Developmental venous anomalies and brainstem cavernous malformations: a proposed physiological mechanism for haemorrhage.

The incidental diagnosis of both developmental venous anomalies (DVAs) and cavernous malformations (CMs) in the central nervous system is increasing with improved imaging techniques. While classically silent diseases, these cerebrovascular pathologies can follow an aggressive course, particularly when present in the brainstem. In the last decade, substantial research has focussed on KRIT1-mediated tight junction gene expression and their role in CM development. However, our understanding of the physiologic conditions precipitating symptomatic CM development or CM haemorrhage with and without concomitant DVAs, remains lacking. The only established risk factor for CM haemorrhage is a previous history of haemorrhage, and literature currently reports trauma as the only precipitant for symptomatic events. While plausible, this occurs in a minority, with many patients experiencing occult events. This manuscript presents a hypothesis for symptomatic CM events by first discussing the anatomical pathways for intracranial venous outflow via the internal jugular veins (IJV) and vertebral venous plexus (VVP), then exploring the role of venous flow diversion away from the IJVs under physiologic stress during dynamic postural shift. The resultant increase in intracranial venous pressure can exacerbate normal and pre-existing structural DVA pathologies, with repeated exposure causing symptomatic or CM-inducing events. This pathophysiological model is considered in the context of the role of the autonomic nervous system (ANS) in postural intracranial venous outflow diversion, and how this may increase the risk of DVA or CM events. It is hoped that this hypothesis invokes further investigation into precipitants for DVA or CM events and their sequela and, also, furthers the current knowledge on pathophysiological development of DVAs and CMs.