Causes of meningocele include teratoma and other tumors of the sacrococcyx and of the presacral space, and Currarino syndrome.A meningocele may also form through dehiscences in the base of the skull. These may be classified by their localisation as occipital, frontoethmoidal or nasal. Endonasal meningoceles lie at the roof of the nasal cavity and may be mistaken for a nasal polyp. They are treated surgically. Encephalomeningoceles are classified in the same way and also contain brain tissue. Myelomeningocele
Myelomeningocele (MMC), also known as meningomyelocele, is the type of spina bifida that often results in the most severe complications and affects the meninges and nerves. In individuals with myelomeningocele, the unfused portion of the spinal column allows the spinal cord to protrude through an opening. Myelomeningocele occurs in the third week of embryonic development, during neural tube pore closure. MMC is a failure of this to occur completely. The meningeal membranes that cover the spinal cord also protrude through the opening, forming a sac enclosing the spinal elements, such as meninges, cerebrospinal fluid, and parts of the spinal cord and nerve roots. Myelomeningocele is also associated with Arnold–Chiari malformation, necessitating a VP shunt placement.Toxins and conditions associated with MMC formation include: calcium-channel blockers, carbamazepine, cytochalasins, hyperthermia, and valproic acid. Myelocele
Spina bifida with myelocele is the most severe form of myelomeningocele. In this type, the involved area is represented by a flattened, plate-like mass of nervous tissue with no overlying membrane.
In some individuals, this causes significant traction and stress on the spinal cord and can lead to a worsening of associated paralysis, scoliosis, back pain, and worsening bowel and/or bladder function. Neurological problems
Many individuals with spina bifida have an associated abnormality of the cerebellum, called the Arnold Chiari II malformation. In affected individuals, the back portion of the brain is displaced from the back of the skull down into the upper neck. In about 90% of the people with myelomeningocele, hydrocephalus also occurs because the displaced cerebellum interferes with the normal flow of cerebrospinal fluid, causing an excess of the fluid to accumulate. In fact, the cerebellum also tends to be smaller in individuals with spina bifida, especially for those with higher lesion levels.The corpus callosum is abnormally developed in 70–90% of individuals with spina bifida myelomeningocele; this affects the communication processes between the left and right brain hemispheres. Further, white matter tracts connecting posterior brain regions with anterior regions appear less organized. White matter tracts between frontal regions have also been found to be impaired.Cortex abnormalities may also be present. For example, frontal regions of the brain tend to be thicker than expected, while posterior and parietal regions are thinner. Thinner sections of the brain are also associated with increased cortical folding. Neurons within the cortex may also be displaced. Executive function
Several studies have demonstrated difficulties with executive functions in youth with spina bifida, with greater deficits observed in youth with shunted hydrocephalus.