Although not entirely clear how adenomyosis initiates, two proposed theories can explain the majority of cases encountered in everyday clinical practice.

Invagination of the endometrial basalis into the myometrium, the most widely accepted theory, holds that a traumatised junctional zone, either as a result of aberrant hyperestrogenic environment and hyperperistalsis, or an iatrogenic insult, leads to invasion of the myometrium by endometrial tissue.

Interesting to note that the tissue injury and repair mechanism (TIAR) can either take the form of a chronic disorder and manifest in later reproductive years, or be initiated after an acute iatrogenic insult and develop in younger ages.

It would be interesting to see whether spontaneously occurring hyperestrogenic states such as oligomenorrhoea cycles in PCOS, or iatrogenically induced, as in ovarian superovulation in the context of ART, are more often associated with the development of adenomyosis in future.

As for the theory of metaplasia of Mullerian remnants or differentiation of adult stem cells into endometrial tissue, in practice it may explain a smaller number of cases, without being clear what initiates this transformation. However, this second theory holds many common principles with the development of endometriosis

As it becomes clear that adenomyosis is a complex estrogen-dependent condition with potentially serious implications ranging from dysfunctional menses and infertility to increased association with endometrial carcinoma it is all too important to actively look for this condition and when embarking in ART treatment to actively promote mild ovarian stimulation regimes and minimise uterine instrumentation to the bearest minimum.

©2021, Nicholas Christoforidis, Fertility Matters
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