Overview

Typically the infant is found dead after having been put to bed, and exhibits no signs of having suffered.

SIDS is a diagnosis of exclusion. It should only be applied to an infant whose death is sudden and unexpected and remains unexplained after the performance of an adequate postmortem investigation including

1. an autopsy;
2. investigation of the scene and circumstances of the death;
3. exploration of the medical history of the infant and family.

SIDS was responsible for 0.543 deaths per 1,000 live births in the U.S. in 2005. It is responsible for far fewer deaths than congenital disorders and disorders related to short gestation, though it is the leading cause of death in healthy infants after one month of age.

SIDS deaths in the U.S. decreased from 4,895 in 1992 to 2,247 in 2004. But, during a similar time period, 1989 to 2004, SIDS being listed as the cause of death for sudden infant death (SID) decreased from 80% to 55%. According to Dr. John Kattwinkel, chairman of the Center for Disease Control (CDC) Special Task Force on SIDS "A lot of us are concerned that the rate (of SIDS) isn't decreasing significantly, but that a lot of it is just code shifting”.

Nomenclature

Australia and New Zealand are shifting to the term Sudden Unexplained Death in Infancy (SUDI) for professional, scientific and coronial clarity.

The term SUDI is now often used instead of Sudden Infant Death Syndrome (SIDS) because some coroners prefer to use the term ‘undetermined’ for a death previously considered to be SIDS. This change is causing diagnostic shift in the mortality data.

SIDS Back To Sleep campaign: history and theory

In 1985 Davies reported that in Hong Kong, where the common Chinese habit was for supine infant sleep position (face up), SIDS was a rare problem. In 1987 the Netherlands started a campaign advising parents to place their newborn infants to sleep on their backs (supine position) instead of their stomachs (prone position). This was followed by infant supine sleep position campaigns in the United Kingdom, New Zealand, and Australia in 1991, the U.S. and Sweden in 1992, and Canada in 1993.

This advice was based on the epidemiology of SIDS and physiological evidence which shows that infants who sleep on their back have lower arousal thresholds and less slow-wave sleep (SWS) compared to infants who sleep on their stomachs. In human infants sleep develops rapidly during early development. This development includes an increase in non-rapid eye movement sleep (NREM sleep) which is also called quiet sleep (QS) during the first 12 months of life in association with a decrease in rapid eye movement sleep (REM sleep) which is also known as active sleep (AS). In addition, slow wave sleep (SWS) which consists of stage 3 and stage 4 NREM sleep appears at 2 months of age and it is theorized that some infants have a brain-stem defect which increases their risk of being unable to arouse from SWS (also called deep sleep) and therefore have an increased risk of SIDS due to their decreased ability to arouse from SWS.

Studies have shown that preterm infants, full-term infants, and older infants have greater time periods of quiet sleep and also decreased time awake when they are positioned to sleep on their stomachs. In both human infants and rats, arousal thresholds have been shown to be at higher levels in the electroencephalography (EEG) during slow-wave sleep.

In 1992, a SIDS risk reduction strategy based upon lowering arousal thresholds during SWS was implemented by the American Academy of Pediatrics (AAP) which began recommending that healthy infants be positioned to sleep on their back (supine position) or side (lateral position), instead of their stomach (prone position), when being placed down for sleep. In 1994, a number of organizations in the United States combined to further communicate these non-prone sleep position recommendations and this became formally known as the “Back To Sleep” campaign. In 1996, the AAP further refined its sleep position recommendation by stating that infants should only be placed to sleep in the supine position and not in the prone or lateral positions.

In 1992, the first National Infant Sleep Position (NISP) Household Survey was conducted to determine the usual position in which U.S. mothers placed their babies to sleep: lateral (side), prone (stomach), supine (back), other, or no usual position. According to the 1992 NISP survey, 13.0% of U.S. infants were positioned in the supine position for sleep. According to the 2006 NISP survey 75.7% of infants were positioned in the supine position to sleep.

Since 1998 there have been several studies published which report that infants placed to sleep in the supine position lag in motor skills, social skills, and cognitive ability development when compared to infants who sleep in the prone position. In a 1998 article entitled “Effects of Sleep Position on Infant Motor Development.” by Davis, Moon, Sachs, and Ottolini, the authors state “We found that sleep position significantly impacts early motor development.” The prone (stomach) sleeping infants in this study slept an average of 225.2 hours (8.3%) more in their first 6 months of life than the supine (back) sleeping infants.

In the 1998 article entitled “Does the Supine Sleeping Position Have Any Adverse Effects on the Child? II. Development in the First 18 Months” by Dewey, Fleming, Golding, and the ALSPAC Study Team the objective of the study was “To assess whether the recommendations that infants sleep supine could have adverse consequences on their motor and mental development.” They used the Denver Developmental Screening Test (DDST) and studied infants at 6 and 18 months. According to the study, at 6 months of age, the infants who were placed to sleep in the prone position had statistically significant higher social skills scores, gross motor scores, and total development scores than those infants who were put to sleep in the supine position. In the 2005 article entitled “Influence of supine sleep positioning on early motor milestone acquisition” by Majnemer and Barr they used the Alberta Infant Motor Scale Scores (AIMS Scores) to analyze the impact of infant sleep position. They reported that “Typically developing infants who were sleep-positioned in supine had delayed motor development by age 6 months, and this was significantly associated with limited exposure to awake prone positioning.” But, the authors also note that awake prone (stomach) positioning is associated with prone (stomach) sleeping. No studies have been conducted which compare supine sleeping infants who have regular awake prone positioning (tummy time) to prone sleeping infants who have regular awake prone positioning (tummy time).

Placing infants on their stomachs while they are awake (tummy time) has been recommended to offset the motor skills delays associated with the back sleep position but positioning the infant on their stomach while awake will not impact the amount of slow wave sleep since tummy time only occurs when an infant is awake.

Undiagnosed conditions

Some conditions that may be undiagnosed and thus could be alternative diagnoses to SIDS include:

• medium-chain acyl-coenzyme A dehydrogenase deficiency (MCAD deficiency)
• infant botulism
• long QT syndrome (accounting for less than 2% of cases)
• infections with the bacterium Helicobacter pylori
• shaken baby syndrome and other forms of child abuse
• overlying

For example an infant with MCAD deficiency could have died by 'classical SIDS' if found swaddled and prone with head covered in an overheated room where parents were smoking. Genes of susceptibility to MCAD and Long QT syndrome do not protect an infant from dying of classical SIDS. Therefore presence of a susceptibility gene, such as for MCAD, means the infant may have died either from SIDS or from MCAD deficiency. It is impossible for the pathologist to distinguish between them.

Risk factors

The cause of SIDS is unknown. Any proposed causation factor must be either necessary and sufficient to cause SIDS by itself (as the rabies virus causes rabies) or necessary and insufficient to cause SIDS by itself (as the typhus bacillus may or may not cause typhoid, see Typhoid Mary). Although studies have identified risk factors for SIDS, such as putting infants to bed on their stomachs, there has been little understanding of the syndrome's biological cause or potential causes. The frequency of SIDS appears to be a strong function of the infant's sex, age and ethnicity, and the education and socio-economic-status of the infant's parents.

According to a study published on November 1, 2006 in the Journal of the American Medical Association, babies who die of SIDS have abnormalities in the brain stem (the medulla oblongata), which helps control functions like breathing, blood pressure and arousal, and abnormalities in serotonin signaling. According to the National Institutes of Health, which funded the study, this finding is the strongest evidence to date that structural differences in a specific part of the brain may contribute to the risk of SIDS.

In a British study released May 29, 2008 researchers discovered that the common bacterial infections Staphylococcus aureus (staph) and Escherichia coli (E. coli) appear to be a risk factor in some cases of Sudden Infant Death Syndrome. Both bacteria were present at greater than usual concentrations in infants who died from SIDS. SIDS cases peak between eight and ten weeks after birth, which is also the time frame in which the antibodies that were passed along from mother to child are starting to disappear and babies have not yet made their own antibodies.

Listed below are several risk factors associated with increased probability of the syndrome based on information available prior to this recent study.

Prenatal risks

• maternal nicotine use (tobacco or nicotine patch)
• inadequate prenatal care
• inadequate prenatal nutrition
• use of heroin, cocaine and other drugs
• subsequent births less than one year apart
• alcohol use
• infant being overweight
• mother being overweight
• Teen pregnancy (if the baby has a teen mother, it has a greater risk)
• infant's sex (60% of SIDS cases occur in males)

Post-natal risks

• mold (can cause bleeding lungs plus a variety of other uncommon conditions leading to a misdiagnoses and death). It is often misdiagnosed as a virus, flu, and/or asthma-like conditions.
• low birth weight (in the U.S. from 1995-1998 the rate for 1000-1499 g was 2.89/1000 and for 3500-3999 g it was 0.51/1000)
• exposure to tobacco smoke
• prone sleep position (lying on the stomach, see sleep positioning below)
• not breastfeeding
• elevated or reduced room temperature
• excess bedding, clothing, soft sleep surface and stuffed animals
• Co-sleeping with parents or other siblings may increase risk for SIDS, but the mechanism remains unclear
• infant's age (incidence rises from zero at birth, is highest from two to four months, and declines towards zero at one year)
• premature birth (increases risk of SIDS death by about 4 times. In 1995-1998 the U.S. SIDS rate for 37–39 weeks of gestation was 0.73/1000; The SIDS rate for 28–31 weeks of gestation was 2.39/1000)
• anemia

Risk reduction for SIDS

Though SIDS cannot be prevented, parents of infants are encouraged to take several precautions in order to reduce the likelihood of SIDS.

Environment

• Sleep positioning

Sleeping on the back has been recommended by (among others) the American Academy of Pediatrics (starting in 1992) to avoid SIDS, with the catchphrases "Back To Bed" and "Back to Sleep." The incidence of SIDS has fallen sharply in a number of countries in which the back to bed recommendation has been widely adopted, such as the US and New Zealand. However, the absolute incidence of SIDS prior to the Back to Sleep Campaign was already dropping in the US, from 1.511 per 1000 in 1979 to 1.301 per 1000 in 1991.

Among the theories supporting the Back to Sleep recommendation is the idea that small infants with little or no control of their heads may, while face down, inhale their exhaled breath (high in carbon dioxide) or smother themselves on their bedding—the brain-stem anomaly research (above) suggests that babies with that particular genetic makeup do not react "normally" by moving away from the pooled CO2, and thus smother. Another theory[63] is that babies sleep more soundly when placed on their stomachs, and are unable to rouse themselves when they have an incidence of sleep apnea, which is thought to be common in infants.

Arguments against infant back-sleeping include concerns that an infant could choke on fluids it brings up. Hospital neonatal-intensive-care-unit (NICU) staff commonly place preterm newborns on their stomach, although they advise parents to place their infants on their backs after going home from the hospital.

Other concerns raised about the Back to Sleep Campaign have included the possible increased risk of positional facial and head deformities (see positional plagiocephaly), possible interference with development of good sleep habits (which in turn may have other bad effects), and possible interference with motor skills development (as infants delay attempts to lift their heads, crawl, etc.).

• Breastfeeding

A 2003 study published in Pediatrics, which investigated racial disparities in infant mortality in Chicago, found that previously or currently breastfeeding infants in the study had 1/5 the rate of SIDS compared with non-breastfed infants, but that "it became nonsignificant in the multivariate model that included the other environmental factors". These results are consistent with most published reports and suggest that other factors associated with breastfeeding, rather than breastfeeding itself, are protective." However, a more recent study shows that breast feeding reduces the risk of SIDS by approximately 50% at all infant ages.

• Co-sleeping

In nearly all incidences, the higher the rate of co-sleeping, the lower the rate of SIDS and vice versa. The data has suggested that almost all SIDS deaths in adult beds would be occurring when other prevention methods, such as placing infants on their backs, are not used. Co-sleeping studied in the West has been present mostly in poorer families where other risk factors are present. While co-sleeping in other cultures such as in China is more prevalent and is done in combination with practices such as sleeping children on their back, correlating with a significantly lower rate of SIDS than the West. Further studies have suggested that factors associated with safe co-sleeping such as enhanced infant arousals are responsible for a positive contribution to SIDS prevention.

A 2005 policy statement by the American Academy of Pediatrics on sleep environment and the risk of SIDS deemed co-sleeping and bed sharing unsafe. One article reports that co-sleeping infants have a greater risk of airway covering than when the same infant sleeps alone in a cot.

• Secondhand smoke reduction

According to the U.S. Surgeon General’s Report, secondhand smoke is connected to SIDS. Infants who die from SIDS tend to have higher concentrations of nicotine and cotinine (a biological marker for secondhand smoke exposure) in their body fluids than those who die from other causes. Parents who smoke can significantly reduce their children's risk of SIDS by either quitting or smoking only outside and leaving their house completely smoke-free.

The maternal pregnancy smoking rate decreased by 38% between 1990 and 2002.

Sleeping area

• Bedding

Product safety experts advise against using pillows, sleep positioners, bumper pads, stuffed animals, or fluffy bedding in the crib and recommend instead dressing the child warmly and keeping the crib "naked."

Blankets should not be placed over an infant's head. It has been recommended that infants should be covered only up to their chest with their arms exposed. This reduces the chance of the infant shifting the blanket over his or her head.

• Sleep sacks

In colder environments where bedding is required to maintain a baby's body temperature, the use of a "baby sleep bag" or "sleep sack" is becoming more popular. This is a soft bag with holes for the baby's arms and head. A zipper allows the bag to be closed around the baby. A study published in the European Journal of Pediatrics in August 1998 has shown the protective effects of a sleep sack as reducing the incidence of turning from back to front during sleep, reinforcing putting a baby to sleep on its back for placement into the sleep sack and preventing bedding from coming up over the face which leads to increased temperature and carbon dioxide rebreathing. They conclude in their study "The use of a sleeping-sack should be particularly promoted for infants with a low birth weight." The American Academy of Pediatrics also recommends them as a type of bedding that warms the baby without covering its head. The use of swaddling clothes, a traditional form of infant restraint which leaves only the head uncovered, is controversial.

• Pacifiers

According to a 2005 meta-analysis, most studies favor pacifier use. According to the American Academy of Pediatrics, pacifier use seems to reduce the risk of SIDS, although the mechanism by which this happens is unclear. SIDS experts and policy makers haven't recommended the use of pacifiers to reduce the risk of SIDS because of several problems associated with pacifier use, like increased risk of otitis, gastrointestinal infections and oral colonization with Candida species. A 2005 study indicated that use of a pacifier is associated with up to a 90% reduction in the risk of SIDS depending on the ambient factors, and it reduced the effect of other risk factors. It has been speculated that the raised surface of the pacifier holds the infant's face away from the mattress, reducing the risk of suffocation. If a postmortem investigation does not occur or is insufficient, a suffocated baby may be misdiagnosed with SIDS.

• Bumper pads

Bumper pads may be a contributing factor in SIDS deaths and should be removed. Health Canada, the Canadian government's health department, issued an advisory recommending against the use of bumper pads, stating:

The presence of bumper pads in a crib may also be a contributing factor for Sudden Infant Death Syndrome (SIDS). These products may reduce the flow of oxygen rich air to the infant in the crib. Furthermore, proposed theories indicate that the rebreathing of carbon dioxide plays a role in the occurrence of SIDS.

Other hypotheses

• Mattress bugs

A 2004 study hypothesized that bugs feeding on baby vomit and dust could be fatal for small children, creating 'supertoxins' which spur the baby's body into overreacting, leading to anaphylactic shock.

• Brain disorder

A recently published research article showed evidence that cells in the brainstem fail to develop receptors for serotonin in the womb. This abnormality can continue postpartum until the end of the first year. This would account for there being few to no SIDS deaths after the first year of infancy and the reason the risk is more for premature infants. Males have fewer serotonin receptors than females, perhaps contributing to the increased incidence of SIDS in the demographic.

In addition, a study done in 2006 showed that a possible cause of SIDS is because parents leave their infants in a position known as Trendelenburg position. This position can cause the brain stem to fall, and in a result, the brain becomes "crushed". The proper position for an infant is either Fowler's position or Sims'.

• Air circulation with fan use

According to a study of nearly 500 babies published the October 2008 Archives of Pediatrics & Adolescent Medicine, using a fan to circulate air correlates with a lower risk of sudden infant death syndrome. Researchers took into account other risk factors and found that fan use was associated with a 72% lower risk of SIDS. Only 3% of the babies who died had a fan on in the room during their last sleep, the mothers reported. That compared to 12% of the babies who lived. Using a fan reduced risk most for babies in poor sleeping environments. Author De-Kun li said that "the baby's sleeping environment really matters" and that "this seems to suggest that by improving room ventilation we can further reduce risk."

However, Dr John Olssen at East Carolina University has pointed out that this study had a number of methodological flaws, such selection and recall bias, low enrollment numbers, and dissimilar study groups. Olssen argues that although fan use is probably not harmful, it should not be recommended as a means to reduce the risk of SIDS

• Vitamin C

In the 1970s, high doses of vitamin C were touted as a preventive measure for SIDS, although the claim was controversial even then. Subsequent study failed to support a preventive role for vitamin C in SIDS. To the contrary, a 2009 study found that high levels of vitamin C were strongly associated with SIDS, possibly through a pro-oxidant interaction with iron.

• Toxic gases

In 1989, a controversial piece of research by UK Scientist Barry Richardson claimed that all cot deaths were the result of toxic nerve gases being produced through the action of fungus in mattresses on compounds of phosphorus, arsenic and antimony. These chemicals are frequently used to make mattresses fire-retardant.

Support for this hypothesis was based on the observation that the risk of cot death rises from one sibling to the next. Richardson claimed that parents are more likely to buy new bedding for their first child, and to re-use that bedding for later children. The more frequently used the bedding is, the more chance there will be that fungus has become resident in the material; thus, a higher chance of cot death. A paper by Peter Fleming and Peter Blair references evidence from other studies that both supports and refutes the increasing occurrence of SIDS with mattress sharing and suggests that this is still inconclusive.

Dr. Jim Sprott recommends new parents either buy bedding free of the toxic compounds or to wrap the mattresses in a barrier film to prevent the escape of the gases. Sprott claims that no case of cot death has ever been traced back to a properly manufactured or wrapped mattress.

However, a final report of The Expert Group to Investigate Cot Death Theories: Toxic Gas Hypothesis, published in May 1998, concluded that "there was no evidence to substantiate the toxic gas hypothesis that antimony- and phosphorus-containing compounds used as fire retardants in PVC and other cot mattress materials are a cause of SIDS. Neither was there any evidence to believe that these chemicals could pose any other health risk to infants." The report also states that "in normal cot-like conditions it is not possible to generate toxic gas from antimony in mattresses" and "babies have also been found to die on wrapped mattresses."

Contrary to media publicity, the 1998 UK Limerick Report did not disprove the toxic gas theory—as a highly qualified environmental scientist has stated in the New Zealand Medical Journal. In fact, the Limerick Committee's experiments proved the fungal generation of toxic gases (forms of stibine and arsine) from cot mattress materials.

According to Dr. Sprott, as of 2006, the New Zealand government has not reported any SIDS deaths when babies have slept on mattresses wrapped according to his method. While the Limerick report claims that babies have been found to die on wrapped mattresses, Dr. Sprott argues that a chemical analysis of the bedding should be performed. He additionally claims that this part of the report was flawed:

In February 2000 Dr Peter Fleming (a co-author of the Limerick Report and principal author of the UK CESDI Report) conceded that the claim that three babies in the United Kingdom had died of cot death on polythene-covered mattresses could not be substantiated.

• Central Respiratory Pattern Deficiency

There is ongoing research in the pediatric/neonatal community that has begun to associate apnea-like breathing cessations in animal models with unusual neural architecture or signal transduction in central pattern generator circuits including the pre-Bötzinger complex. It is possible that irregularities in neurotransmitter release (such as GABA, adenosine, and NMDA) or deficiencies in their associated receptors (including both GABAA, GABAB subtypes and NMDA-glutamate receptors) are linked to incomplete prenatal development as is evident in pre-term infants.

• Cervical spinal injury from birth trauma

During birth, if the infant's head is traumatically turned side to side, upper cervical spinal injury can result. Difficulty breathing is a classic sign of upper spinal cord and brain-stem injury. When infants with undiagnosed upper cervical spinal cord injury are continually placed on their stomach for sleep, they are forced to turn their head to the side to breathe. This is hypothesised to aggravate and prolong the spinal cord injury sustained during birth, preventing proper healing and ultimately leading to fatal breathing difficulty.

• Genetics

There is a consistent 50% male excess in SIDS per 1000 live births of each sex. Given a 5% male excess birth rate (105 male to 100 female live births) there appear to be 3.15 male SIDS per 2 female SIDS for a male fraction of 0.61. This value of 61% in the U.S. is an average of 57% black male SIDS, 62.2% white male SIDS and 59.4% for all other races combined. Note that when multiracial parentage is involved, infant "race" is arbitrarily assigned to one category or the other; most often it is chosen by the mother. The X-linkage hypothesis for SIDS and the male excess in infant mortality have shown that the 50% male excess could be related to a dominant X-linked allele that occurs with a frequency of ⅓ that is protective of transient cerebral anoxia. An unprotected XY male would occur with a frequency of ⅔ and an unprotected XX female would occur with a frequency of 4⁄9. The ratio of ⅔ to 4⁄9 is 1.5 to 1 which matches the observed male 50% excess rate of SIDS.

Although many authors have found autosomal and mitochondrial genetic risk factors for SIDS they cannot explain the male excess because such gene loci have the same frequencies for males and females. Supporting evidence for an X-linkage is found by examination of other causes of infant respiratory death, such as suffocation by inhalation of food and other foreign objects. Although food is prepared identically for male and female infants, there is a similar 50% male excess of death from such causes indicating that males are more susceptible to the cerebral anoxia created by such incidents in exactly the same proportion as found in SIDS.

The JAMA 2006 study which indicated that there was a relationship between fewer serotonin binding sites and SIDS noted that the boys "had significantly fewer serotonin binding sites than girls,". but the authors could not reproduce it in their 2010 paper. However, such neurological prematurity decreases with age, but the male fraction of approximately 0.61 persists each month throughout the first year of life. Furthermore, this cannot explain the identical male fraction of 0.61 in other respiratory mortality causes such as respiratory distress syndrome or suffocation from inhalation of food or foreign objects cited above, that also exists for all ages 1 to 14 years in the U.S. from 1979 to 2005.

• Child abuse

Several instances of infanticide have been uncovered where the diagnosis was originally SIDS. This has led some researchers to estimate that 5% to 20% of SIDS deaths are infanticides. In 1997 The New York Times, covering a book called The Death of Innocents: A True Story of Murder, Medicine and High-Stakes Science, wrote:

The misdiagnosis of infanticide as SIDS "happens all over," Ms. Talan, a medical reporter at Newsday, said. "A lot of doctors and police don't know how to handle it. They don't take it as seriously as they should." As a result of the book's revelations, people are starting to scrutinize possible cases of this "perfect crime," which involves no physical evidence and no witnesses.

A former pediatrician Roy Meadow from United Kingdom believes that many cases diagnosed as SIDS are really the result of child abuse on the part of a parent displaying Munchausen syndrome by proxy (a condition which he was first to describe, in 1977). During the 1990s and early 2000s, a number of mothers of multiple apparent SIDS victims were convicted of murder, to varying degrees on the basis of Meadow's opinion. In 2003 a number of high-profile acquittals brought Meadow's theories into disrepute. Several hundred murder convictions were reviewed, leading to several high-profile cases being re-opened and convictions overturned.

The Royal Statistical Society issued a media release refuting the expert testimony in one UK case in which the conviction was subsequently overturned.

• Nitrogen dioxide

A 2005 study by researchers at the University of California, San Diego found that "SIDS may be related to high levels of acute outdoor NO2 exposure during the last day of life." While nitrogen dioxide (NO2) exposure may be one of many possible risk factors, it is not considered causal, and the report cautioned that further studies were needed to replicate the result.

• Vaccination

According to the US Centers for Disease Control and Prevention, several studies have failed to provide sufficient evidence of a causal link between vaccinations and SIDS. They state:

From 2 to 4 months old, babies begin their primary course of vaccinations. This is also the peak age for sudden infant death syndrome (SIDS). The timing of these two events has led some people to believe they might be related. However, studies have concluded that vaccines are not a risk factor for SIDS.

• Inner ear damage

Records of hearing tests (oto-acoustic emissions, OAEs) administered to certain infants show that those who later died of SIDS had differences in the pattern of these tests compared with normal babies. To be specific the OAE signal to noise ratio was reduced in the right ear in the SIDS babies. (Rubens DD et al. Early Human Development 84, 225-9 (2008)). It should be noted this was a small study (n=31 cases and 31 controls), had serious limitations (several significant factors were not controlled), and has been criticised from various perspectives. The authors' suggestion for the cause of SIDS is that the deaths are caused by disturbances in respiratory control (from other than suffocation). The vestibular apparatus of the inner ear has been shown to play an important role in respiratory control during sleep. It is speculated that this inner ear damage could be linked to SIDS. It is speculated that the damage occurs during delivery, particularly when prolonged contractions create greater blood pressure in the placenta. The right ear is directly in the "line of fire" for blood entering the fetus from the placenta, and thus could be most susceptible to damage. If the findings are relevant, it may be possible to take corrective measures. Researchers are beginning animal studies to explore the connection.

Side effects of SIDS risk reduction recommendations

Dr. Rafael Pelayo from Stanford University and a number of other pediatric sleep researchers in the U.S. have stated that they believe that the American Academy of Pediatrics' recommendations regarding cosleeping and pacifier use may have unintended consequences. They have stated that the SIDS prevention strategy of the American Academy of Pediatrics which keeps infants at a low arousal threshold and reduces the time in quiet sleep may be unhealthy for children. They state that slow wave sleep is the most restorative form of sleep and limiting this sleep in the first 12 months of life may have unintended consequences to both the sleep and the infant.

According to a 1998 study by British researchers that compared back sleeping infants to stomach sleeping infants there were developmental differences at 6 months of age between the two groups. At 6 months of age the stomach sleeping infants had higher gross motor scores, social skills scores, and total development skills scores than the back sleeping infants. The differences were apparent at the 5% statistical significant level. But, at 18 months the differences were no longer apparent. The researchers deemed the lower development scores of back sleeping infants at 6 months of age to be transient and stated that they do not believe the back sleeping recommendations should be changed. Other scientists have stated that the conclusion that the negative effects of back sleep at 18 months of age is transient is based upon very little evidence and that no long-term randomized trials have been completed.

Other side effects of the back sleeping position include increased rates of shoulder retraction, positional plagiocephaly, and positional torticollis. Some scientists dispute that plagiocephaly is a negative side effect. Dr. Peter Fleming, who is co-author of the study that deemed delays at 6 months of age to be transient, has stated that he does not think plagiocephaly is a negative side effect of back sleep. In an interview with the Guardian Dr. Fleming stated "I do not think it is a medical problem—it is more of a cosmetic one. Mothers may feel it is a syndrome and a problem when it really is nonsense." A research study on children with plagiocephaly found that 26% had mild to severe psychomotor delay. This study also showed that 10% of infants with plagiocephaly had mild to severe mental development delay.

Because of the delays caused by back sleep some medical professionals have suggested that the "normal" ages at which children had previously attained developmental milestones should be pushed back. This would enable medical professionals to consider "normal" children who previously were considered developmentally delayed.

Additional studies have reported that the following negative conditions are associated with the back sleep position: increase in sleep apnea, decrease in sleep duration, strabismus, social skills delays, deformational plagiocephaly, and temporomandibular jaw difficulties. In addition, the following are symptoms that are associated with sleep apnea: growth abnormalities, failure to thrive syndrome in infants, neurocognitive abnormalities, daytime sleepiness, emotional problems, decrease in memory, decrease in learning, and a delay in nonverbal skills. The conditions associated with deformational plagiocephaly include visual impairments, cerebral dysfunction, delays in psychomotor development and decreases in mental functioning. The conditions associated with gross motor milestone delays include speech and language disorders. In addition, it has been hypothesized that delays in motor skills can have a negative impact on the development of social skills. In addition, other studies have reported that the prone position prevents subluxation of the hips, increases psychomotor development, prevents scoliosis, lessens the risk of gastroesophageal reflux, decreases infant screaming periods, causes less fatigue in infants, and increases the relief of infant colic. In addition, prior to the “Back to Sleep” campaign many babies self-treated their own torticollis by turning their heads from one side to the other while sleeping in the prone position. Supine sleeping infants cannot self-treat their own torticollis.
 

Epidemiology

Hydrocephalus affects both pediatric and adult patients. According to the NIH website, there are an estimated 700,000 children and adults living with hydrocephalus.

Pediatric hydrocephalus affects one in every 500 live births, making it one of the most common developmental disabilities, more common than Down syndrome or deafness. It is the leading cause of brain surgery for children in the United States. There are over 180 different causes of the condition, one of the most common acquired etiologies being brain hemorrhage associated with premature birth. Pediatric hydrocephalus may also be a heritable condition, and mainly affects males. Hydrocephalus may be detectable during prenatal ultrasound examinations.

One of the most performed treatments for hydrocephalus, the cerebral shunt, has not changed much since it was developed in 1960. The shunt must be implanted through neurosurgery into the patient's brain, a procedure which itself may cause brain damage. An estimated 50% of all shunts fail within two years, requiring further surgery to replace the shunts. In the past 25 years, death rates associated with hydrocephalus have decreased from 54% to 5% and the occurrence of intellectual disability has decreased from 62% to 30%.

Pathology

Hydrocephalus is usually due to blockage of cerebrospinal fluid (CSF) outflow in the ventricles or in the subarachnoid space over the brain. In a person without hydrocephalus, CSF continuously circulates through the brain, its ventricles and the spinal cord and is continuously drained away into the circulatory system. Alternatively, the condition may result from an overproduction of the CSF fluid, from a congenital malformation blocking normal drainage of the fluid, or from complications of head injuries or infections.

Compression of the brain by the accumulating fluid eventually may cause convulsions and mental retardation. These signs occur sooner in adults, whose skulls no longer are able to expand to accommodate the increasing fluid volume within. Fetuses, infants, and young children with hydrocephalus typically have an abnormally large head, excluding the face, because the pressure of the fluid causes the individual skull bones — which have yet to fuse — to bulge outward at their juncture points. Another medical sign, in infants, is a characteristic fixed downward gaze with whites of the eyes showing above the iris, as though the infant were trying to examine its own lower eyelids.

The elevated intracranial pressure may cause compression of the brain, leading to brain damage and other complications. Conditions among affected individuals vary widely. Children who have had hydrocephalus may have very small ventricles, and presented as the "normal case".

If the foramina (pl.) of the fourth ventricle or the cerebral aqueduct are blocked, cereobrospinal fluid (CSF) can accumulate within the ventricles. This condition is called internal hydrocephalus and it results in increased CSF pressure. The production of CSF continues, even when the passages that normally allow it to exit the brain are blocked. Consequently, fluid builds inside the brain causing pressure that compresses the nervous tissue and dilates the ventricles. Compression of the nervous tissue usually results in irreversible brain damage. If the skull bones are not completely ossified when the hydrocephalus occurs, the pressure may also severely enlarge the head. The cerebral aqueduct may be blocked at the time of birth or may become blocked later in life because of a tumor growing in the brainstem.

Internal hydrocephalus can be successfully treated by placing a drainage tube (shunt) between the brain ventricles and abdominal cavity to eliminate the high internal pressures. 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. If CSF accumulates in the subarachnoid space, the condition is called external hydrocephalus. In this condition, pressure is applied to the brain externally, compressing neural tissues and causing brain damage. Thus resulting in further damage of the brain tissue and leading to necrotization.

Classification

Hydrocephalus can be caused by impaired cerebrospinal fluid (CSF) flow, reabsorption, or excessive CSF production.

• The most common cause of hydrocephalus is CSF flow obstruction, hindering the free passage of cerebrospinal fluid through the ventricular system and subarachnoid space (e.g., stenosis of the cerebral aqueduct or obstruction of the interventricular foramina – foramina of Monro secondary to tumors, hemorrhages, infections or congenital malformations).
• Hydrocephalus can also be caused by overproduction of cerebrospinal fluid (relative obstruction) (e.g., papilloma of choroid plexus).

Based on its underlying mechanisms, hydrocephalus can be classified into communicating and non-communicating (obstructive). Both forms can be either congenital or acquired.

Communicating

Communicating hydrocephalus, also known as non-obstructive hydrocephalus, is caused by impaired cerebrospinal fluid resorption in the absence of any CSF-flow obstruction between the ventricles and subarachnoid space. It has been theorized that this is due to functional impairment of the arachnoid granulations, which are located along the superior sagittal sinus and is the site of cerebrospinal fluid resorption back into the venous system. Various neurologic conditions may result in communicating hydrocephalus, including subarachnoid/intraventricular hemorrhage, meningitis, Chiari malformation, and congenital absence of arachnoidal granulations (Pacchioni's granulations). Scarring and fibrosis of the subarachnoid space following infectious, inflammatory, or hemorrhagic events can also prevent resorption of CSF, causing diffuse ventricular dilatation.

• Normal pressure hydrocephalus (NPH) is a particular form of communicating hydrocephalus, characterized by enlarged cerebral ventricles, with only intermittently elevated cerebrospinal fluid pressure. The diagnosis of NPH can be established only with the help of continuous intraventricular pressure recordings (over 24 hours or even longer), since more often than not instant measurements yield normal pressure values. Dynamic compliance studies may be also helpful. Altered compliance (elasticity) of the ventricular walls, as well as increased viscosity of the cerebrospinal fluid, may play a role in the pathogenesis of normal pressure hydrocephalus.
• Hydrocephalus ex vacuo also refers to an enlargement of cerebral ventricles and subarachnoid spaces, and is usually due to brain atrophy (as it occurs in dementias), post-traumatic brain injuries and even in some psychiatric disorders, such as schizophrenia. As opposed to hydrocephalus, this is a compensatory enlargement of the CSF-spaces in response to brain parenchyma loss – it is not the result of increased CSF pressure.

Non-communicating

Non-communicating hydrocephalus, or obstructive hydrocephalus, is caused by a CSF-flow obstruction ultimately preventing CSF from flowing into the subarachnoid space (either due to external compression or intraventricular mass lesions).

• Foramen of Monro obstruction may lead to dilation of one or, if large enough (e.g., in colloid cyst), both lateral ventricles.
• The aqueduct of Sylvius, normally narrow to begin with, may be obstructed by a number of genetically or acquired lesions (e.g., atresia, ependymitis, hemorrhage, tumor) and lead to dilation of both lateral ventricles as well as the third ventricle.
• Fourth ventricle obstruction will lead to dilatation of the aqueduct as well as the lateral and third ventricles.
• The foramina of Luschka and foramen of Magendie may be obstructed due to congenital failure of opening (e.g., Dandy-Walker malformation).

Congenital

The cranial bones fuse by the end of the third year of life. For head enlargement to occur, hydrocephalus must occur before then. The causes are usually genetic but can also be acquired and usually occur within the first few months of life, which include 1) intraventricular matrix hemorrhages in premature infants, 2) infections, 3) type II Arnold-Chiari malformation, 4) aqueduct atresia and stenosis, and 5) Dandy-Walker malformation.

In newborns and toddlers with hydrocephalus, the head circumference is enlarged rapidly and soon surpasses the 97th percentile. Since the skull bones have not yet firmly joined together, bulging, firm anterior and posterior fontanelles may be present even when the patient is in an upright position.

The infant exhibits fretfulness, poor feeding, and frequent vomiting. As the hydrocephalus progresses, torpor sets in, and the infant shows lack of interest in his surroundings. Later on, the upper eyelids become retracted and the eyes are turned downwards (due to hydrocephalic pressure on the mesencephalic tegmentum and paralysis of upward gaze). Movements become weak and the arms may become tremulous. Papilledema is absent but there may be reduction of vision. The head becomes so enlarged that the child may eventually be bedridden.

About 80-90% of fetuses or newborn infants with spina bifida—often associated with meningocele or myelomeningocele—develop hydrocephalus.

Acquired

This condition is acquired as a consequence of CNS infections, meningitis, brain tumors, head trauma, intracranial hemorrhage (subarachnoid or intraparenchymal) and is usually extremely painful.

Symptoms

Symptoms of increased intracranial pressure may include headaches, vomiting, nausea, papilledema, sleepiness, or coma. Elevated intracranial pressure may result in uncal and/or cerebellar tonsill herniation, with resulting life threatening brain stem compression. For details on other manifestations of increased intracranial pressure:

The triad (Hakim triad) of gait instability, urinary incontinence and dementia is a relatively typical manifestation of the distinct entity normal pressure hydrocephalus (NPH). Focal neurological deficits may also occur, such as abducens nerve palsy and vertical gaze palsy (Parinaud syndrome due to compression of the quadrigeminal plate, where the neural centers coordinating the conjugated vertical eye movement are located).

Effects

Because hydrocephalus can injure the brain, thought and behavior may be adversely affected. Learning disabilities including short-term memory loss are common among those with hydrocephalus, who tend to score better on verbal IQ than on performance IQ, which is thought to reflect the distribution of nerve damage to the brain. However the severity of hydrocephalus can differ considerably between individuals and some are of average or above-average intelligence. Someone with hydrocephalus may have motion and visual problems, problems with coordination, or may be clumsy. They may reach puberty earlier than the average child (see precocious puberty). About one in four develops epilepsy.

Treatment

Hydrocephalus treatment is surgical. 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.

Shunt complications

Examples of possible complications include shunt malfunction, shunt failure, and shunt infection. 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.

The diagnosis of cerebrospinal fluid buildup is complex and requires specialist expertise.

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 in a short amount of time. 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. 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.

Shunts in Developing Countries

Since the cost of shunt systems is beyond the reach of common people in developing countries, most people with hydrocephalus die without even getting a shunt. Worse is the rate of revision in shunt systems that adds to the cost of shunting many times. Looking at this point, a study done by Dr. Benjamin C. Warf compares different shunt systems and highlighting the role of low cost shunt systems in most of the developing countries. This study has been published in Journal of Neurosurgery: Pediatrics May 2005 issue. It is about comparing Chhabra shunt system to those of the shunt systems from developed countries. The study was done in Uganda and the shunts were donated by the International Federation for Spina Bifida and Hydrocephalus.