Resmiye Oral, M.D.
The University of Iowa Department of Pediatrics
Peer Review Status: Internally Reviewed
First Published: 2003
Last Revised: August 2003
Introduction
Trauma is the most common cause of death in childhood (40% in children 1 to 4 years of age) and inflicted head injury/homicide is the most common cause of traumatic death in infancy. Over 90% of serious intracranial injuries and one third of all head injuries in infants younger than 1 year of age are reported to be due to child abuse. Inflicted head trauma makes up 12% of all physical abuse cases and 80% of deaths from head trauma in children less than 2 years of age. Shaken impact syndrome (SIS) constitutes 10-12% of all child abuse deaths. Thus, AAP recommends assuming serious injuries in infants, particularly those resulting in death, to be intentional until proven otherwise.
Injuries to the head may occur in four compartments; the scalp, the skull, the meninges, and the brain itself. The injuries in the scalp may occur in or in between five layers in this anatomical structure: The skin, dense connective tissue, galea, loose connective tissue, and pericranium. The injuries may range from bruising, abrasions, lacerations, and loss of hair to subgaleal hematoma. The more common of these injuries in non-accidental head injury is the subgaleal hematoma. Subgaleal hematoma may occur due to direct impact or forceful hair pulling.
The skull may be subjected to fractures of various kinds; simple linear or compound; namely bilateral, diastatic (> 5 mm wide), basilar, and depressed (> 2 mm depressed). The later four fractures in addition to multiple, and suture crossing ones are more specific to intentional head trauma. However, even in intentional head trauma, linear skull fractures are more common. Linear fractures are rarely associated with alteration of consciousness since the skull has absorbed the forces of impact with little transmission of it to the brain. In 50% of intentional head traumas, children suffer from an accompanying skull fracture.
The meninges consist of dura, arachnoid and pia mater. The space between dura and arachnoid is a potential space appreciated only when there is a collection of blood or fluid in it. Subarachnoidal space, in turn, is a true space with cerebrospinal fluid (CSF) circulating within. In head injuries, epidural (EDH), subdural (SDH) and subarachnoidal hemorrhages (SAH) are the major lesions we may encounter.
The brain itself may be subjected to bruising (contusions), diffuse swelling, ischemic stroke, shearing and laceration of the brain tissue, diffuse axonal injury, and herniation both at brainstem level and through the faIx. Lack of oxygen during seizures, strangulation, apneic episodes or due to increasing cerebral edema, and forceful impact to the tissue itself, may cause deleterious events occurring at cellular level with subsequent death of neurons in the area of injury.
When initially described as a constellation of findings in infants, which included retinal hemorrhages (RH), SDH and/or SAH, and little or no evidence of external injuries, shaking forces were thought to be responsible for such extensive injuries. The mechanism of injury was explained as follows: An infant's head makes up almost 20-25% of its body weight. In addition, neck muscles are weaker in the infant unable to stabilize the head when moving too fast. Thirdly, subarachnoid space is relatively larger. Lastly, infants have incomplete myelination of the white matter rendering it vulnerable to injuries. Thus, the shaking forces cause the brain to move differentially compared to the skull and dura mater tearing the bridging cortical veins in the subdural space with subsequent bleed.
Later studies showed that it is more the rotation of the brain around its center of gravity that causes diffuse brain injury. This rotation is brought about by sudden deceleration associated with the forceful striking of the head against a surface, not simply by shaking. Recent studies showed that forceful striking of the head against a surface generates at least 50 times as much of a rotational force as does shaking alone. If the striking surface is soft, the force of impact is dissipated and there may be no external sign of impact, yet severe brain injury. It is not necessary to shake the infant's head 50-100 times. One severe shake coupled with a strong enough impact to exceed a threshold for rotational forces are all that are needed to injure the brain severely. However, shaking alone can also cause the spectrum of injuries seen with shaking and impact together. In usual household falls, or unintentional impacts to the head during routine play, low velocity translational forces are involved making severe injuries very unlikely since this type of force moves the center of gravity of the brain on a straight line rather than rotationally, hence less injurious.
The current assumption today is that shaken impact syndrome (SIS) is a spectrum ranging from mild undiagnosed cases to severe fatal cases. Milder cases as well may be brought about by simple short duration shaking whereas the more severe cases may involve both shaking and impact forces.
Rib fractures, which are frequently part of the shaken impact syndrome spectrum, are caused by squeezing forces applied to the rib cage. As an adult holds an infant firmly by the rib cage, s/he applies significant force on the ribs while decreasing the antero-posterior diameter of the chest. This may exert significant pressure on the ribs posteriorly and laterally with subsequent rib fractures.
Shaking may cause cervical fractures and dislocations. Impact following shaking may cause skull fractures. Slamming the infant on a surface after shaking on the buttocks may cause vertebral fractures.
Mechanisms for retinal hemorrhages (RH) are:
Some combination of mechanical trauma, hemorrhage, hypoxia, and possibly seizure activity overwhelms the compensatory mechanisms of the immature brain, resulting in massive swelling and widespread neuronal loss. These lead to cerebral atrophy and/or infarction in the subacute phase with subsequent cystic encephalomalacia in the long run.
SIS is largely limited to infants younger than 3 years of age, with the majority being under 1 year of age. In one study, less than 2 years of age, 24% of all head injuries were the result of abuse, in severe head injuries the percentage was higher. Almost 60% of victims are male.
Risk factors for SIS include young parents, unstable family conditions, low socioeconomic conditions, and disability or prematurity of the child. Perpetrators are most frequently fathers, boyfriends, female babysitters, and mothers; 70% being male. Caretakers may be unaware of the consequences of the shaking action, however people who may be observing the act would recognize it as violent and dangerous. Shaking is usually a loss of control, either to excessive crying or irritability. These parents may be immature in that they may be expecting their needs to be met by the child. In some cases, the extent of the injuries may imply an intention of the perpetrator to at least injure the child if not kill. In others, it may not be so clear.
Accurate history is rarely provided. The characteristic of the history is rather vague, varying over time or by historians, involving a minor trauma to the head (falling off a couch), a mechanism incompatible with the extent of the injury or developmental level of the child, or no history at all. History of shaking is obtained in a minority of cases. Recent family stresses, delay in seeking medical attention, unrealistic parental expectations of the child, diapering/toilet training difficulties may be identified during history taking. In one third of diagnosed SIS patients, missed diagnosis in the past is observed.
Typical constellation of shaken impact syndrome involves subdural hemorrhage with brain injury such as cerebral edema, diffuse axonal injury, and parenchymal tears; retinal hemorrhages; soft tissue injuries, skull, rib or metaphyseal fractures.
Symptoms may include poor feeding, decreased appetite/vomiting, lethargy and or irritability. This extent of symptoms may be attributed to viral illness, feeding dysfunction, or even infantile colic. However, more severe cases may present with seizures, loss of consciousness, decreased/increased tone, breathing problems, apnea, decreased infantile reflexes, bulging fontanel, inability of eyes to focus or follow, no smiling or vocalization, unequal pupils, and meningismus. Half of the patients diagnosed with SIS fall into the more severe category, and 40-70% present with seizure.
Clinical findings may include bruising, swelling, patterned cutaneous marks, burns, significant changes in head circumference, or no external findings. Some cutaneous findings may develop a few days into admission. Some soft tissue injuries, especially scalp injuries, are noted at autopsy.
Child should be undressed and following sites should be examined to search for injuries:
Retinal hemorrhage is seen in 50-90 % of patients. Pupils must be dilated to rule in/out RH, and exam should be done by an experienced ophthalmologist. Bleed may be unilateral or bilateral; in small amounts, depending on the forces applied, or extensive, and associated with retinal folds and detachments. RH occurs rarely in accidental injuries, and never in encephalitis. The location of bleed may be intraretinal (flame type bleeds indicate superficial bleed, dot and blot bleeds indicate deeper bleeds), preretinal and subretinal. Retinal bleeds are almost always present in fatal SIS.
RH may be seen in vaginally delivered babies but resolve in 3-6 weeks. When seen after 6 weeks of life and if there is retinal detachment or folds, and are associated with any anatomic or visual deficit, SIS should be highly suspected. In a suspected abuse case, RH associated with a normal head CT should call for MRI or repeat head CT in a few days.
Hemoglobin may be decreased mildly to moderately due to SIDH. Coagulation studies should be performed. PT, PTT may be prolonged not necessarily due to a coagulopathy, but due to underlying brain injury. Platelet count and Von Willebrand panel also should be documented. Elevated transaminase levels may indicate occult liver injury. Lumbar puncture done as part of sepsis work-up in most of these infants may reveal bloody spinal fluid. Sample should be centrifuged immediately to look for xanthochromia.
As part of work up due to respiratory symptoms, chest film is done revealing normal bony structures or several unexplained rib fractures. When intentional injury is suspected, skeletal survey should be done to search for other fractures, which gives a yield of 30-70% in SIS. This should include long bones, skull, chest, and spine. Multiple, bilateral, or cross suture skull fractures and cervical fractures are suggestive of nonaccidental trauma. Plain films are superior to CT in detection of skull fractures, which are found mostly in occipital and parietooccipital region. However CT may appreciate a diastatic fracture and basilar fracture better. A skull fracture may start as a simple linear one. If there is significant cerebral edema and/or subdural hematoma, it may grow to become a diastatic fracture due to pressure building up in the cranium.
Highest specificity for abuse includes posterior rib, metaphyseal, scapular, spinous process, and sternal fractures. Specialized views coned down to metaphyses may delineate subtle corner or bucket handle fractures. In significant suspicion when initial films reveal no fracture, radionuclide study or repeat skeletal survey may be done in 2 weeks to delineate subtle fractures.
CT scan of the head without contrast is the first choice of imaging studies when SIS is suspected, including soft tissue and bone windows. In acute SIDH and SAH, CT is superior to MRI. SIDH are typically located posteriorly between the two hemispheres or over the convexity of the brain as high-density collections of blood. These hemorrhages may be small initially and are rarely cause of death. As time goes by during degeneration of the clot, water is drawn into it and the accumulation may increase in volume. Another finding on initial CTs is the extensive loss of graywhite matter differentiation and diffuse hypodensity indicating cerebral edema due to diffuse brain injury. Since basal ganglia are spared they may appear hyperdense with surrounding hypodense cerebrum (reversal sign). Repeat head CT in a week may show evolving infarction in patients with initial significant cerebral edema and midline shift.
When CT findings are equivocal, MRI is useful in detecting small extraaxial hemorrhages and parenchymal contusions especially if performed several days after the presumed injury time. MRI also can determine the age of bleeding more accurately than CT due to changes in signal of the hematoma secondary to transformation of hemoglobin degradation products. However due to clot shrinkage and serum extrusion from the clot, or tear through the arachnoid allowing cerebrospinal fluid to dilute the clot, there is growing controversy regarding the accuracy of MRI in dating the subdural bleeds. SIDH is classified as hyperacute when less than 12 hours old, acute between 12 hours and 3 days, subacute between 3 days and 3 weeks, and chronic when older than 3 weeks. It is very important to determine 1) how many lesions there are, 2) their specificity for abuse, and 3) their approximate ages in ruling in/out SIS, and MRI is the best tool to do that.
The imaging modality to be chosen varies depending on the initial presenting findings. When an infant presents with acute neurologic symptoms, CT is the best modality to start with. If abuse risk is low and head CT is negative, there is no need for further work up. If CT is positive for subdural hematoma or brain injury then a follow up MRI is warranted in 1-2 weeks. If head CT is negative but suspicion for abuse is high, then an MRI within 4-7 days should be done. If the child presents with chronic symptoms or no symptoms at all but suspicion for abuse is high, then MR[ is the best modality to start with.
External injury evidence, mostly in the head and the neck, has been found in 85% of children dying due to SIS. Scalp trauma may be revealed after head is shaved. Fractures may be detected in 25% of patients. If not done postmortem skeletal survey may be done. Ribs should definitely be palpated. Fractured bones should be removed for histologic examination. SDH located posteriorly in parietooccipital convexity or in the interhemispheric fissure is the most consistent finding. SDH is typically 2-15 ml in amount, and rarely causes death due to mass effect.
Gliding contusions, tears of the corpus callosum, diffuse axonal injury, and damage to brainstem may be observed from extreme rotational forces. Acute hemorrhage along the sheath of the optic nerve is most prominent at the junction where the nerve enters the globe. Subhyaloid, submembranous, subretinal, choroidal, and intrascleral hemorrhages may be observed if the eye globes are removed, which should be a routine practice in cases of suspected child abuse.
Cervical spine and the brain should be removed together and cervical spine searched for injury, especially in the C1-C4 region. Gross hemorrhage and diffuse axonal injury on microscopy may be observed.
Demarcated cavities, widespread cystic or non-cystic gray matter damage, scars in centrum ovale, corpus callosum, and chronic optic nerve degeneration may be observed.
It is important to determine when the child was last normal before developing the symptoms leading to admission. A time line of events, chain of caretakers, and onset of symptoms should be created by interviewing the caretakers one at a time to catch inconsistencies if any. All this information should be quickly passed on to child protective and law enforcement agencies. Lucid interval between the offending event and development of findings, was less then 24 hours in 80% of shaking injuries, in 72% of shaking-impact injuries, and in 69% of blunt injuries in one study. Other studies on the other hand, reported that of the fatal head injury cases, only those with EDH exhibit a lucid interval. In all other types of injuries, the timing of injury can be restricted to after the last confirmed period of normal consciousness for the child. The more severe the insult is to the brain the shorter the lucid interval tends to be. In other words, if an infant is violently shaken and slammed on a surface, respiratory arrest may follow within seconds. If insult is mild, the child may become slightly lethargic several hours after the insult and recover on his/her own without any medical intervention.
Actually no other medical condition fully mimics SIS when all the features are there. When there is a history of trivial or no trauma, acute SDH, RH, unexplained extracranial bony injuries or inflicted soft tissue injuries, it is reasonable to make a diagnosis of SIS. However, list of differential diagnosis should include unintentional trauma; physiologic variants such as hydrocephalus, gastroeosaphageal reflux, sudden infant death syndrome (SIDS); organic disease conditions such as seizure disorder, meningitis/encephalitis, failure to thrive, viral syndromes, shock, apnea; hemorrhagic diathesis, cranial malformations that may cause intracranial bleeding, and some rare metabolic disorders, acute life threatening event (ALTE); and bone fragility disorders.
The single most common diagnosis mimicking SIS is unintentional head trauma. Unintentional SAH and EDH may be mistaken for SDH when small. MRI can help in differentiation. Unintentional SDH may occur after motor vehicle accidents or falls from significant heights involving angular deceleration. EDH may occur due to a short fall and with some lucid interval due to delay because of high pressure bleeding in a tight space. In these cases history is clear and consistent and there would be no unexplained skeletal injuries. The only differential diagnostic problem may remain in children with increased extraaxial space such as in shunted hydrocephalus or benign extra-axial subdural fluid collection in which lesser degrees of trauma is considered by some to cause SDH or SAH. However there is no literature data, yet, indicating that this actually happens unless child has underlying cerebral atrophy. In a child with chronic subdural bleed, rebleeding with minor trauma is a consideration, but the clinical presentation is different compared to acute SDH in SIS. In rebleeding, the child's head circumference gradually increases, mental status gradually deteriorates rather than abrupt changes.
Hemophilia, Von Willebrand, and Vitamin K deficiency may be associated with intracranial hemorrhages. However in these cases history and clinical course would imply to hemorrhagic diathesis prior to presentation. Transient prolongation of PT, and disseminated intravascular coagulopathy have been associated with parenchymal brain injury. In the presence of underlying brain parenchymal injury, it is highly unlikely that these coagulation abnormalities reflect a preexisting hemorrhagic diathesis. Congenital arterio-venous malformation or cerebral aneurysm may cause SAH unintentionally. However none of these hemorrhagic conditions show retinal bleeding.
Osteogenesis imperfecta may pose a differential diagnostic problem especially when there are multiple unexplained fractures. However SDH is a rare complication of the disease. Still, if in doubt, tissue cultures for impairment of production of collagen type I may be done.
Glutaric aciduria Type I is a metabolic disease caused by a defect of glutarylcoenzyme A dehydrogenase. Findings of the disease are acute or insidious developmental delay, hypotonia, dyskinesia, cortical atrophy, and subdural collections. Urine organic acids and serum carnitine levels will help in differentiation. However skeletal and retinal findings have not been described as part of the disease. If in doubt, urinary screening for this disorder should be considered.
When children present to the hospital with SIDS and ALTE it is very important to consider SIS in differential diagnosis since in 33% of ALTE patients abuse was the underlying cause. Although there are several case reports of cardiopulmonary resuscitation (CPR) leading to RH, there are at least two large studies, which reported no cases with post-CPR RH. One study reported only one case with postCPR RH, which were small and punctuate among 43 patients. Rarely, resuscitation may cause rib fractures if done by lay people or if the child has underlying metabolic bone disease.
In milder forms, symptoms in SIS, may mimic gastroenteritis, systemic viral illness, meningitis, encephalitis, apnea, gastro-eosaphageal reflux. Unfortunately, when these patients present to settings, that are specialized, investigation oriented, fascinated with rare conditions, chances to miss the diagnosis of SIS are higher. In order to diagnose SIS appropriately, first thing to do is to consider SIS in the differential diagnosis. Secondly, comprehensive retinal exam should be done by an experienced ophthalmologist in every patient younger than 2 years of age presenting with unexplained neurological findings. In SIS, symptoms are usually at their peak at the time of admission whereas in encephalitis or metabolic disease, they tend to become more manifest for a while after admission. If the child has no fever, metabolic and neuroradiological examinations should be done. If there is fever, encephalitis and meningitis should be ruled out via lumbar tap.
Poor prognostic factors are unresponsiveness upon admission, need for intubation, age less than 6 months, diffuse RH at presentation, and diffuse hypodensity on initial CT of the head. Uncontrollable hypertension due to loss of autoregulation resulting from ischemia is invariable in fatal cases. It is imperative to identify parenchymal injuries because of their grave prognostic implications such as cortical and white matter atrophy. Post-traumatic encephalopathy interferes with dendrogenesis, axongenesis, gliogenesis, and myelination, which are all very active during the first year, causing several of the neurological impairments seen in survivors.
Grossly, one third (25-40 %) of these patients dies, one third survives with a major neurological condition, and only one third survives in good condition. Neurological impairment may be as high as 45%. The most frequent neurological impairments are learning disabilities, cerebral palsy, visual disabilities, speech disabilities, seizure disorder, chronic subdural collections, and hydrocephalus. However, the total spectrum of neurological impairment can be appreciated as late as 6 years of age. Preliminary studies show that by using magnetic resonance spectroscopy, neurologic prognosis may be predicted when clinical signs do not give any indication of long-term outcome.
Management of SIS is a very costly process. One child surviving with sequels for three years costs $1 million, initial hospital management of each child costs $75,000 to $95,000. This information should be used to decide where to direct the resources.
Pediatricians have responsibility to provide anticipatory guidance to each family they encounter. They may try to find out what the parental level of stress is in taking care of an infant as well as how they respond to crying, thus advise parents the risks of shaking. However the most important preventive effort has been home visitation of families with infants younger than 2 years of age.
Education of the public at-large is very important with cards, posters, videos, etc. Starting from high school years, all prospective parents should be educated regarding developmental milestones, good child discipline practices, how to handle a crying child, dangers of shaking, stress and/or anger management, etc. Target populations, namely males should be identified for education. Professionals (health care, childcare providers, child protective services workers) should be educated for proper recognition of victims of SIS.
SIS is a common serious injury resulting from major mechanical forces. If the history, physical and radiological findings are suggestive of this diagnosis, the patient should be admitted to the hospital for treatment. A thorough, unbiased evaluation is essential by the child abuse team including radiology, ophthalmology, neurology, and neurosurgery in addition to the pediatrician. If abuse is suspected, the law requires that the appropriate child-welfare and law enforcement agencies be notified. Caretakers should be informed, in a nonaccusatory manner, that the diagnosis is suspected, and the investigative procedures will be necessary for the welfare of the child. When there are other children in the family, they need to be evaluated, too. The medical record has great legal importance, and careful documentation including photographs, will later benefit the physician, who may be subpoenaed to testify in court.
The future safety of a child with SIS rests on the physician's ability to recognize its characteristic features. Improved understanding of the pathophysiology and causes of this common disorder will guide effective prevention strategies.
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See related Provider Topics Brain and Nervous System, Child Abuse, Child and Teen Health, Food, Nutrition and Metabolism, Head and Brain Injuries, Injuries and Wounds, Pediatrics or Social/Family Issues.
See related Patient Textbooks about Pediatrics.
See related Patient Topics Brain and Nervous System, Child Abuse, Child and Teen Health, Food, Nutrition and Metabolism, Head and Brain Injuries, Injuries and Wounds, Pediatrics or Social/Family Issues.
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