Pathophysiology
The etiology of RPON is still unknown and remains controversial - some scientists believe that RPON is a subtype of migraine, while others believe that it is a neuropathic disorder. As such, different potential etiologic mechanisms have been proposed based on case reports, including migrainous and neuropathic mechanisms. Yet, the renaming of RPON from OM indicates that the neuropathic cause may play a more important role than the migrainous cause in the pathophysiology of RPON. Migrainous mechanism
RPON was previously thought to be having a migrainous origin since it shares some common characteristics with migraine, and their only differences are the intensity and duration of headaches. Therefore, it was postulated that migraine caused ophthalmoplegia in RPON. However, the major argument against a migrainous origin is the long latency period between the onset of headache and ophthalmoplegia (up to 14 days), which is not consistent with a typical migraine. Nevertheless, several migrainous mechanisms have been proposed. Nerve compression
Compression mechanism is the first theory postulated regarding the pathophysiology of RPON. It is proposed that headache is caused by direct pressure on CNIII (compression neuropathy) within the cavernous sinus due to edema of the walls of the internal carotid artery (ICA) or posterior cerebral artery (PCA) during migraine episodes. Ischemia
Cavernous section of the ICA and a perforating vessel from the proximal PCA are responsible for supplying CNIII, CNIV, and CNVI. During migraine attacks, vasoconstriction of the ICA and PCA may lead to a reversible and ischemic breakdown of the blood-brain barrier.
A hydrosalpinx is a condition that occurs when a Fallopian tube is blocked and fills with serous or clear fluid near the ovary (distal to the uterus). The blocked tube may become substantially distended giving the tube a characteristic sausage-like or retort-like shape. The condition is often bilateral and the affected tubes may reach several centimeters in diameter. The blocked tubes cause infertility. A Fallopian tube filled with blood is a hematosalpinx, and with pus a pyosalpinx.Hydrosalpinx is a composite of the Greek words ὕδωρ (hydōr – "water") and σάλπιγξ (sálpinx – "trumpet"); its plural is hydrosalpinges. Signs and symptoms
Symptoms can vary. Some patients have lower often recurring abdominal pain or pelvic pain, while others may be asymptomatic. As tubal function is impeded, infertility is a common symptom. Patients who are not trying to get pregnant and have no pain, may go undetected. Endometriosis, ruptured appendicitis, and abdominal surgery sometimes are associated with the problem. As a reaction to injury, the body rushes inflammatory cells into the area, and inflammation and later healing result in loss of the fimbria and closure of the tube. These infections usually affect both Fallopian tubes, and although a hydrosalpinx can be one-sided, the other tube on the opposite side is often abnormal. By the time it is detected, the tubal fluid usually is sterile, and does not contain an active infection. (Not symptoms)

Cause
The major cause for distal tubal occlusion is pelvic inflammatory disease, usually as a consequence of an ascending infection by chlamydia or gonorrhea.