Complications Associated With Cerebrospinal Fluid Diversion




Highlights





  • Endoscopic third ventriculostomy complications include hemorrhage, neurologic deficits, and failure of the ventriculostomy.



  • Ventricular shunt complications can be broadly categorized as infections, mechanical failures of the shunt, and long-term complications.



  • Careful preoperative planning and meticulous surgical techniques may help prevent complications related to cerebrospinal fluid diversion.



  • Potential complications should be investigated thoroughly to allow for appropriate treatment as needed.





Background


Cerebrospinal fluid (CSF) diversion is important, and often lifesaving, in the treatment of several common disorders, including hydrocephalus, intracranial hypertension, and CSF leaks or fistulas. When possible, treatment of hydrocephalus starts with correcting the underlying pathology. Reestablishment of physiologic CSF circulation and absorption, via either removal of the anatomic obstruction or creation of alternative fluid pathways, should be a primary consideration for these patients. When these options cannot be achieved, CSF may also be diverted using implanted shunts. Many surgical options allow for treatment to be individualized to patient-specific anatomic and pathologic factors, and with each technique there are known potential complications. The relative risks of these surgical options must be discussed with patients and their families as treatment plans are developed.




Anatomic Insights


Endoscopic Third Ventriculostomy


Endoscopic third ventriculostomy (ETV) should be considered for patients with obstructive hydrocephalus and favorable ventricular anatomy. Entry point and trajectory through the frontal horn of the lateral ventricle are determined preoperatively by careful review of the imaging. A straight line from the floor of the third ventricle through the foramen of Monro can be extended to allow measurements in sagittal and coronal planes at the surface for optimization of skin incision ( Fig. 30.1 ). Neuronavigation may be considered for more challenging cases. An adequate prepontine space to avoid the basilar artery, a large enough lateral and third ventricle to insert the neuroendoscope through the foramen of Monro without injuring the fornix, and lack of significant intraventricular or subarachnoid adhesions on imaging are also reassuring as an ETV is planned.




Fig. 30.1


An appropriate trajectory and entry point for endoscopic third ventriculostomy can be determined by extending a straight line from the floor of the third ventricle through the foramen of Monro. Neuronavigation may be helpful in cases with challenging ventricular anatomy.


Understanding of intraventricular anatomy is critical for surgeons performing an ETV. Within the lateral ventricle, the foramen of Monro is identified in association with the choroid plexus, the anterior septal vein, and the thalamostriate vein ( Fig. 30.2A ). The endoscope is then advanced into the third ventricle, and the floor of the third ventricle is confirmed in the midline, anterior to the mammillary bodies and posterior to the infundibular recess ( Fig. 30.2B ). The floor of the third ventricle was subsequently fenestrated in a standard fashion, often with balloon dilation through the endoscope.




Fig. 30.2


The endoscopic anatomy encountered while performing an endoscopic third ventriculostomy (A) at the foramen of Monro, and (B) within the third ventricle.


Ventricular Shunt Placement


A thorough review of preoperative imaging should precede any ventricular shunt placement or revision given the potential for abnormal anatomic variations in patients with hydrocephalus. Careful note should be made of ventricular size and configuration, patient history including any prior incisions, and aberrant anatomy such as distorted venous sinus locations.


Frontal and occipital entry points are most often employed for ventricular shunt placement, with typical termination in the frontal horn. The impact of entry site selection on risk of shunt malfunction is controversial within the literature, with systematic review not demonstrating clear evidence in favor of either location. Positioning the catheter within a defined CSF space, away from ventricular walls and choroid plexus, may lower shunt malfunction risk. It is important to always include a reservoir in the shunt system to tap the shunt in an emergency or to evaluate for infection.


The peritoneal space is the most frequent distal terminus for ventricular shunts. Other considerations include the pleural space and the right atrium of the heart, though these are primarily chosen in cases where the peritoneal space is contraindicated. A pleural shunt is often not tolerated in a child less than 2 years of age due to poor absorption from the pleural space. An atrial shunt may need to be revised in a young child due to growth, since the catheter would migrate out of the right atrium and into the subclavian vein and thrombose. In patients with significant prior abdominal surgical history or with less common distal terminus sites, surgical assistance from specialists trained in accessing these anatomic areas safely and minimally invasively is often appropriate.



Red Flags





  • Patients with lower chances of ETV success can be identified preoperatively using the ETV Success Score.



  • Risk of shunt infection is highest directly after external ventricular drainage, especially if this was in the setting of a recent infection.



  • Age less than 6 months, cardiac comorbidities, and use of an endoscope for ventricular catheter placement are factors that have been statistically correlated with higher risk of shunt malfunction in a large multiinstitutional analysis.






Prevention


Good surgical outcomes start with appropriate patient and procedure selection. Determining which patients would most benefit from ETV or shunting requires familiarity with not only the respective procedures but also the best available data to guide clinical decisions.


Endoscopic Third Ventriculostomy Complications


Preoperatively, the chances of successfully treating hydrocephalus with an ETV should be considered and discussed with patients and their families. The ETV Success Score is a validated measure that allows calculation of this potential risk. Patient age is the largest determinant of this score, followed by the etiology of hydrocephalus and history of prior shunting ( Table 30.1 ).



TABLE 30.1

ETV Success Score, With the Sum of Scores in Three Categories Approximating the Probability of Successful Hydrocephalus Management With an ETV Alone







































Score Patient Age Hydrocephalus Etiology History of Prior CSF Shunt
0 <1 month Postinfectious Yes
10 1–6 months No
20 Myelomeningocele, intraventricular hemorrhage, nontectal brain tumor
30 6–12 months Aqueductal stenosis, tectal tumor, other
40 1–10 years
50 >10 years

CSF, Cerebrospinal fluid; ETV, endoscopic third ventriculostomy.


Bleeding is a risk of any intraventricular procedure. Hemorrhage risk is mitigated by careful avoidance of the vascular choroid plexus, except in cases where choroid plexus cauterization is added to decrease CSF production. Minimizing nonaxial endoscope movement limits the risk of ependymal bleeding; this is much easier with careful preoperative incision planning, aided by neuronavigation in more challenging cases and using a peel-away sheath in the brain. Most recently, robotic assistance has been used to ensure precise navigation and steady endoscope positioning. The most dreaded complication of ETV, however, is injury to the critical basilar and pontine vessels immediately subjacent to the floor of the third ventricle. Injury to these vessels can be avoided by confirming an adequate prepontine space on preoperative imaging, by a good understanding of the anatomy of the third ventricular floor, by identifying the clivus through the floor utilizing tactile feedback, and by aborting the procedure in favor of other treatment options in cases where the endoscopic anatomy is not clear enough to proceed safely. If an injury to the basilar or posterior cerebral arteries occurs intraoperatively, it is important not to pull back the endoscope but instead to use the endoscope to hold pressure on the artery and to irrigate for several minutes to stop the bleeding. Consider direct transfer to the angio suite for a neurointerventional procedure to coil the vessel if needed. If the endoscope is pulled back, which can be a natural reflex at the moment, the blood will quickly fill the ventricles, and visualization will be lost.


Other complications of ETV include CSF leak or pseudomeningocele, wound infection, meningitis, new neurologic deficits, endocrinopathies, and perioperative seizure. Occlusion of the epidural opening before closure and meticulous wound management may mitigate these risks. The fornix is at highest risk within the brain, with injury noted in up to 16.6% of cases and thus potential permanent short-term memory loss ; as with hemorrhage, this risk is lowered by minimizing nonaxial endoscope movement and torque applied at the level of the foramen of Monro. Other complications, such as third nerve injury or hypothalamic disturbances, may be similarly avoided.




Shunt Complications


Shunt Infection


Shunt infections present a challenge given the requisite foreign bodies and direct communication with the central nervous system. Infection is reported in 4% to 30% of cases, varying according to patient history, presence of external drainage, and history of recent infection. The latency between surgery and presentation for infection ranges from 15 days to 12 months, with a bimodal distribution weighted toward early presentation. Gram-positive organisms cause most shunt infections, with coagulase-negative staphylococci reported in 17% to 78% of cases and Staphylococcus aureus found in 4% to 30%. Risk factors for shunt infection are numerous and include prematurity and low birth weight, relative immunosuppression, repeat shunt revisions or aspirations, and lack of compliance with established infection-control protocols both in the operating room and perioperative setting.


Operative protocols have demonstrated success in reducing shunt infection rates, and currently most institutions have established perioperative management plans regarding antibiotics, skin sterilization, handling of shunt components, and flow of operating room personnel. Antibiotic-impregnated catheters may have some benefit, though conclusive data for this is limited. As with any procedure, infection rates are likely improved with careful and meticulous surgical technique, copious irrigation, and adherence to wound-healing principles with the incisions and closure.


Mechanical Shunt Failure


Shunt failure can take many clinical forms and often is patient-specific in presentation. Frustratingly to the surgeon, there are no absolute ways of preventing shunt failures. The highest risk of failure is in the early postoperative period after insertion or revision, though in practice, examples of late failures are easily produced as well. The largest prospective cohort studying risk factors for shunt failure identified three risk factors associated with reduced shunt survival: age less than 6 months, a cardiac comorbidity, and use of an endoscope for ventricular catheter placement. Of these, use of an endoscope is the only modifiable risk factor, so an endoscope is generally not recommended for routine ventricular catheter placement.


Shunt occlusion can occur at the proximal catheter, valve, or distal system. As described above, the choice of frontal or occipital entry site does not appear to affect shunt survival, though maintaining an open CSF space around the catheter, away from the ventricular walls and choroid plexus, may reduce shunt malfunction. Selection of valve design does not change the risk of shunt malfunction. Laparoscopic placement may reduce the risk of distal catheter occlusion in ventriculoperitoneal shunts.


Shunts may disconnect, fracture, or migrate. The risk of disconnection may be mitigated by securing the shunt system tightly with nondissolvable suture and limiting the number of connections when possible. Placement of the valve and connections over the skull, where these connections are not subjected to repetitive movement at the neck, is also encouraged. Shunt fracture is typically seen in older, calcified catheters and does not require a history of significant trauma. Early shunt migrations are avoided by securing the ventricular catheter and valve to the pericranium or skull as possible, avoiding unnecessary subgaleal dissection, and closing the abdominal wall layers securely around the distal catheter. Late migration of the shunt catheters, including the ventricular catheter into the brain parenchyma and the distal catheter out of the abdomen or other terminus, may be seen as a result of relative growth of the child; this late migration can be minimized when the shunt is inserted by accounting for the child’s anticipated growth.


Overdrainage


Multiple longer-term risks of CSF diversion are related to CSF overdrainage. Creation of subdural hematomas or hygromas, slit ventricle syndrome, shunt-induced craniosynostosis, low-pressure headaches, and ventricular collapse with loculations are all complications of shunt overdrainage. Valve selection, including the setting of programmable valves, may help avoid some of these complications, though predicting CSF hydrodynamics is imperfect and incompletely studied. Patients are routinely followed clinically and radiographically, with intervention as needed, to avoid these concerns and their sequelae as possible.


Long-Term Shunt Complications


There are many complications related to CSF shunts that deserve recognition by patient care teams, especially as general health maintenance of these patients is challenged by comorbidities and paucity of multidisciplinary transitional clinics. These findings should be periodically screened, with referral to appropriate experts as needed to prevent significant progression.


Shunted patients may have endocrine disturbances. Growth hormone abnormalities can be seen as a result of intracranial hypertension or can be related to tumor treatment when applicable. Early puberty and infertility are related concerns. Diabetes insipidus is an uncommon complication after ETV. Obesity is a significant problem in the shunted population, with the higher risk related to both associated neurologic deficits and potential contributions from hypothalamic dysfunction.


In addition to findings related to their underlying pathology, shunted patients may present with long-term neurologic complications. Headaches unrelated to shunt function are common, reported in up to 44% of patients with shunts. Epilepsy is found in 30% of patients with nontumoral hydrocephalus. Neuropsychologic and cognitive sequelae of chronic shunting are understudied and undertreated.


There is always a question as to whether a patient will remain shunt dependent years after the shunt placement. It is most likely that, if the shunt was placed early in life, the patient is still dependent on the shunt. If a patient presents with a shunt disconnection and is asymptomatic, CSF may still be draining via the previously established tract. To confirm shunt independence, a shunt may be surgically ligated with the patient carefully observed in the hospital, or the shunt can be externalized with the external ventricular drain (EVD) clamped to monitor intracranial pressure over 3 to 5 days. A patient with a history of a meningomyelocele is usually shunt dependent for life.

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Jun 29, 2019 | Posted by in NEUROSURGERY | Comments Off on Complications Associated With Cerebrospinal Fluid Diversion

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