USMLE® Step 1 style questions USMLE
A 28-year-old nulliparous woman comes to the office because of chronic intermittent dull pelvic pain for 7 months. The pain usually begins a day before menses and resolves 1-2 days after the menstruation stops. She also complains of crampy pain with defecation. Menarche was at age 13. Her cycles are regular but are associated with heavy bleeding for 5 days. She is not sexually active, and there is no history of sexually transmitted disease. Family history is remarkable for ovarian cancer in her maternal grandmother. Vitals are within normal limits. BMI is 33 kg/m2. Abdominal examination shows no abnormalities. Pelvic examination shows a fixed anteverted uterus and palpable right-sided adnexal mass. Transvaginal ultrasound of the right ovary is shown below.
Reproduced from: radiopedia.org
Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH, Yifan Xiao, MD
Endo- means internal and -metrium means womb, so endometrium is the innermost layer of the womb, and endometriosis is where these endometrial cells grow outside of the womb.
The female internal sex organs are the ovaries, which are the female gonads; the fallopian tubes, two muscular tubes that connect the ovaries to the uterus; and the uterus, which is the strong muscular sack that a fetus can develop in.
It’s a hollow organ that sits behind the urinary bladder and in front of the rectum.
The top of the uterus above the openings of the fallopian tubes is called the fundus, and the region below the openings is called the uterine body.
The uterus tapers down into the uterine isthmus and finally the cervix, which protrudes into the vagina.
It’s is anchored to the sacrum by utero-sacral ligaments, to the anterior body wall by round ligaments, and it’s supported laterally by cardinal ligaments as well as the mesometrium, which is part of the broad ligament.
The wall of the uterus has three layers: the perimetrium, which is a layer continuous with the lining of the peritoneal cavity, the myometrium, which is made of smooth muscle that contracts during childbirth to help push the baby out, and the endometrium, a mucosal layer, that undergoes monthly cyclic changes.
In endometriosis, the cells that make up the endometrium migrate and implant themselves in other parts of the body.
Once there, they will set up camp and start growing to form a mass of endometrial tissue.
Most often, this affects the ovaries, fallopian tubes, and uterine ligaments.
But it can also affect other structures in the pelvis and abdomen like the perimetrium, the rectovaginal septum, the recto-uterine pouch, also called the pouch of Douglas, and even the intestines or bladder!
Although we are unsure of the exact cause of the endometrial cell migration, there are at least five main theories that try to explain this phenomenon.
First, retrograde menstruation theory says that during menstruation, some blood carrying endometrial cells will flow backwards into the fallopian tubes and implant into nearby tissue.
Sometimes, there could also be a patented fallopian tube, meaning there’s an opening in it, so the adventurous endometrial cells could actually escape and travel to the other pelvic and abdominal structures!
Now, because retrograde flow is much more common than endometriosis, other factors probably come into play.
So the second theory is that there’s a dysfunction with the immune system where B and T cells don’t respond to endometrial implants and allow it to grow.
Third, the metaplastic theory suggests that cells of the peritoneum, which come from the same cell line as endometrial cells, can transform spontaneously into endometrial tissue.
This theory explains how in rare cases, a woman that underwent a hysterectomy, where the uterus was surgically removed, can still develop endometriosis.
The fourth and fifth theories are especially useful for explaining how endometrial implants show up in places like the lungs or heart.
Benign metastases theory says that endometrial cells can travel to distant organs through the lymph and blood, while extrauterine stem cell theory says that stem cells in the bone marrow differentiate into endometrial cells and then travel to other parts of the body.
In addition to these proposed causes, there are some risk factors for developing endometriosis.
These include a family history of endometriosis, never having been pregnant, early menarche, and late menopause.
Now, whatever the cause, endometriosis implants are benign so they don’t grow out of control like cancerous cells.
However, because they’re functionally the same as the epithelial cells found within the uterus, they have the same estrogen receptor.
So they go through the same proliferation, secretion, and menstruation cycle just like the normal endometrial cells.
But, there are two key differences between normal endometrial cells and endometriosis implants.
First, the implanted cells contain high levels of the enzyme aromatase, which allows them to produce their own estrogen.
Second the implanted cells release pro-inflammatory factors which causes inflammation and scarring.
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Endometriosis and Infertility: How and When to Treat?" Frontiers in Surgery (2014)
- "Medical Management of Endometriosis" Clinical Obstetrics & Gynecology (2017)
- "Endometriosis" Endocrine Reviews (2019)