**3.2. Pathophysiology**

Cognitive impairment associated with brain tumors can be induced by direct or indirect compression of normal brain tissue by reactive edema [42].

Tumor tissue can also invade directly into functional brain regions or indirectly disconnect the structures which can further contribute to cognitive deficits [43].

The mechanisms via which brain tumors affect brain function varied, highly malignant tumors grow quickly so they tend to infiltrate and displace the normal brain tissue, while the lower grade tumors tend to grow and infiltrate slowly disrupting brain function causing cognition deficit.

Tumors of ventricular system causes increase in intracranial pressure and hence affect the cognitive function; also large ventricular tumors affect the cognition directly through its compression effect. Functioning brain tumors which secrete hormones may have role in cognitive deficit through endocrine disturbance [44].

The main pathophysiology causes of cognitive dysfunction are not well known, different hypotheses were placed; progression of brain tumors seems to be the predominant one [45], also late treatment effects, for example, surgery, RT, chemotherapy, uses of antiepileptic drugs or corticosteroids), the psychological distress also may contribute in cognitive dysfunction [46].

The cognitive function disturbance in brain tumors may be due to combination of these factors.
