What is the difference between endometrioma and endometriosis?

Difference Between Endometrioma and Endometriosis

Endometrioma is a specific subtype of endometriosis, representing a cystic form that occurs when endometriotic tissue forms a blood-filled cyst specifically within the ovary, while endometriosis is the broader condition characterized by endometrial-like tissue growing outside the uterine cavity in various locations throughout the body.

Key Differences

Definition and Classification

• Endometriosis: A chronic inflammatory systemic disease characterized by the presence of endometrial-like tissue outside the uterus, typically on pelvic organs and tissues 1. It affects approximately 10% of women in their reproductive years.
• Endometrioma: Specifically refers to ovarian endometriotic cysts (also called "chocolate cysts" due to their dark, brown fluid content), which represent one manifestation of endometriosis 2. These are blood-filled cysts that form when endometriotic tissue invades the ovary.

Location

• Endometriosis: Can occur in multiple locations including peritoneal surfaces, ovaries, bowel, bladder, uterosacral ligaments, rectovaginal septum, and even rare distant sites like the diaphragm 3.
• Endometrioma: Exclusively found in the ovaries, though a patient may have other forms of endometriosis concurrently 2.

Imaging Characteristics

• Endometrioma:

  • On ultrasound: Appears as an adnexal or ovarian mass with homogenous low-level internal echoes. Often contains echogenic foci in the wall (hemosiderin deposits) or multilocularity 3.
  • On MRI: Shows high signal on T1-weighted with low signal on T2-weighted images (T2 shading) due to intracellular methemoglobin, crosslinking of proteins, and iron 3.

• Endometriosis (non-endometrioma):

  • Deep infiltrating endometriosis presents as low signal intensity regions with or without hyperintense foci on T2 and/or T1-weighted MRI images 3.
  • On ultrasound, non-ovarian endometriosis appears as hypoechoic nodules outside the ovaries 3.

Formation Mechanism

• Endometrioma: Hypothesized to form through:

  1. Endometriotic invasion or metaplasia of functional ovarian cysts
  2. Ovarian surface endometriosis that bleeds into the ovarian cortex 2

• Endometriosis: Primarily thought to arise from retrograde menstruation, but other factors include altered immunity, inflammatory responses, epithelial-mesenchymal transition, and genetic susceptibility 1.

Size and Characteristics

• Endometrioma: Range from small (1-3 cm) densely fibrotic cysts to large (up to 20 cm or greater) cysts with varying degrees of fibrosis 2. In rare cases, they can present as free intra-abdominal cysts 4.
• Endometriosis: Typically presents as superficial peritoneal implants or deep infiltrating lesions of various sizes 1.

Clinical Implications

Impact on Fertility

• Endometrioma: Has specific and direct impacts on ovarian reserve and function:

  • Can cause ovarian aging through local inflammatory mechanisms 5
  • Surgical removal (cystectomy) may further damage normal ovarian tissue 5
  • Associated with higher risk of premature ovarian insufficiency 5

• Endometriosis: Affects fertility through multiple mechanisms:

  • Anatomical distortion and adhesions
  • Altered peritoneal environment
  • Impaired implantation
  • Reduced oocyte quality 1, 6

Diagnostic Approach

• Endometrioma: Can often be diagnosed non-invasively:

  • Transvaginal ultrasound has high sensitivity and specificity 3
  • MRI has 82-90% sensitivity and 91-98% specificity for endometriomas 3

• Endometriosis (overall): Definitive diagnosis traditionally requires surgical visualization with histological verification, though imaging is increasingly used for non-invasive diagnosis 1.

Treatment Considerations

• Endometrioma:

  • Ovarian cystectomy is preferred over cyst ablation or sclerotherapy for pathologic diagnosis, symptom improvement, recurrence prevention, and optimizing fertility outcomes 2
  • Special surgical considerations due to dense fibrosis of the cyst capsule 2

• Endometriosis (overall):

  • Treatment depends on symptoms and reproductive goals
  • Options include hormonal suppression, analgesics, and surgical excision of lesions 1, 6

Clinical Pearls and Pitfalls

• Endometriomas are often bilateral and may coexist with other forms of endometriosis.
• The presence of Doppler blood flow in a suspected endometrioma should prompt investigation for neoplasm, as endometriomas are typically avascular 3.
• While endometriosis is primarily a disease of reproductive-aged women, endometriomas can rarely occur in postmenopausal women 4.
• When evaluating pelvic pain and infertility, both endometriomas and other forms of endometriosis should be considered in the differential diagnosis.
• Preoperative imaging is crucial before surgery for endometriosis, as it helps inform patient decision-making, surgical planning, and management 3.

Understanding the distinction between endometrioma and endometriosis is essential for proper diagnosis, treatment planning, and patient counseling regarding long-term implications for fertility and quality of life.