Diffuse Axonal injury and Hypoxic Brain Damage in Craniocerebral Trauma

Introduction

The most important mechanism of primary brain damage in head injury is Diffuse Axonal Injury and the most important mechanism of Secondary brain damage is Hypoxic Brain Injury. Even though the clinical setting may be helpful in the diagnosis of these conditions, a CT Scan of the head or gross brain specimen at autopsy may not show any specific change. So in order to confirm the diagnosis of DAI and hypoxic brain damage histopathological studies of rain specimens is essential. In these study we made an attempt to evaluate the histopathological changes in Diffuse Axonal Injury & Hypoxic brain damage in grain specimens taken from clinically relevant cases at autopsy.

Materials and Methods

Twenty selected cases from 200 consecutive cases of fatal head injuries admitted to Medical College Calicut during the period of 1998 – 2000 were included in this study . This study was conducted in collaboration with The department of Forensic Medicine Medical College Calicut and Neuropathology department of NIMHANS Bangalore.

In all these cases clinical and radiological correlations were available and the patients were categorized into two groups.

Group I – Unconscious patients with or without brain stem signs and normal CT Studies Suspected to have DAI. At postmortem sections were taken from predilection sites for DAI and subjected to histopathological examination.

Group II – Patients who had severe chest injury and Minor head injury and who required prolonged ventilatory support because of the respiratory insufficiency and low Pao2 – Suspected cases of hypoxic brain damage. At Postmortem Sections were taken from predilection areas for Hypoxic brain damage and sent for histopathological examination.

The predilection areas for DAI include Grey / White junction, Dorosolateral brain stem and Corpus Callosum , and the predilection areas for Hypoxic damage include Basal Ganglia , Cortical Grey matter and Hippocampus, For DAI Special stains such as Bodian silver stain and H&E Stain were used for the demonstration of Axons. In Hypoxic brain injury we have studied the changes in the neurons, Axons, Astrocytes, Nerve tracts, and Myelin sheaths by using specific stain such as H& E Bodian silver stain and Luxon Fast Blue

Results

Out of 20 cases, in 10 cases we suspected diffuse Axonal Injury and the cut sections of the brain were subjected to H& E and Bodian Silver Stain. In 8 Cases we were able to demonstrate characteristic changes suggestive of DAI The demonstration of Axonal Retraction bulbs.

In 10 cases Hypoxic brain damage was suspected.

Cut sections of the brain were subjected to H& E stain for the demonstration of changes in the Neurons and Astrocytes , Bodian Silver Stain was used to demonstrate changes in the axons, Luxon fast Blued Stain was used to demonstrate changes in the myelin sheath.

Macroscopic findings in DAI

1. No changes
2. Petechial hemorrhages

Microscopic findings in DAI

Axonal retraction bulbs demonstrated in all 8 cases

Sites

1. Dorsolateral Brain stem
2. Corpus Callosum
3. Grey / White junction

Macroscopic changes in Hypoxic Brain Damage

1. Symmetrical Atrophy of cortical grey matter with scalloping
2. Atrophy of putamen.

Microscopic changes in Hypoxic brain damage

I. Neurons

1. Swelling and vacuolation of the cytoplasm
2. Shrinkage / angulation of neurons
3. Intense eosinophilia – Red Neurons
4. Karyolysis – fragmentation of nucleus
5. Ghost cell

II. Axon: Swelling and disruption of the axon

III. Astrocytes: proliferation of astrocytes

IV. Nerve tract: Oedema

V. Myelin sheath: Vacuolation 1 – 3 days following hypoxia

Conclusions

1. Histopathological studies of Brain Trauma are seldom done in our country
2. With meticulous HPE it is possible to demonstrate Axonal Retraction bulbs sine qunon of DAI.
3. Histopathological demonstration of findings of Hypoxic brain damage has Medical, legal and research implications.

Departments of Neurosurgery and Forensic Medicine, Medical College, Calicut Kerala, South India

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