Endometriosis is a common pathology, affecting about 10% among women of reproductive age. MRI is the best imaging modality for presurgical mapping of pelvic endometriosis and for follow-up after medical or surgical treatment. In 2021, the Enzian classification was published, proposing a new comprehensive classification system of endometriosis, combining a complete staging of deep infiltrative endometriosis with the evaluation of peritoneal/ovarian/tubal localizations and the presence of adenomyosis, showing a good correlation between pre-operative MRI features and intraoperative findings in patients with endometriosis.
Enzian Classification System Overview
The Enzian classification is a system that classifies endometriosis based on the following main characteristics:
- Stage of disease: It evaluates the anatomical distribution and severity of endometriotic lesions.
- Location: The classification divides endometriosis into specific anatomical compartments of the pelvis, including the ovaries, posterior and anterior compartments, and the peritoneum.
- Types of lesions: It categorizes lesions into ovarian endometriomas, deep infiltrating endometriosis (DIE), and superficial peritoneal endometriosis.
MRI and Enzian Classification Correlation
The correlation between MRI findings and the Enzian classification provides a detailed mapping of endometriosis severity and extent. MRI plays a key role in:
O- Endometriomas: applicability of #Enzian classification to the MRI: yes
- characterized by low signal intensity on T2-weighted images and high signal intensity on T1-weighted images
- may present with a “shading” or “fluid-fluid level” sign, indicating the presence of blood in various stages of resolution
- includes all the endometriomas and infiltrating ovarian surface foci > 5 mm and it is a sum of all diameters
- there are 3 different stages:
O1 Σ < 3 cm - are usually not treated surgically
O2 Σ 3–7 cm - often treated surgically
O3 Σ > 7 cm - treated surgically
P- Peritoneum: partial applicability of #Enzian classification to the MRI
- peritoneal endometriotic implants can be visualized when present in the uterine wall and/ or on ovaries surface like small, nodular lesions, sometimes hyperintense T1fs spots, or areas of nodular thickening of the peritoneum
- superficial peritoneal implants with a sub-peritoneal invasion of less than 5 mm are considered
- they are categorized based on the sum of all maximal diameters as:
P1 Σ < 3 cm
P2 Σ 3–7 cm
P3 Σ > 7 cm
T - Tubo-ovarian condition
- in tubo-ovarian condition we can speak about adhesions, mobility of the ovaries, fallopian tubes and tubal patency
- Adhesions: partial applicability of #Enzian classification to the MRI
- adhesions are seen as spiculated low signal intensity strands extending between the organs on both T1W and T2W images
- can be in multiple locations: tubo-ovarian, pelvic side wall, uterus, uterosacral ligaments (USL) and bowel
- are divided into three categories:
T1: adhesions between the ovary and pelvic side wall ± tubo-ovarian adhesions
T2: T1 + adhesions between the ovary and the uterus/ isolated adhesions between the adnexa and uterus
T3: T2 + adhesions to the USL and/or bowel/ isolated adhesions between the adnexa and the USL and/or bowel
- Mobility of the ovaries and fallopian tubes: no applicability of #Enzian classification to MRI
- Tubal patency: potential applicability of #Enzian classification to the MRI by MRI-hysterosalpingography (MR-HSG) – not widely accepted
DIE - Deep Infiltrating Endometriosis -applicability of #Enzian classification to the MRI: yes
- hypointense areas on T2-weighted images
- may involve the uterosacral ligaments, rectum, bladder, and bowel
- may lead to distortion and adherence of adjacent structures
- in cases of multifocal lesions, the sum of the total length involved should be measured.DIE is partited in 3 compartiments, each of them subdivided into other 3 subcategories as it follows:
Compartment A: rectovaginal space, vagina, retrocervical area (maximal diameter measured on the sagittal T2W images) -in case of multiple involvement: the maximum diameter of the whole involvement
A1 = < 1 cm
A2 = 1–3 cm
A3 = > 3 cm
Compartment B: uterosacral ligaments, cardinal ligaments, pelvic side wall (maximal diameter measured on the axial T2W images small field of view)
B1 = < 1 cm
B2 = 1–3 cm
B3 = > 3 cm
Compartment C: rectum/ extension of lesions in the anterior wall of the rectum (maximal diameter of the lesion is measured in the sagittal T2W images)
C1 = < 1 cm
C2 = 1–3 cm
C3 = > 3 cm
FA- Adenomyosis - applicability of #Enzian classification to the MRI: yes- is characterised by the presence of ectopic endometrial glands and stroma within the myometrium, whose involvement can be focal or diffuse
- a region of adenomyosis appears as an ill-defined ovoid/diffuse region of thickening, often with small high T2 signal regions representing small areas of cystic change
- thickening of the myometrium-endometrium junction line greater than 12 mm
- the inner third of the myometrium might be affected in the case of internal adenomyosis, or the outer two-thirds in the case of external adenomyosis
FB- Bladder- applicability of #Enzian classification to the MRI: yes
- endometriotic tissue invading the detrusor muscle of the bladder, sometimes protruding into the lumen, with invasion of the mucosal layer
- peritoneal surface of the bladder are considered peritoneal endometriosis
FI- Intestinum- applicability of #Enzian classification to the MRI: yes
- lesions cranial to the rectosigmoid junction (above 16 cm from the annal verge) – sigmoid, transverse colon, cecum, appendix and small bowel
FU- Ureter- applicability of #Enzian classification to the MRI: yes
- the ureteral involvement and hydronephrosis are classified as FU compartment
F (…) - applicability of #Enzian classification to the MRI: yes
- lesions on other locations, such as the abdominal wall, pleural, diaphragm and nerve, are annotated as F (anatomical site) directly in brackets.
Paired organ compartments, including compartment O, T and B, were assessed, and documented separately for each side (left/right).