Objective:

Investigate the relationship between the structure of abdominal wall endometriotic nodules in MRI and their localisation in abdominal wall layers in order to better understand nodule origins.

Design:

Women who had an MRI prior to surgical treatment of an abdominal wall endometriotic nodule between 2005 and 2016.

Population:

Thirty-six patients including four patients with two nodules.

Methods:

MRI images were reviewed. Each nodule was analysed according to its structure (fibrous, cystic, mixed), localisation (subcutaneous fat, intra muscular, intermediary position), and size.

Results:

Forty nodules were analysed in MRI with no relationship found between localisation and nodule structure (p = 0.48). 87.5% of mixed nodules were revealed to have a cystic superficial rim extending towards the subcutaneous fat layer. This finding suggests that the glandular part of the nodule is the active part of the disease from which nodule progression occurs. Intermediary and intramuscular nodules were respectively statistically larger than subcutaneous fat nodules indicating a relationship between nodule size and localisation (35 mm (22–53) vs 17 mm (17–23)) (p = 0.03).

Conclusion:

Despite differences in environments surrounding the nodules, no significant relationship between nodule structure in imaging and abdominal wall localisation was found. Data from mixed nodules indicate however the possible role of nodule environment on structure and that the mechanism of nodule growth may be linked to development of cystic superficial rims, at the forefront of disease progression, abdominal wall nodules growing from deep to superficial. Studies are required to further investigate our findings and enable greater understanding of the origins of AWE.