Fourth Nerve Palsy

Hypertropia; Superior Oblique Paresis; Inferior Oblique Overaction; Fourth Nerve Palsy; Trochlear Nerve; Bielchowsky Test; Head TiltDouble visionThe patient is a 32 year old, left handed chemistry teacher who presented with intermittent vertical double vision. In August 1992 she noted, particularly late in the evening when reading in bed, vertical double vision. The images were one on top of the other and on occasions one image was slightly oblique. In September 1992 she consulted an ophthalmologist who documented a 2 diopter esotropia and hypotropia. She was prescribed prism reading glasses which helped. At the same time, she consulted a neurologist because her vision went out of focus after turning her head from side to side quickly. She denied headache and vertigo. Neurological examination by the consultant was normal apart from a "lag of abduction of the right eye". Brain MRI with and without gadolinium: Normal. Blood studies: Anti-acetylcholine receptor antibodies negative. Thyroid tests: Normal. In December 1992 she went to Nevada to see her mother. She consulted a neuro-ophthalmologist, Dr. Francis Grenn, a former post-graduate fellow of mine. Dr. Grenn obtained the history that when she changed the position of her head she could correct her diplopia. In bed at night if she tilted her head to the left, she had no double vision. She also had a single image with either eye covered. Diagnosis: Right fourth nerve palsy On return to Boston she came to the Neurovisual Clinic at the Massachusetts Genera Hospital. Symptomatic Inquiry: Negative for ptosis, bulbar muscle weakness or generalized weakness to suggest myasthenia gravis. Past History: Head trauma in 1978 when she was hit by a lacrosse ball and sustained a black eye and swelling of the right side of her face. She was stunned by the blow but not knocked out. It took several days for her to recover. During that time, she can not recall having double vision. No strabismus as a child and never wore prism glasses Family History: Father died of a myocardial infarct Mother had thyroid surgery for hyperthyroidism. Social History: Negative for alcohol abuse Non-smoker Neuro-ophthalmological examination: Visual acuity 20/25 OD 20/20 OS Visual fields, pupils and fundus examination normal. No ptosis No exophthalmos No ocular bruit Tests for diplopia: Slight right (ipsilateral) head tilt Absent stereopsis in the reading, downgaze position 1/3 animals in primary gaze Good stereopsis 4/6 circles with prism glasses Cover/uncover test: Hypertropia OD primary gaze Hypertropia most marked with right head tilt Hypertropia diminished, almost absent, left head tilt Hypertropia almost fully corrected with prism glasses at distance. Ocular Motility OD: Hypertropia and excyclotorsion Superior oblique (SO) paretic Inferior oblique (IO) overaction with elevation of the globe looking left. Cranial nerves 3 and 6 normal Ocular Motility OS: Full eye movements Hypotropia on cover/uncover test CT of the Orbit: Normal. Bone windows, no evidence of fracture Review of her old photographs The patient's old soccer photograph showed her with a slight head tilt to the right. This observation helped to establish a diagnosis of a longstanding post-traumatic fourth nerve palsy. Treatment: Strabismus surgery was discussed with the patient but she elected to wear prism glasses. In January 1997 she returned to consult the strabismus surgeon again but still elected to wear prism glasses.This tape records the "diplopia" history. The patient answers a list of specific questions with regard to her vertical double vision from a right fourth (trochlear) nerve palsy. She had no diplopia with one eye covered confirming binocular diplopia. With a history of vertical diplopia, attention is paid to the ocular muscles controlling vertical gaze. • SO: Paresis SO resulted in impaired downgaze in the adducted position with absent incyclotorsion of the eye • IO: Overaction of IO with elevation of the eyeball on gaze left, in the adducted position Alternate cover test: OD moved down to take up fixation (hypertropia) OS moved up to take up fixation (hypotropia) Two simple techniques which aid in the analysis of vertical diplopia are shown on this tape. 1. Viewing a horizontal bar The patient is seated in front of a black screen to view a horizontal bar (opaque line of tape). She confirms that she is seeing two images slanted with respect to each other, with the apparent intersection of the lines pointing toward the side of the affected, excyclodeviated eye. In this patient with a right fourth nerve palsy, the point of intersection is to the right. 2. The Lancaster red/green test requires the patient to wear a pair of red/green goggles, red lens OD, green lens OS. The patient holds a projector that places a red line on the screen. The examiner holds a projector that places a green line on the screen. The patient is directed to place the red line on top of the green line with her head in primary gaze, with head tilted to the right and with head tilted to the left - Bielchowsky head tilt test. The test was positive - there was no separation of the images on head tilt to the contralateral (left) side. An old soccer picture of the patient attached shows a very subtle right head tilt indicating the chronicity of the fourth nerve palsy. Two photographs of another patient, with a left fourth nerve palsy, first when quite young with his golf partners and then years later at a cocktail party, show a right contralateral head tilt. The clinical diagnosis in this case utilized the Three-Step Test. Step 1 - Identify which eye is hypertropic e.g. hypertropia OD. Step 2 - Determine whether the hypertropia increases on right or left gaze Step 3 - Bielchowsky's head tilt test: Tilt the head to the right and to the left. Hypertropia is maximized as the head is tilted toward the side of the lesion and minimized on contralateral head tilt, as in this case. The most reliable clinical test to diagnose fourth nerve palsy is the Bielchowsky's head tilt test. During right head tilt, the right eye incyclotorts (SO and SR), and the left eye excyclotorts (IO and IR) During left head tilt, the right eye excyclotorts (IO and IR) and the left eye incyclotorts (SO and SR). The question always asked is why does the hypertropia increase on right head tilt in right fourth nerve palsy. The explanation is as follows: During right head tilt, the otolith-ocular reflex (ocular counter roll) is activated, such that the right eye incyclotorts (SO and SR) and the left eye excyclotorts (IO and IR). The primary action of SO is incyclotorsion, and its secondary action depression, whereas the primary action of SR is elevation and its secondary action is incyclotorsion. Thus, normally, during the right head tilt, the net movement of the right eye is incyclotorsion with minimal vertical movement because the vertical action of the SO and SR cancels each other out. In a right fourth nerve palsy, the elevating action of SR is unopposed by the palsied SO; thus, the hypertropia increases during right head tilt. Differential Diagnosis: 1. Skew deviation 2. Thyroid-related ophthalmopathy 3. Brown's Syndrome 4. Primary inferior oblique overactionNo imaging studies are available in this patient. In patients who lack a history of head trauma, Brain MRI may show relevant brainstem lesions and gadolinium enhancement usually demonstrates infiltrative or inflammatory processes involving the long course of the fourth nerve. Often the cause of the fourth nerve cannot be ascertained. These patients require long term follow-up.The nucleus of the fourth (trochlear) nerve lies at the ventral border of the periaqueductal gray matter at the level of the inferior colliculus in the brainstem. It lies at the dorsal margin of the medial longitudinal fasciculus. The fascicle of the fourth nerve crosses the midline at the anterior medullary vellum (anterior floor of the fourth ventricle, before exiting the brainstem) thus, the right fourth nerve fascicle becomes the left fourth nerve which innervates the left superior oblique muscle. The fourth nerve is the only cranial nerve that exits the brainstem on the dorsal surface and it has the longest intracranial course (approximately 75mm). In the subarachnoid space the nerve curves around the lateral surface of the upper pons, passing between the superior cerebellar and posterior cerebral arteries to reach the prepontine cistern. It then runs forward on the free edge of the tentorium for 1 to 2 cm before penetrating the dura of the tentorial attachment and entering the cavernous sinus. Within the lateral wall of the cavernous sinus, the nerve lies below the third cranial nerve and above the ophthalmic division (V1) of the fifth (trigeminal) nerve. It then crosses over the third nerve and receives filaments from the carotid sympathetic plexus. To reach the orbit the nerve enters through the superior orbital fissure above the annulus of Zinn. In company with the frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve. It divides into several small fascicles that innervate the superior oblique muscle.TraumaTrauma is the commonest cause of a fourth nerve palsy. Head trauma can result in a contusion or hemorrhage of the tegmentum at the junction of the midbrain and pons. Because of the short course of the fourth nerve fascicle in the brainstem, distinguishing a nuclear from a fascicular fourth nerve palsy is virtually impossible. Damage to the descending sympathetic fibers from the hyperthalamus in the dorsal brainstem, causes a Horner's syndrome, and lesions of the trochlear nucleus or fascicle may be accompanied by a Horner's syndrome. For example, a right sided midbrain lesion causes damage to the right trochlear nucleus (resulting in a left fourth nerve palsy) and damage to descending sympathetic fibers results in a right Horner's syndrome. If the lesion affects the fascicle of the fourth nerve as it crosses the midline, then the Horner's syndrome is on the same side as the fourth nerve palsy.1. Occlusion 2. Prism glasses 3. Strabismus surgery only after the palsy has been stable for at least six months using one or a combination of the following procedures: a) Weakening of the ipsilateral inferior oblique (the antagonist of the affected superior oblique) b) Weakening of the contralateral inferior rectus (the yoke muscle of the affected superior oblique) c) Strengthening the affected superior oblique1. Arruga J, DeRivas P, Espinet HL, Conesa G. Chronic isolated trochlear nerve palsy produced by intracavernous internal carotid artery aneurysm. J Clin Neuro-Ophthalmol 1991;11:104-108. http://www.ncbi.nlm.nih.gov/pubmed/1832682 2. Brazis PW, Lee AG. Binocular vertical diplopia. Mayo Clin Proc 1998;73:55-66. http://www.ncbi.nlm.nih.gov/pubmed/9443680 3. Cackett P, Fleck B, Mulhivill A. Bilateral fourth nerve palsy occurring after shaking injury in infancy. J AAPOS 2004;8:280-281. http://www.ncbi.nlm.nih.gov/pubmed/15226732 4. Gentry LR, Mehta RC, Appen RE, Weinstein JM. MR imaging of primary trochlear nerve neoplasms. Am J Neuroradiol 1991;12:707-713. http://www.ncbi.nlm.nih.gov/pubmed/1882749 5. Jacobson DM, Warner JJ, Choucair AK, Ptacek LJ. Trochlear nerve palsy following minor head trauma. A sign of structural disorder. J Clin Neuro-ophthalmol 1988;8:263-268. http://www.ncbi.nlm.nih.gov/pubmed/2977142 6. Keane JR. Fourth nerve palsy: historical review and study of 215 inpatients. Neurology 1993; 43:2439-2443. http://www.ncbi.nlm.nih.gov/pubmed/8255437 7. Leigh JR, Zee DS. Diagnosis of Peripheral Ocular Motor Palsies and Strabismus. Chp 9;385-474. In: The Neurology of Eye Movements, 4th Edition. Oxford University Press 2006. 8. Lepore FE. Disorders of ocular motility following head trauma. Arch Neurol 1995;52:924-926. http://www.ncbi.nlm.nih.gov/pubmed/7661732 9. Richards BW, Jones FR, Younge BR. Causes and prognosis in 4,278 cases of paralysis of the oculomotor trochlear and abducens nerves. Am J Ophthalmol 1992;113:489-496. http://www.ncbi.nlm.nih.gov/pubmed/1575221 10. Schievink WI, Mokri B, Garrity JA, Nichols DA, Piepgras DG. Ocular motor nerve palsies in spontaneous dissection of the cervical internal carotid artery. Neurology 1993;43:1938-1941. http://www.ncbi.nlm.nih.gov/pubmed/8413949curriculum_fellow; MTemspfourthtrochlear; MTneurodisfourthtrochlear; VBbraininjury; NOTE-EXAMCN34