Fractures of the cerebral skull are clinically divided into fractures of the roof and those of the base of the skull. Both fractures are much rarer than fractures of the facial skull and the mandible.
Fractures of the cerebral skull are often associated with intracranial hemorrhage and edema, which lead to neurologic deficits in the cerebral areas involved. This underlines the importance of a neurologic examination when presented with a patient with a skull fracture.
Head trauma results from collision with immovable objects, kicks from other horses or from falls during which the head sustains a forceful impact, and most are accompanied by soft tissue injuries. Although bone injuries are common in head trauma, injuries to the central nervous system (CNS) are relatively rare, with the exception of horses that rear over backward and hit their head on a hard surface during their fall. The prognosis is particularly poor when the base of the occipital bone is affected.
Cerebral skull fractures: Examination
In addition to clinical and radiographic examination, computed tomography is an important and often indispensable diagnostic procedure for the assessment of the entire extent of a fracture . The severity of a head fracture is frequently underestimated in cases where computed tomography was not used. A recent study on skull fractures in the horse revealed only about half of all fractures were detected by radiography alone.
Endoscopic examination of the upper airways serves to identify neurologic deficits involving the larynx and pharynx and to diagnose injuries to the hyoid bone, or hemorrhage into the guttural pouch. Cytologic analysis of the cerebrospinal fluid may provide a lead in obscure cases or help confirm a tentative diagnosis. A final diagnosis is often not possible, especially when diagnostic modalities are limited; however, a diagnosis may be reached on the basis of the patient’s response to treatment. After the initial examination, follow-up examinations should be carried out at regular intervals to monitor the progress of the healing phase.
Cerebral skull fractures: Clinical signs
Injury to the CNS after a head fracture commonly results in changes in behavior and demeanor such as depression, apathy, stupor or coma. Other common signs are muscle spasms, opisthotonus, vestibular dysfunction and specific cranial nerve deficits. The latter are most easily diagnosed when they involve the eyes. Affected horses may have nystagmus with the fast phase directed away from the lesion, strabismus, bilateral mydriatic unresponsive pupils, bilateral miosis, or anisocoria. These manifestations usually indicate severe head trauma and a guarded prognosis.
Fractures of the base of the skull may be associated with brainstem lesions (see picture), and can lead to changes in heart and respiratory rates. Other possible accompanying signs are hemorrhage into the external ear canal and leakage of cerebrospinal fluid from the ears and nares. The severity of the clinical signs generally is closely correlated with the severity of the lesions in the CNS, although the absence of neurologic signs does not rule out CNS involvement. Following severe head trauma, affected horses may go down or die acutely.