Cisternostomy

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

In head injuries, the principle of “CSF-Shift Edema” plays the pathophysiological role in increasing the intracranial, or more precisely, the intra-parenchymal pressure as a consequence of traumatic subarachnoid hemorrhage. Cisternostomy reverses the “CSF-Shift” by opening the cisterns to atmospheric pressure, hence 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 stretch.

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 dissection of the orbito-meningeal band. The dura is opened at the base and the blood is washed out following dissection of the optico-carotid cister. 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 getting lax. Cisternostomy is increasingly being regarded as a more efficient and effective primary surgical intervention for moderate to severe TBI. Its potential application is highly due to its immediate effect in lowering intracranial pressure (ICP) and its role in the improvement of brain oxygenation and metabolism.

Pathophysiology

The physiological basis of this procedure, “CSF shift edema”derives its understanding from the fact that the CSF communicates from the cisterns to the interstitial fluid (ISF) via Virchow Robin spaces. The interaction of the CSF through the VRS with the interstitial spaces in the brain plays a vital role in cisternostomy. As compared to the 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 the CSF from the ventricles. Research done using weight-drop models to mimick severe TBI in mice models indicated the extensive communication of the cisternal CSF versus the ventricular CSF. The MR images post-TBI in this study clearly revealed that ventricular CSF only traverses the immediate periventricular region,while the subarachnoid CSF from the basal cisterns enter the brain parenchyma rapidly through perivascular Virchow Robin spaces. Severe head trauma results in subarachnoid hemorrhage. This results in blood entering the cisterns at a relatively higher pressure and this results in increased pressure within the cisterns. The increase in pressure within the cisterns results in a gradient that pushes the CSF from the cisterns into the brain parenchyma. This is the basis of CSF shift edema and this has been proven with animal experiements by Dr. Garnette Surtherland Once the understanding of the pathophysiology is established, it becomes evident that the opening of the cisternal spaces to atmospheric pressure favours the resolution of the CSF shift edema by reversing the gradient of CSF flow. The positive effect of the cisternal drainage in relieving brain swelling is presumed to be due to the reversal of CSF shift edema. The effect is further enhanced if the CSF is drained through a cisternal drain in the postoperative period as well.

Procedure

The surgical procedure is performed with the patient in the supine position. The head is rotated and extended about 10-15° to the contralateral side, until the malar eminence reaches the uppermost part. A frontotemporal craniotomy is performed. The sphenoid ridge resection starts in the lateral-medial direction. The sphenoid ridge is drilled off with a drill burr until the orbito-meningeal arteries are encountered. The drilling is continued until a flattened bone surface is obtained. At this point, the skull drilling stops and the dura is carefully detached from the bone. This maneuver allows one to get to the base very close to the cisterns. The basal dura is opened in a linear fashion near the orbital roof. This maneuver allows easy (and sometimes rather difficult) access to the interoptic, optico-carotid and the lateral carotid cisterns that can now be opened for draining. Cerebrospinal outflow immediately provides brain relaxation which enables further reaching the membrane of Liliequist. The membrane of Liliequist can be approached through the optico-carotid window or the lateral carotid window. The membrane, made up of two layers, can be opened by a sharp dissection. After the membrane is widely opened, the basilar quad consisting of the basilar artery, both P1 segments, the superior cerebellar arteries and the Occulomotor nerve on both sides is visualized. A number 8 feeding tube is inserted to drain the CSF from the cisterns. A rapid decrease in brain tension and a regain of pulsatility in the brain matter is observed after this stage is completed. After the brain becomes lax, we have noticed that interestingly all venous oozing stops and a clean field is seen. Presence of profound ischemia is the only time, the brain swelling does not resolve. This is because the mechanism of edema in this scenario is primarily cytotoxic and will not be amenable to opening the cisterns. The dura is closed with just approximation and the drain is left in place for at least five days for continued CSF drainage that helps prevent the cascade of secondary damage, by efficiently regaining the CSF flow . Bipolar coagulation is almost never used and hemostasis is done with the help of oxidized cellulose and continuous irrigation. As a result of traumatic brain injuries, the cisterns are usually filled with blood. Irrigation provides blood and clots removal, and stops any venous bleeding avoiding the use of the bipolar coagulation. Once the cisterns are opened, a feeding tube, 2mm in diameter, is positioned into the prepontine cistern which helps to irrigate out the blood for up to five days. Procedural changes can also occur in case of a surface hematoma with significant mass effect. Hemostasis is achieved using oxidized cellulose and continued irrigation. A bipolar coagulation is needless in this procedure..

Uses and Outcomes

Cisternostomy proves to be useful in cases that primarily demand a need for decreased intracranial pressure secondary to intracerebral hemorrhage. Timing of intervention is an important indicator of Cisternostomy as the primary surgical management in moderate to severe brain injury. The rationale of Cisternostomy based on the reversal of CSF-Shift edema is applicable when there are clinico-radiological signs of raised ICP and imminent transtentorial herniation. According to a clinical study, the deterioration of motor score on the Glasgow Coma Scale from 5 to 4, with associated radiological sign of ipsilateral cerebello-pontine angle (CPA) cistern widening, warrants immediate Cisternostomy to prevent the ongoing herniation. Outcomes following Cisternostomy in moderate to severe brain injury have been remarkable till date. The current studies and reports from centers performing Cistenrostomy have well-established the efficacy of this procedure in playing a two-fold 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
• Decrease in lactate/pyruvate ratio
• Prevention of herniation and brainstem compression
• Decreased ICU and Ventilator days

Limitations

Being regarded as a complex micro-surgical procedure, Cisternostomy has its limitations in terms of availability of microscope, especially in low-to-middle income countries; as well as thorough knowledge of skull base anatomy and surgical skills needed to perform such a procedure in an emergency setting. This demands a steep learning curve and expertise required to tackle complex microsurgery. The technical difficulties of performing cisternostomy with a tight edematous brain requires a great amount of training to be able to successfully carry it out and is the main reason as to why DHC, a technique that is over 110 years old and requires much less precision, training and infrastructure is more prevalent. The utility of subfrontal retraction in severe head trauma has been a point of concern.. The retraction damage of orbitofrontal gyri is a small price to pay in bringing down intracranial pressure is what Dr Cherian feels about this.[3] Although not applicable if ischemic changes have set in, a basal approach and the use of the “2-minute window” surgeons get after removing the subdural hematoma allows access to the inter-optic cisterns. . [3] The possibility that the pediatric brain may alter the predictable response and a sliver of basifrontal lobe may need to be removed in subpial fashion at times to reach the cisterns. Limitation: In pediatric age group, lack of compliance of the brain might often pose a need to perform thin basi-frontal lobectomy in a subpial fashion to achieve cisternal access. The dural opening left for continued Cisternal drainage post-operatively is prone to the formation of a pseudomeningocele probably due to the accumulation of the CSF into the sub-galeal space. The procedure has been observed not to work when associated ischemia occurs; in cases of hypovolemia and with malignant brain infarcts.

Development

The procedure of Cisternostomy, or more precisely CSF drainage or “let out” has not been uncommon in neurosurgical practice. Most neurosurgeons do this for aneurysms and when there is brain swelling. It was a common practice to cut the tentorium with or without temporal lobectomy in trauma to reach the cisterns ( This “ lateral cisternostomy” was practiced in many centres.

In fact, fractures of the skull base, petrous bone and the cribriform plate result in CSF otorrhea and rhinorrhea, which itself, is “auto-cisternostomy” provides an alternative leakage to the CSF that would have otherwise shifted into the brain parenchyma as per the above-stated hypothesis. The similar effect was observed when the cisterns were opened serendipitously assuming an aneurysm repair rather than a traumatic brain by Dr. Iype Cherian during his practice in India. The surprisingly significant brain laxity observed led to further clinical observations, with the initial years of performing a hybrid Cisternostomy with bone flap removal, and a considerably improved prognosis in patients.

Cisternostomy and the manoeuvres to access the skull base have been routinely practised in neurosurgery for skull base tumours and aneurysms. However, when introduced as a primary surgical procedure for traumatic brain injury, this faced significant challenges in terms of acceptance. There is a reluctance to adopt a change in the current practice of DHC regardless of the rising mortality and vegetative states it leads to. Over the course of a decade with evidently positive prognosis in some centres in India, Nepal, China and parts of Europe have created waves in the field of neurotraumatology. Comparative studies to assess the prognostic value of Cisternostomy over DHC have clearly shown that opening the basal cisterns in a traumatic brain instantly reduces the brain edema. Furthermore, the replacement of the bone flap back in a single procedure prevents the cortical stretch which otherwise alters the topography of the motor and sensory cortices of the brain that leads to hemiplegia and other forms of morbidity seen in patients undergoing DC Further studies are also evaluating the recognition of Cisternostomy as a protocol for emergency neurotrauma provided the available expertise and instruments is available. An on-going neurotrauma study, Global Neurotrauma Outcomes Study funded by the NIHR regards cisternostomy as one of the techniques vital to the reduction of ICP in emergency TBI. Other trials and studies to evaluate alternate surgical options for moderate to severe TBI are based on the principles of a single-staged surgery, preventing decompression as much as possible for a positive outcome.

References

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