Uterine anatomical deviations are classified as normal uterus U0, dysmorphic uterus U1, septate uterus U2, bicorporeal uterus U3, hemi-uterus U4, aplastic uterus U5 and still unclassified cases U6.⁴ Each main class is further divided into sub-classes (Figure 5 and Figure 6).⁴

A uterus having an interostial straight or curved line with less than 50% of the uterine wall thickness, internal indentation in the midline fundus and a flat external contour on coronal MRI section is considered a normal uterus U0 (Figure 7).

A dysmorphic uterus is sub-classified by the shape of the uterine cavity as T-shaped, infantile and others. The other category is used to differentiate minor deformities.

This is due to an absorption defect. A uterus having a flat external contour and more than 50% internal fundal midline indentation is classified as a septate uterus. It is divided into subtypes a and b (partial [Figures 8 and 9] and complete [Figure 10] septate) by the extension of the septum above or below the internal cervical os, respectively. When two cervices are identified at clinical examination, it should not be interpreted as uterine didelphys, where no treatment is required. Imaging is mandatory.⁶ Septate uteri with two cervices (Figure 10) have been documented in the literature.^14,15,16,17 The optimum treatment is resection of the septum.¹⁸

An arcuate uterus may be classified as a partial septate uterus in the ESHRE–ESGE classification (Figure 8). Somayya et al. state that the diagnosis of septate uterus is made frequently by following the ESHRE–ESGE classification, resulting in increased hysteroscopic metroplasty.¹⁹ This could be considered as one of the limitations of the study.

Ludwin et al.²⁰ identified the median length of septum as 10.7 mm by the ESHRE–ESGE classification and as 21.1 mm by the ASRM criteria. In 36.4% of cases of septate uterus, internal fundal indentation was <1 cm by ESHRE–ESGE criteria and is usually considered as a normal uterus by ASRM. Their study further stated that the septate uterus was overdiagnosed and needed to be redefined for determining the treatment option of hysteroscopic metroplasty.²⁰ Ludwin et al. stated that using three-dimensional ultrasonography and the ASRM classification with morphometric criteria is preferable and that further study with a larger sample size should be evaluated for reliability.²¹

Patients with a complete septate uterus may have multiple associated findings. Myomas were seen in the septum and left broad ligament in one of our patients (not shown). There was an associated Gartner’s duct cyst that appeared hyperintense on the T1 sequence, extending from the fornix to the anterior vaginal wall. This patient also had a left ureterocoele with a short ureter ending blindly. She had a normal right kidney and an absent left kidney with an incidental left adrenal adenoma (Figures 3a–f). A blind-ending ureteral bud in association with renal agenesis and a ureterocoele are rarely reported.^22,23,24 Magnetic resonance imaging is the modality of choice for diagnosing an atretic ureterocele; other cross-sectional imaging modalities have limited value.²³

A bicorporeal uterus is caused by fusion defects, characterised by external indentation of more than 50% of the uterine wall thickness. This is subdivided into partial and complete (Figure 11) by the extension of the division above or up to the level of the cervix. A bicorporeal septate uterus (Class U3c) has a coexistent absorption defect in addition to the fusion defect and shows fundal indentation exceeding 150%.

Increased risk of placental abnormalities has been reported with uterine anomalies,²⁵ especially with uterus didelphys (Figure 12) and bicornuate, unicornuate and septate uteri. Uterine didelphys (bicorporeal U3b) with a vaginal septum and obstructed hemivagina resulting in haematometra along with ipsilateral renal agenesis is known as Herlyn–Werner–Wunderlich syndrome (Figure 13). The treatment for class U2 and U3c is metroplasty. It is also recommended in cases of arcuate uterus with repeated pregnancy loss.^26,27

A unilaterally formed uterus, which occurs as a result of a formation defect with an absent or incompletely formed contralateral part, is usually laterally deviated. It is sub-classified into subtypes a and b by the presence or absence (Figure 14) of a functional cavity in the contralateral component (rudimentary horn communicating or non-communicating). Laparoscopic removal of the rudimentary horn is advised if there is a functional cavity. Forty percent of hemi-uteri have associated renal anomalies.²⁸

An aplastic uterus is a formation defect with bilateral (Figure 15) or unilateral, complete or partially absent uterine cavity or rudimentary horn, with or without a cavity or uterine remnants. Presence (Figure 15) or absence of a functional cavity sub-classifies an aplastic uterus into subtypes a and b.

Fundal, body and cervix differentiation as well as endometrial–myometrial differentiation are not seen (Figure 2).

Failure of the Müllerian duct to develop leads to Müllerian agenesis. Parikh et al. state that the most common cause of primary amenorrhea is Müllerian agenesis.⁵ Uterovaginal aplasia or hypoplasia is referred to as Mayer–Rokitansky–Küster–Hauser syndrome. In type I or the typical form, there is isolated uterovaginal aplasia. Laparoscopy can identify Müllerian remnants as symmetric muscular buds and normal Fallopian tubes.²⁹ In type II (Figure 16) or the atypical form, other upper urinary tract, vertebral, cardiac and otologic malformations are seen.²⁹

Rare anomalies or combined pathologies that do not comply correctly with one of the above six groups are categorised into unclassified (Figure 17). Ectopic Müllerian tissue anomalies such as an accessory-cavitating uterine mass³⁰ and tricavitated uterus¹³ belong to this category.

Figure 18 represents a case of vaginal aplasia (V4).