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The tentorium slopes up acutely and therefore the patient’s neck needs to be very flexed to minimize the awkward direction of the surgeon looking up all the time. Extra padding under the buttock might be needed for small patient. The patient must be strapped securely to allow tilting forward of the table if necessary. This is best tested at the end of positioning. A special Mayfield crossbar is needed for the sitting position.
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Test this out the day before surgery if you have not done this before to make sure everything will go smoothly.

In contrast to management of other posterior fossa tumours, pre-operative hydrocephalus should be shunted before excision of tumour.

One must have an excellent anesthetist. Central venous line is helpful to allow one to remove the air in the right atrium in case of air embolism. Intra-arterial line to monitor blood pressure is useful. Precordial ultrasound and end tidal pCO2 monitoring are advisable to allow one to detect air-embolism early. The patient should be hyper-hydrated and moderate positive pressure ventilation should be given to prevent air-embolism.

To prevent air-embolism, a stepwise cautious progression starting from skin incision is important. Coagulation of any bleeding especially venous bleeder is essential. Regular check for venous bleeding by asking the anesthetist to squeeze the neck is extremely important. Before the skin incision is made, the anesthetist should practice getting under the drape to squeeze the neck (both internal jugular veins) to ascertain easy access. After each step of skin incision, subcutaneous incision, cutting of ligamentumnuchae, muscle stripping from bone and especially each small step of bone removal, I ask my anesthetist to squeeze the neck. Constant irrigation of normal saline by assistant will minimize blood being sucked into any venous opening.

For skin incision, I prefer a midline vertical incision from 3-5 cm above external occipital protuberance to lower cervical area. Bony exposure is needed up to about 3 cm lateral to midline, superiorly all the way to lower margin of transverse sinus. Inferiorly, one does not need to go all the way to the foramen magnum but sufficient inferior exposure is important to allow the cerebellum to flop downward. Dura opening is as shown in Picture 9 to allow maximal exposure to the tentorium. The cerebellar falx and the accompanying sinus is stitched (or coagulated) and divided.

 

Once the dura is opened, the microscope is brought in to look for the bridging veins to be cleared.

One needs to look as lateral as possible to see all the veins, lest unexpected rupture and bleeding occurs later when cerebellum flops down more due to gravity. All midline draining veins can be divided at this stage. A Yarsagil retractor arm can be introduced to depress the cerebellum. An elbow rest is useful to minimize arm muscle fatigue.

A thick white arachnoid membrane over the quadrigeminal area needs to be divided to see the pineal tumour.

I usually start tumour excision with the middle of the tumour before going inferiorly. Ultrasonic aspirator may be very useful for firm and hard tumour.

 

The superior end with the veins should be tackled last.

The vein of Galen is often pushed superior and comes into view only at the end of excision. Laterally, the basal veins of rosanthal can be seen as they run upward to the confluence of veins.

After complete excision of tumour, one can see the posterior aspect of the third ventricle. Usually there is a layer of ependymal lining before one enters the third ventricle. The columns of fornix, internal cerebral veins and telachoroidea can be seen in the third ventricle.

Dura is closed and I usually use a titanium mesh and screws to bridge the bony defect. This gives much better cosmetic results.