Introduction 

Most nervous system conditions worsen with time. Thus, early diagnosis and timely intervention are essential to achieving good patient outcomes, preventing complications, preserving function, minimising surgical risks and enhancing the patient’s quality of life.

Brain biopsy methods have advanced from open craniotomy (part of the skull is removed and brain is exposed to obtain tissue samples), which was invasive and had an increased risk of complications, to frameless stereotactic methods, which are minimally invasive and use imaging and navigation systems to guide the biopsy needle to the target site with precision.

Shunt surgery for hydrocephalus (excessive cerebrospinal fluid [CSF] accumulation in the ventricles [brain cavities that produce and circulate CSF], which increases pressure inside the brain) was initially performed by ventricular puncture with glass wool to drain CSF into the subdural space (space between the meningeal layers, dura and arachnoid mater). This was followed by gold and rubber tubes to modern-day shunt systems with valve-regulated fluid flow.

This article focuses on frameless brain biopsy for obtaining brain tissue specimens for the characterisation of brain lesions seen in imaging and shunt surgery for hydrocephalus treatment.

Frameless brain biopsy

Neurosurgeons consider brain biopsy an important tool for obtaining a definitive diagnosis of unidentified brain lesions on imaging, aiding in suitable treatment recommendations.

A stereotactic brain biopsy is a minimally invasive procedure that uses a 3D coordinate-based navigation system equipped with magnetic resonance imaging (MRI) or computed tomography (CT) images of the patient to accurately guide biopsy needle placement. This type of biopsy is used to obtain samples from tumours and lesions due to infection, inflammation, neurodegenerative diseases and demyelinating diseases. Stereotactic biopsies are not recommended for vascular tumours (tumours formed from cells that create blood or lymph vessels) due to the increased risk of haemorrhage.

Although frame-based stereotactic biopsies are considered the gold standard for collecting biopsy specimens with excellent accuracy, precision and diagnostic yield, they have certain limitations. Patient discomfort due to the placement of frame, screws and head pins; anxiety caused due to head immobilisation; difficulty in navigating the operative field due to obstruction by the bulky head frame; prolonged pre-operative procedure, including frame fixing, imaging and calculations have shifted the preferences of neurosurgeons towards frameless brain biopsy.

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Also Read: Neuro-navigation the game-changer in Neurosurgeries

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Principle of neuronavigation 

In frameless systems, there are two coordinate systems: one associated with the pre-operative image and the other with the surgical field. Point-pair registration establishes the alignment between the pre-operative images and the patient’s anatomy during surgery. A set of at least three non-colinear points (also known as fiducials) must be defined in the image coordinates. The fiducial points can be bone-implanted or skin-applied markers or natural anatomic landmarks (tragus [part of the ear], nasion [the depression seen between the eyes], or lateral canthus [meeting point of the upper and lower eyelids]).

These fiducial points are once again defined in the surgical field’s coordinate system. Once the spatial relationship is determined using software, it is used throughout the procedure to map the patient’s anatomy with the pre-operative images. This necessitates head immobilisation using a surgical head clamp or tracking units attached to the head to correct the errors caused by patient or operating table movement.

Procedure

• Fiducial markers (doughnut-shaped stickers) are reference points placed on the patient’s head.
• Pre-operative images (MRI/CT) are obtained a few days before or on the day of the biopsy.
• The patient is given general anaesthesia, and the three-point Mayfield clamp is fixed. An algorithm registers the surface coordinates of the patient to the corresponding CT/MRI image points. Upon completion of registration, the real-time movement of the surgical instrument to the MRI/CT scan can be seen on a computer screen.
• A small portion of the patient’s hair is shaved off, and an incision is made in the scalp to access the skull bone.
• The neurosurgeon drills a burr hole (a dime-sized hole in the skull) to gain access to the brain and inserts the biopsy needle.
• The trajectory, angle and depth of the needle can be monitored to ensure the needle tip accurately reaches the lesion to obtain the sample without damaging any other part of the brain.
• The surgeon immediately sends the sample to the pathologist for a quick evaluation of the sample’s usability. Depending on the pathologist’s assessment, the surgeon can collect more samples for histopathological analysis.
• The burr hole is closed with a metal plate and screws. The skin is sutured, and a bandage is placed on the incision site.

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O-arm and Stealth navigation

Intra-operative complications, such as acute bleeding or haemorrhage, can be observed only in post-operative CT scans in traditional frameless brain biopsy procedures. Using a 3D fluoroscopy system, such as the O-arm (an intra-operative CT scanner), closes this gap by providing neurosurgeons with real-time imaging during the procedure. These images can be integrated with the pre-operative scans using the Stealth neuronavigation system to track and guide the biopsy needle to the target.

Robotic compatibility in frameless brain biopsies 

Robotic compatibility refers to the efficient integration of surgical robots with frameless neuronavigation systems to assist in trajectory planning and biopsy needle guidance. Several robots, such as the Neuromate Robot, the Robotised Stereotactic Assistant (ROSA), and the Remebot Robot, have been integrated with different navigation systems and offer several advantages, such as accuracy, safety, efficiency (rapid tool positioning) and flexibility (multiple trajectory options).

The Remebot robot system comprises the following:

• A planning system used for building 3D images from the collected image data and defining the trajectory and surgical target.
• A video metric tracking system with three built-in cameras for recording the markers placed on the patient’s head and aligning with the image obtained in the planning system to facilitate patient-robot registration.
• An operating arm that moves to the target site to complete the biopsy specimen collection.

Artificial intelligence (AI) in frameless brain biopsies 

AI is rapidly getting integrated into neurosurgeries and finding applications both pre- and intra-operatively. AI algorithms can analyse vast imaging datasets and identify and define tumours, blood vessels and critical brain areas, allowing neurosurgeons to plan the trajectory and reduce complication risks.

AI can analyse intraoperative MRI/CT scan data and provide real-time guidance by alerting the neurosurgeon if there are any deviations in the planned trajectory to prevent damage to critical brain structures and healthy brain tissues.

AI is also being integrated with robotic systems, where AI algorithms analyse patient data to create personalised procedural plans, effectively executed by robots. In the future, AI-powered robots could perform procedures with limited human intervention, benefiting remote areas lacking experienced neurosurgeons.

Advantages

• Unlike frame-based systems, which require the frame placement, imaging and surgery to be done on the same day, in frameless systems, imaging can be separated from surgery; for example, imaging can be done a few days before surgery. This reduces procedural time, allows flexible planning and improves patients’ comfort as they can move freely with fiducials.
• As one can visualise the biopsy needle approaching the lesion, samples can be collected from targets other than those pre-planned in the same procedure.
• There is no involvement of a bulky head frame, which reduces patient discomfort and allows the surgeon to easily navigate the operative field.

Limitations

• The possibility of drift and tremor (involuntary movements) increases as this technique requires complex hand-eye coordination. This can reduce registration accuracy.
• In cases of CSF loss and brain shift (brain tissue movement), the target area can be misidentified.
• Poor image quality and incorrect fiducial placement can cause registration errors.

Shunt surgery 

The cerebrospinal fluid (CSF) circulates throughout the brain and spinal cord, protecting them against damage. However, neurological conditions such as brain tumours can block the normal circulation of CSF, causing CSF accumulation in the brain cavities, called ventricles and increasing the pressure on the brain. This condition is called hydrocephalus and causes symptoms such as headaches, nausea, vomiting, loss of balance and memory and blurred vision. If left untreated, hydrocephalus can lead to complications such as physical, developmental and learning disabilities and death.

Once hydrocephalus is diagnosed, shunt surgery should be immediately performed. A tube or catheter, called a shunt, is placed in the brain to divert excess CSF to other parts of the body where it is absorbed into the bloodstream. The shunt has valves that allow the CSF to flow only in one direction (away from the brain).

Shunt placement 

A shunt (proximal catheter) is placed in the ventricle by drilling a hole in the skull. Then, it is connected to the valve (placed behind the ear) that regulates CSF drainage. The tube and the valve run underneath the skin and cannot be seen externally. The distal catheter is connected to the valve that drains the CSF into another part of the body.

Types of shunts

Ventriculoperitoneal shunt

This is the most commonly employed shunt system and carries the least risk compared with other shunt systems. Excess CSF is drained from the ventricles into the peritoneal cavity (abdominal space holding the digestive organs), where it is absorbed into the bloodstream.

Ventriculoatrial shunt 

The distal catheter placed in the neck vein drains CSF into the heart.

Ventriculopleural shunt

CSF is drained from the brain into the chest cavity.

Lumboperitoneal shunt

CSF is drained from the spine into the peritoneal cavity.

Types of valves

The CSF diverted from the ventricles is controlled by the valve that operates based on the pressure difference between the brain and the part of the body where the fluid is absorbed. Two types of valves are used:

Fixed valves

These one-way valves are implanted with a pre-defined setting wherein the amount of fluid drained is based on a pre-set pressure that must be maintained inside the brain. The settings can only be altered with additional surgery.

Programmable or adjustable valves

These valves also regulate the pressure inside the brain based on a particular pressure setting; however, the neurosurgeon can adjust the pressure settings non-invasively using an external adjustment tool.

Complications and management

The common complications associated with shunt surgery usually occur at a later time and include the following:

Shunt obstruction

This is the most common complication due to tissues, red blood cells or debris obstructing the tube placed in the brain or another part of the body where the CSF is drained. CSF accumulates and increases pressure within the brain, causing hydrocephalus symptoms to resurface. A neurosurgeon will conduct tests to determine the severity and location of the obstruction and may have to perform a revision surgery, involving the removal or replacement of the whole or part of the shunt.

Shunt infection

Shunt infections are commonly caused by Staphylococcus epidermidis and can occur up to 6 months following shunt placement. The shunt is removed, and a temporary drain called an external ventricular drain is placed to manage hydrocephalus. A new shunt is implanted after the infection is cleared with antibiotic treatment.

Excess drainage

This occurs due to excessive or rapid CSF drainage, which causes the ventricles to shrink. Over-drainage is characterised by headaches, vomiting, nausea, blurred vision and dizziness, with symptoms aggravating in the standing position. If the patient has a programmable valve, the valve settings can be externally adjusted to normalise CSF flow. A shunt malfunction requires the removal or replacement of shunt components to allow proper CSF drainage. In some cases, an anti-siphon device (pressure regulator) is included to prevent over-drainage in the standing position.

Conclusion

Frameless brain biopsy has become the method of choice for neurosurgeons as it uses imaging and navigation software to target lesions without the need for a bulky head frame. This has significantly reduced patient discomfort and procedural time. This system has seen several advancements, such as intra-operative monitoring, robotic compatibility and AI integration, which have significantly improved the procedure’s accuracy, efficiency and safety.

Shunt surgery is used for hydrocephalus treatment to divert excess CSF to other parts of the body where it is naturally absorbed. The shunts have fixed valves (pre-determined pressure setting) or programmable valves (settings can be changed externally by the neurosurgeon) that regulate the amount of CSF to be removed from the brain to maintain normal pressure.

These advancements in neurosurgery have increased diagnostic accuracy, precision and effective treatment options, improving patient experience and clinical outcomes.

Frequently Asked Questions

What is a frameless brain biopsy?

A frameless brain biopsy is a minimally invasive procedure that uses advanced imaging and navigation systems to accurately obtain brain tissue samples without a bulky head frame.

How does a frameless biopsy differ from a frame-based biopsy?

Unlike frame-based biopsies, frameless methods improve patient comfort, allow flexible scheduling, and offer better surgical field access.

What is shunt surgery used for?

Shunt surgery is performed to treat hydrocephalus by diverting excess cerebrospinal fluid (CSF) from the brain to other parts of the body for absorption.

Are robotic systems used in frameless brain biopsies?

Yes, surgical robots like ROSA and Remebot assist in precise needle placement and trajectory planning, enhancing safety and accuracy.

What are the types of shunt systems used in hydrocephalus?

Common types include ventriculoperitoneal, ventriculoatrial, ventriculopleural, and lumboperitoneal shunts, depending on where the CSF is redirected.

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