The radiological appearances of agenesis of the corpus callosum.

The first case of agenesis of the corpus callosum was reported by Reil in 1812. Eighty-two cases, in which the condition was encountered incidentally at necropsy, were collected from the literature up to 1933 by Baker and Graves. Despite the introduction of pneumo-encephalography by Dandy in 1918 it was not until 1934 that Davidoff and Dyke established its value in the diagnosis of agenesis of the corpus callosum. In the first of three cases described by these authors the pneumo-encephalogram was interpreted as showing a cyst of the septum pellucidum. However, at necropsy, following a craniotomy, complete agenesis of the corpus callosum was found. The diagnosis is now usually made on the encephalographic findings, and Davidoff and Dyke (1934) enumerate the following diagnostic points: (1) marked separation of the lateral ventricles; (2) angular dorsal margins of the lateral ventricles (" bicornuate" appearance of Hyndman and Penfield, 1937); (3) concave medial borders of the lateral ventricles; (4) dilatation of the posterior horns of the lateral ventricles; (5) enlargement of the interventricular foramina; (6) dorsal extension and dilatation of the third ventricle; (7) a radial arrangement of the medial cerebral sulci around the roof of the third ventricle and extension of these sulci through the zones normally occupied by the corpus callosum. In 1937 Hyndman and Penfield reported a series of five cases in which pneumo-encephalograms had been performed, and confirmed the importance of the above criteria. They consider that the bicornuate appearance of the lateral ventricles, together with the raised roof of the third ventricle, are diagnostic, but Bunts and Chaffee (1944) in a review of the encephalographic appearances of all published cases, find that while the third ventricle is always raised, the bicornuate shape is not constant. Hyndman and Penfield also describe the appearances which they consider to be due to partial agenesis and which they call " fish-tailing"' of the posterior part of the third ventricle. It may be doubted, however, whether this is anything more than enlargement of the suprapineal recess of the third ventricle (Robertson, 1946) and is thus quite independent of the condition of the corpus callosum itself (Fig. 1). If, however, it is indicative of partial agenesis this condition must be much more common than is suspected, since the appearance is found fairly frequently by chance in otherwise normal ventriculograms and encephalograms. Since then over 20 cases have been reported in