A 28-year-old woman has bursting pain in the lower abdomen during menstruation; chocolate-like discharges from vagina. It is known from the anamnesis that the patient suffers from chronic adnexitis. Bimanual examination revealed a tumour-like formation of heterogenous consistency 7x7 cm large to the left from the uterus. The formation is restrictedly movable, painful when moved. What is the most probable diagnosis?