Laparoscopy is the gold standard for diagnosing endometriosis because it allows for direct visualization of endometrial implants on pelvic organs. During laparoscopy, surgeons can identify, biopsy, and sometimes remove endometriotic lesions, providing definitive evidence of the disease. Other imaging modalities, like ultrasound or CT scan, lack sensitivity and cannot reliably confirm endometriosis. Pap smear is unrelated to diagnosis of pelvic endometriosis. Hence, laparoscopy offers both diagnostic and therapeutic opportunities in secondary dysmenorrhea due to endometriosis.

Reference: Williams Gynecology, Berek JS, 3rd Edition.