by R.M. Clemmons, DVM, PhD

Associate Professor of Neurology & Neurosurgery

One of the important aspects of evaluating any neurologic patient is to determine the location of the lesion. Luckily, the function of the nervous system is intimately tied to its structure. As such, when a function is lost, the structure involved is uncovered. Signs of neurologic disease can be divided into those representing diseases above the foramen magnum (head signs) and those below the foramen magnum (spinal cord signs). Head signs include seizures, head tilt, cranial nerve deficits, whole body and head tremors, and ataxia. Spinal cord signs include quadriparesis and paraparesis. The peripheral nervous system shows signs consistent with the distribution of the nerve involved. (See Table 1) Once the disease process is localized, the differential diagnosis can be made and the diagnostic approach determined.
Table 1. Neurologic Signs and Lesion Location.
Neurologic Sign Location of Lesion
Change in Behavior or Personality Cerebral Cortex, Thalamus, Hypothalamus
Seizures Cerebral Cortex, Thalamus, Hypothalamus
Visual Dysfunction Retina, Optic nerve, Visual pathways, Cerebral Cortex
Signs of Cranial Nerve Dysfunction
Anisocoria Sympathetic or Parasympathetic innervation to the eye
Strabismus CN III, CN IV, CN VI
Dropped jaw CN V
Changed facial sensation CN V
Paralysis of eyelid, lip or ear CN VII
Dysphagia CN IX, CN X
Megaesophagus CN X
Laryngeal paralysis CN X, CN XI
Paralysis of tongue CN XII
Head tilt, circling, nystagmus CN VIII (vestibular system)
Deafness CN VIII (auditory system)
Incoordination of the Head and Body Cerebellum
Paraparesis or Paraplegia TL Spinal Cord
Paralysis of one Limb Peripheral nerve
Flaccid Anus, Tail and Bladder Cauda Equina

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