INTRODUCTION — The pathogenesis of retinal hemorrhages in abusive head trauma (AHT) will be reviewed here. Other aspects of AHT and the management of suspected child abuse are discussed separately. (See "Child abuse: Eye findings in children with abusive head trauma (AHT)" and "Child abuse: Epidemiology, mechanisms, and types of abusive head trauma in infants and children" and "Child abuse: Evaluation and diagnosis of abusive head trauma in infants and children" and "Physical child abuse: Diagnostic evaluation and management".)
BACKGROUND — AHT is also known as nonaccidental head injury, inflicted head injury, or inflicted childhood neurotrauma. One subset is referred to as shaken baby syndrome, with a constellation of inflicted injuries in young children characterized by repeated acceleration-deceleration injury with or without blunt head impact [1-5].
Characteristic clinical features may include the following findings, though no finding is essential or pathognomonic for the diagnosis (see "Child abuse: Evaluation and diagnosis of abusive head trauma in infants and children", section on 'Clinical features'):
●Retinal hemorrhages (often but not always bilateral, multilayered, and extensive)
●Intracranial injury (intracranial hemorrhage and/or hypoxic ischemic injury)
●Cervical spine injury
●Abdominal organ injury (eg, liver laceration, small bowel perforation, or pancreatic contusion)
●Occult fractures (particularly of the ribs and long bone metaphyses)
Multiple episodes of trauma may occur before the abuse is detected [6-9]. Early recognition can be lifesaving.
ANATOMY — The retina is comprised of several layers (figure 1). The retinal vessels are contained in the neural portion of the retina . The large vessels course through the nerve fiber and ganglion cell layers. Smaller vessels are located between the nerve fiber and inner nuclear layers. There are three layers of retinal capillaries: those within the nerve fiber and ganglion cell layers, those in the inner nuclear layer, and the radial peripapillary capillaries.
Overview — Several mechanisms have been proposed to play a role in the development of retinal hemorrhages. The most widely accepted involves vitreoretinal traction-related injury. Different types of retinal hemorrhages may have different mechanisms, and more than one mechanism may operate in any given instance (figure 2 and figure 3 and figure 4 and figure 5).
Autopsy studies demonstrate an increased rate of orbital hemorrhage in AHT victims compared with victims of unintentional (accidental) head injury . Repetitive acceleration-deceleration (shaking) forces appear to play a primary role in the development of orbital and subdural hemorrhage in AHT [11-16]. The role of repetitive acceleration-deceleration forces in the pathogenesis of subdural hemorrhage in AHT is discussed separately. (See "Child abuse: Epidemiology, mechanisms, and types of abusive head trauma in infants and children", section on 'Mechanisms of injury'.)
It is unknown how much force is necessary in AHT for ocular injuries to occur. Based upon the frequency of the types of eye injuries in 23 AHT fatalities, one group suggested that relatively less force is needed to cause intraretinal, subhyaloid, or optic nerve sheath hematoma than retinal detachment, choroidal hemorrhage, or vitreous hemorrhage . However, given that these were fatal injuries, the involved forces for all injuries were likely to have been severe.
Repetitive acceleration-deceleration — Repetitive acceleration-deceleration induces shearing forces at the vitreoretinal interface, directly damaging the retinal vessels. The shearing forces are applied to the retina at points of firm attachment (eg, the macula, retinal vessels, and the vitreous base) (figure 6) . The high frequency of hemorrhages at the vitreous base (ie, far peripheral retina, where it meets the ciliary body anteriorly) and the distinctive macular retinoschisis and perimacular retinal folds of AHT provide supportive evidence for the role of shaking and vitreoretinal traction in the pathogenesis of AHT . Imaging of vitreoretinal microstructure using optical coherence tomography, a noninvasive method that provides a cross-sectional image of the retina using light waves, has permitted direct visualization of vitreoretinal traction, vitreous separation from the retina, and subclinical retinoschisis, providing direct evidence of the role of vitreoretinal traction [15,18,19]. Animal studies of inertial head trauma reveal ocular hemorrhage in areas of strong vitreoretinal attachment in the animals, both posteriorly and anteriorly at the vitreous base . (See "Child abuse: Eye findings in children with abusive head trauma (AHT)", section on 'Retinal folds and retinoschisis'.)
Repetitive acceleration-deceleration also may disrupt the autonomic supply of the retinal vessels, which may lead to retinal hemorrhage through disruption of retinal vascular integrity and autoregulation . (See "Child abuse: Eye findings in children with abusive head trauma (AHT)", section on 'Optic nerve sheath hemorrhage'.)
Repetitive acceleration-deceleration (shaking) forces appear to play a primary role in the development of orbital hemorrhage in AHT [11-16]. The optic nerve and other intraorbital structures are firmly attached to the globe and to the apex of the orbit . However, the optic nerve is longer than the distance between the apex of the orbit and the back of the globe. This allows the globe and orbital contents to move if a child is shaken. Injury may occur at the tethering locations as a result of translational and rotational movements of the globe. (See "Child abuse: Eye findings in children with abusive head trauma (AHT)".)
This mechanism of direct optic nerve injury within the orbit provides an explanation for the optic atrophy that is often seen in survivors of AHT . It also provides an explanation for the anterior predominance of optic nerve sheath hemorrhage (a finding that argues against the continuous tracking of blood from the intracranial space, as described below). (See 'Intracranial bleeding' below.)
Increased intracranial pressure — Increased intracranial pressure (ICP) is another proposed mechanism for retinal hemorrhages in AHT . One theory postulates that increased ICP (secondary to cerebral edema and compressive subdural hemorrhage) causes increased venous pressure and obstruction in the retinal vasculature that ultimately leads to rupture of the retinal vessels. Another theory speculates that paroxysmal cough can progressively increase ICP to the point that retinal hemorrhage occurs .
Several observations argue against a major role for ICP in the development of retinal hemorrhages in AHT. These include [14,22]:
●Branch or central retinal vein occlusion, which has a very characteristic funduscopic appearance, is a highly uncommon manifestation of AHT (picture 1 and picture 2). (See "Retinal vein occlusion: Epidemiology, clinical manifestations, and diagnosis".)
●Retinal hemorrhage is uncommonly seen in other causes of increased ICP, and when it is, the hemorrhages are superficial, flame-shaped, intraretinal hemorrhages in the peripapillary region and adjacent to a swollen optic nerve head, which also is uncommon in AHT. Thus, the patterns of hemorrhages associated with increased ICP without AHT do not match those seen with AHT [23-25]. For example, in a study of 100 children with elevated ICP caused by nontraumatic mechanisms, only 16 patients had retinal hemorrhages. These hemorrhages were intraretinal, limited to the peripapillary region, associated with papilledema, and occurred only with a very high ICP (mean 42 mmHg) . In a separate observational study, fluctuations in ICP were not associated with increased numbers or worsening types of retinal hemorrhage among the 31 children with continuous ICP recording .
●The veins of the orbit permit extensive distribution of pressure because they do not have valves.
●The lack of correlation between signs of elevated ICP and retinal hemorrhage in AHT .
●Examination of 35 infants hospitalized with pertussis and 100 other infants with severe cough due to other etiologies did not identify any patients with retinal hemorrhages [26,27].
Intracranial bleeding — The syndrome of retinal or vitreous hemorrhage in association with subarachnoid hemorrhage is known as Terson syndrome . In adult patients with subarachnoid hemorrhage, Terson syndrome is associated with poor prognosis . Terson syndrome merely refers to the association between vitreous and occasionally retinal hemorrhage as well as subarachnoid bleeding and does not imply a specific etiology. Thus, it should not be misconstrued as an alternative explanation for retinal hemorrhage in children with AHT. The intraocular hemorrhages associated with aneurysmal rupture are more typically vitreous hemorrhage or preretinal hemorrhage adjacent to the optic nerve head, and typically fewer in number and not associated with numerous intraretinal hemorrhages, as in AHT. Thus, the pattern of intraocular hemorrhages seen with a sudden rise in intracranial pressure, such as aneurysmal rupture, is not the same as the pattern of retinal hemorrhages seen in AHT. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis", section on 'Evaluation and diagnosis'.)
Terson syndrome is uncommon in infants and young children [14,16,30]. In a prospective series of 57 children with intracranial hemorrhage not caused by child abuse, only two patients (1.5 percent) had retinal hemorrhages, and both had other feasible explanations for the hemorrhages . The retinal hemorrhages in children not subject to AHT were superficial and confined to the posterior pole [28,30].
The pathogenesis of Terson syndrome is not known. One theory is that blood from the intracranial space tracks along the optic nerve sheath and into the eye and/or compresses the central retinal vein [14,31]. However, in an autopsy study of 13 infants who died of acute intracranial injuries after inflicted trauma, optic nerve sheath hemorrhage was present only in the intraorbital portion of the nerve, which argues against the continuous tracking of blood from the intracranial space . In addition, in a series of 75 children with AHT, there was no correlation between the laterality of intracranial bleeding and the laterality of retinal findings .
Increased intrathoracic pressure — A severe and abrupt increase in intrathoracic pressure may cause intraocular abnormalities, possibly related to a sudden increase in retinal venous pressure, in what is called Purtscher retinopathy . The primary classic finding of Purtscher retinopathy is white retinal patches, and a secondary finding is few retinal hemorrhages.
This mechanism has been proposed for the retinal findings in AHT and is thought to be supported by the evidence of transiently increased intrathoracic pressure in victims who also have rib fractures. However, it is unlikely that abrupt increases in intrathoracic pressure account for the intraocular findings in most cases of AHT because white retinal patches are distinctly unusual in AHT [14,32,34]. In addition, not all victims of AHT have rib fractures, and among those who do, not all have retinal hemorrhages [6,13,35]. Increased intrathoracic pressure may also be seen with cardiopulmonary resuscitation (CPR), but CPR in the absence of significant trauma is only rarely associated with retinal hemorrhages, which (when present) are very few in number, intraretinal, and located in the posterior pole [36-38].
●Background – Abusive head trauma (AHT) describes a constellation of inflicted injuries in young children, including retinal hemorrhages, subdural hematoma, cutaneous bruising, cervical spine injury, abdominal organ injury (eg, liver laceration, small bowel perforation, or pancreatic contusion), and/or occult fractures. (See 'Background' above.)
●Pathogenesis – Repetitive acceleration-deceleration (shaking) forces appear to play a primary role in the development of retinal hemorrhages seen in AHT, as well as macular retinoschisis, perimacular retinal folds, and orbital and subdural hemorrhage. While several other mechanisms have been proposed to play a role in the development of retinal hemorrhages, the patterns of hemorrhages seen in those conditions do not match patterns of retinal hemorrhage in AHT. (See 'Overview' above.)
Repetitive acceleration-deceleration induces shearing forces at the vitreoretinal interface, directly damaging the retina, retinal vessels, and the optic nerve. The primary role of repetitive acceleration-deceleration forces in AHT is supported by the retinal hemorrhage patterns observed; the distinctive macular findings, including retinoschisis and retinal folds; and vitreoretinal traction directly visible using optical coherence tomography, a noninvasive method that provides a cross-sectional image of the retina using light waves. (See 'Repetitive acceleration-deceleration' above.)
Other proposed mechanisms for the development of retinal hemorrhages in AHT include increased intracranial pressure, intracranial bleeding, and increased intrathoracic pressure. These mechanisms are less well supported than repetitive acceleration-deceleration and vitreoretinal traction. (See 'Increased intracranial pressure' above and 'Intracranial bleeding' above and 'Increased intrathoracic pressure' above.)
ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Brian Forbes, MD, PhD, who contributed to earlier versions of this topic review.
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