Embryonal tumors, in essence, are malignant tumors that form in the brain from the remnants of embryonic cells left from fetal development. It is a form of brain cancer and it is usually detected during early childhood. Whilst there are different types of embryonal tumors, all can easily spread throughout the brain and the spinal cord, causing damage to healthy tissue. Therefore, early detection and appropriate treatment is crucial to prevent the progression of the tumorous growth and avoid dire consequences. Nevertheless, this type of tumor is relatively rare - 1 in 100 of all brain tumors diagnosed between 1995-2017 in England were embryonic in origin.¹ The aim of this article is to inform the reader on what embryonal tumors are, their causes and what are the typical symptoms experienced by those with it. 

Understanding Embryonal Tumors 

Embryonal tumors are malignant forms of cancerous growth that is found in the brain. These tumors develop from embryonic (fetal) tissue left over from fetal development in the mother's womb. The cells of this fetal tissue continue to divide and grow when they are not supposed to, leading to tumor formation. Embryonal tumors are usually present in infants and young children, however can also be detected later in life. These tumors can grow and spread via the fluid that surrounds the brain and the spinal cord, invading healthy tissue and causing damage. 

There are different types of embryonic tumors, but the most common types include: medulloblastomas, atypical teratoid/rhabdoid tumor (AT/RT), embryonal tumor with multilayered rosettes (ETMR) and central nervous system (CNS) neuroblastomas.²

Medulloblastoma

Medulloblastomas are the most common type of embryonic tumor and the most common pediatric tumor. It’s usually diagnosed within the first five years of life. This tumor originates in the back-base of the brain (the medulla). Due to its location towards the base of the brain, as the tumor increases in size, it can interfere with circulation from the spinal cord to the brain and result in a build up of pressure in the brain. This type of tumor is caused by layered signaling mechanisms that control tumor growth. Some inherited conditions predispose a child to developing this type of tumor, including Turcot syndrome, Rubinstein-Taybi syndrome, Gorlin syndrome and others.³ Medulloblastomas are treatable by surgery, chemo- and radiotherapy. The survival rate of this type of tumor is about 60%, if it has metastasized to neighboring brain regions and the spinal cord.⁴

The symptoms of medulloblastoma are often associated with the cerebellum - the location of the tumor and the functions this part of the brain governs. These include: 

• Problems with walking and with coordination
• Increased stumbling and falling

As the tumor grows, it begins to interfere with the circulation from the spinal cord to the base of the brain and pressure begins to build up in the brain. As a result, the patient may experience: 

• Frequent headaches-these can get more painful after laying down and on waking up from sleep
• Fatigue
• Nausea
• Problems with feeding (common and noticeable in infants)
• Vision difficulties

As the tumor spreads to the spinal cord, it can cause: 

• Backaches
• Problems with walking
• Bladder and bowel issues

Atypical teratoid/rhabdoid tumor (AT/RT)

This type of tumor can develop anywhere in the central nervous system, whether it be the brain or the spinal cord. AT/RT is a fast growing type of tumor and is quite aggressive. It is caused by DNA mutations in genes that are involved in controlling cell growth SMARCB1 and SMARCA4. These mutations can be occurring de-novo (spontaneously, for the first time in an individual of a family) or can be inherited - predisposed for, by certain inherited conditions. Treatment for AR/RT includes surgery to remove the tumor, however this largely depends on the location of the tumor and its level of progression. The prognosis for this type of tumor is, unfortunately, not great due to how fast it progresses. Survival time ranges from months to years, with a five year survival rate being 32%. However, generally patients whose tumor was operable and who were diagnosed at an older age have better recovery and survival rates.⁴

Common symptoms associated with AT/RT include: 

• Frequent headaches 
• Nausea and vomiting 
• Fatigue 
• Coordination issues

Due to the ambiguity of AR/RT symptoms (which are shared with many other conditions) and the difference from case to case based on where the tumor is located, AT/RT remains a difficult tumor to diagnose and often is noticed when it has progressed to later stages.

Embryonal tumor with multilayered rosettes (ETMR)

This is another example of an embryonal tumor, identified by a specific mutation. A specific DNA sequence on chromosome 19 is amplified - increased in production. This results in abnormal growth of embryonic stem cells. This type of tumor is usually found in the cerebral hemisphere of the brain. ETMR is a malignant type of tumor with low survival rates of only around a year. Some of the symptoms associated with this type of tumor include headaches, seizures and facial paralysis.⁵

CNS Neuroblastoma 

This type of tumor occurs in neuroblast cells of the central nervous system, which is a type of nerve cell, in this case, left behind from embryonic development. This type of tumor is most common in children under 1 year old. The prognosis depends on the stage of the cancer. If the tumor is diagnosed early, the survival rates can be promising. 

The symptoms include:⁵

• Fatigue, tiredness 
• Loss of appetite 
• Bone pain 
• Weakness 

Summary

Whilst all embryonal tumors develop from tissue left behind in embryonic development, this tissue begins to uncontrollably grow and differentiate due to different mutations, each associated with a specific type of embryonic tumor. This article covered a few types of embryonal tumors - medulloblastomas, atypical teratoid/rhabdoid tumors (AT/RT), embryonal tumors with multilayered rosettes (ETMR) and CNS neuroblastomas. These four are the most commonly diagnosed embryonal-origin tumors and are usually found in young children. Symptoms of these tumor types are often shared with each other and with other diseases, making it difficult to diagnose. Symptoms also depend on where in the central nervous system the tumor begins to grow. As many of these tumors progress very quickly and are quite debilitating, early detection is vital to ensure best prognosis and survival.