Awake Craniotomy, Neuronavigation and 5-ALA Fluorescence

Awake craniotomy is brain tumour surgery performed while the patient is conscious, speaking and moving, so that the surgeon can test speech and limb function in real time as the tumour is removed. Dr. Rahul Gupta, Senior Director & HOD Neuro and Spine Surgery, Fortis Hospital, Noida, India, combines it with neuronavigation and tumour fluorescence, and in his experience awake surgery sharply reduces post-operative deficits.

These three tools solve the same problem from different angles. Neuronavigation tells the surgeon where the tumour is. Fluorescence shows where malignant tissue ends and normal brain begins. Awake testing confirms, minute by minute, that the brain being touched is not doing anything the patient cannot live without. This article explains each tool, the cases Dr. Gupta used to illustrate them, and the supporting technology that makes them work. The wider diagnostic pathway is set out in the complete guide to diagnosis and management of brain tumours.

The operating microscope: the non-negotiable baseline

Dr. Gupta is unequivocal that, in the modern era, no patient should undergo brain tumour surgery without an operating microscope. It provides magnification and strong illumination, records the operation, and relays the view to a screen so that assistants and theatre staff can follow each step and help more effectively. It is also the platform for the advanced features: neuronavigation can be incorporated into the microscope, and so can tumour fluorescence filters.

Around the microscope, the modern theatre adds ultrasonic surgical aspirators, used both to remove tumour and to drill bone; good-quality cautery, including suction-irrigated cautery; and endoscopes, with which some operations are performed entirely.

Neuronavigation: smaller openings, more accurate removal

Neuronavigation works like satellite navigation for the brain. The patient's MRI is registered to the head in theatre, and a tracked pointer shows the surgeon, on screen, exactly where an instrument sits relative to the tumour. Dr. Gupta regards it as very important for any brain tumour operation, and lists its advantages:

• A smaller incision and a smaller craniotomy, so less bone is removed.
• A small opening in the brain surface, or none at all. The surgeon can follow a sulcus, one of the natural grooves between folds of the brain, instead of cutting through cortex (a trans-sulcal approach).
• Accurate localisation, so the lesion is not missed and the surrounding brain is not damaged.
• Minimal collateral damage with near-total or total excision.
• Satellite lesions lying a little away from the main tumour can be found as well.
• Posterior fossa lesions, in the cerebellum and hindbrain, can be targeted.

Navigation can also be fused with tractography, the MRI sequence that displays nerve fibre tracts. Dr. Gupta showed a midbrain lesion with the corticospinal (motor) tracts mapped beside it, and a thalamic lesion with its tracts displayed by integrating the navigation system with the MRI images. The surgeon can then plan a corridor that avoids them.

Navigation-guided biopsy versus frame-based stereotactic biopsy

When only a biopsy is needed, the traditional method is frame-based stereotactic biopsy: a Leksell frame is fixed to the head and a needle is passed to the target through a small burr hole. Dr. Gupta outlined its limitations:

• The skull is a solid barrier, and deep-seated lesions are hard to reach.
• Highly vascular lesions can bleed during biopsy, and through a burr hole that bleeding is hard to control.
• In the posterior fossa the frame cannot be used.
• Around the ventricles, the brain can shift once a ventricle is entered, moving the target.

His team now prefers biopsy guided by neuronavigation. It can be done with the head fixed in a frame or frameless, which matters in children, in whom a frame often cannot be applied. Markers called fiducials are registered without a cumbersome frame, and the burr hole can be converted into a mini craniotomy, so that bleeding can be controlled and a lesion that is hard to find can be located under direct vision. The instruments are the standard set already available, so, as Dr. Gupta noted, the approach adds no cost. In his practice, navigation-guided biopsy has largely replaced stereotactic biopsy.

Awake craniotomy for tumours in eloquent areas

Dr. Gupta uses awake craniotomy for tumours in eloquent brain, which he defines simply: the motor area on either side, and the speech area in the dominant hemisphere. "Eloquent" brain is brain whose function is critical and immediately noticeable if lost, chiefly the speech areas and the motor cortex that controls limb movement.

How hemisphere dominance is judged

In a right-handed person, the dominant hemisphere for language is usually the left; in a left-handed person, it may be the right. Dominance can occasionally sit on the same side as the writing hand, so handedness is a guide, not a guarantee. It can be tested by selective angiography, which is rarely performed.

How an awake craniotomy works

The neuroanaesthetist gives a scalp block, a local anaesthetic injection around the nerves of the scalp, and keeps the patient comfortable and calm. Navigation localises the tumour and guides the incision. As the tumour is removed, the patient is asked to speak or to move the limbs, so that function is checked in real time. Dr. Gupta credits newer neuroanaesthetic drugs with making this possible, and stresses that it depends on an expert neuroanaesthesia team able to talk to and settle the patient throughout.

Awake surgery can be combined with neuromonitoring, in which grid electrodes placed on the surface of the brain map the functional areas. Because the patient has not had a general anaesthetic, post-operative recovery is very fast. In Dr. Gupta's experience, awake surgery sharply reduces post-operative deficits. In a meta-analysis of more than 8,000 glioma operations, resection guided by intraoperative brain mapping cut the rate of lasting severe deficits from about 8% to about 3%, while allowing more extensive removal.

The one drawback he describes: if the tumour bleeds heavily, or if the patient has a seizure during the procedure, the operation may have to be converted to general anaesthesia.

Two cases from the motor cortex

Dr. Gupta illustrated the technique with footage from two operations.

The first patient was a young woman with focal seizures in the hand, caused by a tumour in the motor cortex. With her head fixed in a head frame and her eyes open, the navigation pointer marked the tumour on the scalp. Through a small incision, the team entered along a sulcus without cutting the brain, and removed the tumour under the microscope while she moved her hand on request and talked with the team. The bone flap was replaced and the incision closed. After surgery she had no deficit. The tumour was a grade 2 astrocytoma, a slow-growing glioma.

The second patient had a lesion in the motor cortex that was bright (hyperintense) on MRI. She too was awake, fixed in the head frame and breathing oxygen without a tube in her airway. During removal she moved her right hand, then her leg and foot, on request. Her movements remained absolutely normal.

A third case in the session, another tumour in an important area, was removed totally using navigation and awake craniotomy, and the patient did very well after surgery.

Fluorescence-guided surgery: 5-ALA and fluorescein

In fluorescence-guided surgery, a dye given before or at the start of surgery collects in the tumour, and a special filter and software in the microscope make the tumour glow. This addresses a core difficulty: malignant tumours, gliomas in particular, often have ill-defined borders that look much like normal brain under white light.

Dr. Gupta uses two agents:

5-ALA is taken up by malignant glioma cells, which convert it into a fluorescent compound. Fluorescein works differently: it accumulates where the blood-brain barrier has broken down, which in practice marks the enhancing tumour. Either way, the surgeon can separate tumour from normal brain, remove the tumour selectively and leave healthy tissue alone: minimum collateral damage with maximum tumour removal.

Dr. Gupta summarised the advantages: fluorescence works during the operation and in real time, it is designed for malignant tumours, fluorescein is given at induction, and it is economical, fluorescein especially so. It is most valuable in tricky cases, particularly tumours close to eloquent areas. He showed a glioma, outlined on MRI, viewed first under normal microscope light and then through the fluorescence filter, with complete excision of the tumour. A second patient with a diffuse lesion on the left side of the brain, seen on CT and on the FLAIR MRI sequence that best shows the true extent of such tumours, was operated on with the same side-by-side normal and fluorescent views.

Intraoperative imaging and neuromonitoring

Beyond navigation and fluorescence, the surgeon can image the brain during the operation itself:

• Intraoperative MRI. After removing part of a tumour, the team can scan to see what remains, either by moving the patient into an MRI room or by bringing the MRI into the theatre in a combined MRI suite.
• Intraoperative CT, used in the same way.
• Intraoperative ultrasound, which gives a real-time image of the lesion and its anatomical position. It is especially useful when the tumour has a cyst, which can be found and drained directly.

Neuromonitoring uses grid electrodes placed on the surface of the brain to identify the motor, sensory and speech areas. In patients with active epilepsy, the same electrodes can locate the epileptic focus.

Why neuroanaesthesia makes the difference

Much of this depends on the anaesthetist. Dr. Gupta credits dedicated neuroanaesthesia with transforming brain tumour surgery: with good control during the operation, his team hardly ever sees the brain bulge during surgery. The same specialists act as neurocritical care doctors in the neuro intensive care unit after surgery, so one team manages the patient from induction to recovery.

How these advances shape complications and recovery, and what a centre needs at minimum to operate safely, is covered in recovery and follow-up after brain tumour surgery. Dr. Gupta's answers to doctors' questions from the session are in the live discussion, his practice is summarised on his doctor profile, and indicative costs for the operation are on the craniotomy for brain tumour excision cost page. Navigation, fluorescence and intraoperative imaging are also reviewed, from a separate masterclass, in Dr. Anil Kumar Kansal's article on brain tumour surgery techniques.