Posterior reversible encephalopathy syndrome (PRES), is a neurotoxic state with characteristic changes at MRI and CT. Recognized in various conditions like eclampsia, BMT, organs transplant, autoimmune disease, arterial blood hypertension, infection, and sepsis.

The symptoms can be acute and subacute and include headaches, visual changes, paresthesia, hemianopsia, nausea and altered mental status. 

Hypertension is not present or not reach the upper limits of self-regulation (150-160 mmHg) in 25% of patients.

The PRES mechanism remains controversial  but there are two main theories:

1. High blood pressure leads to loss of self-regulation, hyper-perfusion with endothelial damage and vasogenic edema.

2. Endothelial dysfunction leads to vasoconstriction and hypo-perfusion resulting in cerebral ischemia and subsequent vasogenic edema.

There are three main imaging patterns:

1. holohemispheric at watershed zones
2. superior frontal sulcus
3. parieto-occipital dominance

Interestingly in our case, the patient had no increase in blood pressure. In fact, she had a myriad of conditions correlated to HIV/ AIDS that probably had resulted in a state toxic/inflammatory that begat PRES.