesis, leading to various malformations of the female reproductive organs.[1] [2] These anomalies can be seen in up to 7% of women.[3] [4] Clinically, it can present as infertility and miscarriage in young women[5] or can present with outflow obstruction symptoms at menarche in adolescent girls. Obstructed anomalies can also be associated with endometriosis due to retrograde menstruation. The spectrum of Müllerian anomalies comprises a wide range of malformations affecting the uterus, cervix, and vagina.[6] Correct diagnosis and classification of Müllerian anomalies is critical for surgical and clinical management. In this review, we discuss the imaging findings and the different classification systems of Müllerian anomalies.

 

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Embryology

Embryologically, one pair of mesonephric ducts (Wolffian ducts) and one pair of paramesonephric or Müllerian ducts develop at 6 weeks of gestation. Bilateral Müllerian ducts grow in both directions with suppression of the mesonephric duct due to the absence of Müllerian inhibiting factor and the stimulation by maternal hormones on the female fetus.[4] Further, they migrate to the midline and then fusion of Müllerian ducts occurs with resorption of the septum, resulting in the development of the uterus and upper two-thirds of vagina ([Fig. 1]). Arrest at any stage of embryological development results in different types of Müllerian anomalies. According to embryological development, Müllerian anomalies can be categorized as developmental anomalies, which include Müllerian hypoplasia and unicornuate uterus, fusion anomalies, which include uterus didelphys and bicornuate uterus, and resorption anomalies resulting in a septate uterus.[7] Vertical and lateral fusion defects result in transverse and longitudinal vaginal septae.

Fig. 1 Illustration showing the embryological stages of development of Müllerian structures.

 

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Imaging Modalities

Transabdominal and transvaginal ultrasonography are the initial imaging modalities for evaluating female pelvic organs, including the uterus, cervix, and vagina.[8] However, 3D transvaginal ultrasound and magnetic resonance imaging (MRI) have emerged as better imaging modalities for the evaluation of Müllerian anomalies.[9] Three-dimensional ultrasound provides high-resolution real-time imaging and is useful for assessing the contour of the uterus and internal indentation of the cavity, best visualized in the midcoronal section of the uterus ([Fig. 2]).[10] MRI gives excellent soft tissue contrast with multiplanar evaluation. T2-weighted FSE MRI sequence performed with orthogonal planes of the uterus gives a definite evaluation of the anomaly with additional information about the adnexa. The 3D T2W sequence enables us to perform oblique multiplanar reformations. Fat-saturated T1W sequences can give us information regarding the retained blood products in obstructed systems, like hematometra and hematosalpinx ([Table 1]).

Fig. 2 Oblique coronal maximum intensity projection reconstructed image from 3D ultrasound shows a uterus showing (A) a normal uterine fundal contour with normal endometrial cavity and (B) a septate uterus with normal fundal contour with internal indentation of more than 1.5 cm (double arrow).

Table 1 MRI Protocol for evaluation of Müllerian anomalies

Clinical purpose	Recommended sequence and parameters	Imaging plane
General pelvic survey	T2-weighted TSE sagittal, 3 mm slices; entire pelvis	True sagittal to body axis
Uterus-oriented imaging (coronal)	T2-weighted TSE, 3 mm slices; FOV limited to pelvic organs, aligned to uterine long axis	Coronal plane aligned to the uterine long axis
Uterus-oriented imaging (axial)	T2-weighted TSE, 3 mm slices; FOV limited to pelvic organs, aligned to the uterine short axis	Axial plane aligned to the uterine short axis
High-resolution 3D sequence for MPR or anatomy	3D T2-weighted SPACE (or equivalent), thin isotropic slices (e.g., 0.9 mm); nonfat-suppressed	Acquired sagittal/axial; reformat in coronal/oblique planes
Blood product detection	T1-weighted vibe DIXON or T1 TSE (with and without fat suppression), 3 mm slices; entire pelvis	True axial to body axis
Renal and ectopic ovary evaluation	T2-weighted HASTE coronal, 6 mm slices; large FOV covering kidneys and adnexa	True coronal to body axis

Hysterosalpingography (HSG) is the primary imaging modality of evaluation for tubal patency in infertility patients, which also gives information about the uterine cavity. Abnormalities in uterine cavity configuration point toward further evaluation of suspected Müllerian anomaly[11] ([Fig. 3]). When two diverging uterine horns are seen in HSG, the wide angle of divergence (>105 degrees) raises suspicion of a bicornuate uterus. In general practice, on HSG, septate and bicornuate uteri cannot be precisely differentiated, as the diagnostic accuracy of HSG is 55%, which also depends upon the angle of X-ray during HSG.[12]

Fig. 3 Hysterosalpingography (HSG) images, (A) arcuate configuration of endometrial cavity with fundal indentation into the endometrial cavity < 1 cm, (B) septate uterus showing angle between two diverging uterine horns < 105 degrees, and (C) bicornuate uterus showing angle between two diverging uterine horns > 105 degrees and intercornual distance more than 4 cm.

 

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Classification

Müllerian anomalies are broadly divided into developmental, fusion, and resorption anomalies according to failure at a particular stage of embryological development. Different classifications are available to describe Müllerian anomalies. The most widely used classification is the American Society for Reproductive Medicine (ASRM) classification, which was first published by the American Fertility Society (AFS), now called the ASRM, in 1988.[13] This classification was user-friendly with easy descriptions and simple illustrations, and it also correlates to the prognosis with recommendations for appropriate management.[14] Main drawback of this classification is that it did not include obstruction anomalies of cervix and vagina. Another classification was published in 2013 by the group of the European Society of Human Reproduction and Embryology (ESHRE) and the European Society of Gynecological Endoscopy (EGE).[2] This classification is more comprehensive in terms of the clinical management of these anomalies. The ESHRE/EGE classification also includes significant cervical and vaginal anomalies along with uterine anomalies. It incorporates six main classes in which uterine wall thickness is taken into account and further subcategorized according to the presence of an anomaly of the cervix and vagina ([Table 2]). Cervical and vaginal anomalies can be further classified into clinically significant subcategories. Thus, it simplifies the complex anomalies of different parts (uterus, cervix, and vagina) regardless of the origin of the anomaly. ESHRE/EGE system also describes other associated non-Müllerian anomalies like involvement of the renal collecting system.

Table 2 ESHRE/ESGE classification of female genital tract anomalies

Uterine anomaly			Cervical/vaginal anomaly
Main class		Sub-class	Co-existent class
U0	Normal uterus		C0	Normal cervix
U1	Dysmorphic uterus	a) T-shaped b) Infantilis c) Others	C1	Septate cervix
U2	Septate uterus	a) Partial b) Complete	C2	Double “normal” cervix
U3	Bicorporeal uterus	a) Partial b) Complete c) Bicorporeal septate	C3	Unilateral cervical aplasia
U4	Hemi-uterus	a) With a rudimentary cavity (bi- or unilateral horn) b) Without rudimentary cavity (bi- or unilateral uterine remnants/aplasia)	C4	Cervical aplasia
U5	Aplastic	a) With a rudimentary cavity (bi- or unilateral horn) b) Without rudimentary cavity (bi- or unilateral uterine remnants/aplasia)	V0	Normal vagina
			V1	Longitudinal nonobstructing vaginal septum
			V2	Longitudinal obstructing vaginal septum
			V3	Transverse vaginal septum and/or imperforate hymen
			V4	Vaginal aplasia
U6	Unclassified malformations

Recently, in 2021, ASRM updated the classification of Müllerian anomalies published by AFS in 1988 ([Fig. 4]). In the updated classification, the categories were expanded and modified. There was an addition of three more groups, including longitudinal vaginal septum, transverse vaginal septum, and complex anomalies, in addition to Müllerian agenesis, cervical agenesis, unicornuate uterus, uterus didelphys, bicornuate uterus, and septate uterus, resulting in nine categories. Line diagrams were also updated for better understanding. It also included descriptive terms of anomalies in detail. Clear description and pictorial representation, which can be reflected in MRI images, help us in making a quick and accurate diagnosis of Müllerian anomalies. Although ASRM classification does not include any specific category for the associated non-Müllerian anomalies, it strongly recommends imaging of the urinary tract in patients with Müllerian anomalies. Uterine hypoplasia is also not included in any of the categories in the ASRM classification. Many additional classifications have been published, but the ASRM and ESHRE/EGE classification is used widely. We will be discussing the Müllerian anomalies according to the updated ASRM classification.

Fig. 4 ASRM classification of Müllerian anomalies.

 

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Müllerian Agenesis

Müllerian agenesis is a group of developmental anomalies caused by the interruption of embryological development of Müllerian ducts, leading to hypoplasia or agenesis of the uterus, cervix, and vagina. It is commonly known as Mayer–Rokitansky–Kuster–Hauser Syndrome (MRKHS). The term Müllerian agenesis is a misnomer, as many of these patients sometimes have unilateral or bilateral rudimentary horns ([Fig. 5]). The incidence of Müllerian agenesis is 1 in 4,500, and the patients usually present with primary amenorrhea at the age of menarche.[15]

Fig. 5 A 18-year-old girl with primary amenorrhea, coronal T2W MRI image (A) showing bilateral divergent rudimentary uterine horns (white block arrows), (B) showing normal bilateral ovaries (thin arrows), and (C) the uterus is not visualized in the sagittal T2W image.

Initial evaluation with ultrasound shows the absence of a uterus or the presence of a hypoplastic uterus. MRI gives us better visualization of small rudimentary uterine horns along with the evaluation of bilateral ovaries, which can be found in atypical locations due to a lack of normal descent into the pelvis. Many patients of Müllerian agenesis show bilateral or unilateral rudimentary noncommunicating uterine horns. Some of these rudimentary horns show endometrium with different thicknesses of myometrium. As ovarian function is normal, these girls have normal secondary sexual characteristics. Rudimentary horns are usually seen caudal to the ovaries.[15] MRI shows a T2 hypointense fibrotic band connecting the rudimentary uterine horn in the midline into the pelvis.[16] The extent of vaginal agenesis or hypoplasia may vary in patients with Müllerian agenesis, and in most cases, the vagina is not visualized on MRI and is replaced by fat. HSG does not help in the evaluation of these patients.

Müllerian agenesis is sometimes associated with renal agenesis and also fusion anomalies of the cervico-thoracic spine,[17] which is also known as MRKHS type II.

The primary target of treatment in Müllerian agenesis is to create a neovagina to perform normal sexual function. These include gradual vaginal dilatation to surgical correction by sigmoid vaginoplasty. MRI is very crucial for preoperative assessment.

 

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Hypoplastic Uterus

This entity is not very clearly described in the literature. It was described as category 1 in the old AFS classification without any separate illustration. In the recent updated version, it has been removed from the ASRM classification. The term hypoplastic uterus is used interchangeably with infantile uterus. It is defined as a small uterus with a maintained body: cervix ratio of 2:1, short intercornual distance of < 2 cm, and low endometrial/myometrial width.[18] Sometimes, it is described as a hypoplastic uterus where the uterus shows low T2 signal intensity and indistinct zonal anatomy, but a thin endometrial stripe can be seen[19] ([Fig. 6]).

Fig. 6 A 17-year-old girl presented with primary amenorrhea. T2W sagittal (A) and axial (B) images show a hypoplastic uterus (thick white arrows) with low T2 signal intensity and indistinct zonal anatomy; a thin endometrial stripe can be seen.

In the ESHRE Classification, it is described as a uterine anomaly in a subcategory under the main class of dysmorphic uterus (class Ib). It is described as a small uterus with a narrow uterine cavity but without lateral wall thickening, and the ratio of the uterine body and cervix is reversed, with one-third and two-thirds, respectively.[2] Many cases of Müllerian agenesis are associated with hypogonadism. Hormonal analysis is important for these patients, and if it is associated with an absent ovary, karyotyping is indicated.

Cervical Agenesis

Cervical agenesis is described in the second category in the ASRM classification. In this anomaly, only the body of the uterus is formed with functional endometrium, and the cervix is absent. Patients present with primary amenorrhea and cyclical pain. On imaging, the distended endometrial cavity is seen with nonvisualization of the cervix ([Fig. 7]). Hematosalpinx and endometriosis can also be seen due to retrograde menstruation. It can be associated with atresia of the upper two-thirds of the vagina, and the distal one-third of the vaginal canal is seen as normal.

Fig. 7 A 17-year-old girl presented with primary amenorrhea and cyclical pain. T2W MRI, sagittal (A), shows an anteverted uterus with an atretic cervix and nonvisualization of the endocervical canal and proximal two-thirds of vaginal canal. T2W axial images (B) show a distended endometrial cavity with hematometra (C); the lower one-third of the vagina is seen (thin white line).

 

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Unicornuate Uterus

In a unicornuate uterus, one Müllerian duct is normally developed, with partial or complete arrest of development of the other Müllerian duct. It is commonly associated with a rudimentary horn, which may contain an endometrium (cavitary) or may have no cavity. If a cavity is present, it can be noncommunicating or can be communicating with the endometrial cavity of the normally developed contralateral horn. ASRM classifies it into four types. Type 1: unicornuate uterus with no rudimentary horn ([Fig. 8]), type 2: unicornuate uterus with rudimentary horn with no cavity, type 3: unicornuate uterus with a distal rudimentary horn which has functional endometrium ([Fig. 9]), type 4: unicornuate uterus with rudimentary noncommunicating horn and type 5: unicornuate uterus with rudimentary horn communicating at the level of cervix. Approximately 40% of unicornuate horns are associated with renal anomalies, the most common being renal agenesis.[20] On ultrasound, the uterus is visualized off midline as an oblong structure. Rudimentary horn is visualized when it is small and atrophic. The distal bulky uterine horn is visualized on the other side of the pelvis and can be misdiagnosed as an adnexal mass.[21] On HSG, it is seen as a fusiform uterine cavity on one side of the pelvis with ipsilateral fallopian tube opacification. Sometimes, a rudimentary cavity can be seen. A noncommunicating rudimentary horn cannot be ruled out on HSG.[22] MRI shows an oblong unicornuate uterine horn directed toward one side of the pelvis, and it has normal zonal anatomy of myometrium and endometrium.[18] Rudimentary horns can be seen according to their subtype. If there is no endometrial tissue, it is seen as a hypointense structure on the contralateral side. If there is endometrial tissue present, it can be seen as a normal noncommunicating horn. The cavity can be distended with blood products after menarche when the patient presents with dysmenorrhea. These patients need surgical intervention.[23]

Fig. 8 A 24-year-old woman with primary infertility (A) hysterosalpingography image shows a fusiform uterine cavity on the left side of the pelvis with ipsilateral fallopian tube opacification, (B) T2W axial MR image of the pelvis shows a single right-sided uterine horn with no rudimentary horn on the right side. (C) Three-dimensional ultrasound image of the same patient's unicornuate uterus showing only one cornua with an oblong configuration of the endometrial cavity.

Fig. 9 Unicornuate uterus with right rudimentary functioning horn-T2W coronal MRI images. (A, B) The uterus is deviated toward the left side of the pelvis with a normal cervix, showing communication with the left horn. Noncommunicating functional right rudimentary horn (thick white arrows) is seen in a distended endometrial cavity. T2W axial and T1W fat sat axial images (C, D) show T2 Hypointense and T1 hyperintense contents, suggesting blood products.

 

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Uterus Didelphys

Uterus didelphys is a fusion anomaly that developed as a result of the complete failure of fusion of Müllerian ducts, leading to duplication of fully developed Müllerian structure, including the uterine horns, cervix, and proximal two-thirds of vagina.[24] It can present as three variants: (1) uterine didelphys with a complete longitudinal vaginal septum, (2) uterus didelphys with a partial longitudinal vaginal septum, and (3) uterus didelphys with a transverse hemivaginal septum causing ipsilateral obstruction and hematometrocolpos.[23] The first two variants are usually asymptomatic. A patient with uterus didelphys with obstructed hemivagina presents with dysmenorrhea due to obstruction and symptoms of endometriosis caused by retrograde menstrual flow.[25] This variant is also commonly associated with renal agenesis on the same side, which is also known as obstructed hemivagina and ipsilateral renal agenesis(OHVIRA; [Fig. 10]).

Fig. 10 T2W MRI axial images. (A, B) Showing two separate uterine cavities. The right-sided cavity is distended (thick arrow), and the left cavity is normal. T2W coronal image (C) of the pelvis shows a duplicated cervix and vagina with a transverse septum (thin arrow) in the right vagina with distended uterine, cervical, and vaginal cavities (hematometrocolpos). T2W coronal image of the upper abdomen shows an absent right kidney. Overall features are suggestive of obstructed hemivagina and ipsilateral renal anomaly (OHVIRA).

For HSG in these patients, we need to cannulate two cervicovaginal canals separately, one by one, which would demonstrate two separate oblong uterine cavities with normal fallopian tubes ([Fig. 11]). In the presence of a transverse hemivaginal septum, only one cervix is cannulated. It can give a misdiagnosis of a unicornuate uterus. On ultrasound, two widely divergent, separate uterine horns are seen with noncommunicating endometrial cavities and two separate cervices.[23]

Fig. 11 Hysterosalpingography for a woman with uterus didelphys. The right-sided cervix was cannulated first, (A) showing opacification of the right-sided oblong uterine cavity and fallopian tube with peritoneal spillage. (B) Showing left-sided cannulation with opacification of the left-sided uterine cavity and fallopian tube with peritoneal spillage.

MRI also shows two divergent uterine horns with two cervices ([Fig. 12]). In uterus didelphys, the zonal anatomy of the uterine horns is normal with a normal endometrial to myometrial ratio.[18] Double proximal vagina is also well visualized on MRI. In a patient with an obstructed hemivaginal septum, the obstructed uterine cavity can be seen markedly distended and filled with blood products, which appear hyperintense on T1W imaging (hematometrocolpos).

Fig. 12 Uterus didelphys T2W coronal (A), axial images (B–E), and oblique coronal images show two separate uterine cavities with divergent apices, two separate cervices (thick arrow) and vagina (thin arrow).

 

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Bicornuate Uterus

A bicornuate uterus is a fusion anomaly where incomplete or partial fusion of the Müllerian ducts results in two separate symmetrical uterine horns, which appear to be fused at the mid-part of the uterus or the lower end. It accounts for approximately 10% of the Müllerian anomalies. It is characterized by an external fundal indentation of more than 1 cm. Two uterine cavities communicate with each other, with a single cervix, called bicornuate unicollis, or there is nondegeneration of fused lower uterus and cervix, resulting in two uterine cavities and two cervixes called bicornuate bicollis. Sometimes, a longitudinal vaginal septum (approximately 25%) can be seen associated with a bicornuate uterus, where it is difficult to differentiate from a uterus didelphys.

These patients are usually asymptomatic. Sometimes, there is hematometra due to associated cervical stenosis, which is described in the ESHRE system. They need surgical intervention. In ESHRE classification, a bicornuate uterus is called a bicorporeal uterus and is defined by an external fundal indentation > 50% of the thickness of the uterine wall.

On HSG, it is seen as two symmetrical oblong uterine cavities with two fallopian tubes. The intercornual angle is more than 105 degrees, and sometimes it is difficult to differentiate a bicornuate uterus from a septate uterus on HSG.[26] On ultrasound, a deep fundal cleft is seen with two divergent uterine horns. Two separate endometrial cavities can be visualized, which can be best seen during the secretory phase due to the thick echogenic endometrium. On MRI, both the uterine horns show normal zonal anatomy. A double cervix is also seen in the case of bicornuate bicollis, giving an owl's eye appearance ([Fig. 13]). When there is associated cervical stenosis, blood products are seen in the obstructed uterine cavity as hyperintense contents. Women with a bicornuate uterus are usually asymptomatic but can present with cyclical pain due to hematometra when it is associated with cervical stenosis or vaginal septum, and it needs surgical intervention.[27]

Fig. 13 Bicornuate bicollis: T2W Axial images (A, C, D) and oblique coronal image (B) show two separate uterine cavities with external indentation > 1 cm with divergent apices with two separate cervices suggestive of bicornuate bicollis. A few Nabothian cysts can be seen in the cervices.

Septate Uterus

A septate uterus is the most common Müllerian anomaly, with a prevalence of approximately 55%.[28] It results from failure at the stage of resorption of tissue between the two Müllerian ducts. It can be partial or complete. The new ASRM classification described six variants of the septate uterus; (1) partial septate uterus, (2) arcuate uterus/normal variant, (3) complete septate uterus with duplicated cervix and longitudinal vaginal septum, (4) complete septate uterus with septate cervix and longitudinal vaginal septum, (5) complete septate uterus with duplicated cervix and obstructed hemivagina ([Fig. 14]), and (6) Roberts' uterus.

Fig. 14 A 18-year-old girl with severe dysmenorrhea, coronal T2W MRI images. (A, B) Images showing a T2 hypointense complete uterine septum (white block arrow) with a distended left-sided endometrial and vaginal cavity with a unilateral transverse vaginal septum (thin white arrow). Axial T2W MRI image shows a distended left vaginal cavity. The right-sided cavity is normally communicating with the vagina.

An arcuate uterus is the mildest form of Müllerian resorption failure and is not clinically significant. Now, it is also considered a normal variant. In an arcuate uterus, the depth of the protruding fundal myometrium into the endometrial cavity is < 1 cm with an obtuse angle > 90 degrees. Septal depth is more than 1 cm with an angle < 90 degrees, as is seen in a septate uterus.[29] Patients with a suspected septate uterus present with a history of mid-trimester miscarriage.[18] Septum can be partial or complete. It can extend up to the cervix and further into the vagina in one fourth of patients[30] ([Fig. 15]). The cervix can be divided by a septum or by duplication of the cervix, which can be seen in one variant.[23] The septum in a septate uterus can be variable in tissue composition. It can be fibrous or muscular, depending on the different proportions of fibrous and myometrial tissue.[26]

Fig. 15 Septate uterus with duplicated cervix and vagina-T2W coronal (A) and axial images (B, C) show a septate uterus (external contour < 1 cm) with two separate cervices (white solid arrows) and vagina (black solid arrows).

HSG has a debatable role in the diagnosis of a bicornuate uterus, as it cannot differentiate between a bicornuate and a septate uterus due to a lack of information about the external uterine contour. Conventionally, an angle less than 75 degrees was suggestive of a septate uterus over a bicornuate uterus,[31] but it is no longer a reliable feature due to significant overlap.

On ultrasound, we can see the septum in the midline arising from the fundus. The fibrous septum appears hypoechoic as compared with the myometrium, which is better seen in the coronal plane. The coronal plane can be acquired using 3D ultrasound, selecting the true orthogonal plane in the long axis of the uterus. On the coronal plane, a septate and a bicornuate uterus can be differentiated by drawing a line between the two uterine ostia. In a septate uterus, the external fundal contour is > 5 mm above the inter-ostial line. In a bicornuate uterus, the fundal apex is below or < 5 mm above the inter-ostial line.[28] On MRI, the evaluation of fundal contour is also an important step to differentiate a septate uterus from a bicornuate uterus.[32] Septum is better evaluated on T2W MRI. It can be as hyperintense as the myometrium, predominantly in the upper part, and the fibrous septum is hypointense, which can extend till the cervix.[33] One variant can also show a duplicated cervix. Recognizing the consistency of the septum is very important to describe it as a muscular or fibrous septum. This is because a fibrous septum can be treated with hysteroscopic septoplasty, while a muscular septum needs abdominal surgical intervention.[6]

 

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Roberts' Uterus

Roberts' uterus is a rare variant of a septate uterus with only a few case reports available. Here, the septum turns obliquely in the inferior part to join the uterine wall, obstructing one of the uterine cavities. The obstructed uterine cavity is distended and filled with blood products, causing hematometra, which further retrogradely fills the fallopian tube and adnexa, resulting in ipsilateral hematosalpinx and endometrioma.[34] [35] The other uterine cavity normally communicates with the normal cervix and vagina. Clinically, these patients present young with complaints of cyclical pain or dysmenorrhea. Ultrasound shows hematometra in the obstructed uterine cavity and normal external fundal contour, better seen with 3D ultrasound. There can be associated hematosalpinx and endometrioma also. MRI gives a better and complete evaluation of this anomaly, showing an oblique septum obstructing one of the uterine cavities. Fundal contour is normal with a normal unilateral uterine cavity. The obstructed cavity is distended and filled with T1 hyperintense contents suggestive of hematometra ([Fig. 16]). The ipsilateral fallopian tube is also filled with T1 hyperintense contents.[36] [37]

Fig. 16 Robert's uterus-T2W Axial MRI image (A) shows a T2 hypointense oblique thick uterine septum (thick white arrow) asymmetrically dividing the uterus into two hemicavities, the right cavity is normal with a normal cervix and communicating with the vagina, and a large left noncommunicating cavity. T1W axial image (B) showing left endometrial cavity distended with blood seen as T1 hyperintense content (hematometra; thin white arrow).

Management for the Roberts' uterus varies from complete excision of the obstructed uterine cavity, ablation of the functional endometrium in the obstructed uterine cavity, or excision of the septum to connect both the cavities.[34] [38] [39] Excision of the septum can be done either by a hysteroscopic or a laparoscopic approach. When there are associated findings like endometrioma and adhesions, open laparotomy is preferred.[40] [41]

 

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Vaginal Septum

Vaginal septum can be transverse or longitudinal. A transverse vaginal septum results from a vertical fusion anomaly. It is usually isolated and not associated with other Müllerian anomalies. These patients present in adolescence with primary amenorrhea and abdominal pain due to hematometrocolpos caused by a transverse vaginal septum. MRI accurately demonstrates the level of transverse vaginal septum ([Fig. 17]). Vaginal gel should be used whenever possible, as it can further tell us the thickness of the vaginal septum. A longitudinal vaginal septum is a lateral fusion anomaly, and it can be partial or complete. Its position in the vagina can be central or eccentric.[42] It can be obstructive or nonobstructive and is seen in a majority of cases with uterus didelphys (70–100%). However, septate uterus is the most common anomaly associated with longitudinal vaginal septum because of the reason that the septate uterus is the most common Müllerian anomaly overall.[43]

Fig. 17 A 15-year-old girl presented with severe cyclical pain. T2W and T1W axial (A, B) and T2W sagittal (C) and coronal images (D) show a distended uterine and vaginal cavity with blood products (hematometrocolpos) with T2 layering (thin black arrow) and a bulging T2 hypointense transverse vaginal septum (thick white arrow).

Women with a longitudinal vaginal septum are generally asymptomatic when it's nonobstructive. The patients may present with infertility when associated with other anomalies or with cyclical pain in the obstructed subtype. Longitudinal vaginal septum is seen as a hypointense band-like structure in the vagina on T2W MR sequences acquired with vaginal gel. The length of the septa can be evaluated on coronal images. The ESHRE/ESGE classification system has a subcategory for coexisting vaginal anomalies according to the orientation of the septum and whether the septum is obstructing or not.[44]

Complex Anomalies

The ninth category in ASRM classification is complex anomalies, where a combination of two or more Müllerian anomalies is seen. These include a bicornuate uterus with bilateral obstructed endometrial cavities, a uterus didelphys with communicating bilateral uterine horns and unilateral (R/L) cervicovaginal atresia, obstructed unilateral (R/L) vagina with normal ipsilateral hemiuterus and cervix with normal separate contralateral hemiuterus cervix and vagina, bicornuate uterus with (R/L) communicating tract and transverse vaginal system, and uterine isthmus agenesis. Patients with these anomalies can present with cyclical pain with dysmenorrhoea or primary amenorrhea, depending on the structural malformation. MRI gives a complete, detailed visualization of these anomalies, which further helps in the proper management planning.

 

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Accessory Cavitated Uterine Mass

Accessory cavitated uterine mass (ACUM), also known as cavitated adenomyoma, or accessory cavitated mass, is a less common type of uterine malformation where there is an extra uterine cavity that does not connect to the main uterine cavity and is not linked with other congenital uterine issues.[45] Categorized under the group of unclassified uterine malformations, the patients may have complaints like dysmenorrhea and infertility.[46] Among the various theories proposed, the most accepted one is that it comes from duplicated Müllerian tissue at the round ligament attachment.[47] ACUM has a functioning endometrium surrounded by muscle-like cells, but no connection with the uterine cavity exists. The functioning endometrium can lead to bleeding inside the cavity, leading to dysmenorrhea. Other theories include heterotopias and metaplasia.[48]

On imaging, a cavity is seen along the myometrium, near the ligamentum teres uteri, with blood products. On the ultrasound, the cavity can be characterized as a solid mass with mixed contents representing blood and degraded blood products ([Fig. 18])

Fig. 18 A 24-year-old female presenting with cyclical pain. Transvaginal USG (A) and transabdominal ultrasound (B) showed a thick-walled cystic mass in the left myometrium near the left cornua of the uterus. T2W axial (C) and T1W fat-suppressed (D) MRI images show an accessory cavity in the left uterine wall filled with blood (T1 hyperintense; white arrow). Both the cornua seen with normal features are consistent with the diagnosis of an accessory and cavitated uterine mass (ACUM).

On MRI, which is the problem-solving tool, the accessory cavitated mass shows T2 bright endometrial lining and blood products with normal uterus and ovaries.[49]

 

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Müllerian Anomalies and Endometriosis

There is a higher incidence of endometriosis in women with obstructive Müllerian anomalies, which is possibly due to retrograde menstruation. It can be seen in up to 17% of women with obstructive Müllerian anomalies.[50] Rarely can it be seen in Müllerian agenesis, which can be attributed to celomic metaplasia, when the germinal epithelium (peritoneal lining) transforms into endometrial cells.[51]

MRI is the modality of choice in these patients to evaluate endometriosis in addition to evaluation of Müllerian anomaly, as well as evidence of deep infiltrating endometriosis.[52]

 

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Conclusion

Müllerian anomalies are a wide spectrum of developmental disorders that occur due to abnormal development of Müllerian ducts during embryogenesis. These anomalies can be detected on HSG or ultrasound, but can be best evaluated using MRI and classified according to the available systems. The most widely used classification systems are the ASRM and ESHRE classifications. The new ASRM classification is more practical as it appears simpler and more user-friendly, it uses illustrations with clear descriptions rather than symbols, and gives us a whole view of the anomaly. These can sometimes be complex, unclassifiable, and are frequently associated with urinary tract anomalies. Most of the anomalies can be classified with both classifications, except the hypoplastic uterus, which is mentioned only in the ESHRE classification. Complete classification of all Müllerian anomalies is impossible, and more variations can be encountered in our day-to-day practice. Imaging has a crucial role in the workup of patients with Müllerian anomalies who present with primary amenorrhea in adolescence and with infertility and/or recurrent miscarriages in adults. While reporting the Müllerian anomaly along with description and classification of the anomaly, we should also mention the associated features like hematometra, endometriosis, and any renal or vertebral anomalies, or we can use a structured reporting template with all the checklists. ([Annex 1], available in the online version only) Accurate diagnosis of these anomalies and their associations helps in the tailored management, thereby facilitating optimization of reproductive health.

 

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Conflict of Interest

None declared.

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Publication History

Article published online:
25 September 2025