Medulloblastomas are the most common primary malignant brain tumors of childhood. They are responsible for about 20-40% of all brain tumors in children. Rarely, they also occur in adults, but here they account for less than 1% of all brain tumors. The standard therapy consists of surgery in combination with radiation and chemotherapy, which are individually adapted. Here you will find information on the clinical significance as well as an insight into the treatment options and the course of therapy here at Inselspital.
Medulloblastoma is an embryonal tumor of the cerebellum, meaning that it arises from immature, undifferentiated cells of the central nervous system (CNS) and grows very rapidly. Medulloblastomas are highly malignant. Meanwhile, genetic analysis of the tumors has identified 4 molecular subtypes of medulloblastoma, which differ in their molecular genetic features and also have different prognoses.
A medulloblastoma arises predominantly from the superior medullary velum. Thus, medulloblastomas are typically found in the posterior fossa in the area of the fourth ventricle (fluid-filled cavity). Spread of tumor cells via the cerebrospinal fluid (CSF) to other brain regions or the spinal cord is possible. Most commonly, medulloblastoma locally infiltrates the cerebellum and brainstem. Spread to the cerebrum is more commonly found in adults.
Due to the rapid and aggressive growth of medulloblastomas, adjacent vital structures can be displaced and damaged. Furthermore, depending on its exact location, the tumor can cause a life-threatening blockage of the CSF flow.
Medulloblastoma is primarily caused by a spontaneous, unpredictable degeneration of cells of the nervous system. The cause of this sudden and uncontrolled cell growth is still unclear. However, a correlation between the occurrence of a medulloblastoma and some rare hereditary diseases has been observed. These include:
- Gorlin-Goltz syndrome
- Rubinstein-Taybi syndrome
- Turcot syndrome
- Li-Fraumeni syndrome
The age of onset for medulloblastoma varies with the subtype of tumor. There is a bipartite age distribution: one in young children, the other in adults over 16 years of age. 10–50% of medulloblastomas have already spread at the time of diagnosis. The most common are drip metastases. These spread along the subarachnoid space or the spinal axis. Metastases outside the nervous system are much rarer. These occur in only about 5% of patients.
Usually, symptoms develop within a short time because of the rapid growth. When the cerebellum and the fourth cerebral ventricle are affected by the medulloblastoma, dizziness with nausea and vomiting, coordination problems and movement disorders such as gait unsteadiness occur.
However, it can also happen that the brain stem is affected, which can lead to cranial nerve failures. This manifests itself in visual disturbances, double images, facial paralysis or similar.
When cerebrospinal fluid flow is obstructed, hydrocephalus results from the accumulation of CSF with a corresponding increase in intracranial pressure. Patients then suffer from symptoms such as headaches, nausea, vomiting or pronounced fatigue and drowsiness. In addition, confusion and personality changes may also occur. In young children, an above-average and fast-growing head is sometimes noticeable. This macrocephaly is a sign of increasing cerebrospinal fluid and increasing intracranial pressure. Affected children appear very sleepy or react irritably.
Spinal metastases can lead to pain and sensorimotor deficits due to the space-occupying effect on the spinal cord.
On computed tomography (CT), medulloblastoma typically looks bright and takes contrast. Often, calcium deposits are seen in the tumor. However, magnetic resonance imaging (MRI) is considered the imaging gold standard, and should include the spine in addition to the skull to rule out possible metastases throughout the central nervous system.
In addition to imaging, a lumbar puncture is performed to examine the cerebrospinal fluid, as tumor cells can occasionally already be detected here. However, a definitive diagnosis can only be made after histological evaluation of the surgically removed tumor tissue. The fine tissue composition has a direct influence on the therapy and also on the prognosis of the patient.
The therapy of choice is microsurgical resection of the tumor. The planning of the operation and the subsequent treatment is done in intensive collaboration of an interdisciplinary team consisting of neurosurgeons, neuroradiologists, neuropathologists, oncologists and radiation oncologists. Due to the relatively rapid and aggressive growth of these tumors, current treatment consists of a combination of surgical removal of the tumor as completely as possible with maximum sparing of the healthy surrounding brain tissue, followed by radio and/or chemotherapy.
The therapy is based on individual criteria such as the subtype of the tumor, the patient's age, the patient's general state of health as well as the possible extent of surgical rehabilitation, metastasis and, last but not least, the patient's tolerance to the therapeutic measures.
With the help of this aggressive therapy, up to 80% of medulloblastoma patients can be cured. However, the chances of success vary depending on the subtype of tumor. In children under 3 years of age, radiotherapy has severe side effects (neuropsychological deficits, endocrinopathies), so only postoperative chemotherapy is given to such young patients. The primary goal of surgical treatment is safe minimally invasive yet maximally radical removal of the tumor with restoration of unrestricted CSF outflow. If the patient's own CSF outflow cannot be restored, a ventriculoperitoneal shunt may be required. In this case, the CSF is drained via a catheter under the skin into the abdominal cavity.
Depending on the location of the medulloblastoma, there is a certain risk of damaging neighboring brain structures during surgery. To keep this risk of complications as low as possible, we use the latest technical procedures such as neuronavigation and intraoperative neuromonitoring. These allow our neurosurgeons to work with maximum precision and safety and still achieve the maximum tumor resection.
Robinson GW, Rudneva VA, Buchhalter I et al. Risk-adapted therapy for young children with medulloblastoma (SJYC07): therapeutic and molecular outcomes from a multicentre, phase 2 trial. Lancet Oncol. 2018;19:768-784.
Harbaugh R, Shaffrey CI, Couldwell WT. Neurosurgery Knowledge Update. Thieme; 2015:984.
Greenberg MS. Handbook of Neurosurgery. Thieme; 2016:1664.
The Neurosurgical Atlas: Medulloblastoma (free sign up).