With more than 120 brain tumor types, recognizing and diagnosing rare ones is a difficult task. Here’s what you need to know about a few of the rarest brain tumor types.

According to American Cancer Society ’s statistics, more than 22,500 people were diagnosed with primary brain tumor types in 2015 in the United States alone. Furthermore, it was estimated that approximately 15,000 adults in the country would die of brain tumor complications. Approximately 4,300 teens and children were estimated to be diagnosed with brain tumors in the US in 2015, with more than half this number being under the age of 15 years.

A brain tumor is defined as an abnormal growth of cells that may be malignant or benign in the brain. These abnormal cells are classified as primary brain tumor types when they first develop in the brain. Secondary or metastatic brain tumor types include those cells that started out as cancerous in other parts of the body, and eventually spread to the brain. This classification of brain tumor types is essential as the treatment of brain tumors depends on which part of the body the cancerous cells originate from.

The National Brain Tumor Society classifies more than 120 brain tumor types. Some of these brain tumor types are more common that the others. Brain tumor types like gliomas account for almost 45 percent of all primary brain tumor types. You may not even have heard the names of some of these brain tumor types, because they occur rarely. Here are a few of the not-so-common brain tumor types.

• Ganglioglioma

Accounting for just 1 percent of all brain tumor types, gangliogliomas are rare brain tumors that are known to start from a single cell that begins dividing in the brain. According to the Office of Rare Diseases Research, most gangliogliomas are benign, with just 10 percent of all known cases classifying as malignant brain tumor types. In most cases, this tumor has to be surgically removed completely; if it isn’t, then the patient may have to undergo radiation or chemotherapy.

• Olfactory Neuroblastoma

Also known as esthesioneuroblastoma, this is one of the brain tumor types that is categorized as very rare. It is believed that the olfactory neuroblastoma starts in the olfactory nerve in the patient’s nose. Symptoms of this brain tumor include nasal obstructions and discharge, nosebleeds, changes in olfactory senses, as well as excessive tearing. Treatment options include surgery, chemotherapy, and/or radiation.

• Gliomas in the Brain Stem

One of the rare brain tumor types, the brain stem glioma begins with a tumor at the base of the brain. The symptoms of this tumor develop slowly, and include nausea, facial weakness, double vision, difficulties in speech and swallowing, and weakness in the limbs. Unlike other brain tumor types, this one may not be surgically removed owing to its location, therefore, radiation therapy is the common way to treat this tumor.

• Grade III Meningioma

Meninges are the layers of tissue that cover the brain and the spinal cord, and meningiomas are the brain tumor types that form in these layers. When they start out Grade I meningioma tumors are benign, and only about 1 to 4 percent of tumors ever reach Grade III and become malignant. These tumors present symptoms such a seizures, headaches, vision changes, behavioral and cognitive dysfunction, etc. treatment of these brain tumor types includes radiation and surgery. Chemotherapy for Grade III meningiomas is still in the research phase, with clinical trials being held across the world.

• Pineoblastoma

Commonly found in children, pineoblastomas are brain tumor types that develop in the pineal gland. Research suggests that perhaps this type of tumor is found in those who have RB1 gene mutations. In most cases, the treatment plan for pineoblastoma includes surgery to remove as much of the tumor as possible, followed by chemotherapy and/or radiation to eradicate it completely.

In general, the diagnosis of all brain tumor types begins with a physical examination as well as a look at your complete medical history. During the physical examination, your doctor will conduct a thorough neurological investigation that includes testing the condition of your cranial nerves. Your doctor is also most likely to use an ophthalmoscope to look inside your eyes and check the state of your optic nerve. Further tests such as a CT, MRI, brain scan, angiography, skull x-rays, etc. might be recommended at your doctor’s discretion.