Letter: Genealogy of Training in Vascular Neurosurgery

To the Editor: POSITIONING FOR CRANIAL EXPOSURES (RETRACTOR-LESS) AROUND THE BREGMA NUANCES One of the techniques that have evolved in modern neurosurgery is dynamic retraction or retractor-less surgery.1 The brain retractor itself evolved only in the nineteenth century as dural opening and operative corridors of deep seated lesions evolved.2 Disadvantages of fixed brain retractors, like brain edema and injury, were evident immediately and paved the way for dynamic retraction,3 the underlying concept being to decrease the amount of time the brain is under the pressure of a retractor. Sticking to this concept involves the following components: (1) use the weight of the brain itself to fall away by appropriate positioning, (2) use nonfixed retractors like the hand-held suction tube on a patty or an intermittent hand held malleable retractor, and (3) use fixed brain retractors intermittently with hand stabilizers only when the first 2 options are not possible. As a simple example, positioning for pterional/bifrontal craniotomy to skull base lesions will involve 10° retroflexion of the neck to allow the frontal and temporal lobes to fall away from the skull base.4 This contributes to retractor-less approaches to the frontal skull base. In this letter, we focus on pathologies around midline bregma. We analyze approach side down and approach side up in this letter. All examples included below are for those lesions considered unsuitable for non-surgical treatments like neuro-vascular intervention or radio-surgery by multi-disciplinary team meet. NEUROANATOMY The anterior third of the SSS (Superior Sagittal Sinus) has bridging draining veins directed posteriorly, while the middle third has almost perpendicular bridging veins.5 Of the 3 anterior third SSS bridging veins (anterior, middle, and posterior frontal veins), the posterior frontal vein could drain the pre-central area. There could be overlap with pre-central vein, which normally drains into the middle third of the SSS. Hence the eloquent areas are more towards the mid-third of the SSS. The branches mentioned above drain the lateral surface of the cerebrum. Of particular note is that there are two sets (lateral brain surface and medial brain surface) of veins draining into SSS. Intra-operative neurophysiology and intra-operative angiography will only be synergistic to pre-op imaging and mapping. Approach Side Down In Parafalcine meningioma,6 veins take importance at all stages of meningioma surgery. Usually for large tumors and deep tumors in this area, the brain needs to be handled gently. A retractor, if at all needed, is placed on the falx and not on the brain. Patties are slid along the arachnoid plane between tumor and brain. On the other hand, if the lesion is small and superficial, then there will not be much need for retraction anyway. There is no definite size cut-off mentioned in the literature. An arteriovenous malformations (AVM) with only pericallosal feeders (deep interhemispheric)7 is another situation wherein the approach side is kept down. Usually there are no draining veins coming onto the surface, draining into the SSS, and hence hindering the approach. In such a scenario, the approach side can be down. If there is a draining vein from an AVM draining into the SSS along the approach route, then it needs to be respected so as not to give any tension on this vein. Usually the major draining veins of an AVM (which will appear bright red because of arterialisation) are dealt with only during the late stages of AVM excision. A caudate area AVM requiring a contralateral transcallosal approach needs to positioned with the approach side down. Even in approach side down, it is important for the dural opening to not be very big, otherwise the brain will fall away more than required8 Approach Side Up Parasagittal meningioma6: In small tumors of this type, usually not much retraction is needed anyway. So, a neutral position will keep midline structures in orientation. AVM with pericallosal feeders and SSS drainage: The first approach is not possible here because, the veins have to be respected. Putting the pathology/approach side down will tug on the AVM draining veins and increase the chance of bleeding within the AVM. Intermittent retraction with a suction tube in neutral position seems reasonable. In large surface AVM,7 the craniotomy as such is large enough to allow liberal dural opening. Frontal AVM with feeders from middle cerebral artery areas9 will need a bifrontal and a temporal craniotomy to approach the middle cerebral artery (MCA) feeder efficiently. Here, the pathology site is topmost. Dural opening is liberal, with additional opening on the temporal side to tackle additional feeders. To conclude, although initially fixed retractors can be supplanted with intermittent retraction, a retractor-less surgery is possible even for complex lesions.10 Disclosure The author has no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.