Anatomy of Endometriosis and Adenomyosis

Ashley Davidoff MD

Endometriosis is a disease  caused by misplaced or ectopic endometrial tissues located beyond the uterus most commonly resulting in pain at the time of menstruation. The ectopic endometrial tissue is controlled by the oestrogen and progesterone cycles.  The ectopic tissue  bleeds at the time of menstruation and causes pain.  Since neither the ectopic endometrium nor the blood can be extruded from the body,  recurrent bleeding eventually results in  scar formation which may cause non cyclical chronic pain.

Chronic Pelvic Pain is Unbearable

Endometriosis and adenomyosis cause horrific pain.  For some the pain  may only occur during the menstrual cycle but for others it can  be constant, day and night, excruciating in nature, invading every aspect of normal daily life .  Pain is a common symptom defined by the International Association for the Study of Pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.” This statement characterizes the evolved nature of pain as a warning system and feedback mechanism that influences how we adapt to our environment. However, pain at its core it is  suffering and its persistence can be insufferable for people and diagnostically problematic to those who care for  the sick, as well being  a burdensome cost to society.  

The cause of endometriosis is not truly known.  Long standing hypotheses include spillage of endometrial tissue into the peritoneal cavity via the fallopian tubes or transvascular spread to remote areas .  More recent hypotheses include spillage of stem cells during embryonic development, metaplasia of coelomic epithelium, abnormal vasculogenesis, and environmental factors

Endometriosis occurs in 5-10% of women. When endometrial tissue is located outside of the uterus, it can cause pelvic and back pain, as well as pain with sexual intercourse (dyspareunia). It is also associated with infertility by  distorting  anatomy, (for example Fallopian tube adhesions) , or physiological changes that result in altered immune and hormonal environments with consequent impairment of ovum implantation .

From a structural standpoint, endometriosis most commonly affects the ovaries and Fallopian tubes but can affect any of the pelvic organs including the peritoneal cavity,  bladder, ureters, bowel, broad ligaments, uterosacral ligaments, cul de sac  and even the nerves. Implants range in size from small microscopic implants, but are are commonly about 1-2cm.

The Intraperitoneal Aspect of the Pelvic Cavity

The peritoneal cavity or coelomic cavity is a large cell lined  space via which almost all the abdominal organs are connected .  It may be considered the suburban space around which the houses of the town are positioned.  The ova are released from the ovary into the peritoneal space, but they are quickly directed by the fimbriae into the Fallopian tubes.

Endometriomas 

Endometriomas are large hemorrhagic cysts that occur on the ovary and  may be up to to 20cms in size.  They are usually  round in shape, much like a large blood blister after they have bled.  The nodules can be red-blue to yellow-brown in color, (chocolate cysts) and occur just below the serosa of the organ to which they are attached.  As the lesions undergo recurrent hemorrhage, they can become associated with fibrosis as stated.  Rarely they may be associated with malignant transformation.(<1%).

MRI of an Endometrioma

A T2 weighted image of the pelvis (left) with an overlay of colors on the right shows a 10cms endometrioma (overlaid in red) with internal debris better appreciated in the left image.  The large ‘chocolate cyst” lies above the uterus (pink) and compresses the bladder (yellow)

MRI has a 90% specificity and 90% sensitivity for endometriomas.  On T1 weighted images the endometriomas may be bright and do not lose signal on fat suppressed sequences.  Heterogeneity is due to the presence of degraded products.  Septations may also be present.  Both these features are present in the above image . On T2 weighted sequences “shading”   is caused by repeated episodes of bleeding reflecting  hemorrhagic contents in various stages of degradation.  The wall of the endometrioma may contain hemosiderin which leads to a loss of signal on the T2 weighted sequence.

Unusual Locations

Endometriosis is rarely can be more far reaching and may involve the kidneys, brain, diaphragm, and pleura.  When it involves the diaphragm or pleura, shoulder pain may be associated with the entity.  Pleural disease can cause life threatening catamenial pneumothorax induced by the menstrual cycle .

Endometriosis on the Bladder

A CT scan through the pelvis (left) shows an endometriotic implant  on the bladder wall.  The image on the right shows the endometriotic implant overlaid in maroon on the right anterior surface of the bladder (yellow overlay).  The implant measures about 1.1cms.  The fornix of the vagina is overlaid in pink.  Most peritoneal implants are too small to be visualized by conventional imaging and require laparoscopic evaluation for diagnosis.

Endometriosis in the Skin of the Groin

A CT scan through the pelvis (left) shows an endometriotic implant  in the subcutaneous region of the skin in the left inguinal region (image a, circled).  The region is magnified in image b and the endometriotic deposit is labelled “e” with maroon overlay.  An ultrasound of the left groin(c)  shows the implanted endometriosis (black) medial to the artery (red) and vein (blue).  In image d, the region of endometriosis (e) is overlaid in maroon.

Clinically the entity more commonly occurs in nulliparous women and the degree of pain is variable.  As endometrial tissue, it is responsive to the cyclical hormonal fluxes, and thus may  bleed in response to hormonal changes. Pain commonly occurs at the time of the menses.  The volume of ectopic endometrial tissue does not correlate with the severity of the pain, but rather with the depth of infiltration into the tissue, or the degree of distension that might occur.  The pain is usually recurring and commonly but not necessarily occurs during the menses. With induction of fibrosis, pain may be caused by other structural changes that are unrelated to the menses.

Diagnosis is suspected clinically and confirmed by ultrasound. When a woman in the reproductive phase of her life presents with pain, the imaging study of choice is a pelvic ultrasound.  Hemorrhage into evolving follicles is a common cause of pelvic pain and these could be also quite large.  This entity has to be differentiated from an endometrioma that has a characteristic ultrasonographic appearance shown below

Endometrioma on Ultrasound

A transvaginal ultrasound of the adnexa shows an endometrioma with characteristic low level echoes reminiscent of the texture of the testes on ultrasound.  The image on the right is an overlay in a biloculate cyst.  Some through transmission is present. 

Chocolate Cyst  on US and CT

A 25 year old female presents with painful menses. The ultrasound shows a cystic mass in the pelvis with a large amount of debris in the cystic cavity consistent with a chocolate cyst (a).  Image b is an overlay showing the fine granular appearance of the sediment.  When the patient is in decubitus position (c) , the sediment settles to the dependant portions with a clear supernatant.  Image (d) is a CT scan of the same patient, showing a non specific cyst in the left ovary. In this instance CT has little diagnostic value in the characterization of the abnormality other than localising a large cyst, and excluding other causes for the pain.  Although the appearance on the ultrasound is consistent with endometriosis, a hemorrhagic cysts is possible and the distinction may only be made pathologically.

When a female patient in the reproductive age presents with pelvic pain and ultrasound or  MRI are negative,  laparoscopy is indicated both for diagnosis of small or flat lesions lesions  as well as for therapy.    Microscopic deposits which may cause symptoms will not be identified by imaging techniques and will only be seen laparoscopically.  The reluctance to undergo an “invasive” procedure is understandable, but delaying or worse still missing the diagnosis will cause unnecessary long term suffering.

Laparoscopy

Laparoscopic image of small blood blisters characteristic of endometriotic lesions of the pelvic wall in the peritoneum 

Courtesy Author Hic et nunc.  Acknowledged work is in public domain

Blood Blisters in the Cul De Sac and Sacrouterine Ligament

Laparoscopic image of endometriotic lesions in the pouch of Douglas and on the sacrouterine ligament.
Courtesy Author Hic et nunc.  Acknowledged work is in public domain

Treatment options depend on patient preference, including whether fertility is desired, but include both medical and surgical options.  Medical management frequently involves suppression of regular menses/hormones .  Surgical options include removal of implants  or surgical induction of menopause (i.e. oophorectomy and hysterectomy).

Adenomyosis

Adenomyosis is a disease of the myometrium caused by misplaced or ectopic endometrium in the myometrium resulting in myometrial hyperplasia and smooth muscle hypertrophy clinically manifesting as pelvic pain and uterine enlargement.   The entity can be focal or diffuse

Enlarged and Painful Uterus of Adenomyosis

The exact cause of the displacement is not known but it is presumed that a breach in the endometrial myometrial barrier enables a small amount of endometrium to translocate and remain viable.  There is a high prevalence rate with about 40% of hysterectomy specimens displaying the entity.

The junctional zone of the uterus is the epicenter of the structural abnormality The junctional zone is subendometrial smooth muscle that is more compacted, and contains less water in comparison to the outer myometrium. (McCarthy)  The junctional zone is functionally different from the outer myometrium.

The Normal Junctional Zone on MRI

The normal sagittal view of the uterus is a T2 weighted MRI from a 16 year old female with pelvic pain. The myometrium consists of an outer part (dark red) and an inner more homogeneous part called the junctional zone (light maroon)  Since a T2 weighted image is sensitive to water, we understand from this image that the outer part has greater white signal and therefore contains more  water, and likely more vascularity. The junctional zone (light maroon)  on the contrary has less water and therefore is blacker.  The endometrial canal, cervical canal and vaginal cavity are outlined in yellow and the vaginal wall is overlaid in pink.

 Clinically the patient presents with pelvic pain, dysmenorrhea, menorrhagia and may contribute to infertility.  On exam the uterus is enlarged.

The diagnosis is best made by MRI which shows a thickened junctional zone (>10-12mms) s.  The deposition of acute blood, blood degradation products such as iron, or the presence of fluid filled microglandular deposits in the junctional zone make the MRI findings highly specific for the diagnosis.

Treatment options include pain management with NSAIDS, and hormonal manipulation.  Surgery and hysterectomy is the only current option for cure.

MRI

Adenomyosis with a Thickened Junctional Zone and Enlarged Uterus 

A  T2 weighted MRI (a) shows fluid in the endometrial cavity, surrounded by a thick dark layer of the junctional zone, and then surrounded with a slightly brighter outer myometrium.  The  color overlay in b, shows a small amount of fluid in the endometrial cavity (yellow) surrounded by a thickened subendometrial  junctional zone (light maroon) measuring up to 13 mms characteristic of adenomyosis. The outer myometrium (dark maroon) is normal

The junctional zone thickening is key to the diagnosis of adenomyosis on MRI.  The  junctional zone normally measures 8mm or less.  Between 8-11mm it is considered  indeterminate, and when it measures 12mm or  greater, it is considered diagnostic for the disease.  The junctional zone may thicken normally in the first few days of the menstrual cycle or during myometrial contractions.  Cystic changes in the junctional zone are also characteristic and relatively common and represent small blood blisters.  Linear striations radiating from endometrium to myometrium are also seen but these are not as easy to discern.  These probably reflect a breech in the endometrium reflecting microscopic tears extending into the myometrium.

 Ultrasound

The Normal Junctional Zone on Ultrasound

A transvaginal ultrasound of a premenstrual woman in the sagittal plane (left) reveals a normal view of the uterus with characteristic premenstrual appearance. Image on the right  is an overlay showing the components of the endometrium and subendometrial layers.  The stripe is almost homogeneously echogenic and thick but also shows a hypoechoic halo of the junctional zone or inner myometrium. (salmon) The homogeneous stripe is made up from two histological layers (barely distinguished by this ultrasound)– the inner stratum functionalis (deep orange) that will shed once the spiral arteries vasoconstrict, and the outer stratum basalis (deep yellow) that will not shed, and will be the basis for regenerating the endometrium in the next cycle. The next layer as stated above is the compact myometrium – the junctional zone (aka inner myometrium) , and is followed by the thicker outer myometrium (maroon).

The junctional zone is hypoechoic  due to decreased water content, and is formed by smooth muscle cells that are tightly packed.  The extracellular matrix and water content are sparse.  It usually measures less than 8mm.

Adenomyosis with Ectopic Deposits in the Junctional Zone

Two echogenic nodules (overlaid in green in image on the right) are present  in the subendometrial layer, (junctional zone) in a woman with menorrhagia. The nodules are in close proximity and  have appositional relationships with the endometrial stripe (yellow overlay). They distort the endometrial lining. These findings likely  account for the menorrhagia.  Included in the differential diagnosis are dystrophic changes in prior foci of adenomyosis and submucosal fibroids.  An MRI would assist to characterize  the lesions in the subendometrial layer.