Saccule and tinnitus : is a possible connection?

The saccule is the most mysterious organ of the labyrinth and, for this reason, one of the most fascinating. The aim of this presentation is to explain why the saccule should be taken into consideration for certain forms of tinnitus. For anatomic, embryologic and physiologic reasons the saccule has both auditory and vestibular characteristics, being the connecting link between the vibratory energy and the vestibular response: it is a bridge between the anterior and the posterior labyrinth; the saccule has a common embryologic origin with the cochlea in the pars inferior of the labyrinth; it is also considered to be the main hearing organ in fishes and other ancestral vertebrates. The saccule is an otolith organ involved in vertical linear movement detection and sensing gravitational changes; it controls the tonic components of the antigravity muscles contributing to the postural control. In addition, through the vestibule-sympathetic reflexes it contributes to the control of blood pressure during movement and through postural changes. The anatomical proximity of the saccule to the stapes suggests that an excessive pressure on the footplate may damage the saccular neuroepithelium which lies close to the oval window. Actually, chronic noise exposure has been associated with saccular dysfunction; a possible role of a tonic tensor tympani contraction is discussed. Gussen (1980) reported that a suffering saccular macula dislodges otolith debris that could reach the cochlea through the ductus reuniens and cochlear duct, thus also affecting the cochlear base and the high frequency hearing thresholds. While the effects of detached utricular otoconia are generally accepted as the cause of Benign Paroxysmal Positional Vertigo, what then happens to the saccular otoconia is not well known yet. An intermittent tinnitus has been described in patients with by BPPV, in the same ear affected by the lithiasis (Barozzi et al. 2014). A new theory of Ménière’s disease based on detached saccular otoconia has been recently proposed (Hornibrook and Bird, 2017). Based on these considerations, a cooperation between specialists of various disciplines would be beneficial to fully characterize the role of the vestibular organ on tinnitus.