Large Animal Neurology. Joe Mayhew
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Название: Large Animal Neurology
Автор: Joe Mayhew
Издательство: John Wiley & Sons Limited
Жанр: Биология
isbn: 9781119477198
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Figure 11.3 Ventral eye deviation, as seen in this donkey’s left eye while the muzzle is being raised, with or without a left head tilt, is assumed to be left vestibular disease until proven otherwise. In this case, there also is left facial paresis evidenced by the right deviation of the muzzle. These signs were due to involvement of CN VIII and VII caused by the immune‐associated disease polyneuritis equi.
Although many inflammatory, physical, metabolic, toxic, and nutritional disorders may affect the regions of the brainstem where the oculomotor, trochlear, and abducent nuclei are located, prominent signs of fixed strabismus are rarely seen alone in large animals.16,17 However, many severe asymmetric forebrain diseases result in turning of the head and neck and drifting toward one side, usually the side of the lesion. This can also involve the eyes being drawn toward one side, particularly with thalamic involvement, and these signs collectively comprise the adversive syndrome.18,19 The relative dorsomedial rotation of the eyeballs (Figure 11.5) seen in diseases such as polioencephalomalacia, lead poisoning, water intoxication and bacterial meningitis in ruminants, and with meningitis and hypoxic and neonatal encephalopathy in newborn foals, may not be a specific trochlear nerve paralysis. This is because the eye can be moved in all four directions and out of this rotated position, so it might reflect severe forebrain disease involving the central motor pathways controlling eyeball posture. A similar dorsomedial eyeball rotation can also be seen with congenital cerebellar hypoplasia and with cerebellar abiotrophy in several species likely due to alteration in vestibulocerebellar tonic control of extraocular muscles.
Figure 11.4 Ventral and slight lateral deviation of one eyeball relative to the other is the most frequently seen eye deviation in large animals. It is most often due to vestibular disease. Although it can be referred to as strabismus, the eye is not fixed and can be moved away from the ventral position by movement of the head. This lamb is suffering from listeriosis with the encephalitis worse on the left side of the brainstem. Compared with the more normally responding right eye (A), the left eyeball is ventrally deviated (B) while the head is in a normal posture. The ventral deviation became even more prominent with elevation of the nose and head extension.
Figure 11.5 The term dorsomedial (rotational) strabismus is used to describe what is seen here (A and B). The cow (A) has Salmonella sp. sepsis and meningitis, and the ewe (B) has thiamine‐responsive polioencephalomalacia. Both have rotation of the globe such that the medial aspect of the pupil is now rotated to a dorsal and caudal position. The images of each eye have been rotated such that the palpebral fissure is shown perfectly horizontal, and the equators of the eyeballs are indicated by yellow lines. That this is not a fixed strabismus is attested by the fact that with moving the position of the head the eye can be drawn out of this position.
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12 Dropped mandible and masticatory muscle atrophy
With denervation of the muscles of mastication, the masseter, temporalis, medial and lateral pterygoid, and distal belly of the digastricus muscles on the affected side atrophy rapidly within 1–2 weeks. Unilateral neurogenic muscle atrophy is initially not associated with any major difficulty in chewing food. With time however there is deviation СКАЧАТЬ