Clinical examination is difficult with groin pain and endometriosis should always be considered if there is a history of chronic cyclic groin pain during menstruation. Painful nodules are due to destruction of the endometrial cells [4]. No nervous impingement has been described in the literature. Medical imaging, in particular MRI, may help in the diagnosis of extra-pelvic endometriosis in the groin muscles [7].

Ultrasound and CT are not specifically used for the diagnosis of muscular endometriosis in clinical practice. However, on CT signs of endometriosis are highly polymorphic, with generally a heterogeneous mass riding on muscle and the skin with or without hyperemia; or an isodense mass with or without contrast enhancement.

MRI allows the definitive diagnosis. On MRI, endometriosis lesions are also very polymorphic and are characterized by variable contents of hemorrhagic and/or fibrous lesions [8].

Hyperintense signal on T1-weighted sequences is noted if there is evidence of recent hemoglobin degradation; hypointense signal on T1-weighted sequences occurs in old bleeding lesions. With T2-weighted sequences, signal is quite variable, generally hypointense.