18

Bioinformatics of the Brain

1.7

Brain Tumors

A mass created by uncontrollably multiplying and growing brain cells is called

a brain tumor [125]. Not only brain tumors are difficult to diagnose and cure,

but they are also ranked among the most serious and potentially fatal illnesses

[126].

Brain tumors can be seen as primary, metastatic (secondary), benign or

malignant [127]. Primary brain tumors (PBT) are tumors originating from

cells and structures in the brain [128]. Secondary brain tumors or metastatic

brain tumors start anywhere in the body and spread to the brain [129]. A

benign brain tumor grows within the limited skull, and pressurizes the sur-

rounding tissues, disrupts venous and arterial circulation, causing local symp-

toms [130]. A malignant brain tumor grows rapidly and spreads to the tissues

of the brain and spinal cord. However, spread outside the CNS is rare [131].

Neoplastic structures consist of heterogeneous cells. These cells differ in their

immunogenicity, growth rate, and tissue invasive potential, and are gener-

ally very aggressive. Generally, the tumor cell uses a hematogenous route to

spread. It passes through the tissues adjacent to the vascular bed and through

the lymph. When they reach the lymph node, they are subjected to a mechan-

ical barrier and filter, from where they drain into the venous system. Since

there is no lymphatic system in the brain, all metastases must come through

the internal carotid artery, vertebral artery or blood [132].

1.7.1

Meningeal Tumors (Meningiomas)

Meningiomas usually arise from arachnoid cells in the meninges [133]. Menin-

gioma are benign, highly vascular tumors that do not infiltrate the brain tissue

and can be easily removed by surgery [134]. Treatment of meningioma includes

surgery, chemotherapy, and radiotherapy. In its treatment, partial resection is

sometimes performed in order to preserve functions, and radiotherapy is used

in slowly growing tumors. In addition, stereotactic surgery is used in regions

such as sphenoid, parasagittal, orbital, tentorial, or clivus [129].

1.7.2

Brain Lymphomas

Lymphomas are primary tumors of the lymphoreticular system and are di-

vided into two as Hodgkin lymphoma and non-Hodgkin lymphoma. Hodgkin

lymphoma usually presents as lymph node involvement, and extranodal in-

volvement is more common in non-Hodgkin lymphomas [135]. CNS lym-

phomas are divided into two groups as primary and secondary. While lym-

phomas originating from the brain, medulla spinalis, and meninges are called

primary brain lymphomas, lymphomas caused by a systemic lymphoma in-

volving the CNS are called secondary brain lymphomas. In order for a