Probability of Clinically Important Brain Injury Following Minor Head Injury Using the Canadian CT Rule Analysis

 

NOTE: The Canadian CT Head Rule for performing a CT scan after minor head injury is discussed later in the chapter, under decision rules for imaging studies.

 

Criteria for minor head injury:

(1) initial Glasgow coma score 13 to 15 (I believe this is as determined by the physician in the Emergency Department)

(2) one or more of the following:

(a) witnessed loss of consciousness

(b) definite amnesia

(c) witnessed disorientation

 

Clinically important brain injury = any acute brain injury found on CT scan which would require hospitalization and/or neurological followup. This would include one or more of the following:

(1) cerebral contusion

(2) subarachnoid hemorrhage

(3) subdural hematoma

(4) epidural hematoma

(5) pneumocephalus

(6) intracerebral hematoma

(7) depressed skull fracture

(8) intraventricular hemorrhage

(9) diffuse cerebral edema.

 

Parameters:

(1) vomiting episodes

(2) initial Glasgow Coma Score (GCS)

(3) suspected skull fracture

(4) clinical sign of basal skull fracture

(5) Glasgow Coma Score at 2 hours after injury

(6) age

(7) high risk injury

(8) loss of consciousness

(9) amnesia for events before injury

Parameter	Finding	Points
vomiting episodes	0 or 1	0
	repeated (>= 2)	1
initial GCS	14 or 15	0
	13	1
open or depressed skull fracture	not suspected	0
	suspected	1
clinical signs of basal skull fracture	absent	0
	present	1
GCS at 2 hours after injury	15	0
	< 15	1
age	< 65 years	0
	>= 65 years	1
high risk mechanism of injury	absent	0
	present	1
loss of consciousness	< 5 minutes	0
	>= 5 minutes	1
amnesia for events before injury	<= 30 minutes	0
	> 30 minutes	1

 

where:

• A dangerous mechanism includes (1) pedestrian struck by motor vehicle, (2) occupant ejected from motor vehicle, (3) fall from a height > 3 feet, or (4) fall down stairs > 5 steps

• Signs of basal skull fracture includes (1) hemotympanum, (2) "raccoon" eyes, (3) CSF otorrhea or rhinorrhea, or (4) Battle's sign

• racoon eyes = periorbital ecchymosis

• Battle's sign = discoloration in the line of the posterior auricular artery, with ecchymosis first appearing near the tip of the mastoid process

 

X =

= (1.33 * (points for vomiting)) + (0.79 * (points for initial GCS)) + (1.29 * (points for skull fracture)) + (1.65 * (points for basal skull fracture)) + (1.99 * (points for GCS at 2 hours)) + (1.42 * (points for age)) + (1.02 * (points for high risk mechanism)) + (0.5 * (points for loss of consciousness)) + (0.66 * (points for amnesia)) – 4.27

 

probability of clinically important head injury =

= EXP(X) / (1 + EXP(X))