Sonography of the internal capsule and basal ganglia in infants. Part II. Localization of pathologic processes in the sagittal section through the caudothalamic groove.

Sagittal sonograms through the caudothalamic groove routinely display a gangliothalamic ovoid delimited by the lateral ventricle, the perimesencephalic cistern, and the radiations of the corpus callosum. The caudothalamic groove divides the superior surface of the ovoid into an anterior caudate arc and a posterior thalamic arc. The cerebral peduncle divides the inferior surface of the ovoid into an anterior ganglial arc, a middle peduncular arc, and a posterior thalamic arc. The genu of internal capsule constantly courses from the anterior end of the caudothalamic groove down to the peduncular arc and is easily identified. The gangliothalamic ovoid exhibits four obliquely oriented bands of increased and decreased echogenicity. The anteriormost hyperechoic band 1 corresponds to the head of the caudate nucleus. Hypoechoic band 2 corresponds to the globus pallidus, genu of the internal capsule, and cerebral peduncle. Hyperechoic band 3 corresponds to the ventral and lateral thalamic nuclei (exclusive of the pulvinar). Hypoechoic band 4 corresponds to the pulvinar. Lesions of the medial nucleus of the globus pallidus appear as hyperechoic foci that abut on the anterior surface of genu just above the peduncle and that have a narrow convex caudal margin. Lesions of the lateral nucleus of globus pallidus abut on the genu distant from the peduncle, spare the medial nucleus adjacent to the peduncle, and have a broad caudal border. Lesions of the head of caudate nucleus affect the anterior pole of the ovoid; those of the body affect the caudate arc superior to the caudothalamic groove. Thalamic lesions increase the echogenicity of bands 3 and 4.