Differentiation of mechanism and prognosis of traumatic brain stem lesions detected by magnetic resonance imaging in the acute stage
Introduction
Immediate impact injury of the brain stem has been considered to be primary brain stem injury, and this was differentiated from secondary brain stem injury due to complications such as cerebral herniation or hypoxic damage [6]. Studies involving autopsy cases or computed tomographic (CT) scan findings of primary brain stem injury have been reported by several authors [1], [2], [9], [11]. Some magnetic resonance imaging (MRI) studies of patients with head injuries have been also reported [10], [12]. However, clinical studies involving MRI for primary brain stem injury in acute stage are scant [3], [9].
A previous pathological study showed primary brain stem injury was always accompanied by supratentorial cerebral diffuse axonal injury [9]. Another mechanism was reported to be a direct impact of the brain stem on the free edge of the tentorium [2], [11]. These brain stem injury with diffuse axonal injury and direct brain stem injury without axonal injury have not been yet established clinically or radiologically. We have used MR imaging in our patients with head injuries to find out whether we could assess the clinical outcome based on the findings of the initial MRI. We also compared MRI, CT and ABR findings with clinical course, in an attempt to clarify the diagnostic accuracy of these modalities.
Section snippets
Study population
From 1987 until 1992, 74 patients with head injury were admitted in our hospital. Among them, 17 patients with radiological evidence of a primary brain stem lesion were retrospectively evaluated in this study. Inclusion criteria were head injured patients with positive brain stem intensity change in MR imaging. Those who presented cerebral herniation associated with secondary brain stem injury were excluded. Initial neurological status was evaluated using the Glasgow coma scale (GCS) [15].
Neurological findings
Table 1 shows the age, gender, GCS score on admission, neurological findings on admission and outcome score at discharge. All the patients, except one, had sustained the injury in car accidents. Patients’ age ranged from 16 to 75 years with a mean age of 35.5 years. There were 10 male and seven female patients. The GCS score was less than eight in 12 patients (70.6%). Oculomotor nerve palsy or anisocoria was observed in 10 patients (58.8%) and trochlear nerve palsy was seen in two patients.
Factors influencing the prognosis of patients with brain stem lesions
Our results indicated that a deep dorsal brain stem lesion on MRI and an abnormal ABR were indicative of a poor prognosis. While a surface brain stem lesion on MRI and a normal ABR were indicative of a good prognosis [8]. Most patients with a deep ventral lesion on MRI showed good recovery, so ventral brain stem lesion could be associated with a good prognosis. Surface lesions tend to disappear on follow-up MRI, thus it is important to evaluate MRI taken in the early stage to understand
Conclusion
MRI, especially T2-weighted image in the acute stage, proved to be the most sensitive and specific diagnostic means in case of primary brain stem injury. According to MRI findings, primary brain stem injuries can be divided into two subgroups, one is a superficial focal brain stem injury due to direct impact against the tentorial edge and the other is deep brain stem injury due to shear strain associated with diffuse axonal injury. It is important to differentiate these two subgroups, because
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Present address: Kitaibaraki City General Hospital, 4-5-15 Otsumachi, Kitamachi Kitamachi, Kitaibaraki, Ibaraki, 319–1704, Japan.