Ultrasound mapping of disease´s extent and location enables optimal planning of patient care, supports justification for non-surgical intervention and, when necessary, for the decision to refer patients to a tertiary laparoscopy center while discussing surgical risks and complications of surgery. 

Typical locations for DE implants

In most patients, DE manifests in the posterior compartment, including the uterosacral ligaments (USL’s), rectum and rectosigmoid junction.

Fig 1: Schematich ilustrastion of sagittal section of female pelvis and typical DE implant locations. DE implants can be found in the rectovaginal septum (1), the retrocervical space (2), including the USL’s and torus uterinus, the rectosigmoid colon (3), the vesicouterine space (4), involving bladder and ureters, the uterine serosa (5), ovaries (6),and vagina (7). Adapted from AnatomyTOOL. (n.d.). Leiden Drawing: Sagittal Section of the Female Pelvis with Peritoneum.

Specific maneuvers for evaluation of DE implants 

• Evaluation of the retrocervical space

During retrocervical area scanning, it is essential to evaluate for abnormal hypoechoic areas, particularly in the torus uterinus, retrocervical space, USL’s and anterior wall of the rectum. 

For the longitudinal evaluation, the entirety of the cervix, uterus, and lateral tissues should be included, as far as possible, from right to left. For the transverse evaluation, the uterine fundus should be included, extending as far as possible through the cervix.

• In an anteverted uterus, the area of interest is posterior to the cervix and uterus, located approximately 4–5 cm deep to the cervix.
  

  Fig 2: Anterverted Uterus Structures. The uterus is anteverted and normal in size. The area of interest is a few centimeters posterior of the transducer, highlited in red dots. The posterior compartment appears normal, with no evidence of endometriotic nodules or adhesions in both USLs.
• In a retroverted uterus the area of interest of the torus uterinus and the ULS’s is in the near field just under the transducer.
  

  Fig 3: Normal Retroverted Uterus. The uterus is retroverted and normal in size. The area of interest of the torus uterinus and the USL is in the near field, just under the transducer, in both the longitudinal (A) and transverse (B) axis, as indicated in the red dotted areas.

Normal ULS's have a smooth and echogenic, band-like structures on ultrasound, angling laterally from their attachment to the uterus in the midline near the cervicouterine junction (torus uterinus).

• Uterine and ovarian relative positioning

Deep endometriosis can cause adhesions and fibrosis, leading to fixed or altered positioning of the uterus and ovaries. 

• • Normal Position
    • Uterus: Anteverted or retroverted, with free mobility.
    • Ovaries: Located laterally to the uterus, along the pelvic sidewalls. Direct pressure with the transducer can be applied in order to verify there is some degree of mobility. 

• • Abnormal Position in Endometriosis
    • Fixed Uterus: The uterus may lose its normal mobility due to endometriosis lesions in the posterior compartment.
    • Fixed Retroflexed Uterus: Deep endometriosis can cause the uterus to become fixed in a sharply retroflexed position due to adhesions pulling it backwards.

• • • Kissing Ovaries sign: in severe cases, the ovaries may adhere to each other posteriorly to the the uterus. 
    • Fixed Ovaries: ovaries may become adherent to the uterus, pelvic wall or other structures due to adhesions.

• Uterine sliding sign

• • The uterine sliding sign is a diagnostic test, which involves determining whether the anterior wall of the rectum slides freely across the posterior aspect of the cervix, posterior vaginal wall (for an anteverted uterus) or uterine fundus (for a retroverted uterus). 

• • Immobility of the rectum against the uterus and posterior vaginal fornix is considered as a negative sliding sign, which is a hard marker for rectal or sigmoid anterior wall infiltration by endometriotic adhesions, as well as pouch of Douglas obliteration. 
  • To assess mobility between the uterus and posterior structures, the examiner should apply gentle pressure with the probe and/or their free hand on the abdomen to move the uterus and adjacent organs. 

• Evaluation of the anterior compartment
• The anterior compartment includes the bladder, ureters, and anterior uterine wall, which are potential sites for endometriotic lesions.
• The patient's bladder shoud be in moderately distended to improve visualization of the anterior compartment.

Atlas of ultrasonographic images concerning endometriosis:

• Ovarian Endometrioma

• • Typical ovarian endometrioma: benign, cystic unilocular or multilocular (less than 5 locules) formation, with internal homogeneous low-level echogenic (ground glass) echoes. Usually poorly vascularised on color-Doppler analysys.
    

    Fig 4: Ovarian Endometrioma. Longitudinal (A) and transverse (B) scans of the left adnexa region demonstrate a well-defined, with smooth and regular walls, oval cystic lesion within the ovary, measuring 25x23x27 mm. The lesion demonstrates homogeneous low-level internal echoes - ground-glass appearance. No internal vascularity is detected on Doppler-color (C), consistent with the absence of solid components or papillary projections.
    

    Fig 5: In the right ovary (A), a well-defined, round cystic lesion is identified, measuring 23 x 17 x 25 mm. The lesion demonstrates homogeneous low-level internal echoes, characteristic of an endometrioma (chocolate cyst). The cyst wall is smooth and regular, with no evidence of wall nodularity or solid components. No internal vascularity is detected on Doppler imaging. In the left ovary (B), a cystic structure with no evidence of solid components is noted, measuring 16 x 20 x 23 mm. The lesion exhibits a ring of fire appearance on Doppler-color, indicative of a physiological corpus luteum.
  • An atypical ovarian endometrioma differs from typical endometriomas due to heterogeneous internal echoes, thick or irregular septations / walls, echogenic mural nodules, papillary projections, hypervascularity on Doppler, larger size (>10 cm) and/or irregular shape.
    

    Fig 6: Atypical Ovarian Endometrioma. Longitudinal (A) and transverse (B) scans of the left adnexa region demonstrate a large left unilocular ovarian cystic formation measuring 62x4x66 mm (WxHXL) with ground-glass echogenicity. The lesion’s walls are externally regular, however with internal irregular margins (C) due to solid papillary avascular (D) projections. The enumerated findings are consistent with an atypical endometrioma.

• Uterine serosa DE

• • Uterine implants associated with DE present as ill-defined hypoechoic areas on ultrasound, typically growing from the outside-to-inside, starting from the outer myometrial serosa and extending inward.

• • May contain internal echogenic foci and cystic regions - hallmark features of DE. 

• • Differential diagnosis from Adenomyosis: adenomyosis progresses from the endometrial-myometrial junction outward toward the uterine serosa.

• Retrocervical DE

• • On ultrasound, retrocervical DE typically appears as hypoechoic lesions,  with smooth, irregular, or spiculated margins.
    

    Fig 8: Endometriotic implant in the retrocervical space. The left uterosacral ligament (USL) (A and B) shows a hypoechoic solid nodule with irregular margins, measuring 12 x 8 x 8 mm, extending to the uterine torus (circles). The right uterosacral ligament (USL) (C and D) appears free of lesions.
  • Involvement of Key Structures:
    • The torus uterinus, the midline insertion site of the USL's, is often affected. 
    • Adhesions to one or both ovaries are common.
      

      Fig 9: Adherent structures secondary to endometriotic nodule. Presence of an hypoechoic spiculated retrocervical endometriotic nodule (arrow) measuring 9x3mm leading to the formation od adherences – left ovary, uterus and intestinal loop. Note as the nodule acts as a focal point causing fixation and traction of the adjacent organs. Furthermore, it was painful upon pressure from the endovaginal probe, likely corresponding to an endometriotic nodule and the mobility was restricted. The cystic lesion in the left ovary corresponds to a luteal body.

• Bladder Endometriosis:

• • Isoechoic or hypoechoic masses, with smooth or irregular borders on imaging, often invading the detrusor muscle or the ureters (causing hydronefrosis or strictures).
  • Endometriosis in the vesicouterine space may also be observed, often associated with bladder lesions.
    

    Fig 10: Anterior Compartment Deep endometriosis. A hypoechoic nodule with irregular margins is identified in the vesicouterine space invading the posterior wall of the bladder, measuring 8 x 9 mm. The vesicouterine space showed reduced mobility (loss of sliding sign), suggesting adhesions due to endometriosis.
  • These lesions may or may not protrude into the bladder lumen, and can be cystoscopically occult.

• Rectosigmoid endometriosis
• Solid, markedly hypoechoic elliptical, C-shaped, or Ω-shaped thickenings with tapering ends of the bowel wall (typically anteriorly), causing parietal distortion toward the retrocervical lesion.
  

  Fig 11: Indian Headdress Sign. The involvement of the rectosigmoid colon should be suspected when a nodule (thick arrow) is observed accompanied by thin, hyperechoic, linear echoes (thin arrows) radiating from the center of the mass. This distinctive pattern is referred to as the "Indian Headdress Sign".
  

  Fig 12: Rectosigmoid colon and right USL endometriosis. Transverse (A) and longitudinal (B) transvaginal ultrasound scans demonstrate a spiculated hypoechoic nodule located in the anterior wall of the rectum, 9 cm above the anal margin. It appears to invade the deep muscular layer (C, red dotted rectangle) and extend into the right USL (D, red arrow).
    
• The depth of invasion can be predicted based on lesional thickness and the obliteration of anatomic interfaces.

• Vaginal endometriosis

• • Most commonly occurs in the posterior apex of the vagina as a moderately hypoechoic lesion and an echotexture similar to that of retrocervical DE.
    

    Fig 13: Recto-Vaginal Septum endometriosis. Two different cases of infiltration at the level of the vaginal fornix. In (A) a hypoechoic solid lesion (arrow) measuring approximately 17 x 16 mm is identified. In (B), a solid nodular hypoechoic formation with more identifiable margins, both consistent with vaginal endometriosis, located within the rectovaginal septum.
  • Is often confluent with USL DE and adjacent rectal implants.
    

    Fig 14: At the level of the vaginal fornix (A, B), an isoechoic formation without a cleavage plane with the posterior wall of the cervix (rectangule) is identified, measuring 71x37x39 mm, suggesting an endometriotic lesion with extension to the RVS, bilateral USL and the uterine torus. Adjacent to this lesion, at the level of the anterior rectal wall (C, D), a large hypoechoic, spiculated nodule is identified, suggestive of an endometriotic nodule measuring 57x22x38 mm, with infiltration of the intestinal mucosa. These lesions restrict the movement of the probe, preventing visualization of the anterior rectal wall beyond 8-10 cm from the anal margin.
• Fixed retroflexed uterus
  • A retroflexed uterus that remains fixed, even with direct transducer pressure due to endometriotic adhesions between the cervix and uterus or the rectum and uterine fundus.
    

    Fig 15: The uterus exhibits a question mark configuration, characterized by marked retroflexion - the fundus is curved posteriorly - with the cervix positioned anteriorly. The question mark uterine shape is consistent with severe adhesions secondary to endometriosis, leading to retroflexion and fixation of the uterus.
• Bowel Tethering to the Posterior Uterus without direct visualization of DE
  

  Fig 16: Intestinal Loop Adherent to the Posterior Uterus. The posterior body of the uterus is adherent to an intestinal loop, likely the rectosigmoid colon, with no plane of separation visible and without direct visualization of an endometrioma. The adherent intestinal loop showed reduced mobility during dynamic assessment, suggesting fibrotic adhesions secondary to endometriosis.
• Retropositioned or Kissing Ovaries in DE
  • Key imaging feature of advanced endometriosis, even without endometriomas.
    

    Fig 17: Kissing Ovaries. The ovaries are positioned in close proximity to each other in the midline posterior cul-de-sac, a configuration referred to as "kissing ovaries." Both ovaries showed reduced mobility on dynamic assessment, compatible to pelvic adhesions secondary to endometriosis. No evidence of endometriomas or other cystic lesions is observed within the ovaries.
  • Further evaluation using direct probe pressure or the uterine sliding maneuver can be done to confirm.
• Adenomyosis 
  • Adenomyosis is frequently observed in patients with deep endometriosis.
    

    Fig 18: Uterine Adenomyosis. A heterogeneous echostructure is observed within the myometrium, containing millimetric cystic areas and poorly defined borders, measuring 23 x 18 x 23 mm, with translesional vascularization.
  • Establishing differential diagnosis between both entities is crucial, as these conditions, though related, have distinct pathological features, clinical implications, and treatment approaches.
    

    Table 1: Differential diagnosis between adenomyosis and deep endometriosis of the uterine serosa.
• Hydrosalpinx and Hematosalpinx 
  • Fluid-filled or blood-filled dilated fallopian tube, respectively, often due to obstruction, which may be seen in endometriosis but are nonspecific findings.
    

    Fig 19: Hydrosalpinx. Transverse (A) and longitudinal (B) scans demonstrate the left ovary adherent to the uterine wall and increased in size due to an anechoic unilocular simple cystic formation, suggestive of a functional simple cyst. On images C and D a cystic and elongated anechoic structure wrapping around and adherent to the left ovary, suggesting hydrosalpinx.
    

    Table 2: Hydrosalpinx vs. Hematosalpinx: Key Differences