the posterior thalamo - subthalamic paramedian artery is often unpaired and originates from p1 segment of posterior cerebral artery . it supplies the paramedian part of the upper midbrain and of the thalamus ( intralaminar nuclei , dorsomedial nucleus and internal part of the ventral posterior nucleus ) . unilateral thalamic and midbrain infarcts are uncommon . decreased consciousness , behavioral changes , memory impairment , motor neglect , facio brachial tactile hypoesthesia , up gaze palsy , vohs , weber and claude third nerve fascicular syndromes , loss of convergence , pseudo - sixth nerve palsy , bilateral internuclear ophthalmoplegia , miosis and bright light intolerance , asterixis and delayed movement disorders have been described in posterior thalamo - subthalamic paramedian arterial infarct . unilateral asterixis though relatively uncommon are associated with acute structural lesions and focal cerebral lesions . a 42-year - old young lady presented with 3 days history of acute onset of dizziness , transient loss of consciousness , sudden drooping of left eyelid and binocular diplopia with difficulty in walking unassisted . her admission bp was 210/120 mm hg and her blood sugar was 283 mg / dl with urine acetone positive at admission . there was also bilateral up gaze palsy with monocular left down gaze palsy and the only possible vertical movement was downward movement of right eye suggestive of vertical one and half syndrome . bell 's phenomenon and vertical oculocephalic movement was absent . the muscle strength , sensory system , finger nose and knee heel coordination were normal . she had thalamic astasia , was leaning back while sitting and required support to walk . on outstretched prone arm , dorsiflexed wrist , she had right asterixis which comprised of semi rhythmic flexion movements at wrist and fingers mri imaging showed evidence of t1 hypo intense and t2 , flair hyper intense signal changes in left anterior thalamus , subthalamus , left midbrain including periaqueductal region [ figure 1 ] . there were also bilateral frontal caps , bilateral asymmetric fronto parietal sub cortical white matter and symmetric peritrigonal white matter signal changes . magnetic resonance angiogram was normal and diffusion studies showed restriction [ figures 2 and 3 ] . patient was started on anti - platelets , anti - edema measures , antihypertensive and insulin . midbrain lesions may give rise to the most complex eye movement disorders observed in clinical neurology . the neural structures known to be involved in the control of vertical gaze includes the nucleus of darkschewitsch , the interstitial nucleus of cajal , rostral interstitial nucleus of the medial longitudinal fasciculus ( rimlf ) and the posterior commissure . various neuro - ophthalmic findings like vertical gaze palsy , vohs , weber syndrome , nuclear third nerve palsy , seesaw nystagmus , skew deviation are seen due to involvement of these midbrain centre 's . the arterial supply of the structures involved in the supranuclear control of vertical gaze depends on the posterior thalamo - subthalamic arteries and the paramedian peduncular arteries . the frequent coexistence of both midbrain and paramedian thalamic infarction is related to their vascular supply ; a single vessel arising near the top of the basilar may branch to supply both the paramedian region of the thalamus and the rostral medial mesencephalon . these gaze palsies have been attributed to lesions in the rostral midbrain rather than the thalamic injury . unilateral lesion of the upper midbrain tegmentum is sufficient to generate an up gaze palsy or a combined up and down gaze palsy , whereas an isolated down gaze palsy requires bilateral lesions . dysconjugate vertical gaze syndromes includes vohs , skew deviation and variants , monocular up gaze palsy , ocular tilt reaction , slowly alternating skew deviation , see - saw nystagmus , and the vohs consists of paralysis of upward vertical conjugated gaze and monocular paralysis of downward gaze or vice - versa . it occurs as a consequence of a mesencephalodiencephalic lesion , either unilaterally or bilaterally . in a case report of thalamo - mesencephalic infarct with vohs which evolved subsequently into vertical gaze palsy , it was suggested that in vohs , pathway to contra lateral down gaze neurons could have been damaged due to the unilateral dorsal midbrain lesion before its decussation with the unilateral interstitial nucleus of cajal , the oculomotor nucleus and the rimlf . unilateral lesion destroy the fibres of the posterior commissure and the descending fibres to the ipsilateral subnucleus of the inferior rectus and contralateral subnucleus of the superior oblique just after they decussate , probably above the level of the third nerve nucleus . a similar case of unilateral thalmo - mesencephalic infarct was reported with vohs , weber syndrome , fascicular third nerve palsy and pseudo - abducens palsy . three cases of posterior thalamo - subthalamic paramedian artery infarct with vertical ophthalmoplegia , impaired convergence and altered mental status were reported . none had vohs . in a series of 38 patients of paramedian thalamic artery infarcts , posterior thalamo - subthalamic paramedian artery territory involvement was reported in 89% . neurological manifestations were somnolence ( 87% ) , hemi syndromes ( 79% ) , cognitive deficits ( 58% ) , oculomotor nerve palsies ( 53% ) and vertical gaze palsy ( 39% ) . in a report of 11 patients with vertical gaze palsy in unilateral midbrain stroke , thalamic astasia which is inability to stand unassisted in absence of motor weakness and cerebellar dysfunction is documented after unilateral thalamic lesions . fastigial fibers of the vestibulocerebellar pathway project to the medial ventrolateral nucleus of the thalamus and damage to this pathway may be responsible for thalamic astasia . patient can not maintain a stationary sitting or standing position and has no other conditions that could account for contralateral pulsion such as pyramidal or sensory deficits , kinaesthesia , abnormal proprioceptive sensation , cerebellar ataxia , psychosis or parkinsonism . the romberg sign is negative and finger nose , knee heel and shin tap tests are normal . asterixis manifests as bilateral flapping tremor at the wrist , metacarpophalangeal , and hip joints . it is characterized by brief , arrhythmic interruptions of sustained voluntary muscle contraction usually due to brief lapse of posture . unilateral asterixis can be seen due to focal brain lesions in the genu and anterior portion of the internal capsule , midbrain , medial frontal cortex , parietal cortex or ventrolateral thalamus . interruption of the posture pathway in the rostral reticular formation and abnormal joint proprioception are suggested . the ventro - lateral nucleus of the thalamus is the area in which cerebello - rubral or vestibulocerebellar fibres converge . diffuse , widespread derangement of cns function , abnormal activity in the motor field in the cerebral cortex demonstrated using silent period locked averaging method , dysfunction of the sensorimotor integration occurring in the contralateral parietal lobe and midbrain , a failure in arm posture maintenance that is comparable to failure in leg posture control in patients with astasia are all postulated . it can present with complex neuro - ophthalmic findings including vertical one half syndrome , thalamic astasia and unilateral asterixis . this case is reported for the rarity and unique nature of the presenting clinical features in unilateral thalamo - mesencephalic infarct .
a 42-year - old young lady presented with acute onset of dizziness , drooping of left eye with binocular diplopia and inability to walk unassisted . 
 she had past history of uncontrolled diabetes mellitus and hypertension . on examination 
 , she had left fascicular type of third nerve palsy , vertical one and half syndrome ( vohs ) , left internuclear ophthalmoplegia and skew deviation with ipsilesional hypertropia . 
 she also had thalamic astasia and right unilateral asterixis . 
 her mri revealed t2 and flair hyper intense signal changes with restricted diffusion in the left thalamus , subthalamus and left midbrain . 
 mr angiography was normal . 
 thalamic - subthalamic paramedian territory infarct is relatively uncommon . 
 it can present with oculomotor abnormalities including vertical one and half syndrome , skew deviation , thalamic astasia and asterixis . 
 this case is reported for the rarity of the presenting clinical findings in unilateral thalamo - mesencephalic infarcts .