Congenital fusion of the two cerebral hemispheres without other malformations has also been described; the abnormality does not inter fere with the infant's bodily development (Seeligmann).
4. Porencephalia.—This terin indicates a loss of sttbstance in the cerebrum ateschl, Kundrat), causing funnel-shaped retraction of the brain and sometimes leading to the formation of cysts. The abnormal ity is most frequent in the region of the fissure of Sylvius, correspond ing to the distribution of the arteria fossm SyIvii. Not infrequently cin 30 per cent. of the cases according to Siegmund) both hemispheres are affected. The porencephalous hemisphere is usually retarded in its development and weighs less than its fellow. (In Acker's case the sound hemisphere weighed 670 and the diseased hemisphere 411 grants.) Porencephalia is ft purely anatomic condition and may be congenital or acquired. In the latter case it represents the result of an acute cerebral process, an encephalitis, a meningo encephalitis, a hmmorrhage, or embolic softening. ()pin ions are divided on the ques tion whether congenital porencephalia represents the remains of an intra-uterine morbid process, as formerly believed by Kundrat, or whether it is a developmental disturbance, i. e., a malfor mation in the narrower sense of the term (v. Kahlden). According to the first view, portions of the cerebrum are deprived of their nutrition early in the fwtal period as a result of inflammation or disease of the vessels (embo lism), causing antornic ne crosis, degeneration or absorption of the affected portions of the cere brum. The arguments in favor of a primary developmental anomaly are the scat of the anomaly, which is fairly constant; the regular arrangement of the convolutions in the region of the defect; am microgyria; and especially the association with other malformation of the central nervous system, particularly unilateral deformities of the skull. Certain very- careful investigations of Zingerle go ttt show that at least a certain proportion of the cases of porencephalia are due to intra-uterine cerebral disease.
Clinically, porencephalia usually corresponds to a spastic lietniplegia or diplegia associated with idiocy, epilepsy and disturbance of speech.
The presence of these symptoms does not, however, justify the diagnosis of a porencephalous defect in the cerebrum. The clinical
significance of porencephalia will be considered again in connection with the eerebral palsies of children.
5. Microcephaly.—The term microcephaly embraces a number of congenital diseases of the cerebrum in which the brain constantly', and the skull sometimes, are smaller than normal.
The mauy cerebral malforma tions, representing a great variety of different forms, which are irt eluded under this name have been carefully sifted by Giacomini and divided into pure microcephaly n d pseudomicrocephaly. T h e former represent a general mal formation or arrested development of the cerebrum; the latter, intra uterine disturbances affecting the growth of the cerebrum, tbe result of severe diseases. Searching ana tomical investigation of microceph alous brains has shown that the cases belonging to the first group are much more rare than was at first believed. in these cases the brain is not a miniature edition of a normal human brain, since other abnormal formations, suell as mac rogyria, arrested development of the forebrain in comparison with that of the midbrain and hind brain, and animal types of convo lutions are present. Most of the cases regarded as microeephaly exhibit on section sclerotic and degenerative processes, cysts and hydrocephalus, so that the changes in the cerebrum must be regarded as the reniains of intra-uterine diseases. As a rule, the weight of these microcephalous brains is considerably below the normal (see statistics collected by' Pfleger and Pilez).
In microcephaly changes in the calvarium are the rule, making the diagnosis of microcephaly clinically possible. The alteration con sists in a reduction of the circumference of the skull and in a change of shape, the skull being usually spherical and markedly brachycephal ous; the forehead is flat and receding, and the occipital portion is feebly developed. As the skeleton of the face is well formed and promi nent, a bizarre appearance (bird-face) may result. The measurements of the microcephalous skull are shown in the following table: Ilicrocephaly however occurs also in association with a skull of normal circumference.