To understand the use of external ventricular drains (EVDs) and lumbar drains (LDs), one must be comfortable with the ventricular anatomy and cerebrospinal fluid (CSF) flow. Obstructive hydrocephalus is a state in which CSF flow is blocked within the ventricular system, whereas communicating hydrocephalus occurs when a blockage develops outside of the ventricular system. The indications for EVDs and LDs have expanded over the years beyond treating hydrocephalus. These drains are now used to monitor intracranial pressure and to treat CSF leak, delayed cerebral ischemia, intraventricular hemorrhage, central nervous system infection, and spinal cord reperfusion.
Both external ventricular drains (EVDs) and lumbar drains (LDs) are thin tubes that are placed in the cerebral ventricles and the lumbar cistern, respectively. Their placement and management are discussed in greater detail in later chapters. EVDs and LDs have historically been used to treat hydrocephalus. However, their roles have expanded for other purposes, including intracranial pressure (ICP) management, repair of cerebrospinal fluid (CSF) leak, and drug delivery.
The conceptualization of hydrocephalus will likely undergo a major restructuring within the next 50 years.1 Increasing evidence shows that rather than the bulk fluid flow model, which has been prevailing for decades, a pulsation model may more accurately describe CSF dynamics. However, because the pulsation model has not yet been fully elucidated, we will refer to the classic thinking that is most often used in the medical literature. Hydrocephalus is a state involving the disruption of the normal pathway of CSF movement. The most clinically relevant way to conceptualize this disruption is to identify where it has occurred within that pathway. Establishing this mental blueprint can help answer many of the questions that arise about the different types of hydrocephalus and their management with drains. Thus, we must become intimately familiar with the anatomy of CSF movement.
One can imagine CSF flow as a lake system, similar to the rivers and gorges making up the Finger Lakes in upstate New York. CSF is produced predominantly in the specialized cells of the choroid plexus of the ventricles (although this source has become a topic of debate).2 These slightly transparent beige tufts of choroidal epithelial cells are much like the many small streams and brooks that join to form a river (Fig. 1.1). For the most part, CSF flow is continuous, as is the case with tributaries. The first two rivers can be thought of as existing in the lateral ventricles. As CSF moves along the different parts of the lateral ventricle, the choroid plexus along the medial-inferior wall continues to add more CSF to these hypothetical rivers. The two rivers join at the beginning of the third ventricle as they pass through the foramen of Monro. Here, too, CSF moves downstream, and more small brooks join from the choroid plexus ...