Achondroplasia is a significant genetic disorder of the bone. The word achondroplasia actually means 'without cartilage'. It is a congenital abnormality. The condition of achondroplasia is marked by disproportional development of bones resulting in defects affecting the appearance of a person. Achondroplasia predominantly occurs in infants because of the inheritance of genes associated with skeletal dysplasia also known as short stature syndrome.
The incidence of achondroplasia is dependent on the fibroblast growth factor receptor 3 (FGFR3) protein which is responsible for bone development. The faulty coding of FGGR-3 produced by the FGFR3 gene results in achondroplasia. The inheritance of the faulty gene FGFR3 in a family resulting in achondroplasia is called as autosomal dominant inheritance. The primary defect of this condition is caused because of the abnormal chondrocyte proliferation at the growth plate region. This proliferation process results in the formation of short and proportionately thick and long bones.
The manifestation of this is predominantly seen in the proximal regions such as large head because of intramembranous ossification, lumbar lordosis and saddle nose appearance (mid face hypoplasia). In case of severe spinal deformity, cord compression is noticed. The achondroplastic disorder pertaining to the homozygous nature is more lethal in infants than the sporadic form. Other cases such as pseudoachondroplasia resemble achondroplasia but it does not have skull abnormalities.
Diagnosis and treatment
The diagnosis of achondroplasia is usually done at an early stage. The child is examined for abnormalities affecting bone development. Gene assays are also done to detect the presence of the FGFR-3 mutated genes. In many cases congenital anomalies are also considered a diagnostic measure.
Corrective treatment measures are taken in children who are susceptible to achondroplasia. The child is monitored on a regular basis to identify the abnormalities in bone development and growth processes. Emphasis during observation and treatment is given to the development of head and spine to notice conditions such as hydrocephalus and foramen magnum abnormalities. In case of hydrocephalus, the neurosurgeon drains out the excess fluid through a shunt to reduce the pressure caused to the brain.
Abnormalities of spinal cord are very significant factors determining the onset of cord compression. Some of the characteristic features of spinal cord compression include snoring, sleep apnea in infants and also reduced muscle tone. In such cases, the fluid is drained to reduce the pressure on the spinal cord. Where there is occurrence of Kyphosis, also known as small hump, surgical intervention is done to rectify the condition. Other significant procedures involve drainage from ears to prevent infections and also dental procedures to reduce overcrowding of teeth.
Chiari malformations or CM are structural defects in the cerebellum. The cerebellum and parts of the brain stem rest in an indented space at the lower rear region of the skull. This is situated above a funnel-like opening (called the foramen magnum) to the spinal cord. When a part of the cerebellum is found located below the foramen magnum, it is called Chiari malformation.
Causes of Chiari malformations
When the bony space is smaller than normal, this causes the cerebellum and brain stem to be pushed downward into the foramen magnum and into the upper spinal canal, thereby blocking the flow of cerebrospinal fluid that surrounds and cushions the brain and spinal cord.
It can also be caused by structural defects in the brain and spinal cord during fetal development due to genetic mutations or lack of proper vitamins or nutrients in the maternal diet. This is called primary CM or congenital CM.
It is also caused later in life if the spinal fluid is drained excessively from the lumbar and thoracic areas of the spine due to injury or infection. This is acquired CM or secondary CM. However, primary is more common than secondary CM.
Types of Chiari malformations
They are classified into different types depending upon the severity of the disorder.
Type 1 involves extension of the cerebellar tonsils in the foramen magnum involving brain stem. This commonly occurs in adolescence or adulthood.
Type II is called classic CM and it involves extension of both cerebellar and brain stem tissue into the foramen magnum.
Type III is the most serious form of CM. Here the cerebellum and brain stem protrude or herniate through the foramen magnum and into the spinal cord.
Type IV involves an incomplete or underdeveloped cerebellum, a condition known as cerebellar hypoplasia. This is a rare form of CM.
There is yet another form of this disorder which some researchers call as Type 0, in which there is no protrusion of the cerebellum through the foramen magnum but headache and other symptoms are present.
Neck pain, balance problems, muscle weakness, numbness and other abnormal feelings in arms and legs, dizziness, vision problems, difficulty in swallowing, buzzing in the ears, hearing loss, vomiting, insomnia, depression or headache made worse by coughing or straining are some common symptoms.
Symptoms may change from one person to another depending upon the degree of CSF buildup. Patients with type I CM may not have symptoms at all. Adolescents and adults who have CM but no symptoms initially may later in life develop symptoms such as difficulty in swallowing, irritability when being fed, vomiting, arm weakness, a stiff neck, breathing problems, developmental delays and inability to gain weight.
CM is also sometimes associated with certain hereditary syndromes that affect neurological and skeletal abnormalities and disorders that affect bone formation and growth.
It is estimated that the condition occurs in about one in every 1000 births. However, increased use of diagnostic imaging has shown that CM may be much more common. CM occurs more often in women than in men and Type II malformations are more prevalent in certain groups including people of Celtic descent.
As many exhibit no symptoms, their malformations are discovered only during the course of diagnosis or treatment for another disorder. The doctor performs a physical exam and checks the person's memory, cognition, balance, touch, reflexes, sensation and motor skills.
X ray of the head and neck is done to produce images of bones and certain tissues. Though these cannot reveal a CM, they can identify abnormalities that are associated with CM. a and MRI are most often suggested..
Some CMs are asymptomatic and do not interfere with a person's daily activities of daily living and in some cases, medications are used to ease certain symptoms including pain.
Surgery is the treatment option to correct functional disturbances or halt the progression of damage to the central nervous system. Surgery can help reduce symptoms. More than one surgery may be needed to treat the condition. There are different types of surgery performed on adults with CM to create more space for the cerebellum and to relieve pressure on the spinal column.
Surgery involves making an incision at the back of the head and removing a small portion of the bottom of the skull to correct the irregular bony structure. This surgical technique involves destroying tissue with high-frequency electrical currents. Spinal Laminectomy involves surgical removal of the arched, bony roof of the spinal canal to increase the size of the spinal canal and relieve pressure on the spinal cord and nerve roots.
Sometimes, the surgeon makes an incision in the dura to examine the brain and spinal cord. Additional tissue may be added to the dura to create more space for the flow of CSF. Infants may require surgery to reposition the spinal cord and close the opening in the back.
Hydrocephalus is treated with a shunt system that drains excess fluid and relieves pressure from the head. An alternative surgical treatment to improve the flow of CSF is by making a small perforation in the floor of the third ventricle and the CSF is diverted to relieve pressure. Surgeons may open the spinal cord and insert a shunt to drain a syringomyelia. A small catheter is inserted into the syrinx for continued drainage.
Post surgery follow-up
Since surgery involves risk, including the possibility of infection, fluid in the brain, cerebrospinal fluid leakage or problems in wound healing, it is recommended to discuss the pros and cons with the doctor when deciding whether surgery is necessary or not. Surgery reduces symptoms in most people but if nerve injury in the spinal cord has already occurred then this procedure will not reverse the damage. Regular follow up post surgery with examinations by the doctor and periodic imaging tests to assess the outcome of surgery and flow of cerebrospinal fluid is essential.
Spina bifida is a group of congenital defects of the spine developed during fetal stage. During the first month after conception, the embryonic structure called neural tube is formed which eventually develops into the baby's brain, spinal cord and the surrounding bony structure. In case of spina bifida, the lower part of the neural tube does not develop or fuse fully leading to abnormalities in brain or spinal cord. When the spinal column does not close properly around the baby's spinal cord the nerves start to protrude through the opening causing spina bifida.
Spina bifida is a broader term used for various conditions of the spine. The defect may range from very mild form which may not present itself with any symptoms to a severe one causing disability and disrupting the patient's normal life. There are broadly three types of spina bifida which are discussed below.
Spina bifida occulta
It is a very mild and most common form of spina bifida in which one or two vertebrae are left unfused. The portion of the spinal cord that is not enclosed by vertebrae is covered by skin. Occulta means 'hidden' and since the opening is hidden under the skin, the condition is referred as spina bifida occulta. However, in such cases, nerve roots and the spinal cord are not affected and hence, the person remains asymptotic.
In meningocele, the meninges (membranes that surround and protect the spinal cord) protrude through the spinal opening without affecting the spinal cord. Sometimes a layer of skin is formed over the opening. In few cases of meningocele, when the membranes push through the opening, they get filled with the spinal fluid forming a cyst. With this type of spina bifida, one may experience only mild symptoms or in few cases the damage may be very severe.
Myelomeningocele is the most severe form of spina bifida. Myelomeningocele, almost certainly leads to mental and physical disabilities. The severity of the damage depends upon the site of the opening on the spine as the portion that is below the opening becomes dysfunctional. The higher the location of the opening, the greater will be the impact on the functioning of the body.
The symptoms vary depending upon the type of the spina bifida. In case of spina bifida occulta, the child remains largely asymptotic and there may be a birthmark, a patch, a dimple or hair growth on the skin under which the vertebrae is not joined properly. This condition is usually diagnosed during an ultrasound performed for some other purpose.
Meningocele may or may not show any symptoms. Partial paralysis with urinary and bowel problems are usually associated with meningocele. This condition is diagnosed before birth through fetal ultrasound and other tests. This condition is diagnosed when a test called maternal serum alpha-fetoprotein is performed on pregnant woman.
Spina bifida occulta doesn't require any treatment; however other two conditions are always treated surgically. In case of meningocele, surgery involves pushing back the membranes into the place and closing the vertebrates. Babies born with Myelomeningocele are operated within 24 to 48 hours of their birth. The surgery is mainly performed to prevent infection and further damage to the spinal cord. If the baby develops too much cerebrospinal fluid which is known as hydrocephalus, a shunt will be placed as part of the treatment. In recent times spina bifida is also treated through fetal surgery, wherein the uterus is surgically opened to correct the spine defect and immediately closed back. Spina bifida, particularly Myelomeningocele type, requires lifelong medical support as children with such a condition continue to suffer from neurological, orthopaedic and bladder and bowel related problems.
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Bibliography / Reference
Collection of Pages - Last revised Date: September 23, 2020