Development of the human brain
White matter is one of the two components of the central nervous system and consists mostly of glial cells and myelinated axons that transmit signals from one region of the cerebrum to another and between the cerebrum and lower brain centers. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to its usual preservation in formaldehyde.
White matter is composed of bundles of myelinated nerve cell processes (or axons), which connect various grey matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, increasing the speed of transmission of all nerve signals.
Image: White matter structure of human brain (taken by MRI).
Pterional Craniotomy from the Columbia Neurosurgery Online Curriculum
Carnegie stage 13 Embryo showing neural tube and brain flexures
Rapid growth folds the neural tube forming 3 brain flexures:
- cephalic flexure - pushes mesencephalon upwards
- cervical flexure - between brain stem and spinal cord
- pontine flexure - generates 4th ventricle
Huntington’s disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and psychiatric problems. It typically becomes noticeable in mid-adult life. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea, which is why the disease used to be called Huntington’s chorea. The disease is caused by an autosomal dominant mutation in either of an individual’s two copies of a gene called Huntingtin, which means any child of an affected person typically has a 50% chance of inheriting the disease. Physical symptoms of Huntington’s disease can begin at any age from infancy to old age, but usually begin between 35 and 44 years of age.
MRI is the investigative tool of choice for neurological cancers as it is more sensitive than CT for small tumors and offers better visualization of the posterior fossa. The contrast provided between grey and white matter make it the optimal choice for many conditions of the central nervous system including demyelinating diseases, dementia, cerebrovascular disease, infectious diseases and epilepsy.
Image: MRI image of white matter tracts.
Hydrocephalus is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head, convulsion, tunnel vision, and mental disability. Hydrocephalus can also cause death. Although it does occur in older adults, it is more common in infants.
Image: Hydrocephalus seen on a CT scan of the brain
Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness in the head and face, difficulty swallowing, dizziness, nausea, impaired coordination, and, in severe cases, paralysis.
Image: A T1-weighted sagittal MRI scan, from a patient with an Arnold-Chiari malformation, demonstrating tonsillar herniation of 7mm
Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord. Arachnoid cysts are a congenital disorder, and most cases begin during infancy; however, onset may be delayed until adolescence.
Image: An MRI of a 25 year old woman with left frontotemporal arachnoid cyst.
The ependyma is made up of ependymal cells, ependymocytes. These epithelial-like cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord. The cells are ciliated simple cuboidal epithelium-like cells. Their apical surfaces are covered in a layer of cilia, which circulate CSF around the CNS. Their apical surfaces are also covered with microvilli, which absorb CSF. Ependymal cells are a type of glial cell and are also CSF producing cells. Within the ventricles of the brain, a population of modified ependymal cells and capillaries together form a system called the choroid plexus, which produces the CSF.
Modified tight junctions between ependymal cells control fluid release across the epithelium. This release allows free exchange between CSF and nervous tissue of brain and spinal cord. This is why sampling of CSF (e.g. through a “spinal tap”) gives one a window to the CNS.
Image: Photomicrograph of hematoxylin stained section of normal ependymal cells at 400x magnification.
Dandy–Walker syndrome (DWS), is a congenital brain malformation involving the cerebellum and the fluid filled spaces around it. A key feature of this syndrome is the partial or even complete absence of the part of the brain located between the two cerebellar hemispheres (cerebellar vermis). The Dandy–Walker complex is a genetically sporadic disorder that occurs one in every 30,000 live births. Prenatal diagnosis and prognosis of outcomes associated with Dandy-Walker can be difficult.
The term Dandy–Walker represents not a single entity, but several abnormalities of brain development which coexist. There are, at present, three identified types of Dandy–Walker complexes. These represent closely associated forms of the disorder: DWS malformation, DWS mega cisterna magna and DWS variant.
Image: Variant DWS with dysplasia of the pons and cerebellum in a 8-year old. T2 weighted sagittal MRI.