What are the causes of subdural hemorrhage in 3-month-old infants?

Causes of Subdural Hemorrhage in 3-Month-Old Infants

In 3-month-old infants, subdural hemorrhage most commonly results from non-accidental trauma (shaken baby syndrome), followed by coagulation disorders—particularly vitamin K deficiency—and rarely from vascular malformations or birth trauma. 1

Primary Causes by Frequency

Non-Accidental Trauma (Most Common)

• Shaken baby syndrome is the leading cause of acute subdural hemorrhage in infants at this age. 2, 3
• Classic presentation includes subdural hemorrhage with retinal and preretinal hemorrhages (present in nearly all cases), seizures, and altered consciousness following alleged minor or no trauma. 2, 3
• These infants typically present with bilateral bridging vein ruptures but often have relatively small volumes of subdural blood, distinguishing them from accidental trauma cases. 4
• The combination of multiple bridging vein ruptures with minimal subdural bleeding volume is not compatible with minor accidental falls. 4

Coagulation and Hematologic Disorders

• Vitamin K deficiency is a specific concern at this age, with documented cases of 3-month-old infants developing subdural and intraparenchymal hemorrhage from congenital vitamin K deficiency. 1
• Maternal use of warfarin, phenytoin, or barbiturates during pregnancy can cause vitamin K-dependent coagulation factor deficiencies requiring higher postnatal vitamin K doses. 1
• Other coagulation defects include factor VIII deficiency (hemophilia), factor XIII deficiency, and thrombocytopenia (though thrombocytopenia risk is low with platelet counts >20,000/mm³). 1
• Severe coagulation deficiencies are more likely to cause spontaneous hemorrhage, while milder deficiencies typically require trauma as a trigger. 1

Vascular Malformations (Less Common)

• Arteriovenous malformations (AVMs) and arteriovenous fistulas can present in neonates and young infants, though they more commonly cause high-output cardiac failure in this age group. 1
• Ruptured intracranial aneurysms, though rare, can present with subdural hemorrhage in neonates and may mimic non-accidental injury with seizures and retinal hemorrhages. 5
• Middle cerebral artery aneurysms and distally located peripheral aneurysms are more common in neonates than in adults. 5

Birth-Related Trauma

• Birth trauma can cause subdural hemorrhage, though this typically presents immediately after delivery rather than at 3 months of age. 1

Critical Diagnostic Approach

When to Suspect Non-Accidental Injury

Subdural hemorrhage in a non-mobile 3-month-old infant is highly concerning for child abuse and requires immediate evaluation. 1, 6

Key features suggesting abuse:

• History of trauma insufficient to explain the injury or no trauma history 1
• Retinal hemorrhages on funduscopic examination (mandatory in all cases) 6, 2, 3
• Bilateral subdural collections 4
• Associated injuries (fractures, burns, other trauma) 1

When Bleeding Disorder Evaluation is Required

All 3-month-old infants with subdural hemorrhage require evaluation for bleeding disorders unless:

• Independently witnessed or verifiable significant trauma exists 1
• Other findings definitively consistent with abuse are present 1

Essential laboratory evaluation includes:

• PT, aPTT (detects most factor deficiencies) 1
• Platelet count 1
• Consider von Willebrand disease and factor XIII testing (not detected by PT/aPTT) 1

Imaging Considerations

• Non-contrast CT is first-line for acute diagnosis per American College of Radiology guidelines. 6
• MRI provides superior detection of small hemorrhages, subacute blood products, and associated injuries including cervical spine trauma. 6
• Consider vascular imaging (CTA or MRA) if clinical or imaging features suggest aneurysm or AVM, particularly with blood in sylvian fissure or unusual hemorrhage patterns. 5

Critical Pitfalls to Avoid

• Do not accept "minor fall" explanations without thorough investigation—lethal subdural hemorrhage from minor falls in infants is extremely rare, with no documented cases in some large series spanning decades. 4
• Do not miss vitamin K deficiency—specifically ask about maternal medications during pregnancy and adequacy of postnatal vitamin K administration. 1
• Always perform funduscopic examination—retinal hemorrhages are characteristic and help distinguish traumatic from other causes. 6, 3
• Do not assume all cases are abuse—rare vascular lesions like aneurysms can mimic non-accidental injury and require different management. 5
• Recognize that small subdural collections on imaging do not exclude serious injury—infants with shaken baby syndrome often have minimal subdural blood volume despite severe injury. 4