Surgical Management of Gliomas
Gliomas are the most frequent tumors of the CNS. They stand for approximately 50% of the newly diagnosed brain tumors. According to the World Health Organisation (WHO) classification 2007 there are many different types of gliomas: Astrocytic, Oligodendroglial, mixed oligoastrocytic tumors and ependymomas tumors. Astrocytomas are known to have the highest occurrence. High-grade glioma (malignant glioma) is the most common primary intra-axial tumour of the central nervous system.
Because of the high density of cranial nerve nuclei, fascicles, and pathways contained within the brain stem--all playing important roles in securing normal central nervous system function--this small part of the encephalon has historically intimidated experienced neurosurgeons.
Gliomas are the most unfavourable brain tumor for a patient and are known as the “last frontier” of a neurosurgeon (ability to execute a successful cure)
Surgical treatment includes biopsy only, incomplete resection or complete resection.
The primary objective in the surgical management of patients with glioma is to debulk as much of the tumor as possible without injuring the vital areas of the brain that control critical sensory and motor functions.
The accuracy of histological diagnosis is dependent on the size of the tissue sample.
The recent adjuvants therapies have facilitated the treatment of patients and have complemented maximum and safe neurosurgical removal without morbidity or mortality more routine than ever before.
The basic indications and goals of a glioma surgery are:
* To obtain tissue sample for diagnosis. (histology/ immunohistochemistry/ genetic markers/chromosome deletion) A detailed diagnosis will provide direction for prognosis, surgery and future therapies.
* To decrease tumor mass (cytoreduction)
* To relieve neurological symptoms including epilepsy.
* To remove radio resistant and chemo resistant tissue.
* To provide time so that other treatments such as radiation, chemotherapy etc can be performed.
Survival rates have improved drastically in many glioma patients due to the oncologic principle of achieving total tumour resection by complete excision with a clear margin.
Nevertheless these results are truly difficult to achieve in glioma surgery due to plausible neurological deficits that may encountered with wide margin resection, notably when the tumour is situated near the eloquent cortex tracts.
In contrast wider resection margin coupled with adjuvant therapy would delay recurrence and prolong survival
The evident benefits of glioma resection are symptomatic relief from mass effect and obstructed cerebrospinal fluid (CSF) circulation. Distortion of brain structure and compression of neural pathways contribute to both general symptoms and focal deficits. These may display some degree of improvement succeeding surgical resection. Universal symptoms such as headache, nausea, vomiting and general malaise often show remarkable improvement after surgery. The partial reversal of neurological deficits can be contributed to the relief of local compression. Patients with improved functional status after steroid use are usually the ones who will also show progress in their quality of life after aggressive surgical resection, provided that there is low postoperative morbidity. Gross total resection is associated with better patient neurological performance scores (KPS) compared to those monitored after more limited resections. Moreover, partial excision, with significant residual tumour, possibly will lead to a bigger risk of edema exacerbation and postoperative bleeding.
Improved survival is feasible with a joint modality of surgical resection, radiotherapy and chemotherapy, as compared to surgery or surgery and radiotherapy alone.
Guidelines for the resection of high-grade gliomas:
* Tumour resection should be done for histological confirmation, cytoreduction and to lessen mass effect.
* All fundamental principles of microsurgery viz. Approaching the tumor by sulcal incision, and through relatively non-eloquent region of the brain, extreme gentle handling of brain tissue and preservation of all possible veins and arteries passing through or alongside the affected areas.
* Tumor debulking is usually done from inside to outside so as to remain within the tumor without impacting the neighbouring brain. Exceptionally a highly vascularised lesion maybe excised in toto with a thin rim of neighbouring brain to minimize blood loss whilst ensuring the goal of gross total removal even in very vascular lesions.
The same principle is applicable whilst performing a lobectomy for radical tumor excision.
* Aggressiveness of tumour resection is limited by the risk of incurring further or new neurological deficits, particularly deficits, which hinder postoperative radiotherapy and chemotherapy.
* Adjuvant intra-operative procedures to assist safe tumour resection should be promoted.
Owing to the limited lifespan of high-grade glioma patients, it is crucial that surgical debulking does not compound any existing neurological deficit. Otherwise, any potential gain from the surgical resection would be offset by the morbidity. Many techniques have been developed to identify eloquent cortex, especially language, motor and sensory cortex. (fFMRI and DTI) These adjuncts aid in defining the resection limit and further debulking beyond this limit will likely increase the risk of surgical morbidity.
Functional MRI (fMRI) helps to identify language and motor centres. fMRI of tactile, motor and language tasks is feasible in patients with tumours that are near the eloquent cortex, and shows promise as a means of determining postoperative motor deficit risk following surgical resection of frontal or parietal lobe tumors.
Intra-operative DTI in awake patients potentially permits greater safety during aggressive resection of tumours by providing real time images of residual tumour and the surrounding brain.
It also leads to greater surgical accuracy by minimizing neuro navigation errors due to intra-operative brain shift. Unfortunately, this increase is only marginal because in many cases, the tumour extends into the eloquent brain areas and cannot not be excised safely.
The integrated application of functional navigation on top of intra-operative MRI resulted in a higher tumor yield and lower postoperative morbidity rate. This may become the standard of care in due time owing to the fact that patients with less residual tumour may respond more favourably to adjuvant chemotherapy.
Awake craniotomy with local cortical electrical stimulation helps identify the eloquent motor cortex, which cannot be reliably mapped out by anatomical landmarks. These techniques allow for good functional recovery. Combining awake craniotomy with intra-operative cortical stimulation could reduce early neurological deterioration.
Criteria of patient selection:
* Assessment of Psychological and Mental status
* Neurological status
* Tumor size and relationship with vessels
* Duration of procedure
* Medical fitness
* History and Neurological assessment
* Explaining the procedure in detail, and sometimes even showing videos of previously recorded surgeries
* Establish confidence and trust
* Airway and other pre anaesthetic evaluation
Requisition of Scalp field block:
* Experienced anesthetist
* Knowledge of scalp nerve supply is essential
* Local anesthetic agents: Xylocaine (2%) and Sensorcaine (0.25%) in 1:3
Problems and solutions during Awake Craniotomy:
Nausea , vomiting
Restless and un co-operative
Assurance or GA
Midazolam/propofol of GA
Urine pot or Catheterize
Weakness of Dysphasia
Wait and watch Stop
Success of surgery greatly depends on adequate scalp block
The patient is placed in supine position with the head on a ‘head ring' in neutral position or turned to one side with cushion under the shoulder. All the pressure points are padded and the patient is kept warm. A three point fixator is mandatory if neuro-navigation is utilised. Draping is done in such a way that contact can be maintained with the patient. Monitoring includes electrocardiography (ECG), non-invasive blood pressure, pulse oxymetry and capnography. The patients are not catheterized. Injection mannitol 0.5 to 0.75 gm/kg is given to achieve a relaxed brain. All patients are provided with supplemental oxygen through nasal prong. Appropriate anticonvulsants, antibiotics, antiemetic and steroids are given at the start of surgery. Initial sedation is required to reduce anxiety and pain during scalp block. Injection propofol 20-30mg bolus is given followed by infusion at 25-75mcg/kg/min during drilling and turning bone flap. As the brain is not pain sensitive, sedatives can be switched off after the dura is opened and restarted during closure of wound. Constant communication is maintained to keep the patient aware of the surgery. The hand/ foot movements and speech are monitored. In case of any weakness or slurring of speech, the surgeon is informed to avoid resecting that area of brain, thereby achieving maximum cytoreduction with minimal neurological deficit.
Finally, though there is no sole factor responsible for the treatment or long term survival of gliomas, surgery certainly scores an outright win when dealing with pilocytic astrocytoma and pure oligodendroglioma.
Again, despite there being no substantial gains in terms of long term survival of most gliomas we must not harbour pessimism, because even when gross total removal is not always achievable maximum safe surgical removal sets the stage for effective adjuvant therapies particularly targeted therapy. However, despite advances in surgery, molecular biology still holds the trump card.