Diagnosis is made through a combination of patient history, neurological examination, and medical imaging. Magnetic resonance imaging (MRI) is considered the best imaging modality for Chiari malformation since it visualizes neural tissue such as the cerebellar tonsils and spinal cord as well as bone and other soft tissues. CT and CT myelography are other options and were used prior to the advent of MRI, but they characterize syringomyelia and other neural abnormalities less well.

By convention the cerebellar tonsil position is measured relative to the basion-opisthion line, using sagittal T1 MRI images or sagittal CT images. The selected cutoff distance for abnormal tonsil position is somewhat arbitrary since not everyone will be symptomatic at a certain amount of tonsil displacement, and the probability of symptoms and syrinx increases with greater displacement, however greater than 5 mm is the most frequently cited cutoff number, though some consider 3–5 mm to be "borderline," and symptoms and syrinx may occur above that. One study showed little difference in cerebellar tonsil position between standard recumbent MRI and upright MRI for patients without a history of whiplash injury. Neuroradiological investigation is used to first rule out any intracranial condition that could be responsible for tonsillar herniation. Neuroradiological diagnostics evaluate the severity of crowding of the neural structures within the posterior cranial fossa and their impact on the foramen magnum. Chiari 1.5 is a term used when both brainstem and tonsillar herniation through the foramen magnum are present.

The diagnosis of a Chiari II malformation can be made prenatally through ultrasound.

In the late 19th century, Austrian pathologist Hans Chiari described seemingly related anomalies of the hindbrain, the so-called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation. The scale of severity is rated I – IV, with IV being the most severe. Types III and IV are very rare.

Other conditions sometimes associated with Chiari malformation include hydrocephalus, syringomyelia, spinal curvature, tethered spinal cord syndrome, and connective tissue disorders such as Ehlers-Danlos syndrome and Marfan syndrome.

Chiari malformation is the most frequently used term for this set of conditions. The use of the term Arnold–Chiari malformation has fallen somewhat out of favor over time, although it is used to refer to the type II malformation. Current sources use "Chiari malformation" to describe four specific types of the condition, reserving the term "Arnold-Chiari" for type II only. Some sources still use "Arnold-Chiari" for all four types.

Chiari malformation or Arnold–Chiari malformation should not be confused with Budd-Chiari syndrome, a hepatic condition also named for Hans Chiari.

In Pseudo-Chiari Malformation, Leaking of CSF may cause displacement of the cerebellar tonsils and similar symptoms sufficient to be mistaken for a Chiari I malformation.

Physicians now use magnetic resonance imaging (MRI) to diagnose syringomyelia. The MRI radiographer takes images of body anatomy, such as the brain and spinal cord, in vivid detail. This test will show the syrinx in the spine or any other conditions, such as the presence of a tumor. MRI is safe, painless, and informative and has greatly improved the diagnosis of syringomyelia.

The physician may order additional tests to help confirm the diagnosis. One of these is called electromyography (EMG), which show possible lower motor neuron damage. In addition, computed axial tomography (CT) scans of a patient's head may reveal the presence of tumors and other abnormalities such as hydrocephalus.

Like MRI and CT scans, another test, called a myelogram, uses radiographs and requires a contrast medium to be injected into the subarachnoid space. Since the introduction of MRI this test is rarely necessary to diagnose syringomyelia.

The possible causes are trauma, tumors and congenital defects. It is most usually observed in the part of the spinal cord corresponding to the neck area. Symptoms are due to spinal cord damage and are: pain, decreased sensation of touch, weakness and loss of muscle tissue. The diagnosis is confirmed with a spinal CT, myelogram or MRI of the spinal cord. The cavity may be reduced by surgical decompression.

Furthermore, evidence also suggests that impact injuries to the thorax area highly correlate with the occurrence of a cervical-located syrinx.

Open spina bifida can usually be detected during pregnancy by fetal ultrasound. Increased levels of maternal serum alpha-fetoprotein (MSAFP) should be followed up by two tests – an ultrasound of the fetal spine and amniocentesis of the mother's amniotic fluid (to test for alpha-fetoprotein and acetylcholinesterase). AFP tests are now mandated by some state laws (including California). and failure to provide them can have legal ramifications. In one case, a man born with spina bifida was awarded a $2-million settlement after court found his mother's OBGYN negligent for not performing these tests. Spina bifida may be associated with other malformations as in dysmorphic syndromes, often resulting in spontaneous miscarriage. In the majority of cases, though, spina bifida is an isolated malformation.

Genetic counseling and further genetic testing, such as amniocentesis, may be offered during the pregnancy, as some neural tube defects are associated with genetic disorders such as trisomy 18. Ultrasound screening for spina bifida is partly responsible for the decline in new cases, because many pregnancies are terminated out of fear that a newborn might have a poor future quality of life. With modern medical care, the quality of life of patients has greatly improved.

Tests for neural tube defects include ultrasound examination and measurement of maternal serum alpha-fetoprotein (MSAFP). Second trimester ultrasound is recommended as the primary screening tool for NTDs, and MSAFP as a secondary screening tool. This is due to increased safety, increased sensitivity and decreased false positive rate of ultrasound as compared to MSAFP. Amniotic fluid alpha-fetoprotein (AFAFP) and amniotic fluid acetylcholinesterase (AFAChE) tests are also used to confirming if ultrasound screening indicates a positive risk. Often, these defects are apparent at birth, but acute defects may not be diagnosed until much later in life. An elevated MSAFP measured at 16–18 weeks gestation is a good predictor of open neural tube defects, however the test has a very high false positive rate, (2% of all women tested in Ontario, Canada between 1993 and 2000 tested positive without having an open neural tube defect, although 5% is the commonly quoted result worldwide) and only a portion of neural tube defects are detected by this screen test (73% in the same Ontario study). MSAFP screening combined with routine ultrasonography has the best detection rate although detection by ultrasonography is dependent on operator training and the quality of the equipment.

Whole spine MR imaging may be used to evaluate the extent of syrinx formation (fluid filled cavity within the spinal cord) in CM dogs, developing a thermal camera-based screening test for the disorder and a method of measuring the actual syrinx volume from MR images.

Before the introduction of MRI, the diagnosis of CM and SM were commonly confused with that of allergic skin disorders, disk disease, ear infections and epilepsy. After CM was reported in human patients, the initial research was provided for the diagnosis of animals. MRI in animals is safe, however, to ensure that the patient remains motionless, light general anesthesia is required.

According to recent studies, thermography may be a useful tool in the diagnosis of CM and SM. Thermography requires no sedation or clipping of hair for a dog to be imaged by the infrared camera. After the image is captured, computer software is used to assess changes in the temperature and color pattern to detect abnormality.

Adult presentation in diastematomyelia is unusual. With modern imaging techniques, various types of spinal dysraphism are being diagnosed in adults with increasing frequency. The commonest location of the lesion is at first to third lumbar vertebrae. Lumbosacral adult diastematomyelia is even rarer. Bony malformations and dysplasias are generally recognized on plain x-rays. MRI scanning is often the first choice of screening and diagnosis. MRI generally give adequate analysis of the spinal cord deformities although it has some limitations in giving detailed bone anatomy. Combined myelographic and post-myelographic CT scan is the most effective diagnostic tool in demonstrating the detailed bone, intradural and extradural pathological anatomy of the affected and adjacent spinal canal levels and of the bony spur.

Prenatal ultrasound diagnosis of this anomaly is usually possible in the early to mid third-trimester. An extra posterior echogenic focus between the fetal spinal laminae is seen with splaying of the posterior elements, thus allowing for early surgical intervention and have a favorable prognosis. Prenate ultrasound could also detect whether the diastematomyelia is isolated, with the skin intact or association with any serious neural tube defects. Progressive neurological lesions may result from the "tethering cord syndrome" (fixation of the spinal cord) by the diastematomyelia phenomenon or any of the associated disorders such as myelodysplasia, dysraphia of the spinal cord.

The precise causes of syringomyelia are still unknown although blockage to the flow of cerebrospinal fluid has been known to be an important factor since the 1970s. Scientists in the UK and America continue to explore the mechanisms that lead to the formation of syrinxes in the spinal cord. It has been demonstrated a block to the free flow of cerebrospinal fluid is a contributory factor in the pathogenesis of the disease. Duke University in America and Warwick University are conducting research to explore genetic features of syringomyelia.

Surgical techniques are also being refined by the neurosurgical research community. Successful procedures expand the area around the cerebellum and spinal cord, thus improving the flow of cerebrospinal fluid thereby reducing the syrinx.

It is also important to understand the role of birth defects in the development of hindbrain malformations that can lead to syringomyelia as syringomyelia is a feature of intrauterine life and is also associated with spina bifida. Learning when these defects occur during the development of the fetus can help us understand this and similar disorders, and may lead to preventive treatment that can stop the formation of some birth abnormalities. Dietary supplements of folic acid prior to pregnancy have been found to reduce the number of cases of spina bifida and are also implicated in prevention of cleft palate and some cardiac defects.

Diagnostic technology is another area for continued research. MRI has enabled scientists to see conditions in the spine, including syringomyelia before symptoms appear. A new technology, known as dynamic MRI, allows investigators to view spinal fluid flow within the syrinx. CT scans allow physicians to see abnormalities in the brain, and other diagnostic tests have also improved greatly with the availability of new, non-toxic, contrast dyes.

Treatment depends on the anatomy of the malformation as determined by angiography or Magnetic Resonance Imaging (MRI).

Surgery

Surgical intervention is warranted in patients who present with new onset neurological signs and symptoms or have a history of progressive neurological manifestations which can be related to this abnormality. The surgical procedure required for the effective treatment of diastematomyelia includes decompression (surgery) of neural elements and removal of bony spur. This may be accomplished with or without resection and repair of the duplicated dural sacs. Resection and repair of the duplicated dural sacs is preferred since the dural abnormality may partly contribute to the "tethering" process responsible for the symptoms of this condition.

Post-myelographic CT scanning provides individualized detailed maps that enable surgical treatment of cervical diastematomyelia, first performed in 1983.

Observation

Asymptomatic patients do not require surgical treatment. These patients should have regular neurological examinations since it is known that the condition can deteriorate. If any progression is identified, then a resection should be performed.

Examples of possible complications include shunt malfunction, shunt failure, and shunt infection, along with infection of the shunt tract following surgery (the most common reason for shunt failure is infection of the shunt tract). Although a shunt generally works well, it may stop working if it disconnects, becomes blocked (clogged), infected, or it is outgrown. If this happens the cerebrospinal fluid will begin to accumulate again and a number of physical symptoms will develop (headaches, nausea, vomiting, photophobia/light sensitivity), some extremely serious, like seizures. The shunt failure rate is also relatively high (of the 40,000 surgeries performed annually to treat hydrocephalus, only 30% are a patient's first surgery) and it is not uncommon for patients to have multiple shunt revisions within their lifetime.

Another complication can occur when CSF drains more rapidly than it is produced by the choroid plexus, causing symptoms - listlessness, severe headaches, irritability, light sensitivity, auditory hyperesthesia (sound sensitivity), nausea, vomiting, dizziness, vertigo, migraines, seizures, a change in personality, weakness in the arms or legs, strabismus, and double vision - to appear when the patient is vertical. If the patient lies down, the symptoms usually vanish quickly. A CT scan may or may not show any change in ventricle size, particularly if the patient has a history of slit-like ventricles. Difficulty in diagnosing overdrainage can make treatment of this complication particularly frustrating for patients and their families. Resistance to traditional analgesic pharmacological therapy may also be a sign of shunt overdrainage "or" failure.

The diagnosis of cerebrospinal fluid buildup is complex and requires specialist expertise. Diagnosis of the particular complication usually depends on when the symptoms appear - that is, whether symptoms occur when the patient is upright or in a prone position, with the head at roughly the same level as the feet.

There is neither a single cause of spina bifida nor any known way to prevent it entirely. However, dietary supplementation with folic acid has been shown to be helpful in reducing the incidence of spina bifida. Sources of folic acid include whole grains, fortified breakfast cereals, dried beans, leaf vegetables and fruits.

Folate fortification of enriched grain products has been mandatory in the United States since 1998. The U.S. Food and Drug Administration, Public Health Agency of Canada and UK recommended amount of folic acid for women of childbearing age and women planning to become pregnant is at least 0.4 mg/day of folic acid from at least three months before conception, and continued for the first 12 weeks of pregnancy.

Women who have already had a baby with spina bifida or other type of neural tube defect, or are taking anticonvulsant medication, should take a higher dose of 4–5 mg/day.

Certain mutations in the gene "VANGL1" have been linked with spina bifida in some families with a history of the condition.

In 1996, the United States Food and Drug Administration published regulations requiring the addition of folic acid to enriched breads, cereals, flour and other grain products. It is important to note that during the first four weeks of pregnancy (when most women do not even realize that they are pregnant), adequate folate intake is essential for proper operation of the neurulation process. Therefore, women who could become pregnant are advised to eat foods fortified with folic acid or take supplements in addition to eating folate-rich foods to reduce the risks of serious birth defects.

In Canada, mandatory fortification of selected foods with folic acid has been shown to reduce the incidence of neural tube defects by 46%.

Women who may become pregnant are advised to get 400 micrograms of folic acid daily. Women who have previously given birth to a child with a neural tube defect may benefit from a supplement containing 4.0 mg/5.0 mg in the UK mg daily, following advice provided by their doctor.

Diagnosis of a cerebrospinal fluid leak is performed through a combination of measurement of the CSF pressure and a computed tomography myelogram (CTM) scan of the spinal column for fluid leaks. The opening fluid pressure in the spinal canal is obtained by performing a lumbar puncture, also known as a spinal tap. Once the pressure is measured, a radiocontrast agent is injected into the spinal fluid. The contrast then diffuses out through the dura sac before leaking through dural holes. This allows for a CTM with fluoroscopy to locate and image any sites of dura rupture via contrast seen outside the dura sac in the imagery.

Magnetic resonance imaging is less effective than CT at directly imaging sites of CSF leak. MRI studies may show pachymeningeal enhancement (when the dura mater looks thick and inflamed), sagging of the brain, pituitary enlargement, subdural hygromas, engorgement of cerebral venous sinuses, and other abnormalities. For 20% of patients, MRIs present as completely normal. There is disagreement over whether MRI should be the study of choice. MRIs performed with the patient seated upright (vs. laying supine) are not better for diagnosing CSF leaks, but are more than twice as effective at diagnosing cerebellar tonsillar ectopia, also known as Chiari malformation. Cerebellar tonsillar ectopia shares many of the same symptoms as CSF leak, but originates either congenitally or from trauma, including whiplash strain to the dura.

An alternate method of locating the site of a CSF leak is to use heavily T2-weighted MR myelography. This has been effective in identifying the sites of a CSF leak without the need for a CT scan, lumbar puncture, and contrast and at locating fluid collections such as CSF pooling. Another highly successful method of locating a CSF leak is intrathecal contrast and MR Myelography.

For children younger than eight weeks of age (and possibly in utero), a tethered cord may be observed using ultrasonography. Ultrasonography may still be useful through age 5 in limited circumstances.

MRI imaging appears to be the gold standard for diagnosing a tethered cord.

A tethered cord is often diagnosed as a "low conus." The conus medullaris (or lower termination of the spinal cord) normally terminates at or above the L1-2 disk space (where L1 is the first, or topmost lumbar vertebra). After about 3 months of age, a conus below the L1-2 disk space may indicate a tethered cord and termination below L3-4 is unmistakably tethered. "Cord tethering is often assumed when the conus is below the normal L2-3 level.

TCS, however, is a clinical diagnosis that should be based on "neurological and musculoskeletal signs and symptoms. Imaging features are in general obtained to support rather than make the diagnosis." Clinical evaluation may include a simple rectal examination and may also include invasive or non-invasive urological examination. "Bladder dysfunction occurs in ~40% of patients affected by tethered cord syndrome. ... [I]t may be the earliest sign of the syndrome."

Hydrocephalus can be successfully treated by placing a drainage tube (shunt) between the brain ventricles and abdominal cavity. There is some risk of infection being introduced into the brain through these shunts, however, and the shunts must be replaced as the person grows. A subarachnoid hemorrhage may block the return of CSF to the circulation.

This should be distinguished from external hydrocephalus. This is a condition generally seen in infants and involving enlarged fluid spaces or subarachnoid spaces around the outside of the brain. This is generally a benign condition that resolves spontaneously by 2 years of age. (Greenberg, Handbook of Neurosurgery, 5th Edition, pg 174). Imaging studies and a good medical history can help to differentiate external hydrocephalus from subdural hemorrhages or symptomatic chronic extra-axial fluid collections which are accompanied by vomiting, headaches and seizures.

Hydrocephalus treatment is surgical, creating a way for the excess fluid to drain away. In the short term, an external ventricular drain (EVD), also known as an extraventricular drain or ventriculostomy, provides relief. In the long term, some patients will need any of various types of cerebral shunt. It involves the placement of a ventricular catheter (a tube made of silastic) into the cerebral ventricles to bypass the flow obstruction/malfunctioning arachnoidal granulations and drain the excess fluid into other body cavities, from where it can be resorbed. Most shunts drain the fluid into the peritoneal cavity (ventriculo-peritoneal shunt), but alternative sites include the right atrium (ventriculo-atrial shunt), pleural cavity (ventriculo-pleural shunt), and gallbladder. A shunt system can also be placed in the lumbar space of the spine and have the CSF redirected to the peritoneal cavity (Lumbar-peritoneal shunt). An alternative treatment for obstructive hydrocephalus in selected patients is the endoscopic third ventriculostomy (ETV), whereby a surgically created opening in the floor of the third ventricle allows the CSF to flow directly to the basal cisterns, thereby shortcutting any obstruction, as in aqueductal stenosis. This may or may not be appropriate based on individual anatomy. For infants, ETV is sometimes combined with choroid plexus cauterization, which reduces the amount of cerebrospinal fluid produced by the brain. The technique, known as ETV/CPC was pioneered in Uganda by neurosurgeon Ben Warf and is now in use in several U.S. hospitals.

Gradient-Echo T2WI magnetic resonance imaging (MRI) is most sensitive method for diagnosing cavernous hemangiomas. MRI is such a powerful tool for diagnosis, it has led to an increase in diagnosis of cavernous hemangiomas since the technology's advent in the 1980s. The radiographic appearance is most commonly described as "popcorn" or "mulberry"-shaped. Computed tomography (CT) scanning is not a sensitive or specific method for diagnosing cavernous hemangiomas. Angiography is typically not necessary, unless it is required to rule out other diagnoses. Additionally, biopsies can be obtained from tumor tissue for examination under a microscope. It is essential to diagnose cavernous hemangioma because treatments for this benign tumor are less aggressive than that of cancerous tumors, such as angiosarcoma. However, since MRI appearance is practically pathognomonic, biopsy is rarely needed for verification.

The type of treatment needed for dogs diagnosed with CM/SM depends on the severity of the condition and the age of the dog. Young dogs with clinical signs should be considered for surgical removal to minimize the progression of the disease as the dog ages. Older dogs with little or no clinical signs may be treated medically, rather than surgically. However, severe cases of CM/SM may require surgery regardless of age. The goal of surgery is syrynx decompression through restoration of normal cerebrospinal fluid circulation.

The surgical treatment of CM in dogs is described as "foramen magnum decompression FMD". Despite an approximately 80% success rate with this surgical technique, there is a 25% to 50% relapse, primarily due to excessive scar tissue formation at the decompression site. A cranioplasty may be performed instead, in which a plate, constructed using titanium mesh and bone cement, is fixed to the back of the skull following a standard FMD procedure. The procedure had been effective in humans. The postoperative relapse rate associated with the titanium cranioplasty procedure is less than 7%.

Treatment involves removal of the etiologic mass and decompressive craniectomy. Brain herniation can cause severe disability or death. In fact, when herniation is visible on a CT scan, the prognosis for a meaningful recovery of neurological function is poor. The patient may become paralyzed on the same side as the lesion causing the pressure, or damage to parts of the brain caused by herniation may cause paralysis on the side opposite the lesion. Damage to the midbrain, which contains the reticular activating network which regulates consciousness, will result in coma. Damage to the cardio-respiratory centers in the medulla oblongata will cause respiratory arrest and (secondarily) cardiac arrest. Current investigation is underway regarding the use of neuroprotective agents during the prolonged post-traumatic period of brain hypersensitivity associated with the syndrome.

A 69-year-old male with tethered cord that was low lying and associated with Spina Bifida in the form of meningocele that was operated on as an infant, was studied in this research. He presented with worsened neurological deficits due to progressive lumbar stenosis at the L3-L4 level which was associated with the spinal discs degenerating. Extreme lateral inter body fusion (XLIF) was performed to allow for indirect spinal cord decompression and stability which allowed for neurological improvement. The role of the XLIF approach to this treatment was emphasized and compared to other surgical approaches. It was concluded that surgical decompression should be performed as soon as possible to prevent any further neurological damage. Also concluded was that the XLIF approach is safe and fast and is indicative of a good surgical option to obtain spinal cord indirect decompression and lumbar inter body fusion.

Diagnosing colpocephaly prenatally is difficult because in many cases signs start to appear after birth. Prenatal diagnosis is made by detecting enlargement of either or both occipital horns of the lateral ventricles. Usually prenatal ultrasounds don't show cephalic abnormalities and in cases that they do show abnormality is of low accuracy, making it difficult to diagnose colpocephaly. Often, abnormalities in prenatal ultrasounds can be misdiagnosed as hydrocephalus.

The earliest point at which a CPAM can be detected is by prenatal ultrasound. The classic description is of an echogenic lung mass that gradually disappears over subsequent ultrasounds. The disappearance is due to the malformation becoming filled with fluid over the course of the gestation, allowing the ultrasound waves to penetrate it more easily and rendering it invisible on sonographic imaging. When a CPAM is rapidly growing, either solid or with a dominant cyst, they have a higher incidence of developing venous outflow obstruction, cardiac failure and ultimately "hydrops fetalis". If "hydrops" is not present, the fetus has a 95% chance of survival. When hydrops is present, risk of fetal demise is much greater without "in utero" surgery to correct the pathophysiology. The greatest period of growth is during the end of the second trimester, between 20–26 weeks.

A measure of mass volume divided by head circumference, termed cystic adenomatoid malformation volume ratio (CVR) has been developed to predict the risk of "hydrops". The lung mass volume is determined using the formula (length × width × anteroposterior diameter ÷ 2), divided by head circumference. With a CVR greater than 1.6 being considered high risk. Fetuses with a CVR less than 1.6 and without a dominant cyst have less than a 3% risk of hydrops. After delivery, if the patient is symptomatic, resection is mandated. If the infant is asymptomatic, the need for resection is a subject of debate, though it is usually recommended. Development of recurrent infections, rhabdomyosarcoma, adenocarcinomas "in situ" within the lung malformation have been reported.

Colpocephaly is usually non-fatal. There has been relatively little research conducted to improve treatments for colpocephaly, and there is no known definitive treatment of colpocephaly yet. Specific treatment depends on associated symptoms and the degree of dysfunction. Anticonvulsant medications can be given to prevent seizure complications, and physical therapy is used to prevent contractures (shrinkage or shortening of muscles) in patients that have limited mobility. Patients can also undergo surgeries for stiff joints to improve motor function. The prognosis for individuals with colpocephaly depends on the severity of the associated conditions and the degree of abnormal brain development.

A rare case of colpocephaly is described in literature which is associated with macrocephaly instead of microcephaly. Increased intracranial pressure was also found in the condition. Similar symptoms (absence of corpus callosum and increased head circumference) were noted as in the case of colpocephaly that is associated with microcephaly. A bi-ventricular peritoneal shunt was performed, which greatly improved the symptoms of the condition. Ventriculo-peritoneal shunts are used to drain the fluid into the peritoneal cavity.

Testing for a malformed vein of Galen is indicated when a patient has heart failure which has no obvious cause. Diagnosis is generally achieved by signs such as cranial bruits and symptoms such as expanded facial veins. The vein of Galen can be visualized using ultrasound or Doppler. A malformed Great Cerebral Vein will be noticeably enlarged. Ultrasound is a particularly useful tool for vein of Galen malformations because so many cases occur in infancy and ultrasound can make diagnoses prenatally. Many cases are diagnosed only during autopsy as congestive heart failure occurs very early.