The ocular tilt reaction (OTR) is an eye-head postural reaction consisting of ipsilateral head and neck tilt, skew deviation, and ocular torsion. OTR indicates either a unilateral peripheral vestibular deficit (inner ear or vestibular nerve) or a unilateral lesion of brain stem pathways from the vestibular nuclei to the interstitial nucleus of Cajal in the rostral midbrain.

The anterior inferior cerebellar artery (AICA) supplies the lateral inferior pontine tegmentum and middle cerebellar peduncle, vestibulocochlear nerve including the root entry zone, inner ear, and anterior inferior cerebellum.¹ Although there has been one report of skew deviation owing to an AICA infarction,¹ the cardinal features of the OTR have not previously been documented. We describe two patients with AICA infarction, each of whom had ipsiversive OTR—one with complete OTR, the other with skew deviation and tonic ipsiversive ocular torsion.

The first was a 58 year old man with long standing hypertension who presented with sudden vertigo and imbalance. On neurological examination, he had bilateral gaze evoked horizontal nystagmus, left peripheral facial weakness and numbness, dysmetria of the left limbs, and gait ataxia. There was no caloric response on the left side. Pure tone audiometry showed 65 dB sensorineural hearing loss on the left side. The subjective visual vertical with binocular viewing was tilted 17 degrees to the left (that is, counterclockwise from the patient’s point of view). Fundus photography showed 25° extorsion of the left eye and 12° intorsion of the right eye. He had a skew deviation with a right hypertropia of 20 prism diopters in primary gaze (fig 1). Magnetic resonance imaging (MRI) including diffusion images showed acute infarcts in the left middle cerebellar peduncle and the left lateral inferior pontine tegmentum (fig 1).

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Figure 1

 Tonic ocular tilt reaction in patient 1. Note sustained head tilt and concurrent vertical divergence of the eyes (skew deviation). T2 weighted axial magnetic resonance imaging of the brain showed acute infarcts in middle cerebellar peduncle and lateral inferior pontine tegmentum. There is conjugate leftward torsion of the eyes (that is, counterclockwise from the patient’s point of view): a 25° extorsion of the left eye and a 12° intorsion of the right. HT, hypertropia; LT, left; RE, right eye; RT, right. Patient consent was obtained for publication of this figure.

The second patient was a 58 year old woman with type 2 diabetes mellitus and hypertension who developed severe vertigo, hearing loss, tinnitus on the left side, dysarthria, and imbalance. She had bilateral gaze evoked nystagmus with a horizontal-rotatory component. There was left peripheral facial weakness and numbness, dysmetria of the left limbs, and gait ataxia. Pure tone audiometry showed a 65 dB sensorineural hearing loss on the left side. Fundus photography showed 14° extorsion of the left eye and 3° extorsion of the right eye. Prism testing showed a skew deviation with a right hypertropia of 6 diopters in the primary position. Subjective visual vertical with binocular viewing was tilted 13° to the left (that is, counterclockwise from the patient’s point of view). Caloric response was absent on the left side. MRI showed new infarcts in the left middle cerebellar peduncle, left lateral inferior pontine tegmentum, and anterior inferior cerebellum, possibly including the flocculus. Two months later the subjective visual vertical was normal. Fundus photography now showed 1° of extorsion of the left eye, indicating that the left eye had been extorted by 13° at the first examination (that is, by 14° minus 1°) and 9° of extorsion of the right eye, indicating that at the first examination the right eye had in fact been intorted by 6° (that is, by 3° minus 9°).

Comment

Most earlier reports of AICA infarction have focused on the brain stem or cerebellar findings. Recently, there have been several reports describing the clinical importance of inner ear symptoms, vertigo and/or sudden deafness.^{2, 3} However, a detailed description of OTR as a sign of AICA infarction has not been reported previously.

OTR, a sign of vestibular dysfunction in the roll plane, is characterised by a triad of conjugate ocular torsion, skew deviation, and heal tilt. It results from destructive or irritative lesions of central or peripheral graviceptive vestibular pathways. Although head tilt is a common component of OTR, skew deviation with conjugate ocular torsion often occurs without head tilt as in our patient. Thus the pathophysiology of a partial OTR (that is, skew deviation and conjugate ocular torsion without head tilt) is the same as that of a complete OTR, and skew deviation with conjugate ocular torsion is sufficient for the diagnosis of OTR.

In addition to lesions of the central and peripheral vestibular pathways conveying graviceptive signals, lesions of the cerebellum may also result in OTR. Skew deviation is commonly seen with cerebellar infarction. Mossman and Halmagyi described two patients with cerebellar stroke, presumably in the territory of the posterior inferior cerebellar artery, who had tonic conjugate ocular torsion without associated head tilt.⁴ These investigators speculated that interruption of nodular inhibitory projections to graviceptive neurones in the ipsilesional vestibular nuclei may have accounted for the contraversive conjugate ocular torsion.⁴

Sensorineural hearing loss and canal paresis to caloric stimulation on the left side clearly indicated involvement of the peripheral audiovestibular system. Ipsiversive OTR with acute peripheral vestibular lesions was described in a previous report.⁵ Considering the direction of OTR and known vascular anatomy of the AICA, damage to the inner ear or the root entry zone of the eighth nerve probably accounts for the ipsilesional OTR with AICA infarction.

In conclusion, this is the first report of well documented OTR with AICA infarction. The ipsiversive OTR in these patients probably resulted from infarction of the inner ear or the root entry zone of the eighth nerve.

Acknowledgements

This study was supported by grants of the Oriental Medicine R&D Project (03-PJ9-PG6-SO02-0001), Ministry of Health and Welfare, Republic of Korea.