trochlear nerve palsy may be clinically characterized by vertical diplopia , incomitant hypertropia that increases upon head tilt toward the paralyzed site ( positive bielschowsky 's test ) , excyclotropia , and head tilt .
the differentiation between acutely acquired palsy vs. the decompensation of a congenital palsy is important for an accurate diagnosis .
the presence of acute unilateral trochlear nerve palsy with claude bernard - horner syndrome represents a rare clinical condition . in a review of 215 cases of trochlear nerve palsy examined over a period of 23 years ,
the current report describes a patient with trochlear nerve palsy associated with claude bernard - horner syndrome and contralateral hemiparesis , with onset following a hypertensive crisis .
a 35-year - old caucasian woman with a history of chronic headache and systemic arterial hypertension was admitted with sudden acute intense bitemporal headache , diplopia , dysarthria , and left hemiparesis .
the patient 's blood pressure was lowered with antihypertensive drugs , including sodium nitroprusside , and she regained consciousness the next day .
a neurological examination showed right trochlear nerve palsy , slight ipsilateral claude bernard - horner syndrome ( fig .
1 ) , and left hemiparesis . at rest , the patient presented cyclovertical diplopia when her head was tilted down and to the right . magnetic resonance imaging ( mri ) of the brainstem and cerebellum , acquired on the sixth day , showed multiple small areas localized mainly to the pons and mesencephalon that were distinguished by t1 and t2 hyperintense signals and no contrast enhancement ( fig .
an mri in the fourth week showed remission of the previous lesions ; the patient was asymptomatic at that time and returned to her daily activities .
the most frequent causes of trochlear nerve palsy are traumas , surgical injuries , tumors , demyelinating and inflammatory diseases such as meningitis and cysticercosis .
brainstem stroke represents a rare cause of trochlear nerve palsy , in which infarcts may be extensive or restricted to the microvascular territory [ 4 , 5 ] . the patient presented in the current report developed sudden - onset clinical manifestations associated with arterial hypertension .
these clinical features were suggestive of a vascular etiology , which was supported by the neuroimaging findings ( fig .
2 ) . most likely , small bleedings at the brainstem and cerebellum occurred as consequence of increased blood pressure .
this clinical picture has previously been described in patients with trochlear nerve palsy [ 5 , 6 , 7 ] . the right - side claude bernard - horner syndrome and left - side hemiparesis observed in this patient may be related to the right - side pons lesion that was observed ( fig .
in addition , the right - side trochlear palsy was possibly a result of the left dorsal mesencephalic lesion ( fig .
after exiting the trochlear nucleus , which is ventrolateral to the cerebral aqueduct , the nerve fascicles course posteroinferiorly around the cerebral aqueduct and decussate in the dorsal midbrain [ 1 , 5 ] .
therefore , in the current patient , the involvement of the trochlear nerve must have occurred before the decussation , resulting in contralateral palsy .
the literature also contains descriptions of contralateral trochlear nerve palsy with ipsilateral horner 's syndrome .
guy et al .   describe nuclear or fascicular involvement of the trochlear nerve prior to decussation in the superior medullary velum and impairment of the adjacent sympathetic fibers . in the current report ,
the multiplicity of lesions observed in the patient likely was responsible for the unusual clinical presentation . in the case
presented here , progressive improvement was observed , and the patient was asymptomatic at the end of the fourth week .
similar outcomes have been described in patients with trochlear nerve palsy related to minor vascular lesions
. however , there is not sufficient evidence to draw definitive prognostic conclusions in this rare situation [ 3 , 4 , 6 ] .
 the association of unilateral trochlear nerve palsy with claude bernard - horner syndrome represents a rare clinical condition . we present the case of a patient with this unusual presentation . 
 the investigation performed implicated cerebrovascular disease as the underlying cause of the condition in this patient . 
Introduction
Case Report
Discussion