Primitive Neuroectodermal Tumors (PNETs)
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Primitive neuroectodermal tumors (PNETs) are rare, malignant tumors thought to arise from primitive nerve cells. Several treatment options are available; treatment typically includes a combination of surgery, radiation therapy, chemotherapy, and possibly shunt placement.
PNETs can develop in the central nervous system or peripheral nervous system. This page discusses those that arise in the central nervous system. Read more information about PNETs found in the peripheral nervous system, where they are also called Ewing sarcoma.
The primitive nerve cells from which PNETs develop are left over from the development of the nervous system during gestation. Normally, these immature cells do not form tumors, but develop into neurons, in a process that continues well into adulthood. But in rare instances, a tumor can arise.
Located typically in the cerebrum, PNETs are fast-growing and counted among the most aggressive kinds of tumors found in children. The tumors tend to spread easily through cerebrospinal fluid. In some cases, PNETs may spread by means other than cerebrospinal fluid beyond the central nervous system. Also, these tumors can block the flow of cerebrospinal fluid, causing a condition called hydrocephalus.
A note on nomenclature: As medical research advances, more becomes known about the characteristics of each disease, as well as the relationships among disorders. New evidence has emerged in the study of PNET, and its classification is being refined. This tumor type has now technically been incorporated into the category embryonal tumor with multilayered rosettes (ETMR). The neurosurgeons at Columbia stay up-to-date on such developments; however, PNET is the more familiar term among patients in the clinic, so the name PNET is used on this page.
Symptoms
Symptoms of a PNET depend on the location of the tumor and may include:
- Morning headache or headache that goes away after vomiting
- Lethargy
- Fatigue
- Seizures
- Loss of coordination
- Problems with walking and balance
- Vertigo
- Diplopia
- Unexplained weight loss or weight gain
- Change in personality or behavior
- Weakness or change in sensation on one side of the body
Diagnosis
A neurological examination is usually conducted to evaluate symptoms. This exam consists of assessing sensation, eye movements, hearing, sense of smell, motor function, swallowing, balance, and coordination.
Imaging studies are the key component in the diagnosis of PNETs. Magnetic resonance imaging (MRI) scans primarily are used. This imaging test can show the size and characteristics of the tumor, as well as the presence of hydrocephalus. Computed tomography (CT) scans are also used. For either study, a contrast enhancement can be administered, so neurosurgeons can visualize the tumor against the normal brain in the background.
Sometimes a PNET can be diagnosed by an ultrasonography scan before a child is born.
If a brain tumor is suspected, a biopsy is done before or during surgery to remove the tumor and confirm a diagnosis.
Risk Factors
What causes PNETs is unclear. Most cases are spontaneous, not hereditary.
Individuals who have had previous cranial irradiation, such as that used to treat a brain tumor, are at an increased risk for developing a PNET.
PNETs usually are found in infants, children, and young adults.
Treatments
At Columbia, our neurosurgeons use the latest surgical advances and techniques to treat each PNET, providing the best possible outcome. To determine and implement optimum therapy, treatment planning by a multidisciplinary team of cancer specialists who have experience treating childhood brain tumors is required. Treatment options depend on many factors, a few of which are:
- The age of the individual, overall health and medical history when the tumor is found
- The type, location and size of the tumor
- The amount of tumor remaining after surgery
PNETs can be treated with surgery, radiation therapy, chemotherapy and sometimes by implantation of a ventriculoperitoneal shunt.
Neurosurgeons performing brain tumor surgery for a PNET resect as much tumor as possible. They also work to restore the flow of cerebrospinal fluid, if impaired, without producing neurological deficits. Surgery also provides biopsy samples that can be used to obtain an accurate diagnosis and perform genetic analysis of the tumor.
These tumors tend to invade surrounding brain tissue and spread quickly and erratically, making complete resection difficult and adjuvant treatment with radiation therapy and/or chemotherapy a necessity. Radiation therapy, which uses high-energy X-rays or other types of radiation to kill cancer cells, is typically the next step in order to minimize chances of tumor recurrence. However, radiation therapy is usually not recommended for young, developing brains and is therefore avoided in children under the age of 3. Chemotherapy is also required after surgery for these tumors. Chemotherapy uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping the cells from dividing, and can be used for young children.
If hydrocephalus does not resolve after tumor resection, physicians may need to implant a permanent ventriculoperitoneal shunt after the initial surgery. The shunt maintains a normal level of pressure inside the skull by draining excess cerebrospinal fluid from inside the brain to space in the abdomen.