Most childhood tumors (more than 60%) are located in the posterior fossa (the back compartment of the brain). This area is separated from the cerebral hemispheres by a tough membrane called the tentorium. The posterior fossa includes the cerebellum, the brainstem, and the fourth ventricle. Tumors in this area include medulloblastomas (also called primitive neuroectodermal tumors, or PNETs), cerebellar astrocytomas, brainstem gliomas, and ependymomas.
Brain tumors are often difficult to diagnose because their signs and symptoms may mimic those of other disorders. Symptoms will also vary according to the exact location of the tumor. For example, many childhood brain tumors cause vomiting. However, there are other much more likely causes of vomiting. It is therefore not unusual that a child with vomiting is seen by a gastroenterologist before the proper diagnosis is made. Parents (and pediatricians) often feel distraught that they did not make the diagnosis earlier, but hindsight is always 20/20.