This patient is clearly demonstrating clinical signs of herniation. The examination results of coma with loss of airway protection requiring mechanical ventilation, as well as the neurologic signs such as dilation and loss of reactivity of the right pupil and flexor posturing of the left arm/leg, are strong indicators that the patient is suffering from right-sided brainstem compression. This constellation of neurologic signs is the most concerning issue in this patient’s presentation and, as such, requires the most immediate attention from the treating physician.

A stat CT of the head (Figure 9-1) will demonstrate location of the mass, extent of midline shift, edema, hydrocephalus, lesional (with possible intraventricular) hemorrhage, and type of herniation. In this case, a large (5.5 × 5.6 × 5.7 cm), calcified, hyperdense mass is noted along the superior anterior falx associated with moderate surrounding edema and causing mass effect on the right that is greater than on the left frontal horns. There is no associated hemorrhage or hydrocephalus. There is loss of sulcation indicative of elevated intracranial pressure (ICP), as well as acute infarcts in the bilateral occipital lobes, right greater than left, suggesting an ongoing process of transtentorial (uncal) herniation.

The immediate medical interventions are directed toward lowering the patient’s elevated ICP. First, raising the head of the bed to at least 30° will prevent cerebral venous outflow obstruction. Second, hyperventilating the patient to a goal Paco₂ of 25 to 30 mm Hg will provide transient lowering of ICP by inducing vasoconstriction of cerebral arteries and arterioles, which will lower cerebral blood volume (CBV). Third, administration of sedatives and analgesics, and potentially paralytic agents such as propofol (beginning at 10 mg/kg/min help to control agitation, reduce CBV, and slow cerebral metabolism, actions that contribute to lowering ICP.¹

The next major intervention is the use of hyperosmolar therapy, typically with continuous infusion of 3% hypertonic saline coupled with boluses of 23.4% hypertonic saline (in 30-mL pushes), along with standard mannitol administration (25% solution given at 0.25-1 g/kg). Such agents work by increasing serum osmolality, which brings water from the extracellular space into the serum, thereby reducing brain swelling. The goal serum osmolality is typically > 320 mOsm/kg, and the goal plasma sodium level in such a patient is typically 150 to 155 mEq/L, with sodium level checks every 4 to 6 hours, because a sodium level > 155 mEq/L has not been shown to be of proven clinical benefit.² The side effects of hyperosmolar therapy include electrolyte imbalances (eg, hypokalemia), pulmonary edema (resulting from rapid intravascular volume expansion), coagulopathy, and intravascular hemolysis.³ Despite the radiographic features of this lesion, which point to it being an extra-axial mass such as a meningioma, it is still causing significant vasogenic edema that should be treated with IV steroids. An immediate bolus of 10 mg IV dexamethasone (Decadron), followed by a maintenance dose of 8 to 32 mg/d, should be implemented.⁴ Dexamethasone works by reducing the permeability of the cerebral capillaries.

Given the recent seizure, which likely precipitated the herniation event (seizures transiently elevate ICP, likely from increasing cerebral blood flow), the patient should be maintained on antiepileptic medication, either phenytoin (Dilantin; following a 20-mg/kg loading dose) or levetiracetam (Keppra; following a 1-g loading dose).

Also a discussion should be had regarding insertion of an ICP monitor in this patient. Typically, patients with clinical signs of elevated ICP and a Glasgow Coma Scale score < 8 warrant direct, invasive monitoring of ICP.⁵ Because this patient presented with a known intracranial mass causing elevated ICP, the indication for an ICP monitor is less cogent given that imminent surgery will remove the source of the elevated ICP. For example, in the case of an unresectable lesion or in the obvious case of traumatic brain injury, if the patient were to be stabilized and supported for an extended period of time, then the utility of an ICP monitor becomes clear. In this case, therefore, an ICP monitor was not inserted immediately given the plan for urgent operative decompression.

The initial interventions in this patient are directed at lowering ICP. However, these interventions solve only part of the problem: edema and seizures as contributors to the herniation syndrome. Clearly, the next step needs to be aimed at expeditious resection of the intracranial mass lesion. Once the patient is stabilized, magnetic resonance imaging (MRI) of the brain with and without contrast must be performed to better characterize the lesion in terms of location, type, and precise anatomic relationships to surrounding structures, including associated vasculature. This study will also aid in the decision of whether preoperative embolization is necessary, because this is likely a well-vascularized meningioma.

MRI of the brain was performed with magnetic resonance angiography (MRA) of the head and neck (Figure 9-2), revealing a 5.6 × 7.1 × 4.9 cm heterogeneously enhancing anterior falcine mass with evidence of internal necrosis and significant surrounding vasogenic edema and mass effect, which is consistent with a large parafalcine meningioma. The effacement of right-greater-than-left frontal horns is again demonstrated. There is also diffusion weighted imaging (DWI) restriction in bilateral medial temporal and occipital lobes suggestive of an acute infarct from bilateral posterior cerebral artery (PCA) compression during the recent herniation event (Figure 9-3).

At this point, the decision of preoperative embolization must be addressed. The major risk of embolization in a tumor of this size (which has very recently caused significant herniation) is causing a hemorrhagic or ischemic insult; both hemorrhage and ischemia may occur in the intratumoral or peritumoral region, either of which could precipitate another herniation event.^6,7 There are no strict guidelines for making this decision, and therefore it is left to the cerebral angiographer and the neurosurgeon to decide on its safety and utility. The benefit of embolization is to minimize blood loss during the operation by injecting small particles (typically polyvinyl alcohol [PVA]) into major extracranial feeding vessels. In this case, the decision was made to forego embolization in favor of urgent open resection in the operating room.

The patient underwent a bicoronal craniotomy for resection of a parafalcine meningioma. The operation proceeded uneventfully; of note, the superior sagittal sinus was sacrificed because it was invaded with tumor and did not appear to be patent. A gross total resection was achieved, and the patient returned to the ICU for postoperative management.

The patient returned to the ICU ventilated, maintained on 3% hypertonic saline infusion, and IV dexamethasone and IV phenytoin. A postoperative CT scan was performed that showed complete removal of the meningioma but relatively significant residual edema. Now that the main source of the patient’s elevated ICP has been removed, it is appropriate to begin weaning the patient from the hypertonic saline, keeping in mind that there is moderate-to-severe remaining edema, which must be done in slow, stepwise fashion to avoid rebound cerebral edema that could potentially incite another herniation event, and to check sodium levels at regular 4- to 6-hour intervals.⁸ Begin with decreasing the rate of the 3% hypertonic saline with the goal of keeping the sodium levels within 10 mEq/L of the plateau level within the first 24 hours. The following step is to switch from the 3% to 2% hypertonic saline, again with the goal of keeping the patient’s sodium level > 140 mEq/L over the next 24-hour period. After a minimum of 48 hours after surgery, it becomes possible to switch the patient to a normal saline infusion with a goal of a sodium level in the normal range (135-145 mEq/L) for the remainder of the ICU stay.

The dexamethasone can be tapered off over a 2-week period, given the severity of the edema and the fact that this is a benign extra-axial lesion; however, the patient should be maintained on a steady level of phenytoin for a minimum of 1 month and potentially for 3 to 6 months given that she presented with seizures.⁹ Also the option of transitioning the patient to levetiracetam from phenytoin in favor of a more benign side-effect profile is at the discretion of the treating neurologist.¹⁰ Ventilatory weaning and other intensive care interventions are left to the judgment of the critical care neurologist.

Given the size and location of this malignant-appearing mass lesion, it comes as no surprise that this patient presented with a clinical herniation syndrome. Moreover, as is clear on the CT scan, another alarming radiographic feature of this lesion is its associated edema. In fact, the herniation event was most likely due to the edema and not to the mass itself, as evidenced by the patient’s neurologic improvement after hyperosmolar therapy and the large IV corticosteroid bolus. There is also the possibility that the mass induced a seizure that transiently elevated her ICP, thereby precipitating the herniation episode.

So the question is whether this patient needs to undergo emergent operative decompression of this lesion or whether a delay is permissible in order to allow the steroids to take effect in reducing the edema. Such a brief delay would also allow for other interventions and studies to be pursued. With the observed neurologic improvement, the decision made in this case was to delay surgery. This was done at the risk of the patient’s having seizures and perhaps transiently herniate again, as well as at the risk of developing an intratumoral hemorrhage that could replicate the cascade of events that brought the patient to the ED. By delaying the surgery for 24 to 48 hours, important interventions were either initiated or continued: an MRI with gadolinium contrast was obtained; continuous electroencephalographic (cEEG) monitoring was begun to determine, based on the presence or absence of seizure activity, if the patient required more maintenance phenytoin or a second antiepileptic agent; hypertonic therapy in the form of 3% saline was infused with a goal sodium level of at least 145 mEq/L; and IV dexamethasone was continued at a dose of 10 mg every 4 hours. With the more reliable neurologic examination to follow, it was considered unnecessary at this point to insert an ICP monitor.

The contrast MRI allowed for better operative planning, especially because the noncontrast CT scan was somewhat difficult to interpret in this patient in terms of tumor origin. The MRI revealed that the tumor likely arose from the inferior left parietal lobe (Figure 9-5); there was also a better quantification of the edema along with a more detailed assessment of the degree of necrosis and proximity to important vasculature. All of this pointed to this tumor being a high-grade malignant lesion, likely a glioblastoma multiforme. In addition to the MRI, the cEEG did not reveal any epileptiform activity, although the patient’s sodium level rose in response to the hypertonic saline infusion.

It is also important to note that the surgical delay theoretically reduces the risk of intraoperative bleeding complications because the edema is given a chance to resolve with steroid therapy. An emergent operation on a very swollen brain that is actively herniating carries with it the risk of inducing significant bleeding as well as making the surgical resection of such a lesion more technically challenging when faced with such friable tissue. Therefore, surgery was performed in a 24- to 48-hour window after the acute herniation event and in this case proceeded uneventfully. This delay is weighed against the risk of development of an intratumoral hemorrhage that could precipitate another, perhaps more devastating, herniation event. Such an intratumoral hemorrhage would need to be treated with urgent surgical decompression once the patient is medically stable. For this patient, the postoperative concerns and goals were essentially identical to those described in the aforementioned first case.

Hydrocephalus is the most concerning issue in this patient. Intracranial mass lesions located in the posterior fossa as well as in the pineal region and third ventricle are prone to causing hydrocephalus due to obstruction of cerebrospinal fluid (CSF) outflow. In cases of hydrocephalus, there is a spectrum of clinical severity, ranging from mild headache to more severe headache with vomiting (as in this patient) to significant obtundation, loss of airway protection, and other signs of impending herniation. In this latter, more emergent scenario, the hydrocephalus must be treated immediately and can nearly always be controlled through placement of an external ventricular drain (EVD). This allows for external drainage of CSF prior to addressing the obstructive mass lesion.

In this case, ventricular drainage was considered unnecessary, considering the patient’s clinical status (awake, interactive, orienting). Even in patients who demonstrate long-standing symptoms consistent with chronic hydrocephalus can present with an acute decline that may need to be treated with ventricular drainage.

MRI with and without contrast is the standard imaging study for all mass lesions of the posterior fossa. The MRI characteristics of the lesion in this case were most consistent with hemangioblastoma, a benign well-vascularized central nervous system tumor arising from stromal cells of small blood vessels that typically is located in the cerebellum, brainstem, and spinal cord. In fact, 8% to 12% of all posterior fossa tumors are hemangioblastomas, although they account for only 1.0% to 2.5% of all intracranial mass lesions and are commonly associated with Von Hippel–Lindau (VHL) disease (approximately 25% of all hemangioblastomas). As seen in the patient’s MRI (Figure 9-7), the mass is avidly contrast enhancing, with a characteristic mural nodule and a cystic core. It was considered prudent to start dexamethasone because of the associated edema and the hydrocephalus and headaches.

Because the MRI characteristics of this mass were very suggestive of hemangioblastoma, an additional work-up was conducted that included an ophthalmologic evaluation for retinal lesions (commonly found in patients with VHL); a total spine MRI with and without contrast to search for spinal cord hemangioblastomas, which may be performed after surgery; and vanillylmandelic acid and metanephrine levels (elevated with pheochromocytoma, which is also associated with VHL). Determining the presence of a pheochromocytoma preoperatively is a critical step given the risks from anesthesia associated with this tumor, for example, hypertensive crisis and tachycardia from catecholamine release during anesthesia induction.¹¹ This patient had no retinal lesions, but was ultimately diagnosed with VHL; he also had a pheochromocytoma (elevated urine and plasma metanephrines coupled with an adrenal mass diagnosed on abdominal CT) and a T12-enhancing lesion suspicious for a spinal cord hemangioblastoma. In this circumstance, it is prudent to have an endocrinologist formally evaluate the patient and advise on preoperative and postoperative blood pressure management as well as alerting the anesthesia team to the presence of a pheochromocytoma. The endocrinologist is then in a position to follow the patient long term once the surgery is completed.

There is also the question of preoperative angiography and embolization. Cerebellar hemangioblastomas are well-vascularized lesions that are occasionally embolized preoperatively in an effort to control intraoperative blood loss. Reports vary in terms of preoperative embolization success—more recent studies point to a high enough postembolization risk of hemorrhage such that embolization is not routinely recommended.¹²

As noted earlier, in this case there is no need to manage the hydrocephalus in an urgent fashion. Therefore, the issue is how to manage the hydrocephalus both during and after the operation. In this case, the goal is to obtain control of CSF drainage prior to operative decompression via a retrosigmoid suboccipital craniotomy approach, which will prevent cerebellar herniation through the dural opening made by the neurosurgeon while approaching the mass. Two interventions were made prior to the planned craniotomy: (1) an endoscopic third ventriculostomy (ETV) and (2) placement of a right frontal EVD. The ETV provides both short- and long-term control of hydrocephalus. By creating a new passage through the floor of the third ventricle into the prepontine cistern, the level of the obstruction caused by the hemangioblastoma (at the fourth ventricle) is essentially bypassed, allowing for CSF outflow and absorption to approach normal parameters (Figure 9-8). The EVD is placed preoperatively in the ICU or with the patient positioned supine in the operating room prior to being flipped to the prone position for the craniotomy. Another common practice involves intraoperative placement of the EVD through a Frazier burrhole that is classically placed in the occipital bone. This burrhole can be easily drilled with the patient in the prone position, which is typically how these operative resections are performed (placing this burrhole with the patient in the sitting position is also an option). An EVD is passed through the Frazier burrhole, typically guided by neuronavigation, through a separate incision prior to opening the main incision for the suboccipital craniotomy. This EVD is kept in place for the duration of the operation and is then utilized in the postoperative period.

The hydrocephalus can be expected to resolve following resection of the obstructive mass lesion, but it will not improve rapidly. Postoperative swelling will slow resolution of hydrocephalus; thus, the EVD serves three functions in the recovery period: (1) ICP monitoring, (2) CSF drainage for control of hydrocephalus, and (3) CSF drainage to prevent leakage through the incision site and therefore to promote wound healing. The level at which the EVD is set is determined by the neurosurgeon; in this situation, the typical level is anywhere from 0 to 10 cm H₂O above the external auditory meatus (EAM). Over the next few days, the EVD should be progressively raised above the 10-cm H₂O level, during which the patient’s symptoms (mainly headache, but also level of arousal), ICP readings, and wound must be assessed to determine whether the patient is tolerating weaning from the EVD. Exacerbation of headache, persistently elevated ICPs (typically > 20 mmHg is cause for concern), and leakage from the incision are indications that weaning the patient from the EVD is not being tolerated and that the patient requires additional CSF drainage. If the patient has only mild preoperative hydrocephalus, some neurosurgeons will keep the drain at a low level (0-5 cm H₂O) for 3 to 5 days postoperatively to promote wound healing and then simply will clamp the drain to determine if the wound, namely the fascial layer, has closed adequately to prevent CSF leakage. If there is no evidence of pseudomeningocele formation, the EVD is removed at the bedside.