Paediatric Brain Tumours
In children, tumours of the brain are the most common solid tumour. They can affect all ages including newborns. The presentation will depend on the age of the child as well as the location, size and nature of the tumour.
Most paediatric brain tumours, 80%, occur in the posterior fossa as opposed to the supratentorial compartment which is where 80% of brain tumours in adults occur. The posterior fossa is a smaller area of the intracranial cavity located at the back of the head. It is separated from the larger supratentorial compartment by a fibrous structure called the tentorium cerebelli or ‘tent’.
The posterior fossa contains two main structures – the cerebellum and the brainstem. The cerebellum is a structure of the brain, the main function of which is to co-ordinate movement. The brainstem is one of the most important structures of the brain and connects the main cerebrum to the spinal cord. It also has a number of nerves that arise from it called cranial nerves that have important functions such as movement of the eyes, movement and sensation of the face, swallowing and speech, hearing and balance, and more. In addition, there are a number of important centres within the brain that have important roles in basic important functions such as breathing and blood pressure control.
The brainstem and the cerebellum are separated by the fourth ventricle. The fourth ventricle is a fluid filled space that receives cerebrospinal fluid from the lateral and third ventricles via the cerebral aqueduct, and allows the CSF to flow out around the brain and spinal cord in the subarachnoid space, where it is absorbed by the blood stream. Any blockage of the fourth ventricle can cause fluid to build up in the ventricles. This build-up of fluid is called hydrocephalus.
Tumours of the posterior fossa therefore present through a combination of symptoms. Most commonly patients present with headache, nausea and vomiting. This is from a combination of pressure from the tumour itself, as well as hydrocephalus. Some children also present with imbalance or visual changes. Younger children may not complain of headache and unexplained vomiting may be the first sign. In very young children, usually less than one year of age, the bones of the skull have not yet joined together, that is, they have not yet fused. Therefore, the tumour and hydrocephalus can result in progressive head enlargement.
It is not uncommon for paediatric brain tumours to present in a delayed fashion. The signs are not always obvious or are attributed to other causes. Encouragement of the use of MRI brain scanning to exclude brain tumours, including by general practitioners, has been helpful in this regard.
What are the main types of brain tumours seen in children?
As mentioned, most brain tumours in children are located in the posterior fossa. The pathology of paediatric brain tumours is therefore different to most tumours that occur in adults. The main three tumours that occur in the posterior fossa are pilocytic astrocytoma, ependymoma and medulloblastoma. However, children can also develop many other types of brain tumours including gliomas, choroid plexus papilloma, meningiomas, optic pathway tumours and craniopharyngiomas.
Pilocytic astrocytomas are most commonly seen arising from the cerebellum and often involve the fourth ventricle. They are graded as WHO grade I tumours and in most cases, surgical excision will be curative. They can sometimes be more aggressive and can spread throughout the brain and spine. This is unusual. Most pilocytic astrocytomas have an excellent prognosis.
Ependymomas are also best treated through surgical excision. Some patients will require adjuvant treatment, but initial removal of the tumour is usually the aim. They can metastasise through the brain and spine which can make treatment difficult.
Medulloblastoma are an aggressive tumour that arise from part of the cerebellum. They can also metastasise, and this can sometimes be the case at diagnosis. There are several subtypes of medulloblastoma. Complete macroscopic resection should be the aim of initial surgery. The extent of resection of these tumours has an important influence on prognosis. Patients usually also undergo radiotherapy and chemotherapy. Despite the aggressive nature of the tumours, appropriate treatment can result in high rates of long-term survival.
Craniopharyngiomas arise in the region of the pituitary gland. They can grow to a large size causing both endocrine or hormonal dysfunction as well as visual impairment through pressure in the optic nerves. They can also cause headache and other symptoms due to their size. Craniopharyngiomas are normally a mixture of solid tumour with associated cysts. These tumours require surgical resection but have a high rate of recurrence. The use of focused radiation may reduce the rate of recurrence. The main issue with craniopharyngiomas, apart from propensity to recur, is the potential impact of the tumour and surgical resection on endocrine function in the future which is often impaired.
There are of course many other types of brain tumours that may occur in children which is beyond the scope of this section.
What surgery is involved in treatment of paediatric tumours?
The nature of the surgery will depend on the site and nature of the tumour. For instance, craniopharyngiomas may be treated either through a standard craniotomy or through an endoscopic transnasal transsphenoidal technique. The surgery is tailored to the needs of the individual patient.
For most posterior fossa tumours involving the fourth ventricle or cerebellum, they are resected through a standard type of operation called a suboccipital or posterior fossa craniotomy. This operation is performed with the patient under a general anaesthetic, with the patient positioned face down. A midline incision is made in over the back of the head near the top of the spine. The muscles are disconnected from the back of the skull. An area of bone is removed, and the covering of the brain called the dura is exposed. This is opened to reveal the cerebellum. Under the operating microscope, the area is carefully dissected to expose the tumour. The tumour is then removed using a combination of microdissection, cautery and ultrasonic aspiration. Once the tumour is removed, any bleeding is controlled and the dura is closed with a suture. The bone is then replaced with very small titanium plates. The wound is then sutured closed. The patient is then woken, and their neurological function checked and observed.
In some cases, a small drain called an external ventricular drain will also be left to drain CSF for a few days. Some patients may eventually require a permanent form of CSF drainage called a shunt if their hydrocephalus does not resolve.
During the surgery, a specimen of the tumour will be sent to the laboratory to obtain the histological diagnosis. This is the important aspect of diagnosis as it determines the course of management and whether other treatments such as radiotherapy and/or chemotherapy may be needed. This result will normally take several days. Further testing including tests for various genetic mutations may also be performed to provide further guidance on treatment.
To learn more about craniotomy for tumour, click on the following link:
What happens after surgery?
After a period of recovery in hospital, patients are normally discharged home. Depending on the histological diagnosis, some patients will require involvement of the oncologists and receive ongoing radiotherapy and / or chemotherapy. These arrangements and referrals will often be made during the hospital admission when the histological diagnosis is received.
Patients undergoing additional treatments are normally monitored by the oncologists who are providing treatment. Prof Owler is kept informed and is involved when needed.
Patients are normally reviewed by Prof Owler in his rooms 6 weeks after surgery. In the longer term, for some tumours such as pilocytic astrocytomas, radiological surveillance with periodic MRI scans may be all that is needed. These are normally arranged by Prof Owler. The patient is normally reviewed with their family on an annual basis.
