CAVA SEPTI PELLUCID1 ET VERGE: THEIR NORMAL AND PATHOLOGICAL STATES1

CAVITES within the septum pellucidum are commonly seen at autopsy and are generally considered to'be clinically insigmficant. The cava septi pellucidi et Vergee (1851) are essentially the same structure, one being located anterior and the other posterior to an arbitrary vertical plane formed by the columns of the fornix. Thompson (1937) proposed calling one the cavum septi pellucidi anterius and the other the cam posterius, which would lx a more logical terminology. The two cavities usually communicate freely, but occasionally they are separated by the columns of the fornix which closely approximate each other. Such a narrow communication has been called the aqueduct septi. The cavities vary greatly in size, and there is considerable disagreement concerning their incidence. Only recently has it been rediscovered (Larroche and Baudey, 1961) that they are normal structures, constantly present in the premature normal brain but shrinking just before and after full term birth in most individuals t o a vanishingly small slit which may easily be overlooked. The controversy concerning the eqb.ryology of this structure, whether formed by stretching of the rapidly widenjng lamina terminalis during the third month of gestation (Thompson, 1937) or being merely an inter-hemispheric fissure which fails to fuse (Coming, 1921), has been resolved by the recent studies of Rakic and Yakovlev (1968), who have shown that &e cavity develops in the site of fusion of the cerebral hemispheres (banks of the sulcus medianus telencephali medii) as a secondary cleavage with necrobiosis as the fibres of the corpus callosum cross the midline. In a very exceptional case, the septum may form on only one side, the "cavity " remaining as leptomeningial spaces (Loeser and Alvord, 1968), but normally the cavity does not communicate with either the leptomeningial or ventricular spaces. 'Supported in part by a neuropathology training grant (5-T01-NB-05231) from the Nationa