Cisternostomy

Cisternostomy is a neurosurgical procedure that uses skull base and microvascular techniques to access and open the basal subarachnoid cisterns and reverse brain swelling in moderate to severe head trauma.

In head injuries, the principle of "CSF-Shift Edema" plays a pathophysiological role in increasing intracranial, or more precisely, intra-parenchymal pressure as a consequence of traumatic subarachnoid hemorrhage. Cisternostomy reverses the "CSF-Shift" by opening the cisterns to atmospheric pressure, thus reversing the pressure gradient that caused the cerebrospinal fluid (CSF) to shift into the brain parenchyma through the Virchow Robin Spaces.

Unlike Decompressive craniectomy, cisternostomy avoids the risks associated with bone flap removal and cranioplasty as well as the displacement of the swollen brain to the craniectomy defect, resulting in extensive damage to tracts and axons due to stretching.

The procedure accesses the basal cisterns through the axial and sagittal unlocking of the frontal and temporal lobes by drilling off the sphenoid ridge and dissecting the orbito-meningeal band. The dura is opened at the base, and the blood is washed out after dissecting the optico-carotid cistern. The carotico-oculomotor cistern is opened. The opticocarotid cistern is opened, and the blood is washed out; the carotico-oculomotor cistern is opened. Dissection of the Liliequest membrane leads to the cisterns of the posterior fossa. A feeding tube is inserted into the prepontine cistern and kept for five days to drain CSF.

The entire procedure takes about ten to twenty minutes to complete, post-learning curve. The learning curve to reach the basal cisterns in exceedingly swollen brain is important, as many neurosurgeons find it difficult to retract a swollen brain. However, once the cisterns are reached, even with some retraction damage to the orbitofrontal gyri, the brain starts to become less tense. Cisternostomy is increasingly regarded as a more efficient and effective primary surgical intervention for moderate to severe TBI. Its potential application is high due to its immediate effect in lowering intracranial pressure (ICP) and its role in improving brain oxygenation and metabolism.

Pathophysiology

The physiological basis of this procedure, "CSF shift edema," derives its understanding from the fact that CSF communicates from the cisterns to the interstitial fluid (ISF) via Virchow-Robin spaces. The interaction of CSF through the VRS with the interstitial spaces in the brain plays a vital role in cisternostomy. As compared to cisternal CSF, ventricular CSF does not directly communicate with the parenchyma, and an external ventricular drain placement in severe trauma only helps with the compliance of the system by removing CSF from the ventricles. Research using weight-drop models to mimic severe TBI in mice models indicated the extensive communication of cisternal CSF versus ventricular CSF. The MR images post-TBI in this study clearly revealed that ventricular CSF only traverses the immediate periventricular region, while subarachnoid CSF from the basal cisterns rapidly enters the brain parenchyma through perivascular Virchow-Robin spaces. Severe head trauma results in subarachnoid hemorrhage. This causes blood to enter the cisterns at relatively higher pressure, resulting in increased pressure within the cisterns. The increase in pressure within the cisterns results in a gradient that pushes CSF from the cisterns into the brain parenchyma. This is the basis of CSF shift edema, which has been proven with animal experiments by Dr. Garnette Sutherland. Once the understanding of the pathophysiology is established, it becomes evident that opening cisternal spaces to atmospheric pressure favors the resolution of CSF shift edema by reversing the CSF flow gradient. The positive effect of cisternal drainage in relieving brain swelling is presumed to be due to the reversal of CSF shift edema. The effect is further enhanced if CSF is drained through a cisternal drain in the postoperative period.

Procedure

The surgical procedure is performed with the patient in the supine position. The head is rotated and extended approximately 10-15° to the contralateral side until the malar eminence reaches the uppermost part. A frontotemporal craniotomy is performed. The sphenoid ridge resection begins in the lateral-medial direction. The sphenoid ridge is drilled off with a drill burr until the orbito-meningeal arteries are encountered. Drilling continues until a flattened bone surface is obtained. At this point, skull drilling stops, and the dura is carefully detached from the bone. This maneuver allows close access to the cisterns at the base. The basal dura is opened linearly near the orbital roof. This maneuver allows easy (and sometimes challenging) access to the interoptic, optico-carotid, and lateral carotid cisterns, which can now be opened for drainage. Cerebrospinal fluid outflow immediately relaxes the brain, enabling further access to the Liliequist membrane. The Liliequest membrane can be approached through the optico-carotid window or the lateral carotid window. The membrane, composed of two layers, can be opened by sharp dissection. After the membrane is widely opened, the basilar quad (basilar artery, both P1 segments, superior cerebellar arteries, and oculomotor nerves on both sides) is visualized. An 8-French feeding tube is inserted to drain CSF from the cisterns. A rapid decrease in brain tension and a return of pulsatility in the brain tissue is observed after this step is completed. Notably, all venous oozing stops, and a clean field is evident after the brain becomes lax. Profound ischemia is the only time brain swelling does not resolve. This is because the edema mechanism in this scenario is primarily cytotoxic and will not respond to opening the cisterns. The dura is closed by simple approximation, and the drain is left in place for at least five days for continued CSF drainage, helping prevent secondary damage by efficiently restoring CSF flow. Bipolar coagulation is almost never used; hemostasis is achieved using oxidized cellulose and continuous irrigation. Due to traumatic brain injuries, the cisterns are usually filled with blood. Irrigation removes blood and clots, stopping any venous bleeding and avoiding the use of bipolar coagulation. Once the cisterns are opened, a 2-mm diameter feeding tube is positioned into the prepontine cistern, aiding in irrigating out blood for up to five days. Procedural modifications may be necessary in cases of surface hematomas with significant mass effect. Hemostasis is achieved using oxidized cellulose and continued irrigation. Bipolar coagulation is unnecessary in this procedure.

Uses and Outcomes

Cisternostomy proves useful in cases requiring decreased intracranial pressure secondary to intracerebral hemorrhage. The timing of intervention is an important indicator for cisternostomy as primary surgical management in moderate to severe brain injury. The rationale of cisternostomy, based on reversing CSF-Shift edema, is applicable when there are clinical and radiological signs of increased ICP and impending transtentorial herniation. According to a clinical study, deterioration of the motor score on the Glasgow Coma Scale from 5 to 4, with an associated radiological sign of ipsilateral cerebello-pontine angle (CPA) cistern widening, warrants immediate cisternostomy to prevent ongoing herniation. Outcomes following cisternostomy in moderate to severe brain injury have been remarkable to date. Current studies and reports from centers performing cisternostomy have well-established the efficacy of this procedure in playing a dual role by decreasing ICP and preventing progression to secondary brain injury. Various studies have observed the following outcomes post-cisternostomy:

• Normalization of intracranial pressure (ICP)
• Improved cerebral microdialysis glucose
• Decreased lactate/pyruvate ratio
• Prevention of herniation and brainstem compression
• Decreased ICU and ventilator days

Limitations

As a complex microsurgical procedure, cisternostomy has limitations, including the need for microscopes, especially in low- and middle-income countries, along with in-depth knowledge of skull base anatomy and surgical expertise to perform the procedure in emergency settings. This necessitates a steep learning curve and specialized skills to manage complex microsurgery. The technical challenges of performing cisternostomy in a tight, edematous brain require extensive training for successful execution. This is a primary reason why decompressive hemicraniectomy, a technique over 110 years old, requiring less precision, training, and infrastructure, is more prevalent. The use of subfrontal retraction in severe head trauma has been a concern. Dr. Cherian believes that the retraction damage to orbitofrontal gyri is a small price to pay for lowering intracranial pressure. [3] While not applicable if ischemic changes have occurred, a basal approach and the use of the “two-minute window” after removing the subdural hematoma allow access to the interoptic cisterns. [3] The pediatric brain may alter the predictable response, and a sliver of the basifrontal lobe may occasionally need removal in a subpial fashion to access the cisterns. Limitation: In the pediatric age group, the brain's lack of compliance may necessitate a thin basifrontal lobectomy in a subpial fashion to achieve cisternal access. The dural opening left for continued cisternal drainage postoperatively is prone to pseudomeningocele formation, potentially due to CSF accumulation in the subgaleal space. The procedure is not effective in cases of associated ischemia, hypovolemia, or malignant brain infarcts.

Development

The procedure of cisternostomy, or more precisely, CSF drainage, has not been uncommon in neurosurgical practice. Most neurosurgeons perform this for aneurysms and brain swelling. Cutting the tentorium with or without temporal lobectomy in trauma was a common practice to reach the cisterns (). This "lateral cisternostomy" was practiced in many centers.

In fact, fractures of the skull base, petrous bone, and cribriform plate result in CSF otorrhea and rhinorrhea, which itself is "auto-cisternostomy," providing an alternative leakage path for CSF that would otherwise shift into the brain parenchyma, as per the hypothesis. A similar effect was observed when cisterns were opened serendipitously during aneurysm repair rather than traumatic brain injury by Dr. Iype Cherian during his practice in India. The surprisingly significant brain laxity observed led to further clinical observations, including initial years of performing hybrid cisternostomy with bone flap removal, resulting in improved patient prognosis.

Cisternostomy and skull base access maneuvers have been routinely used in neurosurgery for skull base tumors and aneurysms. However, when introduced as a primary procedure for traumatic brain injury, its adoption faced significant challenges. There's reluctance to change from the current practice of DHC despite rising mortality and vegetative states it leads to. Over a decade, positive outcomes in certain centers in India, Nepal, China, and parts of Europe have influenced neurotraumatology. Comparative studies evaluating the prognostic value of cisternostomy versus DHC have clearly demonstrated that opening the basal cisterns in traumatic brain injury immediately reduces brain edema. Moreover, bone flap replacement in a single procedure prevents cortical stretching, which otherwise alters the topography of the motor and sensory cortices, leading to hemiplegia and other morbidities seen in DC patients. Further studies are also evaluating cisternostomy as a protocol for emergency neurotrauma, provided the necessary expertise and instruments are available. An ongoing NIHR-funded neurotrauma study, the Global Neurotrauma Outcomes Study, considers cisternostomy a vital technique for reducing ICP in emergency TBI. Other trials and studies evaluating alternative surgical options for moderate to severe TBI are based on the principles of a single-staged surgery, minimizing decompression for optimal outcomes.

References

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