Knowing all about Medulloblastomas - presentation and management

Medulloblastomas, are Embryonal tumours, arising from superior part of the vermis and roof of the fourth ventricle.?This is the most common malignant brain tumour in the paediatric population and contribute up to 30 – 40% of Paediatric posterior fossa tumours. It is one of the curable malignancies and hence need aggressive management with cutting edge technology. According to the gene mutations or associated syndrome, the neuroectodermal primitive cells undergo over proliferation and lineage shift thereby resulting in rapid growth of the tumour. They have rapid growth and present with increased intracranial pressure and obstructive hydrocephalus symptoms characterized by headache, projectile vomiting and gait disturbances. MRI is the preferred investigation and needs a gadolinium enhanced craniospinal imaging to assess the extent of the disease

I have always felt more responsible specially when dealing with paediatric posterior fossa tumours since the prognosis is greatly influenced by surgery and the extent of excision. When I sit down to analyse the images I can more or less pick out the characteristics of the tumour. They are often hyper intense to the grey matter, with cyst formation and surrounding oedema which can be better appreciated in T2 and FLAIR sequences of MRI with obvious restricted diffusion. They also heterogeneously enhance in T1 contrast which can vary from vivid enhancement in WNT activated group 1 tumours to poor enhancement in the more common Group 4 tumours. It is important to focus on the tumour and brain stem interface in Ciss-3D images which helps to understand the surgical plane.

Once I am pretty clear with the radiological presentation favouring medulloblastoma, I always keep myself aware of the bleeding associated with it due to the vascular nature of the tumour. Usually a Midline suboccipital craniotomy will make the job easy. I almost always perform C1 posterior arch excision which aids in visualizing the superior angle of the tumour and the aqueduct. Since they arise from the embryonal tissues they are easily suckable and soft. I always go for Gross total excision unless there is any obvious infiltration into the floor of 4th ventricle. Only then it is advisable to leave a thin sleeve over the floor to preserve cranial nuclei. My strategy is to get to the top of the tumour after initial internal decompression and identify the aqueduct. I usually place a patty there to prevent blood entering retrograde into the third and lateral ventricles. Then, the tumour is dissected in the cranio caudal direction from the floor of fourth ventricle. In this way, we can prevent accidental breach of pia of brain stem. Finally, the lateral extensions of the tumour is dissected of the peduncles bilaterally and from foramen of Lushka inferiorly. I prefer copious irrigation of the tumour bed with warm saline for haemostasis and avoid cautery to prevent thermal damage to pia of brain stem floor. Once the bulk is removed off, the CSF pathway is re-established and almost every symptom due to obstructive hydrocephalus and Increased intracranial pressure is resolved. But the postoperative challenges just get started because of cerebellar mutism and ataxia. Educating the family about the short lived immediate postoperative changes are imperative. These do resolve over time. If the floor of fourth ventricle is disturbed then 6th or 7th Cranial Nerve paralysis, swallowing disturbances are known to be some unwanted by-products. So it’s important to keep track of the associated side effects during excision.

Pathologic classification has changed to molecular subtype over the period of time, which gives further insight on the long term prognosis. WNT, SHH, Group 3, and Group 4 are the categories designated by WHO. It is a surgeon’s responsibility to make sure not much of the tumour samples are sucked away during irrigation, but reaches the pathologist. Since the risk grading for the following treatment is not just based on the residual disease size more than 1.5 cm in the tumour bed or metastasis at diagnosis but also by the molecular outcome. The benefits of surgical excision are further strengthened over by giving radiation usually covering the Cranio-spinal Axis along with chemotherapy. Recent studies suggest that proton beam therapy is far superior to photon radiation since it can prevent bone marrow compromise and also minimise radiation spillage to adjacent organs. A good surgical excision and adjuvant treatment of chemo-radiation can improve the 5-year survival by 73% while the 10-year survival improves to 65% in majority of the cases.

The job doesn’t end only by passing the treatment torch to a radiation oncologist or paediatric oncologist for the further treatment, it is a Neurosurgeon’s responsibility in customising the additional care through any specialist (physiotherapist, occupational therapist, speech therapist) as per the kid’s postoperative need to help them cope with the immediate changes.?