Adenomyosis: Endometriosis Growing Into the Uterine Wall
Endometriosis that grows into the uterine wall—specifically infiltrating the muscular layer (myometrium)—is called adenomyosis, which is recognized as a distinct clinical entity and classified as a specific subtype in some deep endometriosis classification systems. 1, 2
Definition and Pathophysiology
Adenomyosis represents endometrial-like tissue that has invaded into the myometrium (the muscular wall of the uterus), distinguishing it from typical endometriosis where tissue grows outside the uterus entirely. 1, 3
- While classic endometriosis is defined as endometrial-like tissue located outside the endometrial cavity associated with inflammation and fibrosis 3, 4, adenomyosis specifically involves the uterine muscle itself 1
- The European Society of Human Reproduction and Embryology recognizes adenomyosis as both a distinct entity and a subtype within certain deep endometriosis classifications 1
- Deep endometriosis is formally defined as lesions extending deeper than 5mm under the peritoneal surface or involving/distorting bowel, bladder, ureter, or vagina 3, 2
Diagnostic Approach
Transvaginal ultrasound using standardized MUSA criteria is the first-line diagnostic tool, demonstrating 82.5% sensitivity and 84.6% specificity for adenomyosis. 2
When to Use MRI
- Reserve MRI for cases where ultrasound findings are indeterminate or the uterus cannot be completely visualized on ultrasound 2
- MRI has the specific advantage of displaying the endometrium even when obscured by adenomyosis on ultrasound, which is a common pitfall 1, 2
Common Diagnostic Pitfall
The endometrium may be obscured on ultrasound in the presence of adenomyosis, potentially leading to missed diagnoses or incomplete characterization—this is when MRI becomes particularly valuable 1
Clinical Context
- Adenomyosis affects women during their reproductive years, similar to other forms of endometriosis 3, 5
- Like endometriosis, it is an estrogen-dependent, inflammatory condition 4, 6
- The condition can present with pelvic pain (reported in 90% of endometriosis patients generally) and may contribute to infertility 4
Relationship to Broader Endometriosis Classification
Adenomyosis is integrated into deep endometriosis classification systems as lesions extending >5mm under the peritoneal surface, though it maintains recognition as a distinct pathological entity. 2