CEREBRAL LOCALIZATION 171 



2. LOCALIZED OR GENERAL CONVULSIONS. Mis- 

 takes are particularly apt to arise if the fit starts in 

 some definite area, follows a slow and orderly march 

 to other areas, and perhaps affects only one side, 

 consciousness being lost late if at all (Jacksonian 

 epilepsy). It must, however, be remembered that 

 all this may occur without any obvious cortical 

 lesion ; indeed, the commonest cause of a localized 

 convulsion is ordinary idiopathic epilepsy. 



Again, localized or general convulsions may give a 

 wrong impression when arising late in the course of 

 an intracranial tumour or abscess, especially if it 

 presses on the ventricular system of the brain and 

 dams back the cerebrospinal fluid, causing hydro- 

 cephalus. The accumulation of fluid in one or both 

 lateral ventricles stretches the overlying cortex, and 

 may give rise to fits, sometimes of a Jacksonian type. 



3. BILATERAL SPASTIC PARESIS. In many cases a 

 hint is given of the true nature of these seizures, by 

 the presence of a slight degree of bilateral spastic 

 paresis, with clumsiness of movement, exaggerated 

 reflexes, extensor plantar response, and a little 

 rigidity. 



Of course, if this should chance to be associated 

 with paralysis of a cranial nerve, such as the sixth, 

 the temptation to diagnose a lesion of the pons would 

 be very great. Fortunately, this would not be of 

 much surgical importance, as the pons is not an 

 accessible structure. Pontine tumours are often 

 unilateral, and optic neuritis is usually absent ; 

 whereas in the class of cases we are now considering, 

 optic neuritis is marked and old-standing, and there 



