Abnormal connection between lateral and posterior semicircular canal revealed by a new modeling process: origin and physiological consequences.

We developed a modeling procedure using CT scans or MRI data for exploring the bony and lymphatic canals of vestibular patients. We submitted 445 patients with instability and spatial de-orientation to this procedure. Out of the 445 patients, 95 had scoliosis, some of them, because malformations were suspected also had CT-scan modeling and functional tests. We focused on a never described, abnormal connection between the lymphatic lateral and posterior canal (LPCC) with a frequency of 67/445 (15%). In the scoliosis subgroup, the frequency was 52/95 (55%). Three scoliotic patients had CT scans. For each of them, the modeling revealed that LPCC was present on the bony canals. LPCC has pathognomic signs: no rotatory vertigo but frequent instability, transport sickness head tilt on the side of the anomaly, and spatial disorientation in new environment. We evaluated the functional impact of LPCC by testing the vestibulo-ocular reflex (VOR) in horizontal and vertical planes and found reproducible abnormal responses: in the case of left LPCC, during a counterclockwise horizontal rotation or a post clockwise horizontal rotation, added to the expected horizontal nystagmus, we found an unexpected upbeat nystagmus induced by the ampullofugal displacement of the fluid in the posterior canal. As LPCC was found in CT scans and MRI modeling for a same subject, we suggest that it could be a congenital abnormal process of ossification of the canals. The responses to the vestibular tests highlighting constant unexpected nystagmus underline the potential functional consequences of LPCC on vestibular perception and scoliosis.