8 The Head and Neck

During the preliminary stage of the clinical examination a detailed inspection of the animal, preferably on a regional basis, should be made before it is subjected to any disturbing influence, such as restraint or the near approach of a strange person, which might modify its be­haviour. This inspection provides the oppor­tunity to observe, among many other features, the general appearance and conformation of the animal, as well as to assess its behaviour and demeanour. In the case of animals normally kept in herds or flocks, separation of an indivi­dual from its group is usually indicative of illness. The significance of any change in the behavioural pattern of animals can only be correctly inter­preted when the observer has a sound knowledge of the ways in which the various species are likely to react under changing circumstances and conditions. Changes in bearing are also most meaningful when the clinician appreciates the full range of reactivity that may be exhibited by animals to constantly changing environmental stimuli.

When inspecting the head, attention should be paid to the facial expression which is a good in­dicator of the mental state and, therefore, of the demeanour of the animal. An animal in good health has an alert appearance and reacts to external stimuli such as sound and movement in the expected manner. Abnormal positioning of the eyes or eyelids will alter the facial expres­sion; the character and causation of these ab­normalities will be discussed later in this chapter. Disturbances in mental condition, including depression or excitation, are appreciated by noting any alteration in behaviour as well as in expression (see p. 19). When an animal exhibits signs of mental disturbance it is more than likely that it is caused by primary or secondary modi­fication of brain function.

Diseases associated with rapid loss of bodily condition, severe dehydration or exhaustion, because of pain, give rise to a haggard expression. When affected with tetanus, the horse has an anxious expression caused by muscular rigidity in conjunction with dilatation of the nostrils and wide separation of the eyelids. The somewhat maniacal expression occurring in rabies and acute lead poisoning is produced by the very intense expression, with partially opened lips and rolling of the eyes.

Evaluation of the anatomical conformation and symmetry of the bony structures and soft tissues of the head and neck region is frequently rewarding. Bulging of the frontal region occurs in calves with congenital achondroplasia, and also in some cases of congenital hydrocephalus and inherited chondroplastic dwarfism. Sym­metrical enlargement of the mandibles and maxillae, causing swelling of the lower part of the head, occurs in osteodystrophia fibrosa; the maxillae are similarly enlarged in chondroplastic dwarf calves. Asymmetrical enlargement of the bones of the lower or upper jaw is a feature of actinomycosis in cattle. Changes in the contours of the soft structures, usually in the form of swellings, involve the intermaxillary space in such inflammatory states as actinobacillosis and strangles, or oedematous conditions including acute anaemia, protein starvation and conges­tive heart failure. Unilateral or bilateral swelling of the cheek region occurs in actinobacillosis and necrotic stomatitis (calf diphtheria). The soft tissues of the nose and face are swollen in necrotic rhinitis (bullnose) of young pigs. Tumours of the head may originate from either bone or soft tissue. Neoplasms, involving the eye and other periorbital structures in horses and cattle, the horn core in cattle and the ear in sheep, are in most cases squamous cell carcino­mas. Other changes in the soft tissues include increased muscle tone in tetanus which, more noticeably in the horse, is responsible for dila­tation of the nostrils, rigidity of the ears, and protrusion of the membrana nictitans. Asym­metry of the soft structures, in the absence of swelling, is most likely to involve the positioning of the ears, the degree of eyelid closure and the position of the lower lip relative to the upper. In facial nerve paralysis there is drooping of the ear and unilateral flaccidity of the lips so that the upper lip is drawn towards the normally functioning side and the lower lip hangs down on the affected side. Drooping of the upper eyelid (ptosis) occurs when the function of the oculo­motor nerve is defective.

Changes in the carriage of the head are indi­cative of functional or organic disease of the central nervous system. Rotation occurs when there is unilateral interference with the function of the vestibular apparatus, as in otitis media in which the affected side is turned downwards, so that the animal invariably falls towards that side. Lateral deviation is a feature of unilateral dys­function of the vestibular nucleus and of the medulla oblongata and cervical region of the spinal cord, as in listeriosis. Opisthotonus (ele­vation of the head) and orthotonus (extension of the head) occur when there is intermittent generalized increase in muscle tone during the convulsive episodes associated with tetanus, strychnine poisoning, hypomagnesaemic tetany, the encephalopathy arising from acute lead poisoning and some cases of encephalitis; exten­sion of both the head and neck is a characteristic feature of strangles and pharyngitis in the horse (see Fig. 108, p. 103).

Examination of the Visible Mucous Membranes

Several of the clinically important visible mucous membranes are associated with the head, so that it is expedient to consider certain general aspects of the clinical examination of all mucosal structures at this point. When considering the condition of any of the visible mucous mem­branes, which include the conjunctival, nasal buccal, vaginal, urethral and rectal, the tissues surrounding the orifice by means of which the particular mucosa communicates with the surface of the body, should be included in the inspection. Changes in these tissues are often closely asso­ciated with disease of the related mucous mem­brane or its contiguous structures.

Inspection of the mucous membrane should be carried out in daylight whenever possible, but if this is not feasible, an electric torch or suitable reflecting mirror should be employed. For examining the mucous membrane of the vagina or rectum an appropriate speculum is used (Fig. 85a; see also Figs 172-3, p. 246). The con­cealed mucous membranes (pharynx, larynx, trachea, stomach, bladder) may be inspected in small animals with the aid of endoscopic instru­ments; in large animals the mucosa of the pharynx, larynx and bladder are ordinarily examined in this way.

During the visual examination, attention is directed towards determining if any of the fol­lowing conditions are present: pallor, hyperemia, cyanosis, jaundice, eruptions, ulcerations, haemorrhages, swellings, discharges, etc.

A discharge may be the secretion of a gland (mucous, lacrimal, anal), the product of inflam­mation (exudate) or the result of venous con­gestion (transudate) or of vascular trauma (haemorrhage). It should be remembered that discharge from a mucous membrane may also contain abnormal forms of the secretions or excretions of the body, and that solid and liquid foodstuffs may be discharged from the nostrils as well as the mouth (vomition in horses), and faeces from the vulva as well as the rectum (rectovaginal fistula).