Medulloblastoma: Tumors of the Cerebellum

By: Neda Brinster

Overview:

Medulloblastoma is a embryonal, malignant tumor that develops in the posterior fossa, a small space in the back of the skull that contains the cerebellum, brainstem, and fourth ventricle.

The cancer spreads through cerebrospinal fluid or CSF, which protects the brain and spinal cord. Medulloblastoma begins in fetal tissue and is the most common brain tumor affecting children. The tumor is fast growing and is likely to spread to other areas of the brain or spinal cord.

Symptoms:

• Double Vision

• Head bobbing

• Lethargy and Confusion

• Hydrocephalus

• Dizziness

• Ataxia

• Nausea

Spinal Cord Symptoms:

• Back pain

• Trouble Walking

• Lack of Bladder / Bowel function control

Diagnosis:

Medulloblastomas are treated by examination of a patient's medical history and symptoms, followed up by medical testing. There are four main tests for diagnosis.

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Neurological Exam

Tests vision, hearing, balance, and coordination. This exam allows doctors to identify the location of the tumor.

Imaging

Determines the location and size of the tumor. It also identifies pressure or blockage of CSF pathways. CT scans and MRI's are the most common methods of imaging.

Tissue Sampling / Biopsies

This is not commonly done but can possibly be recommended if the imaging tests are not clear. Biopsies are used to determine cell type.

Lumbar Puncture

Lumbar Puncture removes CSF for testing by inserting a needle between bones in the lower spine to draw out CSF.

Treatment

There are three main methods of treatment for Medulloblastomas: radiation, chemotherapy, and surgery. Clinical trials are also administered which enroll participants to test the effectiveness of new treatments.

Surgery: Surgery is used to relieve CSF buildup which can put pressure on the brain and cause hydrocephalus. This method surgically creates a pathway for the fluid to drain out of the brain. Surgery can also be used to remove the medulloblastoma, removing the tumor directly. However, this isn't always possible if the tumor has formed near crucial structures in the brain.

Radiation: Radiation therapy is used on the brain and spinal cord to kill cancerous cells. High doses of radiation minimizes radiation exposure to healthy tissue and cells.

Chemotherapy: Chemotherapy uses drugs to kill tumor cells. It is commonly administered through the vein, followed by stem cell rescue. Stem cell rescue is a stem cell transplant of the patient's own stem cells.

Medulloblastoma Classification:

There are four main types of Medulloblastoma: Classic, Desmoplastic, Medulloblastoma with extensive nodularity, and Anaplastic Medulloblastoma.

1. Classic Medulloblastoma: sheets of small, compact, round cells that can vary depending on the type of tumor. Often contain a dark nucleus.

2. Desmoplastic or Nodular Medulloblastoma: round nodules that are surrounded by connective tissue. Nodule is abnormal tissue beneath the skin.

3. Medulloblastoma with Extensive Nodularity (MBEN): This is a distinct variant that is closely related to Desmoplastic Medulloblastoma. It commonly occurs in infants and contains more nodules.

4. Anaplastic Medulloblastoma: This type is highly aggressive, and represents 25% of all medulloblastomas. It is commonly seen in young patients ranging from ages 1-4. It has a tendency to spread through CSF and is composed of large, anaplastic cells.

Classic Medulloblastoma:

This classification is very severe and can be diagnosed through the characteristics seen in the biopsy to the left. The cells are small and compact, but most importantly, the nucleus is dark. The dark nucleus indicates that the cell is rapidly dividing. There is also little to no cytoplasm, which shows that the cancer is spreading.

Desmoplastic Medulloblastoma:

This classification is less severe than classic Medulloblastoma. The biopsy shows more connective tissue (pink), and the pink around the nucleus represents the cytoplasm. This means the cell is dividing less rapidly, and the cancer isn't spreading as quickly. This classification contains round nodules (abnormal tissue) ringed by connective tissue.

Medulloblastoma with Extensive Nodularity:

This classification is similar to Desmoplastic Medulloblastoma, but contains more nodules. This also has a favorable outcome compared to the Classic Medulloblastoma, as the nucleus is not as dark and there is more connective tissue.

Anaplastic Medulloblastoma

This is the most severe classification of Medulloblastoma, which can be represented by the abnormal and dark cells pictured in the biopsy. This is highly aggressive, and it often is difficult to track where the tumor is spreading from, as it appears throughout all cells.

“Webpathology.” Webpathology.com: A Collection of Surgical Pathology Images, https://www.webpathology.com/image.asp?n=9&Case=635.

Citations:

“Brain Tumor.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 6 Aug. 2021, https://www.mayoclinic.org/diseases-conditions/medulloblastoma/cdc-20363524.

“Medulloblastoma.” Medulloblastoma | Johns Hopkins Medicine, 8 Aug. 2021, https://www.hopkinsmedicine.org/health/conditions-and-diseases/brain-tumor/medulloblastoma.

“Medulloblastoma.” St. Jude Children's Research Hospital, https://www.stjude.org/disease/medulloblastoma.html.

“Webpathology.” Webpathology.com: A Collection of Surgical Pathology Images, https://www.webpathology.com/image.asp?n=9&Case=635.