Deep endometriosis (transvaginal ultrasound)
Transvaginal ultrasound (TV) for deep endometriosis is a specialized ultrasound technique used for the detection of deep endometriosis (DE). It differs from a traditional pelvic ultrasound in that the scan is extended beyond the uterus and ovaries to assess the anterior and posterior pelvic compartments and includes a dynamic assessment of organ mobility and site-specific tenderness. In 2016, the International Deep Endometriosis Analysis (IDEA) group published a consensus opinion on the anatomy that should be included and the nomenclature used to describe findings. This article summarizes these descriptions.
Indications
- known or suspected endometriosis
- chronic pelvic pain
- dysmenorrhea
- dyschezia
- dyspareunia
- subfertility
Normal ultrasound anatomy
- uterus and ovaries (as for a routine pelvic ultrasound)
Anterior compartment
- bladder
- will require a small amount of urine within to adequately assess the walls, which may be difficult as an empty bladder is required to optimize the TV ultrasound
- should appear uniformly thin-walled
- vesicouterine space
- the potential space located between the anterior uterus and the poster urinary bladder - in real-time these two structures should be seen to move apart with the sliding sign
- up to one-third of women with a previous Cesarean section will have adhesions in this location
- ureters: hypoechoic tubular structures which are seen to vermiculate (i.e. contract to move urine from the kidneys to the bladder) in real-time
Posterior compartment
- rectosigmoid colon: the colon walls appear sonographically as an alternating hyper/hypoechoic layered structure
- pouch of Douglas
- the use of the sliding sign should reveal the pouch of Douglas to be open
- a small-to-moderate amount of physiological free fluid can be seen in the pouch of Douglas; this can be used as an acoustic window to visualize small (even superficial) lesions within the posterior compartment
- uterosacral ligaments: the normal uterosacral ligaments are seen as a thin hyperechoic line or may not be seen at all. The midline joining point of the left and right uterosacral ligaments is the torus uterinus
- posterior vaginal wall / posterior vaginal fornix: thin, hypoechoic line directly posterior to the face of the transducer
- rectovaginal septum: thin, hyperechoic line between the hypoechoic posterior vaginal wall and the rectum
Technique
Pelvic ultrasound of endometriosis is an extension of the routine pelvic ultrasound. It should be performed in four steps as proposed by the IDEA consensus statement :
Assessment of the uterus and ovaries
This is done as per a routine pelvic ultrasound. Specific attention should be paid to the presence of adenomyosis or ovarian endometrioma. An anteverted/ retroflexed uterus has a strong association with adhesions in the posterior compartment .
Assessment for ‘soft markers’
By applying gentle pressure with the transducer and the sonographers freehand on the abdomen, the ovaries can be seen to move in real-time. If mobility is reduced or not present, this can suggest adhesions.
The sonographer should take note of any sites which are tender when gentle pressure is applied with the transducer as this may indicate superficial disease.
Assessment of the sliding sign
The sliding sign is considered negative (ie. the pouch of Douglas is obliterated) if the structures do not move freely.
Assessment of the anterior and posterior compartments
- bladder
- the bladder walls are difficult to assess without urine in the bladder
- a full bladder, however, will hinder the view of other structures transvaginally
- with the transducer in the anterior fornix, the probe is moved side to side, and cranial-caudal to assess the walls for nodularity
- if needed, the bladder can be assessed fully distended with a transabdominal scan
- vesicouterine space: similar to the sliding sign, with the transducer in the anterior fornix and the sonographers free hand placed over the suprapubic region, the posterior bladder should slide freely over the anterior uterine wall with pressure from both the transducer and the hand
- ureters
- with the transducer in the anterior fornix, move laterally to visualize the vesicoureteric junction (VUJ) at the bladder base and rotate slightly until the distal ureter can be seen running parallel to the bladder. The ureter can then be followed high into the pelvis
- in real-time, the ureters should be seen to vermiculate
- rectosigmoid colon
- with the transducer at the opening of the vagina, trace the lower rectum until the transducer is in the posterior vaginal fornix; continue to follow the longitudinal plane of the rectosigmoid colon until it can no longer be visualized (usually past the level of the uterine fundus and left ovary); repeat in the transverse plane
- due to the normal twisting of the bowel, constant fanning and rotating of the transducer is essential to keep the bowel walls in view
- pouch of Douglas: assess using the sliding sign - the posterior uterus and the anterior rectum should move apart freely with transducer pressure
- uterosacral ligaments
- with the transducer in the posterior fornix, move the transducer laterally and rotate slightly (30-45 degrees); the uterosacral ligaments will be seen in long axis as a thin white line immediately deep to the vaginal wall
- if the white line does not appear crisp (but heterogeneous in nature), the transducer is too lateral and imaging the parametrium
- in the transverse plane, within the transducer in the anterior vaginal fornix, the uterosacral ligaments can be seen immediately lateral to the cervix as the level of the internal os as they travel inferomedial to join at the torus uterinus
- when endometriosis is present, the uterosacral ligaments may appear thicker due to a thickening of the surrounding fat; a hypoechoic nodule may be present
- posterior vaginal wall / posterior vaginal fornix: the walls of the lower vagina are best assessed with the rectovaginal septum
- rectovaginal septum: endometriosis of the rectovaginal septum is rare, it is best assessed whilst removing the transducer from the vaginal at the conclusion of the scan, gently fanning side to side to assess for nodules
Practical points
- the scan should include an assessment of the kidneys if the ureters are dilated or extensive pelvic endometriosis is present
- when endometriosis is present, dynamic assessment and pressure in the posterior compartment can be painful, as such, a throughout explanation of the procedure and frequent checking on the patient's comfort are a must
- mobility of the organs can be affected by the position of the ovaries, body habitus and pain tolerance; care should be taken when labeling an ovary immobile to insure this is pathological rather than technical
- prior (or current) pelvic infection or pelvis surgery can cause adhesions
- visualization of the bowel may be hindered by large pelvic masses (e.g. fibroids or endometriomas)
- as the structures of the posterior compartment require little scanning depth, and the pathology assessed for is small, the highest frequency possible on the transvaginal transducer should be sought.
- if using a three-dimensional mechanical transvaginal transducer, the steering or tilt function can be employed to assess places otherwise difficult to access comfortably (e.g. distal rectum)
- extensive deep endometriosis can cause significant distortion of the normal pelvic anatomy; if the exact location of a nodule cannot be definitively determined, describing as being located in the "anterior compartment" or the "posterior compartment" is most clinically helpful
See also
