Different types of<unk> <unk>  occulta is Latin for "hidden". This is the mildest form of<unk> . In occulta, the outer part of some of the vertebrae is not completely closed. The splits in the vertebrae are so small that the<unk> l cord does not protrude. The skin at the site of the lesion may be normal, or it may have some hair growing from it; there may be a dimple in the skin, or a birthmark. Unlike most other types of neural tube defects,<unk>  occulta is not associated with increased AFP, a common screening tool used to detect neural tube defects in utero. This is because, unlike in most of the other neural tube defects, the dural lining is maintained. Many people with this type of<unk>  do not even know they have it, as the condition is asymptomatic in most cases. A systematic review of radiographic research studies found no relationship between<unk>  occulta and back pain. More recent studies not included in the review support the negative findings. However other studies suggest<unk>  occulta is not always harmless. One study found that among patients with back pain severity is worse if<unk>  occulta is present. Incomplete posterior fusion is not a true<unk>  and is very rarely of neurological significance. Meningocele A posterior meningocele () or meningeal cyst () is the least common form of<unk> . In this form, a single developmental defect allows the meninges to herniate between the vertebrae. As the nervous system remains undamaged, individuals with meningocele are unlikely to suffer long-term health problems, although cases of tethered cord have been reported. 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 A lumbar myelomeningocele Myelomeningocele (MMC), also known as meningomyelocele, is the type of<unk>  that often results in the most severe complications and affects the meninges and nerves. In individuals with myelomeningocele, the unfused portion of the<unk> l column allows the<unk> l 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<unk> l cord also protrude through the opening, forming a sac enclosing the<unk> l elements, such as meninges, cerebrospinal fluid, and parts of the<unk> l 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<unk>  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. The exposure of these nerves and tissues make the baby more prone to life-threatening infections such as meningitis. The protruding portion of the<unk> l cord and the nerves that originate at that level of the cord are damaged or not properly developed. As a result, there is usually some degree of paralysis and loss of sensation below the level of the<unk> l cord defect. Thus, the more cranial the level of the defect, the more severe the associated nerve dysfunction and resultant paralysis may be. Symptoms may include ambulatory problems, loss of sensation, deformities of the hips, knees or feet, and loss of muscle tone. Image:Spina<unk>  pelvis X-ray.X-ray image of<unk>  occulta in S-1 Image:Atlasbogenspalt.X-ray computed tomography scan of unfused arch at C1 File:Meningomyelocele diagram.Myelomeningocele in the lumbar area(1) External sac with cerebrospinal fluid(2)<unk> l cord wedged between the vertebrae
Spina bifida
Teratoma
Hydranencephaly
Anencephaly
Lissencephaly
Exencephaly
Schizencephaly
Cranioschisis