High correlation between ocular tilt reaction and contralateral internuclear ophthalmoplegia in paramedian posterior brainstem lesions

Objectives: The ocular tilt reaction (OTR) is characterized by displacement of the subjective visual vertical (SVV), ocular torsion (OT), and skew deviation (SD); it is most likely caused by lesions of graviceptive pathways (GP). Their anatomical localization within the brainstem is not precisely known, but evidence points to the paramedian posterior tegmental region, next to or within the medial longitudinal fascicle (MLF). Patients with lesions of the MLF regularly present with ipsilateral internuclear ophthalmoplegia (INO). Thus, the aim of the present study was to clarify GP localization by analyzing the correlation of INO, OTR, and brainstem lesions.

Methods: In a retrospective study we analysed 120 patients with INO (87 unilateral, 33 bilateral) for signs of OTR and localization of lesions in magnetic resonance imaging (MRI). All patients underwent a neuro-ophthalmological examination including measurement of SVV (psycho-physical), OT (scanning laser ophthalmoscope), and SD (cover test, prisms). Lesion localization was drawn from thin-slice MRI.

Results: Unilateral INO was accompanied by at least one component of OTR in 98%; all tilt effects were contraversive. SVV tilt was contralateral to the INO in 96% (mean: 6.1 range: 2.6–36.1), corresponding OT in 80% (54% monocular, 26% binocular), and SD in 50% (contralateral eye undermost). MRI detected brainstem lesions in only 68% of all patients with unilateral INO. Most lesions (96%) were in the paramedian posterior pontomesencephalic region on the side contralateral to the OTR, involving the area of the MLF (from levels between the nucleus VI and III). Interestingly, examination of 33 patients with bilateral INO for components of OTR revealed that only three had a pathologic tilt of the SVV, and one, OT and SD.

Conclusion: The high correlation between the side of a unilateral INO and contraversive components of OTR (mainly SVV) suggests that the GP run in the posterior paramedian tegmentum within or near the MLF. In agreement with this hypothesis, patients with bilateral lesions of this region do not present with OTR due to functional counterbalancing in GP of both sides. MRI data confirm that unilateral INO with contraversive OTR is caused by a lesion in the paramedian posterior pontomesencephalic brainstem. Furthermore, our data show that clinical findings (especially SVV deviation) are far more sensitive for monitoring lesions near the MLF than MRI.