Light cupula of the horizontal semicircular canal occurring alternately on both sides: a case report
© Shin and Kim; licensee BioMed Central. 2015
Received: 2 October 2014
Accepted: 25 February 2015
Published: 14 March 2015
The light cupula is a condition wherein the cupula of the semicircular canal has a lower specific gravity than its surrounding endolymph. It is characterized by a persistent geotropic direction-changing positional nystagmus in the supine head-roll test, and the identification of a null plane with slight head-turning to either side.
This study describes a case of recurring light cupula that occurred alternately on both sides. At the first episode, a null plane was identified on the right side, which led to the diagnosis of a light cupula on the right side. At the second episode, a null plane was identified on the left side, leading to the diagnosis of a light cupula on the left side.
This is the first case report of recurring light cupula alternately involving both sides. Although the pathophysiology is not entirely understood yet, the light cupula should be considered as one of causes of recurrent positional vertigo.
KeywordsDirection-changing positional nystagmus Light cupula Head-roll test Positional vertigo
The condition of “light cupula”, characterized by a cupula with a lower specific gravity than its surrounding endolymph, has been introduced as an emerging concept accounting for positional vertigo [1-4]. In cases where the light cupula involves the horizontal semicircular canal (hSCC), a persistent geotropic direction-changing positional nystagmus (DCPN) without latency or fatigability is typically observed in the supine head-roll test. A null plane, in which the nystagmus disappears, can be identified when the patient’s head is slightly turned to the right or left side while the patient is in the supine position. In this report, we will describe a case of recurrent light cupula occurring alternately on both sides with an interval of 2 months.
The patient, after sharing his perspective on the treatment, was prescribed vestibular suppressants for symptomatic relief for one week, and the positional vertigo and nystagmus disappeared within 1 week without adverse effect of the drugs.
Our patient suffered from recurring positional vertigo, which is, as far as we know, the first report of recurring light cupula alternately involving both sides. There are two points that may be addressed from this observation: (1) the orientation of the hSCC cupular axis with regard to the gravitational vector, (2) the pathophysiology of the light cupula.
The pathophysiology of light cupula is still unclear. The attachment of light debris to the cupula has been suggested as a cause of light cupula , but the light debris has not been identified yet. Others have proposed that the increase in the specific gravity of the endolymph may contribute to light cupula [1,5], which was further supported by recent findings suggesting that light cupula can be accompanied by sudden sensorineural hearing loss ipsilaterally , and that the condition of light cupula may involve all 3 SCCs on the same side . The most interesting finding of this case report is that the condition of light cupula occurred on both sides, of which the mechanism is still obscure. If relative specific gravity of the endolymph to the cupula is changed by systemic influence such as hormonal imbalance, or both labyrinths are alternately affected by inner ear ischemia, bilateral involvement of the light cupula may be possible.
In previous studies, the cupular axis of hSCC has been described as running medial to lateral in direction, and the angle between the sagittal plane and the cupular axis was variable, ranging from 11° to 58° [1,2,5,8]. In this condition, the side of the null plane corresponds to the side of light cupula, and is suggested to be the most important finding for the determination of the affected side . At the first episode of vertigo, which was caused by a light cupula in the right hSCC, a null plane was identified on the right side, and the nystagmus was stronger in the left head-roll than in the right. A right-beating nystagmus was observed in the bowing position, and a left-beating nystagmus was observed when the patient was placed in the supine position. At the second episode, persistent geotropic DCPN was more intense in the right head-roll than in the left, and a null plane was identified on the left side. At both episodes of vertigo, the intensity of nystagmus during head-roll test was greater when the head was turned to the healthy side than the lesioned side, which ran counter to Ewald’s second law. Although further investigation is needed to explain this, possible mechanisms can be speculated as follows; (1) incomplete head rotation to the lesioned side in supine head-roll test, (2) anatomical variations of hSCC within the temporal bone such as excessive upward-tilting of anterior end of the hSCC, (3) the influence of otolith organ inputs upon hSCC ocular reflex by way of the velocity storage integrator , and (4) anatomical variation of the cupula within hSCC in a way that the axis of cupula is running lateral to medial in direction.
Because the incidence of light cupula in patients showing geotropic DCPN was as high as 14% , meticulous investigation of the duration and latency of positional nystagmus during supine head-roll test is essential for differential diagnosis between light cupula and hSCC canalolithiasis.
This is the first case report of recurring light cupula alternately involving both sides, which should be considered in the differential diagnosis of recurrent positional vertigo.
Written informed consent was obtained from the patient for publication of this Case report and any accompanying images.
Direction-changing positional nystagmus
Horizontal semicircular canal
This study was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2044883).
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