Overview: Macrocephaly is an incomplete gyrus deficit that is characterized only by a decrease in the number of participating gyri and an increase in their size. Megalimbic gyrus malformation begins with a reduction in the number of gyri, and in severe cases, only the major gyri may be present, and megalimbic gyrus malformation is often combined with anencephaly. Megalimbic gyrus malformation is the result of brain development remaining in the primitive stage, the germinal layer. The developmental disorder occurs before the second month of embryonic life. Microscopic surgery reveals that the 4-layer cellular structure of the primitive cortex is still preserved, the cortical structure is incomplete, and the neural cells are immaturely differentiated. Due to impaired peripheral migration of neuroblasts, ectopic neuroblasts are often found in the white matter, sometimes in groups present in a nodular pattern. Ectopic gray matter masses can be seen in the hemianopia, cerebellar white matter, and brainstem. Severe cases present with mental retardation or even failure to survive after birth, and those who survive often have mental retardation with epilepsy and a poor prognosis. Etiology: Macrocephaly is caused by the brain development remaining in the primitive stage, i.e., the germinal layer becomes impaired before the second month of embryonic life. Microscopically, the 4-layer cellular structure of the primitive cortex is still preserved, with incomplete cortical structures and immature neural cell differentiation. Due to the impaired peripheral migration of neuroblasts, the ectopic neuroblasts are often found in the white matter, sometimes in groups in the form of nodules. Ectopic gray matter masses can be found in the hemianopia, cerebellar white matter, and brainstem. Examination: Giant gyrus malformation, CT imaging presents characteristic manifestations of cerebral hemispheric gyrus widening, cerebral cortex thickening, smooth inner cortical surface, and white matter thinning. Conservative treatment is the main focus, and daily exercise is strengthened.