Variants and anomalies of the brain

Spinal cord. The spinal cord sometimes lacks the pyramidal decussation. In 10% of cases on both sides and in 14% on one side, the anterior corticospinal tracts are absent. The number of spinal cord segments varies between 30-32 due to a decrease or increase in the lumbar and sacral segments. The central canal of the spinal cord may be overgrown in places, the size of the terminal ventricle (Krause) varies significantly. Rarely, some anterior and posterior roots of the spinal nerves, located in the "horse's tail", connect with neighboring roots. The spinal ganglia of the 5th pair of sacral nerves are often located in the sac formed by the dura mater, and not outside it. The ganglia of the sacral spinal nerves are often significantly displaced upward.

Brain. There are many variations in the number, shape and size of the grooves and convolutions of the cerebral cortex. In the frontal lobe, the superior frontal sulcus (1%), inferior frontal (16%) and precentral (6%) may be absent. The interparietal sulcus is absent in 2% of cases, the postcentral sulcus in 25%, and the inferior temporal sulcus in 43% of cases. Many sulci of the cerebral cortex bifurcate. The lateral sulcus bifurcates in its posterior part in 40% of cases and is divided into 3-4 parts in 6% of cases. The superior and inferior frontal sulci merge into a single sulcus in 13% of cases. The supraorbital transverse sulcus is sometimes determined on the inferior surface of the frontal lobe. The postcentral sulcus sometimes merges with the interparietal sulcus and the posterior part of the lateral sulcus (in 31% of cases). In 56% of cases, a parallel groove of the same name passes over the lumbar groove. In 40% of cases, there is an additional arcuate groove of the precuneus. The superior occipital groove is bifurcated (in 55% of cases) or tripled (in 12% of cases) - in the form of two or three transverse grooves. The middle temporal groove is sometimes replaced by several radial or diverging grooves.

Sometimes there is a longitudinal canal in the olfactory tract. Rarely, between the area of divergence of the crura of the fornix and the splenium of the corpus callosum, there is a small flattened quadrangular and closed below slit (triangular slit). The base of this slit faces forward.

The size and shape of the thalamus are variable, rarely two interthalamic adhesions are observed. The sizes of the mammillary bodies also vary. The configuration, relationships of the hypothalamic nuclei, and their sizes are variable. The depth of the interpeduncular fossa, the number of openings in the posterior perforated substance may be different. Variations in the length and size of the substantia nigra and the red nucleus are observed. The depth of the basilar groove of the pons may be different. The shape of the pons, the thickness of the middle cerebellar peduncles are individually variable. Unilateral or bilateral absence of medullary stripes, their oblique or lateral course on the surface of the medulla oblongata are observed. The number of cerebellar convolutions ranges from 127 to 244. Laterally to the anterior surface of the lower part of the vermis, a small additional lobe - a pyramid - may be observed. Additional cerebellar lobes fixed to the vermis by independent handles have been described.

Other variations in the structure of various parts of the brain are possible. Severe malformations of the brain have been described: its absence (agenesis of the brain) or most of it, varying reductions in its size to 600-700 g (microcephaly). Underdevelopment of individual areas of the cortex, corpus callosum, cerebellum is possible. Various forms of underdevelopment of the anterior commissure of the brain, optic chiasm, optic tracts, pineal body, and nuclei of the cranial nerves have been described.