In the early 1900s surgeons like Cushing, Dandy and Krause demonstrated surgical approaches to deep seated brain tumours and redefined neurosurgical principles. The surgeons removed brain tumours and other lesions, with a morbidity and mortality rate that was acceptable at that period of time, taking into consideration the lack of imaging, monitoring, anesthetic and surgical technology. The advent of new imaging technology in the last 20 years, has made possible precise tumour localisation, and characterisation.. This, along with improved monitoring and anaesthesia, has put the onus back on the surgeon to find the means to tackle these lesions which are now so clearly seen and defined.

Intracerebral tumours present to the clinician due to either raised intracranial pressure, or the local effect of the lesion on the brain as seen by seizures or neurological deficit. The main aim of surgery for these lesions is radical excision, while procuring a histological diagnosis. Radical excision in turn benefits the patient by effecting a reduction in the intracranial pressure, and reducing the effects of the lesion on the surrounding brain. It is the duty of the surgeon to ensure that in doing so, the patient improves, or at the least, maintains his or her neurological condition. The goals in front of the surgeon are therefore radical excision of the tumour with a good neurological result. The use of microsurgical techniques at surgery greatly help the surgeon in achieving these goals and it is mandatory that surgeons use the microscope at all surgeries.

Experience with microsurgical techniques has brought in the knowledge that the anatomy of the brain is such that it allows access to deep structures. “The brain is not an isolated compact structure like an island unto itself; rather it is like a continent with a multifaceted coastline with many water inlets; it floats in a sea of CSF , with rivers of cerebrospinal fluid which allows access to its interior”. (M G Yasargil Clin.Neurosurg 1986) Knowledge of this sulcal, fissural and cisternal anatomy is essential for the proper surgical management of brain tumours. While every neurosurgeon is well versed with the gyral anatomy and the partition of the brain into supra and infratentorial compartments, the sulci, fissures and cisterns have generally been excluded from the surgeon’s perspective.

The main reasons for morbidity following surgery on intraparenchymal lesions include:

• surgical trauma to the normal cortex or white matter,
• retraction injury to the brain
• vascular injury

Surgical Injury to the Normal brain tissue

Intraparenchymal lesions may present in the following ways with respect to the brain surface:

• entire tumour surfacing
• small portion surfacing
• below the surface but present within a sulcus
• completely subcortical –not presenting either at surface or sulcus
• intra or paraventricular

The route of approach to the lesion should be chosen such that the trauma caused to the normal brain is minimal. When the entire tumour is surfacing the lesion is removed by going through the surfacing area without disturbing the surrounding normal cortex. When only a small portion of the lesion is surfacing, the surgeon must stay within the surfacing small area of the tumour and debulk the lesion so that the lesion becomes small enough to be removed through the small cortical opening. However when the lesion is not surfacing the surgeon must study the available radiology to decide on the shortest path through normal white matter. The approach then depends on where the lesion is with respect to the gyral and sulcal pattern of the brain. If the tumour is not surfacing but just beneath the surface on the crest of the gyrus, the best approach would be to go through the top of the gyrus. If however the lesion is furthur deep and is close to one of the banks of the sulcus, the surgeon would have to approach the lesion through the sulcus. Similarly, the trans-sulcal approach has to be used when the lesion is deeper or intra-ventricular. Similarly approaches through fissures and cisterns can take the surgeon to deep portions of the brain hitherto thought to be inaccessible.

The mainstay of the transsulcal approach is to use the shortest route between the surcase of the brain and the tumour so that surgical trauma to the normal brain is minimised. While approaching the tumour the microsurgeon is also saddled with the responsibility of looking after the microvasculature of the normal cortex and maintenance of the arachnoidal vessels and layer, so that the normal CSF milieu of the surrounding brain is maintained.

Retraction Injury

The advantage of the operating microscope goes beyond the basic gains of illumunation and magnification, allowing precise dissection. The greatest advantage of the microscope is in the capability of sharp stereoscopic focus in a narrow deep opening with adequate illumination. The microscope creates a telescope effect which allows the surgeon to work at a depth of 10- 12cm through a small opening 5 mm wide and 16 mm long. The ability to work in this narrow and deep field with depth perception and illumination is indispensable. This allows the surgeon to minimise both the opening made in the normal brain tissue and also the use of retractors during surgery. Retractors cause brain injury in two distinct ways. With increasing retractor pressure the brain tissue gets pulled apart displacing and destroying fibre tracts. Increasing retractor pressures can cause venous hemorrhage in the adjacent brain tissue due to impedance to venous flow. Microsurgical techniques used in the removal of intraparenchymal lesions involve staying within the confines of the lesion, prograssive debulking and removal of the tumour inside out. Once the main bulk of the tumour is excised, space is created for finer dissection and removal of the margins of the tumour without furthur retraction.

Thus with the microscope the surgeon does not have to make space (by retraction) to remove a tumour. The surgeon makes use of the space that the tumour has occupied and is therefore able to remove tumours with minimal or no retraction