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Neurological abnormalities of the head and face

image of Neurological abnormalities of the head and face
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Abstract

Recognition of neurological abnormalities of the head and face plays a key role in identifying the distribution of a neurological disease and thereby suggesting possible aetiologies. This chapter deals with anatomy and clinical signs, lesion localization, pathophysiology, differential diagnosis, neurodiagnostic investigation, specific neurological syndromes of the head and face.

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Figures

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12.1 Overview of cranial nerve origins and distribution in the dog. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.2 CN V (trigemial nerve) and its branches. Areas of cutaneous innervation of the head supplied by the branches of CN V. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.3 The palpebral reflex is elicited by touching and stimulating the skin of the medial and lateral canthus of the palpebrae. The sensory (afferent) portion of the pathway enters the brainstem via the trigeminal nerve and synapses in the sensory nucleus within the pons. The motor (efferent) portion of the pathway (facial nerve) is then stimulated, which causes a palpebral blink response. This is an interneuron facilitated reflex. There is also contralateral central recognition of the sensory stimulus from the trigeminal sensory nucleus.
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12.4 A 3-year-old male Greyhound presented with an acute onset of dropped jaw due to an underlying inflammatory disease of the central nervous system. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.5 Severe atrophy of the masticatory muscles affects the profile of the dorsal aspect of the head. Enophthalmos may also occur and can cause periodic protrusion of the third eyelids.
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12.6 The facial nerve (CN VII) exits the brainstem at the level of the medulla and exits the intracranial cavity via the internal acoustic meatus, where it becomes three branches: the major petrosal nerve before the geniculate ganglion, the chorda tympani nerve and the main branch of the facial nerve (as shown). It then leaves the calvaria via the stylomastoid foramen. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.7 CN VII is shown to exit from the medulla oblongata of the brainstem and its branches are depicted innervating the lacrimal glands, the stapedius muscle and the mandibular and sublingual salivary glands. The main component of CN VII exits the stylomastoid foramen to innervate the muscles of facial expression. The superficial branches of CN VII. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.8 Weakness in the muscles responsible for facial expression causes drooping of the lip, widening of the palpebral fissure and poor movement of the pinna. This can be observed even in loose-skinned breeds such as the Boxer.
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12.9 Cross-section of a cochlear coil. The scala vestibuli and tympani are filled with perilymph and the cochlear duct is filled with endolymph. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.10 The pharynx, larynx and oesophagus are innervated by the glossopharyngeal nerve (CN IX) and vagus nerve (CN X). The spinal accessory nerve (CN XI) sends a few fibres to join the vagus nerve. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.11 This dog has such profound tongue weakness that it cannot be withdrawn into the mouth voluntarily. Attempting to grasp the tongue may provide more information in less severe cases.
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12.12 The third order sympathetic axons reaching the eye innervate the smooth muscles of the iris (dilator muscle), the periorbita, the upper and lower eyelids (tarsal muscles) and the third eyelid. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.13 The parasympathetic fibres of cranial nerves III, VII and IX innervate the glands and smooth muscles of the head and eye. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.14 Lesion localization for CNS and PNS causes of disorders of the face and head. The brainstem and CNs are highlighted. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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12.17 Diagnostic approach to cases with abnormalities of the head and face.
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12.18 Normal BAEP tracing showing the five peaks that are typically detected. BAEPs obtained from a 6-week-old Dalmatian puppy with unilateral deafness in the left ear. Trace 01 = normal trace from the right ear stimulated at 80 dB. Trace 02 = recorded after stimulating the left ear at 80 dB. Trace 03 = recorded after stimulating the left ear at 100 dB. Traces 02 and 03 show only wave V. This wave originates from the contralateral (normal) ear due to decussation of the auditory pathways in the rostral brainstem. The absence of waves I to IV in traces 02 and 03 indicates deafness in the left ear. Trace 04 = an abnormal response in the left ear after stimulation at 100 dB with the right ear masked at 30 dB. Abnormal BAEP obtained from an 8-year-old cross-breed dog with severe brainstem compression. Only wave I is clearly discernible.
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12.19 T2-weighted MR image showing a hyperintense lesion (*) in the brainstem of a dog that had reduced facial sensation. The lesion was later confirmed to be granulomatous meningoencephalitis.
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12.22 Poor abduction of the arytenoid cartilages during inspiration can often be detected by real-time ultrasound examination. Note the position of the cuneiform processes (arrowed). * = thyroid cartilage.
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12.24 Radiograph confirming the presence of megaoesophagus. Contrast medium (barium mixed with food) was administered prior to exposure.
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12.27 Nerve supply to the eye and surrounding muscles and structures. Note the close approximation of multiple cranial nerves at the base of the skull. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.

Supplements

Dropped jaw

Golden Retriever with suspected trigeminal neuritis showing a lack of jaw tone. (See pages 215 and 229 in the Manual)

Facial hyperaesthesia

A 7-year-old Scottish Terrier bitch with facial hyperaesthesia. The dog also has bilateral temporal muscle atrophy and the facial electromyogram showed abnormalities. (See page 230 in the Manual)

Laryngeal hemiparesis

Video clip showing left-sided laryngeal hemiparesis in a dog under light anaesthesia. (See page 226 in the Manual)

Palpebral reflex

Lack of palpebral reflex on the right-hand side of the face in a West Highland White Terrier following middle ear surgery. (See pages 216 and 230 in the Manual)

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