Fundamentals of Neurosurgery

 Lameness- deviation from normal gait; incapable of normal locomotion  Plegia and Paralysis – are a complete loss of sensory and motor function to the affected extremity  Paresis – is partial loss of sensation, plus complete or partial loss of motor function on the affected extremity ...

 Lameness- deviation from normal gait; incapable of normal locomotion  Plegia and Paralysis – are a complete loss of sensory and motor function to the affected extremity  Paresis – is partial loss of sensation, plus complete or partial loss of motor function on the affected extremity  Myotonia- a disorder involving tonic spasm of muscles  Spasticity- a condition in which certain muscles are continuously contracted. → tightening of the muscles, causing stiff and awkward movements  Clonus “myoclonus”- alternate involuntary muscular contraction and relaxation in rapid succession.  Tetraparesis (Tetraplegia) – all four limbs affected.  Paraparesis (Paraplegia) – both pelvic limbs affected.  Hemiparesis (Hemiplegia) - front and hind limb on one side affected.  Monoparesis (monoplegia)- one limb affected. A proper systematic examination of animals suspected of having neurologic disorders includes: I. Signalment II. History III. Physical examination IV. Neurologic examination Signalment (i.e., age, sex, breed, and use of animal) correlated with anatomic localization of the lesion. The neurologic examination should establish the presence of neurologic disease and help determine its neuroanatomic location.  Theneurologic examination should be performed in a quiet area free of distractions that has good footing a. Mental status b. Locomotion- posture and gait c. Cranial nerves d. Postural reactions e. Spinal reflexes f. Sensory perception g. Localization of the lesion A. Mental status Allow the animal to move around the examination room: 1. Alert – normal 2. Depressed – conscious, but inactive. Also called obtunded. Unresponsive to environment 3. Stuporous - sleeps when undisturbed, will not respond to harmless stimuli such as noise but will awaken with a painful stimulus. 4. Comatose - cannot be aroused, even with painful stimulus.  B. Posture Evaluated while the animal is free to move about the examination area and can be further assessed by moving the animal into different positions to observe its ability to regain normal posture. Examples: Head tilt, abnormal truncal posture, improper positioning of the limbs, decreased or increased muscle tone. vestibular system movement, speech, balance, and posture C. Gait Evaluation of animal’s gait requires an area with good footing. The animal is observed from the side, moving toward and away from the examiner. Examples: ✓ Proprioception (position sense) – is the ability to recognize the location of the limbs in relation to the rest of the body. (knuckling, misplacement of foot, or scuffing of the toenails)  Ataxia – is lack of coordination without paretic, spastic, or involuntary movements.  Hypotonia- abnormally decreased tonicity or strength of muscles  Dysmetria inability to properly direct or limit motions  Hypermetria- movement that are too long, movement overreach the intended goal.  Hypometria- movement that are too short, movements fall short of the intended goal. D. Purposeful movement  It is an animal’s conscious attempt to move the legs.  It is most applicable to weakly ambulatory and non- ambulatory animals that drag their legs as they pull themselves along. 1. Proprioceptive positioning Is preformed by flexing the paw so the dorsal surface is on the floor. The animal should immediately return to position  Propioceptive Positioning Flex the dog’s paw for 10s Check the time it takes for the dog to return the paw to its usual position  Itis performed by having the animal bear weight on the thoracic limbs while it is being supported under the abdomen. POSTURAL REACTIONS Wheel Barrowing- Thoracic Limb Support the dog under the abdomen and allow the dog to walk on its thoracic limb Observe the dog for deficits The normal dog walks with symmetric movements of both thoracic limbs and head extended in normal position  Is tested with the animal positioned as for wheel-barrowing, except one thoracic OR pelvic limb is lifted. The entire weight of the animal is supported on one limb as the patient is moved medially and laterally. HOPPING- Thoracic Limb Support the pelvic limbs and hold one thoracic limb Let the dog hop on one thoracic limb Move the dog forward and laterally and observe the coordination of the dog Repeat the process on the other thoracic limb HOPPING-Pelvic Limb Support the dog by the thorax so that the thoracic limbs are not in contact with the ground Observe for hopping and strength of the pelvic limb to support the dog’s weight Do the same test for the other pelvic limb Hopping is a test of proprioception, strength and voluntary movement  Isperformed by supporting the animal under the thorax while lowering it to the floor. When pelvic limbs touch the floor they should move caudally in symmetric walking movements to achieve a position of support. Extensor Postural Thrust- Pelvic Limb Hold the dog off the ground by supporting it caudal to the scapula Observe the animal extend its pelvic limbs to support its weight Move the dog forward and backward in this position, observe the symmetry of movement strength and coordination  Are performed by elevating the front and rear limbs of one side so that all the animal’s weight is supported by the opposite limbs.  Lateral walking are then evaluated.  Patient assessment is the same as for wheelbarrowing. Hemistanding & Hemiwalking Hold the one thoracic and one pelvic limb on one side Let the dog walk forward or to the side Observe if the animal can walk forward and sideways; observe for deficits  Tonic Neck Reaction Extend the head so that the dog is directed dorsally A normal dog would respond by extension of all joints in both thoracic limbs  Placing reactions are evaluated first without vision (tactile placing) and then with vision (visual placing). Tactile placing  The examiner supports the animal under the thorax and covers its eyes with one hand.  The distal thoracic limbs (at or below the carpi) are brought in contact with the edge of the table.  The normal response is immediate placement of the feet on the table surface in a position that will support weight. Visual placing  It is tested by allowing the animal to see the table surface.  Normal animals reach for the surface before the carpus touches the table.  It is an involuntary, an instant movement in response to a stimuli.  Part of neurologic examination to assess damage in the central and peripheral nervous system.  Reflex action is mediated via the reflex arc.  Neural pathway that mediates reflex action.  Begins with a peripheral sensory receptor organ and ends with a peripheral effector organ.  Most sensory neurons do not pass through the brain, but synapse in the spinal cord.  This characteristic allows reflex actions to occur relatively quickly.  A.k.a. myotatic reflexes ‘tasis’ → stretch -Test the integrity of sensory and motor components of the reflex arc and the influence of descending motor pathways on the reflex.  Three kinds of responses may be seen: 1. Absence or depressed reflex, indicating complete or partial loss of either the sensory OR motor nerves responsible for the reflex (lower motor neuron [LMN]); 2. Normal reflex, indicating that sensory and motor nerves are intact 3. Exaggerated reflex, indicating an abnormality in the descending pathways from the brain and spinal cord that normally inhibit the reflex (upper motor neuron [UMN]). 1. Patellar reflex 2. Withdrawal reflex 3. Triceps reflex 4. Biceps reflex 5. Anal sphincter reflex 6. Panniculus reflex  The patellar reflex is the most reliable pelvic limb reflex.  It is performed with the animal in lateral recumbency.  The uppermost leg is supported by holding the hock with the stifle slightly flexed.  When the patellar ligament is struck briskly with a reflex hammer the response is a single, quick extension of the stifle.  Absence or depression of the patellar reflex (hypopatellar reflex) and decreased muscle tone (flaccidity) indicate a lesion of the sensory or motor component of the reflex arc (LMN).  Unilateral loss of the reflex suggests a femoral nerve lesion, whereas bilateral loss suggests a segmental spinal cord lesion involving spinal cord segments L4-L6.  Occasionally,old dogs lose their patellar reflex yet maintain their ambulatory ability.  Exaggerated reflexes (hyperpatellar reflex) and increased muscle tone (spasticity), when associated with other signs of UMN dysfunction, suggest a lesion CRANIAL to the L4 spinal cord segment (UMN). Summary Patellar Reflex - Absent or depressed reflex (LMN) Unilateral— femoral nerve Bilateral— lesion at spinal cord segments L4–L6 Exaggerated reflex Bilateral— lesion cranial to spinal cord segment L4  Pelvic limb withdrawal reflex is performed with the animal in lateral recumbency.  The least harmful stimulus possible is applied to the foot; the normal response is flexion of the entire limb.  This reflex primarily involves spinal cord segments L6 to S1 and the sciatic nerve.  Absence or depression of the reflex indicates a lesion of these spinal cord segments or nerves (LMN).  Unilateral absence of the reflex is most likely the result of a sciatic nerve lesion, whereas bilateral absence or depression is more likely the result of a spinal cord lesion.  An exaggerated withdrawal reflex indicates a lesion cranial to spinal cord segment L6 (UMN). Nerve involved? C6-T2 L6–S1  Triceps reflex is performed with the animal in lateral recumbency.  The limb is supported under the elbow; the elbow is fully extended and the entire leg drawn caudally.  The triceps tendon is struck with a reflex hammer just proximal to the olecranon.  Normal response: slight extension of the elbow.  Thetriceps muscle is innervated by the radial nerve, which originates from spinal cord segments C7-T2.  Thetriceps reflex is difficult to elicit in normal animals; thus absent or depressed reflexes may not indicate an abnormality.  An exaggerated reflex, if elicited, indicates a lesion → → cranial to C7 (UMN)  To perform the biceps reflex the index finger of the examiner's hand that is holding the animal's elbow is placed on the biceps tendon cranial and proximal to the elbow.  Theelbow is slightly extended and the finger is struck with the reflex hammer.  Normal response: slight flexion of the elbow.  This reflex is difficult to elicit in the normal animal.  Absent or decreased reflexes suggest a lesion involving spinal cord segments C6-T8 (LMN), but may be normal in some animals.  An exaggerated reflex, if elicited, indicates a lesion cranial to spinal cord segment C6 (UMN).  The crossed extensor reflex may be observed when withdrawal reflexes are elicited.  With the animal in lateral recumbency and legs relaxed, the toes of the uppermost limb (thoracic or pelvic) are gently pinched with fingers, eliciting a withdrawal reflex.  An abnormal response is flexion of the upper limb and simultaneous extension of the lower limb.  The stimulus must be gentle; excessive stimulus causes the animal to attempt to right itself, negating any findings.  The crossed extensor reflex results from a lesion that affects descending inhibitory pathways of the spinal cord (UMN).  This reflex is commonly associated with chronicity, but does not constitute a poor prognosis. righting reflex  The perineal or anal sphincter reflex is elicited by gentle perineal stimulation with a needle or forceps.  A normal response is contraction of the anal sphincter muscle. o Sensory and motor innervation occurs through the pudendal nerve (perineal nerve is sensory; caudal rectal nerve is motor) and spinal cord segments S1-S3.  The anal sphincter reflex is the best indication of functional integrity of sacral spinal cord segments and sacral nerve roots.  Evaluationof this reflex is important in animals with urinary bladder dysfunction.  It may be absent, depressed, normal, or exaggerated.  Absence or depression of the reflex (failure of the anus to contract) indicates a sacral spinal cord or pudendal nerve lesion (LMN).  An exaggerated response indicates a lesion ABOVE the S1 spinal cord segment  Thetwo general components of urinary bladder innervation are autonomic (hypogastric and pelvic) and somatic (pudendal) nerves.  Simplistically, clinical observations of bladder dysfunction can be attributed to spinal cord injury based on the pudendal nerve (S1 and S2).  The pudendal nerve innervates urethral striated muscle and helps maintain urinary continence.  A lesion above the sacral spinal cord segments causes detrusor spasticity, making the bladder difficult to express (UMN). A lesion involving sacral spinal cord segments causes lack of sphincter tone and an easily expressible bladder (LMN).  Panniculus reflex (cutaneous trunci reflex) is elicited by pin- prick stimulus to the skin over the back, beginning at the lumbosacral region and continuing cranially.  Normal response is twitching of the cutaneous trunci muscle on both sides of the dorsal midline, at the point of stimulation and cranially.  Absence of a response occurs one or two segments caudal to the spinal cord lesion.  This reflex must be interpreted with some caution; it may be unreliable with the exception of brachial plexus avulsion injuries, in which it is consistently absent only on the side of the avulsion (ipsilateral).  Clonus refers to a sustained after-contraction or quivering that may be seen or felt when performing spinal reflexes, especially patellar and crossed extensor reflexes.  The hand supporting the extremity being tested may feel this reaction; this reflex is often not visual.  Presence of clonus implies a chronic condition.  Presence or absence of deep pain perception is the most important prognostic test of the neurologic examination and is a reliable indicator of spinal cord integrity.  As a general rule….. sensory evaluation should be done last.  Itis performed by applying painful stimuli to each limb and the tail. A significant behavioral response (e.g., animal attempts to vocalize, turns to look or bite, or attempts to get away from the examiner) indicates the presence of sensation.  Withdrawal of a limb is NOT a behavioral response  Progressively stronger painful stimuli (e.g., hemostatic forceps) are used to assess presence or absence of deep pain perception. 1. Loss of proprioception. 2. Loss of voluntary motor function. 3. Loss of superficial pain sensation. 4. Loss of deep pain sensation.  Therefore,an animal with spinal cord compression that has lost proprioception and voluntary motor function, but still has superficial and deep pain sensation (paresis), → has less severe spinal cord damage One that has lost all four functions (resulting in plegia and paralysis).  Loss of deep pain indicates a severely damaged spinal cord and a poor prognosis.  Asan animal recovers from spinal cord injury, → sensation returns first, then motor function, and lastly proprioception.  Because of the prognostic importance of sensory examination, an evaluation of the animal by a second, unbiased examiner or a repeat of the examination in 1 or 2 hours is critical.  abnormally exaggerated subjective response to painful stimuli.  Hyperpathia is noted when pressure applied to spinous processes and paraspinal muscles of the thoracic and lumbar regions;  Transverse processes and paraspinal muscles of the cervical region results in pain and a behavioral response.  Hyperpathia is increasing pain after repetitive stimulation, which includes continued pain after the stimulus is gone, and pain that radiates to adjacent areas.  Pain perception occurs AT THE LEVEL of spinal cord involvement, making hyperpathia an accurate localizing feature of the neurologic examination.  Thoracolumbar and cervical hyperpathia; digital pressure placed over the  (A1) thoracolumbar paraspinal  (B) cervical paraspinal muscles at the site of an extradural lesion results in pain and a behavioral response from the patient (A2).  C, Pressure placed on epaxial muscles is transferred to the entrapped nerve root (inset), causing nerve root compression and ischemia; the result is pain and a behavioral response.  Sensorylevel is determined by pin-prick stimulus applied to the skin over the back, beginning in the region of the L7 vertebrae and continuing cranially.  The junction between an area of depressed behavioral response and one of normal behavioral response is the SENSORY LEVEL.  Pain perception is noted one or two segments caudal to the level of spinal cord involvement.  Sensory level is the junction between an area of depressed or absent sensation and area of normal sensation.  Because thoracolumbar nerve roots course caudoventrally, the sensory level is one or two vertebral bodies caudal to the spinal cord lesion.  Examination of cranial nerves is important, especially when a brain lesion is suspected.  The olfactory nerve is SENSORY for conscious perception of smell.  Most common causes for loss of olfaction: -Rhinitis -Tumors of the nasal passages -Diseases of the cribriform plate  The optic nerve is the SENSORY pathway for vision and pupillary light reflexes. It is examined by means of three major tests: 1. Menace response (elicited by making a threatening gesture with the hand at each eye) 2. Visual placing reaction 3. Ophthalmoscopic examination Abnormalities include loss of vision, dilated pupils, and loss of pupillary light response (direct and consensual) when light is shined in the affected eye.  Nerve that enables most of your eye movements, some aspects of vision, and raising the eyelid.  Lesions of the trochlear nerve cause lateral rotation of the eye.  The trigeminal nerve innervates muscles of mastication and is sensory to the face.  Motor function is tested by assessing muscle mass and jaw tone of the masticatory muscles. The jaw adductor muscles play the main role in the generation of bite force in dogs and cats.  Sensory function is assessed by checking pain perception of the face, eyelids, cornea, and nasal mucosa.  Bilateral motor paralysis produces a “dropped jaw” and muscle atrophy; unilateral paralysis results in unilateral atrophy of the temporalis muscle and decreased jaw tone and strength.  Aka. Abducent nerve  responsible for the abduction of the eyes on the same (ipsilateral) side. Responsible for causing contraction of the lateral rectus muscle to abduct the eye  The facial nerve is motor to the muscles of facial expression and sensory to the inner surface of the pinna, palate, and rostral two thirds of the tongue.  Facial paralysis generally causes facial asymmetry (e.g., lips, eyelids, and ears may droop) and loss of ability to blink or retract the lips.  The vestibulocochlear nerve has two divisions: 1. Vestibular (which provides information about the orientation of the head with respect to gravity) 2. Cochlear (which means hearing)  Abnormalities associated with nerve dysfunction include ataxia, head tilt, circling, nystagmus, and loss of hearing. "dancing eyes"  Swallowing is controlled by glossopharyngeal and vagus nerves.  The swallowing reflex is elicited by gentle external pressure on the hyoid region.  The gag reflex is elicited by insertion of the finger into the caudal pharynx.  The glossopharyngeal nerve is motor to pharyngeal muscles, and the vagus nerve is motor to pharyngeal and laryngeal muscles.  The vagus nerve is sensory to the caudal pharynx and larynx.  Abnormalities caused by glossopharyngeal and vagus nerve dysfunction include loss of the gag reflex, dysphagia, and laryngeal paralysis.  The hypoglossal nerve is motor to muscles of the tongue.  Abnormalitiescan be observed by wetting the animal's nose and observing its ability to extend the tongue.  Strength of tongue retraction, tongue deviation, and presence or absence of atrophy should be evaluated.  DETERMINE a single neuroanatomic location that explains all abnormal findings.  Thelesion is initially categorized as being located above or below the foramen magnum.  Lesions suspected of being ABOVE the foramen magnum are further localized to one of five locations in the brain: 1. Cerebral cortex 2. Diencephalon (thalamus and hypothalamus), 3. Brainstem (pons, medulla oblongata), 4. Vestibular 5. Cerebellum  Lesions suspected of being BELOW the foramen magnum are further localized to one of five locations in the spinal cord: 1. Cranial cervical (C1-C5) 2. Caudal cervical (C6-T2) 3. Thoracolumbar (T3-L3) 4. Lumbosacral (L4-S3) 5. Sacral (S1-S3)  Altered mental status  Ipsilateral circling, pacing, head pressing  Contralateral postural and proprioceptive deficits  Contralateral cortical blindness (normal pupils and pupillary light reflexes)  Contralateral UMN hemiparesis  Seizure  Altered mental status: aggression, disorientation, hyperexcitability, coma  Contralateral postural and proprioceptive deficits  Bilateral visual deficits  Abnormalities of eating, drinking, sleeping, and temperature (hypothalamus)  Mental status may be unaltered, to severe depression and coma  Ipsilateral UMN hemiparesis or tetraparesis; may circle if ambulatory Cranial nerve deficits involving cranial nerves V through XII  Trigeminal—motor and sensory (drop jaw/eyelid?)  Abducent—medial strabismus  Facial—facial paralysis  Vestibulocochlear—central vestibular signs; hearing loss  Glossopharyngeal/vagus—dysphagia, reduced gag reflex, laryngeal dysfunction  Hypoglossal—abnormal tongue movement  Vestibular Disoriented or unaltered mental status  Ipsilateral head tilt, circling, rolling, falling, asymmetric ataxia, and incoordination  Nystagmus (spontaneous or positional) with fast phase away from the side of the lesion  Ipsilateral ventrolateral strabismus  Must differentiate central from peripheral vestibular disease  Unaltered mental status  Ataxic gait, wide-based stance, dysmetria, head tremor, intention tremor, and truncal ataxia  Visual but may have ipsilateral loss of menace response  Hypermetric postural reactions, goose stepping gait  Muscle tone, segmental reflexes, and sensation are unaltered