External ventricular drainage (EVD) is an important intervention in the management of patients with increased intracranial pressure (ICP), a condition commonly associated with hydrocephalus, trauma, and other causes due to cerebrospinal fluid (CSF) obstruction.[1]
[2] Some of the most relevant questions in conducting the EVD placement include the determination of the optimum side for catheter insertion. Commonly, the right frontal is preferred if it is not contraindicated. However, factors that make a side effective for good drainage with reduced complications involve considering several clinical and demographic characteristics.
Anatomical Considerations
Anatomical Considerations
Mostly, the right frontal approach to EVD placement is favored.[3]
[4] This is mainly due to anatomical accessibility to the lateral ventricles, especially in the dominant right hemisphere of most patients. The right frontal area is usually less encumbered by vascular structures, and the angle of entry thus provided allows for good catheter placement into the lateral ventricle. It serves both the ipsilateral and the contralateral ventricle adequately, provided the third ventricle has not suffered significant compression. However, if the third ventricle is kept patent and unobstructed, unilateral drainage has provided adequate decompression for the entire ventricular system.
Clinical Considerations in Ventricular Dynamics
Clinical Considerations in Ventricular Dynamics
However, in certain clinical scenarios, such as those with mass effect or midline shifts, the traditional approach of right frontal EVD placement needs to be reconsidered. Compression of the third ventricle significantly alters ventricular dynamics. The third ventricle is an important conduit for CSF passage between the two lateral ventricles, and compression may cause altered CSF circulation, raising the potential for hydrocephalus and increased ICP.
In such cases, drainage should be performed on the side that is more responsive to the CSF diversion. In cases of frank obstruction or compression of a ventricle on one side, drainage on the affected side may offer a more effective decompression. The side for EVD placement should be chosen in relation to the site of mass effect, midline shift, or other pathology that may impinge upon the flow of CSF. The side of compression needs to be considered, but more importantly, the amount of deviation of midline structures.[5]
[6]
Risk of Herniation with Entrapped Ventricles
Risk of Herniation with Entrapped Ventricles
Significant brain shifts or entrapped ventricles have to be handled very cautiously to avoid any possibility of herniation. Decompression of one side of the ventricle when it is asymmetric often may result in worsening the brain shift. Decompression of the affected side, therefore, may precipitate the herniation or new neurological deficits. For instance, rapid drainage of CSF may result in a sudden change of pressure when the ventricle is tightly compressed or entrapped by the mass effect; this may facilitate further brain tissue displacement and worse herniation.
In such a case, the general principle of management is gradual drainage. However, ICP is closely monitored to prevent acute decompression. The decision on which side to drain usually depends on the area where CSF diversion does not significantly adversely affect normal surrounding brain tissue and associated structures. At times, contralateral drainage tends to provide safer decompression with less risk of accentuating the shift.
EVD Placement Guided by Individual Pathology
EVD Placement Guided by Individual Pathology
It will be relevant to tailor a decision on the side of EVD placement for an individual patient in regard to his/her specific pathology, considering the various dynamics at play in cases involving brain edema, decompressive craniectomy, stroke, hepatic encephalopathy (HE), and any other conditions affecting ventricular morphology and ICP.
Brain Edema
In patients with severe brain edema, increased brain swelling may compress the ventricular system and therefore increase ICP. In cases where the edema is hemispheric or predominates on one side of the brain, it may affect the contralateral ventricle. On such occasions, decisions regarding the side of placement of the EVD are based on the side where ventricular compression or obstruction is maximum. If both ventricles are involved, clinicians must pick a side that allows for effective diversion of CSF, considering both ventricular size and the risk of aggravating herniation. Careful monitoring and gradual CSF drainage are necessary to avoid sudden shifts that could worsen the brain edema or lead to new neurological deficits.
Decompressive Craniectomy
Decompressive craniectomy is performed in cases of severe brain swelling or mass effect to relieve ICP. After craniectomy, the dynamics of CSF may be altered by the lack of the skull to provide normal containment of ICP. In these cases, the placement of EVD becomes very crucial for the management of residual elevated ICP and prevention of further brain herniation. Typically, EVD placement is on the craniectomy side for an easier pathway to the targeted area of CSF drainage. Great caution, however, has to be taken to ensure that there is no excess decompression of the brain tissue with drainage, which may worsen the shift in complicated cases of posterior fossa strokes or global brain edema.
Bilateral Craniectomy
In patients who have had a bilateral craniectomy, the lack of protection of the skull on both sides of the brain may make EVD placement cumbersome. The decision on which side to drain depends on the overall ICP dynamics and the degree of edema or mass effect on either hemisphere. In such cases, bilateral EVDs may be necessary to achieve adequate CSF diversion. However, careful monitoring for signs of over-drainage should be performed, as rapid changes in brain volume could lead to herniation. Both EVDs must be placed with attention to possible new shifts or changed CSF dynamics to ensure decompression of both ventricles without causing complications of additional shifts.
Stroke Hemicraniectomy
In patients who had a hemicraniectomy for ischemic or hemorrhagic stroke, the use of EVD usually leans toward the hemisphere presenting either the lesion or the mass effect. Hemicraniectomy is performed in relieving pressure and preventing herniation, but on such affected sides, the placing of EVD remains terribly important for monitoring and ICP control. EVD placement can also be considered on the opposite side in cases of involvement of the contralateral hemisphere, especially in cases of massive ischemia, to manage rising ICP due to global brain swelling. In the case of posterior circulation stroke, special caution should be exercised not to create additional shifts or further worsen the situation by placing the EVD in a manner that exacerbates elevation of ICP.
Posterior Fossa Stroke
Obstructed CSF flow may cause brainstem compression and hydrocephalus in posterior fossa stroke. The posterior fossa is a small compartment, and mass effect from strokes within it usually results in laterally displacing the cerebellum and brainstem. When placing an EVD, the direction of drainage must be toward the ventricles affected by the posterior stroke. This may involve either the right or left frontal approach, depending on the site and severity of the stroke. Complex management may be required in cases with bilateral ventricular involvement, with close monitoring of brainstem function and ICP because sudden drainage of CSF will risk further shifts that may lead to brain herniation of the brainstem.
Hepatic Encephalopathy
HE is a metabolic condition resulting from hepatic failure and the accumulation of toxic substances, leading to altered mental status and increased ICP. While HE does not directly cause mass effect or significant brain edema, resultant cerebral edema and alteration in CSF dynamics can also lead to the necessity of EVD placement. In patients with HE, the side for the EVD is chosen according to the degree of brain edema and which ventricle are being involved. For example, unilateral increase in ICP with a shift in the midline may prompt EVD on the same side as the maximum swelling and compression. This must balance out to relieve elevated ICP with avoidance of further metabolic disequilibrium.
Laterality Selection Algorithm for EVD Placement
Laterality Selection Algorithm for EVD Placement
EVD placement decisions are based on a systematic consideration of several clinical factors, including pathology location, findings on imaging, and patient-specific anatomical consideration. A contralateral medial canthus trajectory is preferred to avoid areas of hematomas or mass lesions for the best access to the lateral ventricle. Our algorithm begins with a clinical assessment, followed by a pathology-based decision, an evaluation of patient-specific factors, and concludes with a final safety check (see [Fig. 1]).
Fig. 1 Decision-making algorithm for EVD placement. EVD, external ventricular drain.
Conclusion
Tailoring EVD placement to individual pathology is crucial for optimizing patient outcomes and minimizing complications. Brain edema, decompressive craniectomy, stroke, HE, meningitis, and other conditions all require caution with regard to each patient's specific anatomical and physiological nuances. The aim of the EVD placement is the effective management of the elevated ICP, the relief of mass effect, and the maintenance of brain homeostasis with the avoidance of further brain shifts or herniation. These considerations, with tailoring of the EVD approach, ensure the most appropriate strategy is applied in each individual patient to enhance success rates in challenging neurocritical care scenarios.
