For purposes of description, the brain is divided roughly into two cerebral hemispheres and the posterior fossa (cerebellum, or brainstem). The dividing line between the hemispheres and brainstem is called the tentorium. In children, 60 to 70 per cent of brain tumors occur below the tentorium. Because of this difficult location, they cannot be completely removed. Sometimes they cannot even be reached.
The tumors are classified according to the area of the brain in which they occur and the particular cell type of tumor. The most frequently occurring brain tumors in childhood (75 percent) are gliomas. About two-thirds of these are astrocytomas and medulloblastomas. The remainder are different forms of cell types. The location and cell pattern of the tumor determines whether the symptoms are major or minor. In infants under one or two years of age, a brain tumor will cause the head to get larger and produce signs of increasing intracranial pressure. This may become quite noticeable since the skull bones in the infant are soft and the suture lines allow growth and distention. As the head becomes large. there is compression of the brain due to the obstruction of the flow of cerebrospinal fluid. This fluid bathes the brain, its linings, and structures. When the pressure inside the brain has been markedly increased, the symptoms of headache, vomiting, weakness, lethargy, irritability, and poor appetite occur.
In children above three years of age, where the tumor is located in the cerebellum, signs of a disorder of balance occur. There may be a staggering gait (ataxia), tremors, swallowing and urinary difficulties, slurred speech, facial paralysis, crosseyes, and other eye disorders. If the sixth nerve in the brain is involved, there may be loss of vision and nystagmus (horizontal or vertical oscillating eye movements), double vision, or complete blindness. Marked personality changes may occur. The signs may be temporary or progressive. Other disorders of equilibrium show in clumsiness and difficulty in handling toys. Playful and active children may become listless and lethargic. Other neurological signs depend upon the specific nerves involved. They are called focal signs. It is essential to hospitalize all children in whom such a diagnosis is suspected.