Horizontal sector hemianopia of non-traumatic origin.

Spalding (I952) described four instances of homonymous hemianopia in which narrow sector-shaped defects occurred in the horizontal meridian, involving part of both upper and lower quadrants, and reaching to the fixation point. These emerged from a series of 958 penetrating head injuries, mainly gunshot wounds, of which i88 had field defects attributable to injury of the optic radiations or striate cortex, and in which Spalding had precisely localized the path of the missile and the area of visual pathway affected. He clearly demonstrated that the unusual field picture resulted from damage to the whole horizontal thickness of the intermediate part, i.e. that lying midway between the upper and lower margins, of the optic radiation in its anterior part (Fig. i E interrupted line). The area in question is traversed by a line drawn head to tail through the trigone of the lateral ventricle, at which point the optic radiation forms a relatively flat plate on the lateral aspect of the trigone (Fig. I F). If considered in relation to the skull, the area is posterior to that part of the temporal lobe whereof lesions produce upper partial quadrantopia as described by Meyer (I907) and Cushing (I922), but considered functionally, as part of the visual pathway, it preplaces the Meyer's loop territory. It is in both respects well in front of the posterior optic radiations (Fig. I I) where lesions can produce the familiar upper or lower quadrantopias as described clinically by Holmes (I9I8) and anatomically by Polyak (I934). The arrangement of fibres in this area is similar to that in the adjacent external geniculate body, where the fibres subserving central vision lie above, those for peripheral vision below, and those for intermediate vision between the two. The left visual half field is shown in Fig. I A, with central vision indicated by a stippled pattern, peripheral vision by black, and intermediate vision by white. The associated fibres in the right external geniculate body are similarlv indicated (Fig. I B). If the external geniculate body is visualized as being turned clockwise through go' (Fig. I C), and is thought of as consisting of malleable material which is then compressed from side to side between the finger and thumb (Fig. I D), it becomes easier to understand the position. The conception of continued lateral compression (Fig. i G) may be used to provide a mental picture of conditions existing in the posterior radiations (Fig. I H), where the radiation is a horseshoe-shaped structure embracing the posterior horn of the ventricle. It is not difficult to see how a lesion involving the whole horizontal thickness of the anterior radiation (Fig. i E) will produce field defects as found in Spalding's four patients and in the patient described below.