The term “ICSOL” includes lesions which expand in volume to displace normal neural structures and lead to increase in intracranial tension. These lesions give rise to the following three groups of symptoms in general.
1. Neurological phenomena caused by irritation or destruction of brain tissue, e.g, focal seizures (Jacksonian epilepsy) and paralysis.
2. Features of raised intracranial tension (ICT): The rate of increase of tension and its level depend upon the nature of the lesion and its location. For example, rapidly growing tumors and multiple secondaries give rise to rapid rise in ICT whereas slow growing tumors and cysts may be accommodated within the cranium for considerable periods without symptoms. Moreover, in general, posterior fossa lesions lead to more rapid rise in tension than supratentorial lesions.
3. False localizing signs:
(a) These are neurological phenomena arising from secondary effects of the lesions. As a result of herniation of neural tissue under the falx cerebri or downward herniation through the tentorium cerebrlli and foramen magnum, pressure effects on other parts of the brain develop.
(b) Contre-Cup effect: This is pressure effect caused on the side opposite to the side of lesion when a space occupying lesion expands. The midline structures such as brainstem may be pushed towards the opposite free margin of the tentorum cerebelli to give rise to compression of the normal side as well. In addition to these genera features different lesions may produce symptoms specific to their nature. For example, brain abscess may be associated with fever and other signs of infection. Subarachnoid hemorrhage may be associated with signs or meningeal irritation.
Clinical features: Around 50-60% or neurological disorders in India are constituted by space occupying lesions. Persistent headaches not due to any other detectable cause and unresponsive to simple medication should suggest to possibility of ICSOL. The headache may be felt in the midline over the head of at times it may be referred over the site of lesion, e.g meningioma. It may be continuous and progressive, paroxysmal (as in migraine), or aggravated by coughing, stooping forward or changing postures.
Vomiting and visual loss: In many cases, protracted vomiting is a usual symptom. Projectile vomiting may be moistaken for gastrointestinal or psychiatric disturbances. Failure of vision due to papilliedema is a late phenomenon in most cases. Recent onset of behavioral changes and sudden onset of neurological deficits are also clinical features.
Late onset of seizures: Any type of seizure occurring for the first time after the age of 15 years should suggest the possibility of ICSOL.