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Upward transtentorial herniation: A new role for endoscopic third ventriculostomy

Background: The placement of external ventricular drainage (EVD) to treat hydrocephalus secondary to a cerebellar stroke is controversial because it has been associated to upward transtentorial herniation (UTH). This case illustrates the effectiveness of endoscopic third ventriculostomy (ETV) after the ascending herniation has occurred. Case Description: A 50-year-old man had a cerebellar stroke with hemorrhagic transformation, tonsillar herniation, and non-communicating obstructive hydrocephalus. Considering that the patient was anticoagulated and thrombocytopenic, an EVD was placed initially, followed by clinical deterioration and UTH. We performed a suboccipital craniectomy immediately after clinical worsening, but the patient did not show clinical or radiological improvement. On the 5th day, we did an ETV, which reverses the upward herniation and hydrocephalus. The patient improved progressively with good neurological recovery. Conclusion: ETV is an effective and safe procedure for obstructive hydrocephalus. The successful resolution of the patient’s upward herniation after the ETV offers a potential option to treat UTH and advocates further research in this area.


INTRODUCTION
e gold-standard treatment of a cerebellar stroke with acute neurological deterioration is a decompressive suboccipital craniectomy with dural expansion; it prevents brain herniation and is the preferred treatment even in the setting of associated hydrocephalus. External ventricular drainage (EVD) is recommended in obstructive hydrocephalus but should be followed or accompanied by decompressive craniectomy. [24] Historically, EVD in the setting of acute hydrocephalus secondary to a cerebellar infarction had been associated to higher mortality attributed to upward transtentorial herniation (UTH). [2] UTH is clinically characterized by impaired consciousness and brainstem dysfunction. [2,6] UTH occurs when the pressure exerted from the posterior fossa promotes a dorsal displacement of the brainstem toward the tentorial notch secondary to an acute supratentorial intracranial pressure (ICP) decrease after draining CSF from the EVD. [6] Hydrocephalus management in this setting is controversial. e following case study illustrates the utility of endoscopic third ventriculostomy (ETV) for UTH.

CASE REPORT
A 50-year-old male was admitted for a diagnostic evaluation of chest precordial pain, shortness of breath, nausea, diaphoresis, and abdominal pain. He had a past medical history of hypothyroidism treated with levothyroxine and atrial fibrillation treated with apixaban. Myocardial infarction was ruled out, and the EKG confirmed paroxysmal atrial fibrillation. On the 2 nd day, the patient developed acute suboccipital headache, nausea, vomiting, dizziness, and dysmetria. Subsequently, he developed acute neurological deterioration. On examination, he was in coma, pupils were miotic, corneal, and nausea reflexes were present and symmetrical. Abnormal flexion was observed under pain stimuli. He had hyperreflexia and bilateral Babinski. Laboratory findings revealed thrombocytopenia and brain MRI showed a bilateral cerebellar ischemic stroke in PICA territory with hemorrhagic transformation, tonsillar herniation, and non-communicating obstructive hydrocephalus [ Figures 1a-f].
We initially placed an EVD considering that the patient was anticoagulated and thrombocytopenic. e EVD was connected to ICP monitoring, which measured 35 mmHg. After draining 10 cc of CSF, the patient developed bradycardia, hypertension, and bilateral mydriasis, he was transferred back to the OR, and we performed a middle suboccipital craniectomy; the cerebellum was 5 mm deep from the dura and it did not swell immediately through the dural defect [ Figure 2a]. After the surgery, we sedated the patient using propofol and fentanyl; cerebellar edema and brainstem upward herniation were treated using hypertonic solutions and amines to maintain an adequate cerebral perfusion pressure. e EVD was closed most of the time and only opened when the ICP reached above 20 mmHg. After 5 days of close neurological monitoring and intracranial hypertension management, we did two clinical serial examinations without sedation and the patient persisted in coma with bilateral fixed 5 mm pupils without response, corneal reflexes persisted, but other brainstem reflexes were absent. MRI revealed cerebellar infarction with hemorrhage transformation, cerebellar edema, UTH, and the aqueduct of Sylvius persisted occluded. On the 5 th day, we took out the EVD, and an ETV was performed. During the endoscopy, microhemorrhages were observed on the midbrain, the third ventricle was dorsally displaced and after the premamillary fenestration, an active pulsatile flow from the interpeduncular cistern was visualized [Figures 2b and c]. State of consciousness and brainstem reflexes improved significantly the 1 st day after the surgery. MRI 1 week after the ETV showed upward herniation resolution, less cerebellar edema, and no hydrocephalus. e patient needed a tracheostomy and gastrostomy, and he started with neurological rehabilitation. ree months after the surgery, the patient made a good recovery with mild cerebellar disabilities (GOS 5); however, the MRI revealed mild enlargement of the lateral ventricles and a suboccipital CSF internal leak. A Hakim programmable ventricle-peritoneal shunt was placed. One year after surgery, the patient improved progressively until he recovered his previous functional status and only persisted with mild intention tremor of his left hand.

DISCUSSION
ere have been reported several UTH cases secondary to posterior fossa lesions. In 1920, Meyer gave the earliest descriptions of UTH, [17] when he reported an unusual supratentorial distention of the splenium. In 1938, LeBeau [8,15] reported an UTH in a case of a cerebellar tumor in which, during exploration along the falx, he described severe displacement and elongation of the vein of Galen. In 1964, Dinsdale [7] reported 9 cases of UTH secondary to cerebellar and pontine hemorrhage. Historically, a cerebellar lesion had been the most frequent etiology of UTH (65%), followed by the cerebellopontine angle, pons, and 4 th ventricle lesions. [6] In 1960, McKissok [16] reported 9 cases of cerebellar hemorrhage that died after ventricular tapping or drainage. [11] Cuneo et al. [6] reported that 25% of patients developed UTH after ventricular drainage. Recently, Braksick et al. [5] reported only 2/25 cases (8%), who had clinical worsening after EVD placement, even when they observed preoperative UTH. Using an EVD in the setting of cerebellar lesions has been controversial; however, the reported series are insufficient for proper statistical analysis to determine the actual risk for UTH after EVD. [1,2,[4][5][6][7][8]10,12,13,23] In our case, the patient was initially treated with an EVD to reduce ICP while the anticoagulant activity was reversed; however, the ventricular CSF drainage triggered an UTH because of a pressure gradient difference in the supratentorial and infratentorial compartments that resulted from a sudden pressure resistance decrease of the supratentorial space. [2,3,6] Afterward, a suboccipital craniectomy was performed without clinical benefit. erefore, an ETV was proposed hypothesizing that pressure gradient would be balanced and the ICP would be equalized in both compartments. Although ETV in patients with obstructive hydrocephalus from a posterior fossa lesion has been successful, [22] this is the first case to our knowledge, in which an UTH is reversed using an ETV. e fenestration of the tuber cinereum reversed the pressure gradient difference, which facilitated the resolution of UTH and the acute obstructive hydrocephalus, improving the neurological deficits after the surgery.
e treatment of UTH has been proposed in the literature since 1947 when Ecker recommended a tentorial section and cerebellar aspiration to release the CSF and vein obstruction. [8] Severe neurological deficits and poor outcome after UTH are associated to cranial nerve traction and diencephalic stroke associated to severe vein compression. [6] At present, UTH treatment includes decompression surgery of the posterior fossa, [19,23] hyperventilation, [13] hyperosmotic therapy, [13,20] head elevation, [19] and diuretics. If an EVD is placed, it should have close monitoring, and the drainage must be not <15-20 mmHg above the level of the third ventricle. [13] e clinical diagnosis of UTH is characterized by intracranial hypertension syndrome, altered state of consciousness, loss of brainstem reflexes, and abnormal posturing. [6,10,12,25] On imaging, the vermis covers the tentorial notch, clears the cisterns, showing compression and flattening of the quadrigeminal plate, and the posterior third ventricle;   it can compress the aqueduct of Sylvius, resulting in hydrocephalus. [9,14,18,21] UTH has a poor outcome; [10] therefore, we must make a prompt clinical diagnosis in patients with acute neurological deterioration after an EVD.

CONCLUSION
ETV is an effective and safe procedure for obstructive hydrocephalus. e successful resolution of the patient's upward herniation after the ETV offers a potential option of treatment and advocates further research in this area.

Acknowledgments
anks to Karla Ortega for proofreading this manuscript.

Declaration of patient consent
Patient's consent not required as patients identity is not disclosed or compromised.

Financial support and sponsorship
Nil.

Conflicts of interest
ere are no conflicts of interest.