Top of the Basilar

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opinions 8. reviewsArticle abstract-Infarction of rostral brainstem and cerebral hemispheral regions fed by the distal basilar arte rycauses a clinically recognizable syndrome characterized by visual, oculomotor, and behavioral abnormalities, oftenwithout significant motor dysfunction. Rostral brainstem infarction produces oculomotor and pupillary signs thatare identical to those in thalamic hemorrhage. Somnolence, vivid hallucinations and dreamlike behavior may alsoaccompany rostral brainstem infarction. Temporal and occipital infarctions are frequently accompanied byhemianopia with distinctive characteristics, fragments of the Balint syndrome, amnestic dysfunction, and agitatedbehavior. The top of the basilar syndrome is most often due to an embolus.

NEUROLOGY 30: 72-79, January 1980

'"rap of the basilar syndromeLouis R. Caplan, M.D.

Occlusive vascular disease of the rostral basilarartery frequently causes infarction of midbrain,thalamus, and portions of the temporal and occipi-tal lobes fed by posterior communicating and pos-terior cerebral arterial tributaries of the basilarartery. Clinical signs include an array of visual,oculomotor, and behavioral abnormalities, usu-ally without prominent motor dysfunction, whichmay confuse those inexperienced with these find-ings. Segarra used th e term the syndrome of th emesencephalic artery to describe rostral parame-dian brainstem infarction, and analyzed one typeof behavioral manifesta t ion (somnolentmutism). Others have described clinicopathologicaspects of isolated neuroophthalmologic2~1s ndb e h a v i ~ r a l l ~ ~eatures. This report, based princi-pally on experience from personally examinedcases with autopsy, computerized tomography(CT), or angiographic verification, reviews themajor clinical features. Aspects of the syndromeconsidered in detail elsewhere (e.g., memory10ss20,22333-Mnd alexia without agraphia? ar egiven only passing attention. The top of th e basi-lar syndrome is a recognizable subdivision th atcan be distinguished from the large group of heter-ogeneous conditions usually lumped togetherunder the term vertebrobasilar ischemia or in-sufficiency.Infarction of rostral brainstem and posteriorhemispheres often coexists because of th e commonvascular supply. However, because either mayoccur in isolation, it is appropriate to considerbrainstem and hemisphere manifestations sepa-rately.Part I. Rostral brainstem nfarction.Visual de-fects Disorders of ocular movement. Oculomotordysfunction in patients with bilateral ischemia of

rostral midbrain and posterior thalamus is indis-tinguishable from th at i n patients with thalamichem0rrhage.~5*~~he signs include:Disorders of vertical gaze. Voluntary or reflexvertical gaze (tested by oculocephalic and caloricmaneuvers and Bell phenomenon) is 6ftenabolished. One or both eyes may rest in a down-ward position. Isolated paralysis of upward ordownward gaze occurs less frequently. In humanpatients with vertical gaze paralysis due to vascu-la r disease, bilateral lesions are found in the mid-brain t e g m e n t ~ m . ~ . 1 l * ~ ~n monkeys and hu-mans,411 esions of the pretectum, in th e region ofthe posterior commissure, are necessary to pro-duce paralysis of upward gaze. solated downwardgaze palsy is rare, and may be associated withlesions medial and dorsal to the red nucleus;**elesions causing paralysis of downward gaze aremore ventral and caudal in th e midbrain tegmen-tu m tha n those responsible for deficits of upwardgaze.Disorders of convergence. One or both eyes mayrest in an inward position. Hyperconvergence orconvergence spasm may be observed when th e pa-tient at tempts conjugate latera l or vertical gaze.Convergence retraction n y s t a g m ~ s , ~ ~rhythmicinward beating movement of the eyes, may bespontaneous, but is best elicited by having thepatient fix on an optokinetic stimulus which ismoving upward.

Pseudosixth. This sign, described by Fisher,%refers to failure of ocular abduction which is notdue to dysfunction of th e sixth nerve. The sign isfrequently bilateral and is accompanied byhyperconvergence.Failureof the eye toabduct isdue to two mechanisms: (1)Fixation with thehyperconvergent eye (the right eye in figure 1).When the hyperconvergent eye is covered,~ ~

From the Department of Neurology, Beth Israel Hospital, and Harvard Medical School, Boston, MA.Accepted fo r publication Jun e 11,1979.Address reprint requests to Dr.Caplan, Chairman, Department of Neurology, Michael ReeseHospital, 29th and Ellis Streets. Chicago, IL 60616.

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Figure 1 . Pseudosizthphenomenon. (A) Forwardgaze. Right eye is down an d in; le f t eye is neutral.(B ) Conjugate gaze to the left. Ri gh t eye convergesstrongly. Left eye fails to abdu ct fully and a ddu ctingjerks are visible.

monocular fixation by the abducting eye on a dis-tant object far to the side may elicit further abduct-ing movements. (2) Convergence vectors are alsopresent in the abducting eye and neutralize orcounteract conjugate lateral movements. If theabducting eye is watched carefully, convergenceo radducting jerks of the abducting eye are oftenpresent.Elevation and retraction of the upper eyelids(Collier sign)5 may be unilateral or bilateral;GStraction of one eyelid may contrast with a droop ofthe opposite lid.Sudden darting or l ightning -like oscillations ofthe eyes may complicate horizontal or verticalgaze.Skew d eviat ion (ocular divergence in the verti-cal plane) has been documented in lesions of themiddle cerebellar peduncle and r n e d ~ l l a . ~ ~ . ~ QMidbrain skew has been inferred by Smith,David, and Kl i n tw ~ r t h ~ ~ecause of accompanyingsigns of dysfunction of the pupils and third nervebelieved clinically localizedto the periaqueductalgray region of the midbrain. Autopsy verificationof a rostral brainstem cause of skew deviation isuncommon, but is provided by cases 1 to 3 (de-scribed below).Vertical nystagmus,* conjugate horizontal nys-tagmus, and ocular bobbing are not associatedwith high brainstem infarction.When infarction is more caudal and includes themidbrain tegmentum ventral to the aqueduct,internuclear ophthalmoplegia o r third-nerve pal-sies are present. Bilateral infarction of the thirdnerve nucleus and adjacent reticular formationcauses hypersomnolence and third nerve pal-sies,24.= difficult to distinguish clinically from thebrainstem dysfunction of transtentorial hernia-tion. The sudden onset and the absence of severeheadache, vomiting, or hemiplegia prior to the ap-pearance of stupor are characteristics of primary

midbrain infarction which help to distinguish thetwo entities. Computerized tomography (CT) oc-umenting the absence of a supratentorial space-taking lesion is often a necessary corroborativediagnostic procedure. A unilateral lesion of thethird nerve nucleus may cause severe bilateral~tosis .~*Pupils. Diencephalic dysfunction may interruptthe afferent limb of the pupillary light reflex arc.13Bilateral sympathetic dysfunction usually accom-panies the lesion, so that the pupils are small andthe reaction to light is often transient and of smallmagnitude. A magnifying glass may be needed t oseparate the tiny, poorly reactive pupils ofthalamic disease from small, reactive pontinepupils. With lesions more caudal in the midbrain,large o r midposition fixed pupils are caused bydysfunction of the Edinger-Westphalnucleus or itsfibers.The pupil can quickly assume an eccentric posi-tion in the iris, a phenomenon called corectopiairidis. The pupil may shift from a central positionto an eccentric one intermittently, a sign charac-teristic of midbrain lesions12*14Three examples of rostral brainstem infarctionillustrate the neuroophthalmologic findings.Case 1. An elderly diabetic woman suddenly becamesleepy and unresponsive. Her left eye was deviated lat-erally and the left pupil was midposition and fixed. Theright eye was deviated down and in, and had frequentconvergent inward movements. Neither eye moved ver-tically (either voluntarily or reflexly). On attemptedconjugate lateral gaze, each eye could abduct but did notreach the lateral canthus. The right pupil was 2 mm andhad a transient and minimal reaction to light. Righthemiplegia, hypesthesia to pinprick on the right half ofthe body, and bilateral Babinski signs were present.Postmortem examination revealed a fresh organizingmyocardial infarction. There was a n old cystic infarctionin the right caudate nucleus, putamen, and internalcapsule. A fresh necrotic lesion (figure 2) due to embolicinfarction involved the distribution of the left superiorcerebellar and left posterior cerebral arteries. The re-gion of the left third-nerve nucleus in the midbrain,periaqueductal gray region, red nucleus and cerebralpeduncle were infarcted. The left superior cerebellarsurface wasalso infarcted. There was a tiny infarction inthe left ventrolateral thalamus.Case 2. An 81-year-old woman suddenly believed thelights had been shut off while she was reading. Therewas complete bilateral ptosis; she could not open eithereye. Pupils were 2 mm, and pupillary light reaction wasslight, delayed, and transient. The eyes were deviatedconjugately to the right with sl ight downward position-ing of the left eye. Right conjugate gaze was full; on leftgaze, there was slight adduction of the right eye and onlyminimal abduction of the left eye. There was no verticalgaze. She was hypersomnolent for 1week and exhibitedtransient right visual inattention.Postmortem examination in another hospital yearsafter the stroke revealed a cavitary lesion of the mid-

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brain involving the right third nerve nucleus, right me-dial longitudinal fasciculus and right fourth nerve re-gion and some of the medial right red nucleus dorsally.The lesion extended to the midline dorsal structures, butspared the left third nerve region and the ventral re-gions of the brainstem.Case 3.After 4 days of dizziness and unsteady gai t, an80-year-old woman suddenly collapsed. The r ight pupilwas 2 mm and fixed. The eyes did not move past themidline to the right on oculocephalic or caloric stimuli,but these maneuvers elicited full left gaze. Vertical gazecould be elicited by oculocephalic reflexes. There was aright hemiplegia, right hemisensory loss and righthemianopia. She remained mute. Subsequently, theright eye moved to a down and in position and, on rightgaze, the right eye did not abduct as well as the leftadducted, but conjugate gaze to the right was possible.Postmortem examination revealed occlusion of therostral basilar artery with thalamic and midbrain in-farction and bilateral posterior cerebral artery territoryinfarction, more extensive on the left.

Behavioral abnormalities. Somnolence. Sleepiness, apathy, and lack of attention to the environ-ment result from infarction of the rostral medialreticular formation due t o occlusion of themesencephalic artery (the proximal portion of the

posterior cerebral artery) or its penetratingbranches. Facon, Steriade, and WertheinZ4 de-scribed a patient with bilateral third nerve palsieswho remained in a sleeplike state for 3 years.Postmortem examination revealed occlusion of thetop of the basilar artery and a paramedian infarc-tion in the midbrain and anterior thalamus. Cas-taigne and associatesz5described a patient with abutterfly-shaped infarction destroying in-tralaminar nuclei, the medial part of the centrummedianum, third nerve nuclei and part of thebrachium conjunctivum; hypersomnolence andophthalmoplegia were the major findings.Segarral used the term somnolent mutism t ocharacterize the behavior of patients with highmedial brainstem infarction and contrasted it withthe coma vigil of patients with bilateral cerebrallesions.Peduncular hallucinosis. Hallucinations occurbut are rare in patients with high brainstem in-farction. They may occur without visual field de-fects. These hallucinations are usually vivid andwell-formed. One patient with a clinically unilat-eral midbrain and thalamic infarction saw a col-ored parrot with beautiful plumage off to his right,and another patient with episodic posteriorhemispheral ischemia awakened at night and saw




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pictures of his grandmother flashed on the wall tohis left, as if projected in a home movie. Rarely, thesame patient heard a knocking noise, as if rockswere in a car engine. Though vivid to the patients,the hallucinations were always recognized assomehow not real.The term peduncular hallucinosis was used ina review by van Bogaert32to describe strange hal-lucinations, usually visual, in patients with mid-brain lesions. (The term pdonculaire, when usedin this context, refers to the midbrain, not neces-sarily the cerebral peduncle.) Anatomic verifica-tion of this phenomenon is scanty. Lhermitte,27who w as the first to introduce this term, describeda patient in detail. A 72-year-old woman com-plained of vertigo and subsequently developedheadache, vomiting, and bilateral sixth nerve pal-sies. Left ophthalmoplegia, a left central scotoma,and intention tremor of both arms subsequentlydeveloped. She had vivid hallucinations ofan im al s- ca ts and chickens, with strange appear-ances. She also saw children at play with toys. Achild would suddenly change into an old woman.She would try to touch the images, but was awarethat they were not real. She also had insomnia a tnight and slept a great deal during the day. Hal-lucinations occurred only during late daylighthours, especially at sundown. There was noanatomic verification, but the lesion was thoughtto be a vascular brainstem lesion. Alajouanine,Thurel, and DurUptz1 described another patient,studied only clinically-a young man with a sud-den hemiplegia and hemianesthesia followingamputation of a n infected limb. Nystagmus andophthalmoplegia indicated a brainstem lesion. Hesaw blood and red hair descending toward the bed,and had vivid imaginings of being verticallyplaced on an ambulance bed amid animals. Thiswas a febrile, ill patient, again without anatomicverification.A single pathologically verified case of peduncu-lar hallucinosis concerneda patient with a clinicallesion of the red nucleus31 who died 14 monthslater.32 A 59-year-old woman with rheumaticheart disease developed vertigo, double vision, andataxia. The major findings were a right third nervepalsy, dysmetria of the left limbs, left hyperre-flexia, and gai t a taxia. From the onset, she hadvivid hallucinations accompanied by severe agita-tion. The hallucinations always occurred in theevening; she remained calm and unaffected duringthe day and the remainder of the night. On thewall opposite her , she would see the head of a dogor a n image of a horse or a green serpent against ared background. The images appeared and disap-peared and were never fixed. Intricate lines, oddcolors, and images persisted for 1 to 2 hours, andthen ceased. A t postmortem examination 14months later,32 an infarct was seen in the leftmidbrain, primarily affecting the superior cerebel-

lar peduncle, cerebral peduncle, substantia nigra,red nucleus, and periaqueductal gray region.Baruk40 and Reeves and Plum41 commented thatother lesions along the base of th e brain, affectingthe diencephalon and midbrain, could precipitatehallucinations.The pathologic anatomy and physiology of thesehallucinations is not clear; they may be related toan abnormality of nonspecific cortical excitation(reticular formation), or abnormal stimulation ordeafferentation of specialized thalamic nuclei(e.g., lateral geniculate). Similar visual hallucina-tions in the evening (sundowning) are commonin elderly patients without cerebrovascular dis-ease.Fischer-Perroudon, Mouret, and J o u ~ e t ~ ~e-ported a patient with distal limb pain and diarrheain whom polygraphic EEG recordings confirmedtotal insomnia. Dramatic hallucinations occurredonly between 9 and 11P.M.The hallucinations dis-appeared aft er admin istra tion of 5-hydroxy-tryptophan had caused a return to normal sleep.No central nervous system lesions were foundon postmortem examination.An abnormality of sleep may be the essentialfactor, and w a s present in our patients withhallucinations and in those previously reported.More detailed clinicopathologic correlation isneeded to verify the origin and nature of thisphenomenon. The pathologic anatomy responsiblefor this type of hallucination is probably notlimited to the midbrain alone.Unusu al reports. Pat ie nts with rostra1brZnsteminfarEtiCn may reply in a bizarre way toqueries requiring orientation. For example, onebedridden patient, when asked her whereabouts,replied tha t she was on the beach at Nice sunningherself in a bikini. Another pat ient excused herselffrom replying to a question because she was speak-ing to some friends on the telephone, and pro-ceeded to hold a n imaginary phone before her as fto speak. These reports are similar to those givenby patients with metabolic encephalopathy orfrontal lobe disease.The unusual reports have had the followingcharacteristics: (1) hey are influenced by stimuli,e.g., pictures or preceding conversation in a pa-tients room. A patient in whose room a nativepicture by Gauguin hung on the wall reported tha tshe was in Tahiti. Another patient , when conver-sation nearby concerned travel, reported she wason an airplane. (2)They have no approximation toreality. Patients with amnestic disorders such asthe Wernicke-Korsakoff syndrome ar e frequentlynot oriented exactly to place, but they generallygive an approximate answer after looking aboutfor clues. For example, in a hospital they will sup-ply the name of a medical facility with which theyare familiar. The patient with high brainstem dis-ease frequently replies without exploring the en-

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vironment, and answers are bizarre. (3)Observa-tions or questions of th e interviewer are incorpo-rated into the reply. For example, a patient re-ported that he was driving a car headed towardBeacon Street. When asked who the questionerwas, he replied, You are a policeman, and youmust get out of th e way of the car or you will behit. Patients with unusual reports have all haddisturbances of wakefulness, characterized byperiods of sleep or drowsiness. Stuss and as-s o c i a t e ~ ~ ~onsider this an extraordinary form ofconfabulation; their patients all had frontal lobedisease and the confabulation was attributed toaltered frontal lobe function.Some patients with this phenomenon of un-usual reports have commented th at they dreama lot and often cannot tell dreams from reality.Patients recovering from general anesthesia andnormal individuals awakening from sleep fre-quently have difficulty determining if a mentalconcept arose from an actual event or from adream. Even in the fully awake, normal indi-vidual, thoughts somewhat extraneous to thepractical matters at hand are frequent distrac-tions. The prose of James Joyce and Virginia Woolfcontains easily recognizable examples of thestream of consciousness th at is familiar to all of us.The unusual reports and dreams are equallycharacterized by suggestibility from environmen-tal factors and frequent absurdity. The anatomicsubstratum that helps us separate dreams orthoughts from reality is unknown. The appearanceof dream confusion in sleeplike twilight sta tes andanesthesia suggests a disturbance of nonspecificalerting systems, e.g., the reticular activating sys-tem and thalamic nuclei stimulating hemispheralregions. This could explain the presence of thesereports in disease of either brainstem or cerebralhemispheres. Unusual reports, somnolence, andhallucinations may all be related signs of dysfunc-tion of the rostra1 reticular formation of thebrainstem.Part 11. Posterior cerebral artery territoryhemisphere infarction. A. Unilateral infarc-tion. Visual defects.Hemianopia. A homonymousfield defect may result from a lesion anywhere inthe visual radiation, from optic tract to calcarinecortex. Several features identified in 15 cases ofCT-confirmed unilateral occipital infarction werecorrelated with lesions in or near the calcarinecortex within the posterior cerebral distribution,as opposed to more anteriorly placed lesions inthe territory of the middle cerebral artery.Awareness of the visual deficit. Patients withposterior cerebral artery lesions often complain ofa void or blackness to one side. In middle cerebralartery parietal lesions, the field deficit is usuallyaccompanied by visual neglect, and the visual de-fect is usually not noticed o r acknowledged by the

patient.Preservation of optokinetic nystagmus. Cogansrule tha t optokinetic nystagmus is lost in an occip-ita l lobe mass lesion but preserved if the occipitallobe lesion is vascularu holds up well. Temporal orparietal lesions in middle cerebral artery territoryar e usually associated with loss of optokinetic nys-tagmus to the side of the hemianopia.Partial vision within a hemianopic field. Pa-tients with a calcarine infarction may, on occasion,identify the color, nature or size of an object withinthe blind field; in lesions of the middle cerebralartery territory that interrupt the visual radia-tion, vision is usually all-or-nothing.Homonymous but differing involvement ofsuperior and inferior quadrants in a hemianopicfield. This imdies uneaual involvement of bothIanks of the chcarine fiisure and is less commonin patients with lesions of the optic radiations.Scintillations at the edge of a hemianopic field.Patients with occipital lesions frequently note

poorly formed scintillations in the hemianopicfield as a presenting symptom of posterior cerebralartery occlusion.2 Scintillations also occur whenthe defect is clearing and usually involve the par-tially affected edge of the hemianopic field. Theyare so commonly seen (5/15 patients) t hat I usuallywarn the patient not to be concerned if they ap-pear.Visual perseverations. Perseverations may takeone of several forms. (1)Seeing a n object repeatedtoward the hemianopic side; a train of individualsmay seem to be repeating within the affected field.(2) If the patient looks toward the hemianopicfield, he may continue to see an image th at hadpreviously been in front of him. (3)Persistence ofan image in the center of the field of vision afterthe image has moved. The first two types of visualperseveration have been seen in patients withposterior cerebral artery disease and are not a partof dysfunction due to lesions within the middlecerebral zrtery territory.Absence of visual neglect. Patients with occipitalinfarction do not usually neglect the hemianopicfield. They read a full paragraph or headline, copya full diagram if given time, and do not neglect oneside of space when asked to bisect lines. At theonset of the deficit, however, especially if objectsare shown tachistoscopically and quickly, theremay be a transient tendency to neglect part of thevisual field.Behavioral defects.Left occipital infarction maybe accompanied by anomic aphasia,22 lexia with-out agraphia,22a temporary Korsakoff-like am-nestic syndrome, 1oao*22 or visual a g n o ~ i a . ~ ~ ~ ~ ~ .Right occipital infarction has been associated withthe Charcot-Wilbrand syndrome of defective revi-sualization and absence of visual dreaming andapros~pagnosia ,~~hough the latter is generallyassociated with bilateral infarction. These syn-




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dromes have been reviewed el~e wh er e. 1~B. Bilateral infarction. Visual defects. Corticalblindness. Cortical blindness is the most severevisual defect caused by bilateral occipital infarc-tion. Symonds and Mackenzie 8 reviewed clinicaland pathologic aspects of this syndrome and iden-tified embolus as the most common vascular etiol-o n .The Balint syndrome. Elements of the Balint~ p X m e l 5 . ~ ~re frequently found in infarcts ofthe territory of both posterior cerebral arteries.The major characteristics are:Asimdtagnosia, or difficulty viewing the wholevisual field at once. Patients mav see thingspiecemeal and identify a part insteadof the whok.Useful techniques to elicit this phenomenon in-clude asking the patient to: (1) enumerate thenumber of objects on a paper (letters, words, cross-es, or circles), (2) identify a number of objectsshown simultaneously, (3) explain the action in acartoon or picture, and (4 ) read a paragraph. Pa-tients with the Balint syndrome usually cannotread a paragraph because they omit words orwhole lines. They can, however, read individualwords and letters, in contrast to patients withalexia without agraphia. They may have consider-able difficulty describing the action in a picture orcartoon, or comparing parts of a picture.Optical apraxia, or poor hand-eye coordination.Patients may do better with hand motions whennot under visual control, e.g., touching the hand tothe nose with eyes closed. racing a line diagramor pointing toa precise par t of an object in a pictureare useful in studying this problem.aze. These patients cannot lookw*re t ey esire. Ask the patient to look at oneobject and then direct gaze to another. Watch thepatient observe a picture or scene.Balint syndrome may occur without major fielddefects on tangent screen or perimetry. The nor-mal person perceives a central percept and thensearches the visual environment to amplify infor-mation concerning tha t initial cue. This leads tofurther perception and further searching.33Look-ing and seeing are related functions, but with dif-ferent anatomies. In the patient with the Balintsyndrome, the anatomic connections between oc-cipital and parietal lobes are disrupted, impedingfine interactions between perception and looking.Metamorphosia. Alteration in size, shape, orangulation of objects is an infrequent feature ofcerebrovascular lesions. When it occurs, it isnearly always associated with bilateral occipitalor occipitotemporal lesions. Patients may com-plain of enlargement (macropsia) or diminution(micropsia) of objects. The size a lteration may belimited toone half-field or quadrant, giving objectsa grotesque appearance. Patients may be unable torecognize distance relationships of objects within

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the environment and may have diffkulty compar-ing distant objects with respect to size and depth.Other patients have complained of sharp angula-tion of objects, with the room appearing turned orupside down. When not related to an ocular muscledisorder causing vertical diplopia, this alwaysmeans a posterior hemispheral lesion.Behavioral abnormalities. Memory. Defects inthe acquisition of new information and memoryoccur in patients with bilateral infarction of themedial temporal lobe^.^^.^^ In addition, a unilat-eral left temporal lesion may be responsible for aKorsakoff-like syndrome which may be tempo-rary, last ing for hours or up to 6 months.i0*20*22Agitated delirium. Patients with bilateral le-sions in the distribution of the posterior cerebralarteries occasionally appear agitated and hyperac-tive, a state resembling delirium tremens. I haveseen agitated delirium associated with bilateralvisual defects in several patients with establishedposterior cerebral artery infarction, and in pa-tients with an adverse reaction to vertebral an-giography. In the patients with angiographic reac-tions, the vertebral, basilar, and posterior cerebralarteries were widely patent and the agitated de-lirious s t a t e was accompanied by visual and mem-ory defects. Within 24 hours, the entire syndromecleared, leaving amnesia which extended retro-grade to the period prior to the angiography andanterograde to t he point of clearing.Horenstein, Chamberlin, and ConomyZ6 de-scribed nine patients with infarction of the under-surface of the temporal and occipital lobes whosebehavior included restlessness, agitation, forcedcrying out and easy distractability with exagger-ated responses to visual, auditory, or tactilestimuli. The infarction involved calcarine,fusiform, and lingual gyri in all patients and, insome, the lesion extended to the medial hippocam-pal complex; in six patients, the lesions were uni-lateral and, in three, bilateral. Medina and as-s o c i a t e ~ ~ ~ * ~ ~lso described severe agitation in pa-tients with visual field defects; the syndrome re-mitted within days to 2 months.Motor and sensory defects. Sensory loss accom-panying posterior cerebral artery territory infarc-tion is often profound, with severe loss of touch,posi t ion, and pain apprecia t ion. Despi tesomatosensory deafferentation, the patientssurprisingly retain ability to use the limbs andfrequently walk well. Objects are usually droppedfrom the hand without the patient realizing theloss. Loss of proprioception makes voluntarymovement variable; when strength is formallytested, the patient may fail to perform the move-ment requested, or fail to exert power against re-sistance. If the examiner is patient and awaits thedesired movement, normal strength can often beestablished. When the patient is asked to hold thearm outstretched with eyes closed, the arm exhib-




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iting sensory loss commonly rises or levitates incontrast to the downward drift which accompaniespyramidal system weakness. Some patients havecommented that the a rm or leg seems to be mov-ing on its own, and it is occasionally perceived asdead or separate from the body. One patient with alarge posterior cerebral artery territory infarctionwas surprised to learn tha t a blow to her face hadbeen delivered by her own hand, unwilled andunrecognized.Lesions limited to the ventroposterior-lateralnucleus of the thalamus, as in pure sensorystroke,46 usually cause numbness or pares-thesias without important objectively demonstra-ble loss of perception. Lesions limited to the lateralt h a l a mu s i n t h e d i s t r i b u t i o n of t h ethalamogeniculate arteries cause unilateral limbataxia, clumsiness, and chorea, in addition tovariable sensory loss. The motor disorder isproba-bly related to dysfunction of the ventral anteriorand ventrolateral nuclei and their connectionswith efferents from the cerebellum and ex-trapyramidal systems.Patients with lesions limited to the lateralthalamus usually do not have the severe deaffer-entation seen in patients with a larger posteriorcerebral artery territory infarction or thalamich e mo r r h a g e , l e s i o n s t h a t i n t e r r u p t t h ethalamoparietal radiations.Motor paralysis is uncommon in patients withocclusion of the posterior cerebral artery. Thesepatients usually retain their ability to make finedistal movements, and do not usually have hyper-reflexia, clonus, or extensor plantar reflexes.However, facial weakness is common and may berelated to decreased tone of the facial muscles.Occasional patients with involvement of the veryproximal posterior cerebral artery may have aninfarction of the cerebral ped~ncle,~o tha themiplegia accompanies the usual hemianopiaand hemisensory loss.Discussion. This review has focused on the detailsof the neurologic abnormalities of patients withtop of the basilar territory infarction. The locusof brain dysfunction was corroborated by CT scans,which showed radiolucent lesions in the medialoccipital or inferior temporal lobes (15unilateral,5 bilateral), or by autopsy (5). Unfortunately, inour own series and in those described in the litera-ture, the precise locus and mechanism of the vas-cular compromise is often uncertain. Most patientshave not had full angiography. At postmortemexamination, atherosclerosis of th e vertebrobasi-lar system may be widespread, not allowing recon-struction of th e exact pathophysiology of the in-farction. Furthermore, an embolus present i n lifeoften lyses or moves far distally by the time ofautopsy.Foix and Hillemand4*discussed the anatomy of

small penetrating and circumferential branches ofthe distal basilar artery. Segarra elaborated onth e anatomy of the perforating branches of themesencephalic artery (the proximal portion of theposterior cerebral artery extending from the basi-lar bifurcation to th e posterior communicating ar -tery) and described two examples of infarction inthe distribution of this vessel. However, in neitherof Segarras cases was a lesion identified in thisvessel at postmortem. I n his case 1,a right verte-bral artery occlusion might have served as a nidusfor distal embolization, producing the suddenonset of deficit. His case 2, another patient with asyndrome of abrupt onset, had a heart murmurand atrial fibrillation, but no lesion within thevertebrobasilar arteries at postmortem. Sieben,DeReuck, and Vander E e ~ k e n ~ ~eported two pa-tients with occlusion of the mesencephalic arterydocumented at autopsy. Atherosclerosis with oc-clusion of small basilar branches remains ahypothetical cause of high brainstem infarction,but this has been documented only in branch dis-ease of the lower basilar a r t e r ~ . ~ O * ~ lThe anatomic configuration of the basilar arterywith two arterial vessels merging into a largera r t e r y a n d t h e n b i f u r c a t i n g is un ique .Atherosclerosis is usually most severe at the ori-gin of the vertebral artery in the neck, in th e in-tracranial portion of the vertebral artery, and atthe proximal end of the basilar artery. Castaigneand associates52 commented on the frequency ofembolic material within the distal basilar distri-bution. The basilar artery is widest at its originand tapers distally; an embolus small enough totraverse the vertebral artery would ordinarily notblock the basilar artery except distally. Intra-arterial emboli arise from atherosclerotic plaquesin the carotid arte1y,5~35~nd atherosclerotic foci,prominent in the proximal vertebral arteries,55could serve as a source for distal emboli within thevertebrobasilar system. In case 8 of Caplan andR ~ s e n b a u m , ~ ~mbolization to the distal basilarartery arose from a unilateral vertebral occlusion.The sudden onset of stroke in our patients has ledus to postulate an embolic mechanism (intra-arterial or cardiac) of the vascular occlusion, butthis was anatomically verifiable in only one case(case 1).Clarification of the clinical syndrome and saferangiography may lead to further study andanalysis of the spectrum of possible underlyingvascular pathologies. Therapy will be possibleonly when there is a more thorough understandingof the vascular pathophysiology of the top of thebasilar syndrome.References1. Segarra JM : Cerebral vascular disease and behavior:1. Th esyndrome of the mesencephalic artery. Arch Neurol

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2. Brust JCM, Behrens MM: Release hallucinations as hemajor symptom of posterior cerebral art ery occlusion: Areport of 2 cases. Ann Neurol 2:432-436, 19773. Caplan LR: Ptosis. J Neurol Neurosurg Psychiatry 37:l-7,19744. Christoff N: A clinicopathological study of vertical eyemovements. Arch Neurol31:l-8, 19745. Collier J: Nuclear ophthalmoplegia with especial referenceto retraction of the lids and ptosis and to lesions of theposterior commissure. Brain 50488-498, 19276. Fisher C M Some neuro-ophthalmological observations. JNeurol Neurosurg Psychiatry 30:383-392, 19677. Growdon J , Winkler G, Wray S: Midbrain ptosis. ArchNeurol 30:179-181, 19748. Halmagyi GM, Evans WA, Hallinan JM: Failure of down-ward gaze. Arch Neurol 35:22-26, 19789. Jacobs L, Anderson P, Bender M: The lesions producingparalysis of downward but no t upward gaze. Arch Neurol28:319-323, 197310.Mohr JP, eicester J., Stoddard L, et al: Right hemianopiawith memory an d color deficits in circumscribed left pos-terior cerebral ar tery territory infarction. Neurology (Min-neap) 21:1104-1113, 197111. Pasik P, Pasik T, Bender M: The pretectal syndrome inmonkeys: I. Disturbances of gaze and body posture. Brain

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