Contralateral Ventriculostomy for Intraoperative Brain Relaxation in Supratentorial Brain Tumors
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.279710
Source of Support: None, Conflict of Interest: None
Keywords: Contralateral, herniation, sub-falcine, supratentorial, ventriculostomyKey Messages: Our initial experience with contralateral ventricular drainage shows that, even in the presence of subfalcine herniation, it is a useful strategy for ensuring brain relaxation as a preparatory measure when operating on large supratentorial tumours.
CSF drainage from the ventricular system is a popular strategy for achieving brain relaxation in the presence of hydrocephalus. A slack brain presents several advantages during brain tumor surgery and is especially indispensable for approach to extra-axial brain tumors. A symmetrically dilated ventricular system is conventionally considered a prerequisite for the safe execution of intraoperative ventricular drainage. However, it is frequently observed that large supratentorial tumors produce a sub-falcine herniation with contralateral ventricular dilatation and effaced ipsilateral ventricles. It is commonly believed that tapping the enlarged ventricular chamber in such a setting can worsen the herniation, leading to the patient's detriment. We describe a series of cases where we punctured the contralateral ventricle in such situations establishing the feasibility, safety, and efficacy of this maneuver for achieving a slack brain during surgery for supratentorial tumors.
A 26-year-old gentleman presented with worsening bifrontal headaches and diminution of vision in the right eye which he had noticed over the past 3 months. MR imaging revealed a large clinoidal meningioma [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]e with a chronic sub-falcine herniation of the brain producing an enlargement of the contralateral lateral ventricles. A ventricular drain was placed through the left Kocher's point (3 cm lateral to midline and 1 cm anterior to the coronal suture) and allowed to drain around 20 ml of clear CSF. A pterional craniotomy was fashioned on the right side and the orbital rim was removed. The slack dural compartment greatly facilitated the extradural anterior clinoidectomy which was necessary for devascularizing the tumor. The dura was then opened and, despite the tumor mass, a relaxed brain greeted the surgeon. The tumor was removed in totality [Figure 1]f and [Figure 1]g without any cortical insult due to the effective brain relaxation achieved through the ventricular CSF drainage.
A 12-year-old child had been operated for a left-sided temporal anaplastic ependymoma. After 24 months of the initial surgery, he presented in distress to the emergency room with a decline in consciousness and repeated vomiting [Figure 2]a and [Figure 2]b. Emergent CT imaging revealed a large recurrence at the operative site with severe perilesional edema causing a brain shift and distention of the lateral ventricles on the right side. Anticipating the vascularity of the tumor and the limited physiological capacity of a small child to tolerate exsanguination, strategies for minimization of intraoperative blood loss were considered. The contralateral ventricular puncture site was marked, before positioning the patient for craniotomy. Once the craniotomy flap was elevated, the dural compartment was observed to be extremely tense. Therefore, the ventricular drain was placed in the opposite ventricle before durotomy. We expected that this would lower the ICP and venous tension in conjunction, which would lead to reduced venous bleeding. Our reasoning was confirmed intraoperatively and the tumorectomy could be achieved with relative ease [Figure 2]c and [Figure 2]d with acceptable blood loss due to a conducive brain condition at the beginning of the operation.
A small falcine meningioma was detected in a middle-aged female who complained of severe headaches accompanied by visual obscurations of several weeks duration [Figure 2]e and [Figure 2]f. MRI imaging further revealed extensive edema in the surrounding brain parenchyma with dilatation of the contralateral ventricle, owing to midline shift and sub-falcine herniation. Since the tumor was in an eloquent location, cortical injury during interhemispheric approach to the tumor was anticipated. When the dura was found to be extremely turgid upon the parasagittal craniotomy, a contralateral ventricular drain was placed to achieve brain relaxation which protected the enveloping cortex during tumor removal [Figure 2]g and [Figure 2]h.
An interhemispheric approach was planned for a high-grade glioma judged to be arising from the cingulate gyrus. To facilitate the exposure, a contralateral ventricular drain was placed and the overlying eloquent cortex was protected from adverse effects of physical handling. The intraoperative cryosection pathological diagnosis was strongly suggestive of lymphoma. Therefore, the lesion was only partially enucleated till the mass effect was relieved.
The indispensability of a slack brain for ensuring optimum outcomes of surgeries on intracranial brain lesions has been implicitly recognized by neurosurgeons for long. It becomes especially important when planning extra-axial approaches to deep-seated brain lesions, where the surgeon exploits the space offered by the brain shrinking away from the dural structures. Several strategies have been commonly employed for accomplishing this permissive state of the brain. They include aspects of positioning where the head is kept elevated to facilitate venous drainage, administration of osmotic diuretics to reduce brain volume, and use of intravenous anesthetic agents., However, in patients with large tumors, extensive perilesional edema, and acute clinical presentation, the above methods may prove insufficient to produce an optimum brain condition.
CSF drainage has a dramatic effect on reducing brain turgor and volume. In the setting of traumatic brain injury, drainage of as little as 3 ml of CSF from the ventricles has been effective in reducing the ICP by more than 15%, although the effect is transient. However, when CSF drainage is employed during craniotomy, it sets up a positive feedback cycle progressively drawing CSF from sites distant to the drainage point. This results in increased relaxation of the brain. The potential spaces from which CSF can be drained are the sulci, arachnoid cisterns, and the ventricle.
Opening of multiple sulcal spaces on the surface of the exposed brain is a useful strategy for gradually shrinking a “full” brain, but is insufficient in the presence of hydrocephalus or severe mass effect. For intraoperative brain relaxation, LSD is much more efficacious. However, placement of the lumbar subarachnoid catheter is a procedure in itself as it adds to the operative time and requires dedicated positioning of the patient. Moreover, it is contraindicated in the presence of intracranial mass lesions for the fear of precipitating a tonsillar herniation. Even, in the absence of intracranial space occupying lesions, this can occur as a delayed complication after LSD, as encountered in about 10% cases. “Sinking brain” and “brain sag” are the other troublesome phenomena observed with LSD.
Intraoperative ventricular puncture avoids the issues complicating LSD and has been frequently used when dealing with “angry brains” in the setting of subarachnoid hemorrhage. Paine et al., described a method for tapping the frontal horn through the frontolateral exposure, which has since been revised, increasing its safety and accuracy. The temporal horn may also be similarly cannulated, if the frontal horn is inaccessible. The popularity of these techniques attests to their practical utility when the surgeon is battling an uncooperative and turgid brain. However, when large supratentorial space-occupying lesions efface the lateral ventricle and cause significant shift of anatomical structures, reaching the ipsilateral ventricle becomes difficult and risky. In such situations, the contralateral ventricle presents a potential source for CSF drainage.
The primary apprehension in tapping the contralateral ventricle is a risk of worsening the sub-falcine herniation. It may appear justifiable in view of the observations regarding reverse cerebellar herniation seen with ventriculostomy in posterior fossa tumours and tonsillar herniation linked with LSD. However, important anatomical peculiarities distinguish sub-falcine herniation and those affecting the posterior fossa. The posterior fossa converges toward the tentorial hiatus and the foramen magnum. Therefore, it is likely for the brain parenchyma under pressure to plug these openings in the manner of a “bath plug” upon CSF drainage from distant sites. Even without a rise in ICP, chronic pressure gradients across these narrow hiatuses may precipitate unexpected herniations.,, In contrast, the sub-falcine window is much wider and roomy and it is improbable to have a water tight seal between the hemispheric brain compartments, caused by herniation of brain tissue. Hence, aggravation of the midline brain shift by contralateral ventricular drainage is unlikely. It must be stressed that in all our cases, ventricular drainage was immediately followed by excision of the lesion and we are unsure of the long-term safety of prolonged contralateral ventriculostomy as a temporizing measure for reducing ICP.
Interestingly, Narotam et al. recorded ICP bilaterally from patients who underwent contralateral ventricular drainage following persistently elevated ICP with midline shift. All these patients have undergone surgical evacuation of mass lesions. They observed that though there were initial intercompartmental differences in ICP recordings, with prolonged CSF drainage, a secular trend toward reduction in ICP was seen in both supratentorial hemispheres. This observation supports our hypothesis that the effect of CSF drainage from contralateral ventricle is not compartmentalized.
If needed emergently, during the course of the operation, freehand contralateral ventricular puncture may need to be performed in an anatomically awkward position. Hence, neuronavigation assistance is invaluable. In our cases, we did not use intraoperative navigation. Accordingly, we marked and rehearsed the trajectory for ventricular puncture before draping the head. We also employed table rotation and elevation to make ventricular targeting as anatomical as possible for the surgeon after positioning for the craniotomy. The amount of CSF to be drained from the ventricle depends upon the surgeon's impression of brain relaxation, but usually 20–30 ml was felt to be adequate in our cases.
Contralateral ventricular puncture, in the setting of sub-falcine herniation with ipsilateral ventricular effacement, is an effective, safe, and invaluable strategy for optimizing the brain condition during surgery for large lesions. Though our experience is small, it negates the commonly held apprehension that such operative maneuvers may worsen brain herniation.
CSF = cerebrospinal fluid, EVD = external ventricular drainage, LSD = lumbar spinal drainage, ICP = intracranial pressure.
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[Figure 1], [Figure 2]