J. small Anim. Pract. (1976) 17, 551-554.

R A D I O L O G I C A L R E F R E S H E R - 7

The head-Part I

T R A U M A T I C L E S I O N S O F T H E S K U L L

Cranium Fractures associated with gross displacement of the bones of the cranial cavity

are likely to result in rapid death. However, hairline cracks with little or no separation, and accompanied by clinical signs of brain damage are occasionally encountered. Radiographic demonstration of such lesions provides useful informa- tion supplementary to that obtained from neurological examination, particularly with regard to prognosis and possible indications for surgical intervention.

The exposed vault bones are more likely to be involved than those comprising the base of the cavity which are well protected (Figs 1 and 2), and from the limited number of cases available for review it appears that the smaller canine breeds with domed conformation of the skull are particularly at risk (Fig. 2) .

FIG. 1. Crossbred. 7 months. Lateral radiograph. Fracture of the left parietal bone is represented by radiolucent shadows forming the shape of an inverted ‘Y’ traversing

the lateral wall of the cranial cavity.

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552 T H E H E A D . I

FIG. 2. Yorkshire Terrier. 3 years. On the ventro-dorsal radiograph (a), a fine curved radiolucent shadow caudo-lateral to the left petrous temporal bone extends from the base of the zygomatic arch to a point just cranial to the occipital condyle. A lateral view (b) shows that the fracture site is located well above the skull base in the parietal bone at the level of the tentorium ossium. There is slight inward displacement of the

lower fragment.

Cranial fractures can usually be adequately shown on lateral and/or ventro- dorsal radiographs. However, in equivocal cases, oblique projections may be employed to demonstrate hairline lesions more clearly.

I t is necessary to be familiar with the complex pattern of normal density interfaces in the cranial region in order to identify with confidence the fine linear radiolucent shadows which represent fracture lines. A systematic and detailed inspection of each skeletal structure is required, and comparison with radiographs of a known normal subject of similar skull type may be helpful.

Facial bones The facial bones are particularly exposed to fracture by crushing or glancing

blows. Although such injuries are not uncommon, in the majority of cases radio- graphic examination is not a prerequisite for satisfactory management, since surgical immobilization is required only in the event of gross instability. Never- theless, radiographic demonstration of facial fractures is usually quite straight- forward and may elucidate the cause of pain, swelling or deformity following trauma to the head (Fig. 3) .

Fractures of the frontal bones may be shown to advantage in a tangential projection (Fig. 3b). An occasional complication of such fractures or those causing disruption of the nasal airway is rapidly developing subcutaneous emphysema, represented radiographically by a radiolucent shadow between the skin and facial bones.

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FIG. 3. Crossbred. 1 yeax. Lateral (a) and tangential (b) radiographs showing bilateral multiple fractures of the frontal bones. The largest fragments are inverted, producing

gross deformity of the forehead.

Single fractures of the zygomatic arch produce no displacement, since it is a rigid structure, and present radiographically as hairline radiolucencies (Fig. 4a). Multiple fractures, however, may lead to considerable distortion (Fig. 4b). Figure 5 illustrates a long term complication, where complete collapse of the arch has resulted in partial temporo-mandibular ankylosis.

FIG. 4. Zygomatic arch fractures. Ventro-dorsal radiographs. (a) Miniature poodle. Single fracture on the left side shown as a vertical radiolucency close to the maxilla. A small fragment has also separated anteriorly. (b) Saluki. Double fracture with gross

medial displacement of the anterior portion of the fragment.

FIG. 5 . Alsatian. 2 years. Ventro-dorsal radiograph taken 6 months after trauma to the head. The outline of the left zygomatic arch is absent, but extensive callus occupies the soft tissue space normally seen between arch and mandible, and extends caudally to

involve the temporo-mandibular articulation.

CHRISTINE GIBBS