Modified brain injury guideline (mBIG)

Background

The modified Brain Injury Guidelines (mBIG) is a clinical decision tool that stratifies patients with mild traumatic brain injury and traumatic intracranial hemorrhage on CT into three tiers to guide neurosurgical consultation, ICU admission, and safe discharge decisions. It was derived to reduce unnecessary neurosurgical consultations and ICU admissions without compromising safety in low-risk patients.

• Validated for adults with mild traumatic brain injury (GCS 13–15) and traumatic intracranial hemorrhage identified on CT
• Originally the Brain Injury Guidelines (BIG) were developed at Banner University Medical Center; the mBIG refined and validated this tool

Inclusion criteria

• Adult patient (age ≥18)
• Mild traumatic brain injury (GCS 13–15)
• Traumatic intracranial hemorrhage on head CT (any of the following):
  • Subdural hemorrhage
  • Epidural hemorrhage
  • Subarachnoid hemorrhage
  • Traumatic intracerebral hemorrhage
  • Intraventricular hemorrhage
  • Cerebral contusion

Exclusion criteria

• GCS <13
• Penetrating head trauma
• Coagulopathy (INR >1.5, platelets <100k, on therapeutic anticoagulation)
• Age <18

mBIG tiers

Scope: mBIG applies ONLY to traumatic intracranial hemorrhage in adults with mild traumatic brain injury (GCS 13–15). It is not applicable to spontaneous/aneurysmal subarachnoid hemorrhage, spontaneous intracerebral hemorrhage, or any non-traumatic intracranial hemorrhage.

mBIG 1 (lowest risk)

All of the following must be true:

• GCS 15
• No loss of consciousness (LOC)
• No seizure
• No emesis
• Isolated SDH ≤4 mm, isolated EDH ≤4 mm, isolated tSAH ≤4 mm, cerebral contusion ≤2 cm, or intraventricular hemorrhage ≤2 mm
• No herniation or significant mass effect on CT
• Neurologically intact

Disposition: No neurosurgical consultation required; observation in non-monitored setting acceptable; repeat CT imaging not required if clinically stable; may be appropriate for discharge with reliable follow-up.

mBIG 2 (intermediate risk)

Meets any of the following (but does not meet mBIG 3 criteria):

• GCS 13–14, OR
• LOC, OR
• Isolated seizure, OR
• Emesis, OR
• CT findings larger than mBIG 1 thresholds but without herniation/significant mass effect

Disposition: Neurosurgical consultation warranted; admission to step-down or monitored unit; repeat head CT in 4–6 hours or per neurosurgical guidance.

mBIG 3 (highest risk)

Any of the following:

• GCS <13 (note: if GCS <13, patient may not strictly qualify as "mild TBI" — manage per moderate-to-severe traumatic brain injury pathway)
• Any herniation on CT
• Significant mass effect (midline shift >5 mm, cisternal effacement)
• Bilateral or mixed intracranial hemorrhage pattern with neurologic decline
• Neurovascular injury identified

Disposition: Emergent neurosurgical consultation; ICU admission; operative intervention frequently required.

Management

Anticoagulation and antiplatelet considerations

• Standard mBIG criteria assume no significant coagulopathy; anticoagulated patients require independent coagulopathy assessment and anticoagulation reversal prior to applying the guideline
• Even mBIG 1 patients on antiplatelet therapy should have a lower threshold for neurosurgical consultation and repeat imaging

Repeat imaging

• mBIG 1: Repeat CT generally not required if patient remains neurologically intact and asymptomatic at 4–6 hours
• mBIG 2: Repeat CT at 4–6 hours recommended
• mBIG 3: Repeat CT urgently; neurosurgery to guide imaging cadence

Neurosurgical consultation

• mBIG 1: Not required
• mBIG 2: Recommended
• mBIG 3: Emergent

Disposition

Tier	Neuro consult	Admission level	Repeat CT
mBIG 1	Not required	Observation or discharge	Not required if stable
mBIG 2	Recommended	Step-down/monitored	4–6 hours
mBIG 3	Emergent	ICU	Urgent/per neurosurgery

• mBIG 1 patients may be safely discharged with a reliable caregiver and clear return precautions if all clinical parameters remain stable after 4–6 hours of ED observation

See also

• Head trauma (main)
• Mild traumatic brain injury
• Traumatic intracerebral hemorrhage
• Subdural hemorrhage
• Epidural hemorrhage
• Subarachnoid hemorrhage
• Moderate-to-severe traumatic brain injury
• Elevated intracranial pressure
• Clinical decision rules for head CT in trauma