A pictorial MRI pelvis 'journey' will demonstrate the early and late appearances of endometriosis and its commonly associated complications.
Cases illustrate the typical appearances followed by the malignant effects it can cause secondary to scarring and fibrosis; premalignant and malignant ovarian lesions as well as complications following repeated operations.
Ultrasound is the first-line imaging technique for the evaluation of endometriosis.
It is usually limited to the identification of endometriosis affecting the uterus and ovaries.
It has a poor sensitivity for disease elsewhere,
particularly bowel lesions.
The classical appearances of an endometrioma in the ovary are shown (Fig 1).
A large hypoechoic and homoegenous cystic lesion with low-level echoes and no vascularity on colour flow doppler.
These are often known as 'chocolate' cysts due to their dark appearance and thick fluid on laparoscopy.
MRI is very useful in evaluating and following up endometriosis.
Typically,
endometriomas appear homogenous with high signal on T1 sequences and homogenous or heterogenous with low signal on T2 sequences depending on the age of the blood products.
Sometimes called 'T2 shading'. (Fig 2)
Ultrasound can also be used to evaluate the uterus and the presence of adenomyosis.
This is usually seen as thickening of the myometrium due to the presence of ectopic endometrial tissue.
Cystic changes may also be noted (Fig 3).
Notice the same patient with MR imaging also demonstrating gross thickening of the posterior myometrium relative to the anterior myometrium and T2 cystic changes (Fig 4).
If the endometriomas increase in size they may meet in the midline,
known as 'kissing ovaries' and synonomous for pelvic endometriosis.
This is caused by adhesions to the posterior wall of the uterus and to each other.
It may be noted on ultrasound or more commonly on MRI (Fig 5)
Classical appearances of endometriosis also include dilated fallopian tubes.
The presence of high signal on T1 and fat suppressed T1 sequences is very suggestive of endometriosis causing a haematosalpinx (Fig 6).
Patients may also demonstrate a hydrosalpinx.
The latter is thought secondary to endometrial serosal implants forming peritubal adhesions and then obstruction.
Solid endometrial implants are typically seen along the anterior and posterior surfaces of the uterus.
Common sites include rectovaginal nodules seen on the posterior surface of the vagina (Fig 7).
This causes marked dyspareunia and can frequently be palpated on clinical examination.
Adhesions caused by endometriosis frequently cause tethering of the ovaries to the uterus and bowel loops to the ovaries and uterus (Fig 8).
If severe,
this can lead to a frozen pelvis.
Adhesions frequently extend along peritoneal reflections and the uterosacral ligaments (Fig 9 and 10).
Serosal disease on the bowel surface itself causes scarring leading to puckering or a 'mushroom cap' appearance (Fig 11).
Disease may exend through the muscle wall and into the mucosa.
The rectosigmoid colon is the most common site of disease.
Symptoms can be confused with inflammatory bowel disease due to pain and PR bleeding.
On colonoscopy,
endometrial deposits may be noted in addtion to strictures,
adhesions and fibrosis.
Less frequent sites of disease include the urinary tract.
The bladder is the most commonly affected and usually serosal deposits are seen on the anterior and superior surface.
These can extend into the muscle wall and mucosa.
The disease can also cause marked hydronephrosis secondary to fibrosis within the pelvis.
It is very important to review the localising images as this may be the only visualisation of the ureters.
Note the sagittal localising image demonstrating marked right hydronephrosis (Fig12).
Ectopic sites of disease include surface deposits in the peritoneum,
bowel and abdominal organs.
When a patient complains of monthly abdominal pain linked to menstruation it is important to include fat suppressed T1 images through the abdomen and preferably scan the patient during menstruation.
This allows easier identification of focal solid deposits seen here in the right lateral liver surface and posterior hemidiaphragm (Fig 13).
Abdominal wall endometriosis is typically found within a surgical scar and presumed secondary to iatrogenic transfer of endometrial cells eg.
C- section or episiotomy.
C-section implants are seen most commonly and may occur in the rectus muscles or subcutaneous tissues.
The disease is usually clinically palpable and the patient gives a history of pain during menstruation.
On fat suppressed T1 sequences the disease shows high signal as expected (Fig 14).
Endometriosis over many years causes marked fibrosis due to the repetitive cycles of bleeding,
inflammation,
scarring and adhesions.
These may be more severe than those seen in patients treated for gynaecological cancers with surgery and radiotherapy.
In these patients,
comparison should be sought with prior imaging.
(Fig 15).
There is an increased risk of developing endometriosis in patients with a uterine abnormality.
This is seen in patients with both obstructive and non obstructive malformations (Fig 16)
Association with malignancy is seen with endometriosis.
The disease increases risk for clear cell and endometrioid carcinoma.
Patients with endometriosis are 4.2 x more likely to develop ovarian cancer (2).
All ovarian endometriomas should be reviewed for features suggestive of cancer such as mural nodularity,
solid lesions and rapid growth.
(Fig 17 and 18).