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Coma, stupor and mentation change

image of Coma, stupor and mentation change
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Abstract

Consciousness’ and ‘awareness’ are terms with numerous connotations. In a medical setting, these terms are used to describe the mental state generated through the normal functions of the intracranial nervous system. Consciousness and awareness refer to a state of being able to recognize and respond to a variety of internal and external nervous system stimuli. This chapter looks at aetiology, clinical signs, lesion localization, intracranial pathophysiology, differential diagnosis, neurodiagnostic investigation, comatose animals, degenerative diseases, anomalous diseases, metabolic diseases, neoplastic diseases, nutritional diseases, infectious diseases, idiopathic diseases, toxic diseases, traumatic injury, vascular diseases.

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Figures

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9.2 Lesion localization for coma and stupor: the cerebrum, thalamus (diencephalon) and brainstem are indicated. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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9.3 Anatomical structures associated with maintaining consciousness. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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9.4 Neuroanatomical pathways associated with the conscious perception of nasal stimulation. Nasal stimulation is used to both test the sensory innervation to the nares and observe the behavioural response to the stimulation. If the observer knows that the animal has sensation to its head and face based on brainstem reflexes, then lack of a behavioural response can indicate a failure to integrate sensory information at the cortical level due to a lesion in the contralateral hemisphere. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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9.5 Various types of brain herniation. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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9.7 Clinical approach to patients with altered consciousness and/or behaviour. BMBT = buccal mucosal bleeding time; CSF = cerebrospinal fluid; CT = computed tomography; ECG = electrocardiogram; ICP = intracranial pressure; MRI = magnetic resonance imaging.
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9.8 Swollen neurons in the cerebellum of a dog with the lysosomal storage disease GM2 gangliosidosis. (H&E stain; original magnification X40)
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9.9 Transverse T2-weighted MR image of a Staffordshire Bull Terrier with L-2-hydroxyglutaric aciduria. Note the diffuse symmetrical hyperintense areas within the grey matter structures. The white matter seems relatively reduced in size and has a more hypointense signal.
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9.11 Mixed-breed puppy with bilateral strabismus (‘setting sun sign’) associated with hydrocephalus.
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9.12 Transverse CT image of a dog with congenital hydrocephalus at the level of the midbrain. There is obvious dilatation of the lateral ventricles. The mesencephalic aqueduct is visible (arrowed) and is not dilated.
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9.13 Transverse T2-weighted MR image of a dog with congenital hydrocephalus. The CSF appears white, highlighting marked dilatation of the lateral (arrowheads) and third ventricles (arrowed).
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9.14 Ventriculoperitoneal (VP) shunt with stylet in place. There are fenestrated ventricular (right inset) and abdominal (left inset) segments, which both connect to a unidirectional valve (centre inset). Some shunts come as one piece and some valves are programmable so that the pressure at which they open can be altered based on the status of the patient. Lateral and ventrodorsal radiographs of a dog following VP shunt placement to treat congenital hydrocephalus. The shunt reservoir (valve) is visible in the cervical region (arrowed). (b, c courtesy of N Olby)
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9.15 Transverse T2-weighted FLAIR MR image of a dog with hydrocephalus and an intraventricular shunt (arrowed). The dog acquired an infection as a result of the procedure, which can be seen to have caused hyperintense ventricular signals, periventricular hyperintensities and peri-shunt oedema.
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9.16 Sagittal T2-weighted MR image demonstrating a mass (*) in the olfactory lobe associated with a more caudal cyst (arrowed). Histopathology of the mass confirmed a meningioma.
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9.17 Transverse contrast-enhanced CT image of the brain of a 14-year-old cat that presented with seizures. There is a small contrast-enhanced mass in the right temporal lobe with a mineralized centre (arrowhead). The overlying skull is thickened (hyperostosis; black arrows). As the meningioma is lying in the subarachnoid space, the brain has been pushed away from the skull (white arrows) and there is an accumulation of CSF in the resultant space. (Courtesy of N Olby) Sagittal contrast-enhanced T1-weighted MR image of an 8-year-old Bichon Frise with a meningioma. There is a large contrast-enhancing mass with a broad base in contact with the surface of the brain and extending along the meninges (arrowhead) (dural tail sign).
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9.18 Dorsal post-contrast T1-weighted MR image of a cat with a large well delineated mass in the cerebral cortex. The areas with minimal to no signal (arrowed) are suggestive of haemorrhage and/or mineralization based on the histopathology. The lesion was confirmed to be a meningioma. Note the adjacent hyperostosis (arrowheads) of the skull, which is sometimes seen in response to intracranial meningiomas.
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9.19 Transverse T2-weighted FLAIR MR image of the brain of a Boston Terrier presented with seizures and inappropriate mentation. A large hyperintense lesion predominantly affecting the grey matter and causing a mass effect can be seen. Dorsal view of the gross brain of the dog in (a). Histopathology confirmed the lesion as an oligodendroglioma. (H&E stain; original magnification X10) Transverse T2-weighted FLAIR MR image of the brain of a dog with a large piriform lobe hyperintensity, which was confirmed as an astrocytoma on histopathology. Transverse section of a gross brain showing an astrocytoma in the piriform lobe (arrowed).
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9.20 Sagittal contrast-enhanced T1-weighted MR image of a 9-year-old mixed-breed dog. The mass is an indistinct hypoattenuating area lying in the parietal lobe (arrowed) that has not been enhanced by contrast medium. Histopathology confirmed the mass as a high grade glioma.
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9.21 Transverse contrast-enhanced T1-weighted MR image at the level of the pons in a 7-year-old Border Collie. There is a large homogeneous contrast-enhanced mass in the left cerebellopontine angle (arrowhead) and the fourth ventricle is dilated (arrowed). Histopathology confirmed the mass as a choroid plexus papilloma.
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9.22 Transverse post-contrast T1-weighted MR image of a dog with a pituitary gland-based mass. The uniform contrast medium enhancement with well defined borders suggests a lesion outside the parenchyma. Transverse contrast-enhanced CT image of a 6-year-old Labrador Retriever that presented with unexplained pain and compulsive pacing. A large contrast-enhancing mass is visible over the pituitary fossa. The mass has a cystic area and was confirmed at necropsy to be a pituitary adenocarcinoma. (Courtesy of N Olby)
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9.23 Transverse gradient echo MR image of the frontal lobe of a dog with an oligodendroglioma. Post-surgery the lesion has reduced in size. Note the focal signal void where iron oxide nanoparticle tracers have been used to help follow the administration of a novel treatment by convection-enhanced delivery into the tumour bed.
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9.24 Hippocampus of a dog with rabies showing several intracytoplasmic inclusion bodies (arrowed). (H&E stain; original magnification X20) Hippocampus of a dog demonstrating distinct labelling for rabies virus antigen within the perikaryon of several neurons. (Immunohistochemistry labelled streptavidin biotin method with diaminobenzine substrate; Mayer’s haematoxylin counterstain; original magnification X40) (Courtesy of R Rech)
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9.25 Lateral and ventral views of arterial blood supply to the canine brain. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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9.26 Transverse T2-weighted MR image of a dog following the sudden onset of cerebello-vestibular dysfunction. There is a well defined region of hyperintensity within the cerebellar parenchyma compatible with ischaemic infarction.
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9.27 Dorsal diffusion-weighted MR image of the same dog as in Figure 9.26 . A focal hyperintense lesion (arrowed) is visible, compatible with oedema related to ischaemia. The lesion (arrowed) appears hypointense on apparent diffusion coefficient (ADC) mapping, confirming the presence of an ischaemic infarction.
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9.28 Transverse T2-weighted MR image of the brain of a dog with a haemorrhagic lesion. The lesion appears as an area of hypointensity or signal void. Note also the peri-lesional hyperintensity compatible with oedema. Gradient echo MR image showing the lesion as a hypointense structure, confirming the presence of haem.

Supplements

‘Fly-biting’

A 5-year-old Labrador ‘snapping at the air’. This is commonly referred to as ‘fly-biting’. (See page 138 in the Manual)

Hydrocephalus

Hydrocephalus can be identified using ultrasonography where an open fontanelle exists for paediatric probe placement. In this case, diffuse enlargement of the ventricular system can be seen as hypoechoic cavities contained within the thin parenchyma. (See page 146 in the Manual)

Neuronal ceroid lipofuscinosis

(a) A 2-year-old Domestic Shorthaired cat with neuronal ceroid lipofuscinosis predominately affecting the cerebellum.

Neuronal ceroid lipofuscinosis

(b) A 2-year-old Border Collie with neuronal ceroid lipofuscinosis exhibiting aggression and inappropriate behaviour. (Courtesy of O Yamamoto) (See page 143 in the Manual)

Portosystemic shunt

A 6-month-old Yorkshire Terrier with a portosystemic shunt is seen to walk compulsively and aimlessly. This behaviour provide additional evidence of visual dysfunction. (See page 149 in the Manual)

Severe depression (1)

(a) A 6-year-old Boxer showing severe depression (obtundation).

Severe depression (1)

(b) A 1-year-old mixed Shepherd dog with metabolic encephalopathy showing both severe depression and inappropriate mental function. (See page 137 in the Manual)

Severe depression (2)

A 4-year-old Pug standing in one position, staring vacantly. This demeanor is compatible with severe obtundation. (See page 137 in the Manual)

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