"The lateral pontomedullary membranes are arachnoid membranes located anterolateral to the brainstem at the pontomedullary junction, separating the cerebellopontine cisterns superiorly from the cerebellomedullary cisterns inferiorly 1–3. Cadaveric studies indicate the lateral pontomedullary membranes are likely continuations of the lateral pontomesencephalic membranes 4."