Cerebellar Gray Matter Volume in Tinnitus

What is the role of the hippocampus and parahippocampal gyrus in the persistence of tinnitus?

The hippocampus and parahippocampal gyrus have been implicated as part of a tinnitus network by a number of studies. These structures are usually considered in the context of a "limbic system," a concept typically invoked to explain the emotional response to tinnitus. Despite this common framing, it is not apparent from current literature that this is necessarily the main functional role of these structures in persistent tinnitus. Here, we highlight a different role that encompasses their most commonly implicated functional position within the brain-that is, as a memory system. We consider tinnitus as an auditory object that is held in memory, which may be made persistent by associated activity from the hippocampus and parahippocampal gyrus. Evidence from animal and human studies implicating these structures in tinnitus is reviewed and used as an anchor for this hypothesis. We highlight the potential for the hippocampus/parahippocampal gyrus to facilitate maintenance of the memory of the tinnitus percept via communication with auditory cortex, rather than (or in addition to) mediating emotional responses to this percept.

Tinnitus Triggered by a Cerebellopontine Arachnoid Cyst in an Adolescent

BACKGROUND Tinnitus can be a symptom of a wide range of disorders. The identification and treatment of the underlying condition is essential for management of tinnitus in children. Tinnitus can occur with medical conditions other than sensorineural hearing loss. Cerebellopontine arachnoid cysts are rare and can cause tinnitus and hearing loss in adults. Tinnitus caused by an arachnoid cyst has not been reported in an adolescent. We report clinical and radiological features of a teenager with bothersome tinnitus caused by an arachnoid cyst. CASE REPORT A 14-year-old girl with unilateral tinnitus for 10 months presented to the Pediatric Otolaryngology Clinic. The loudness and duration of tinnitus had progressed gradually. Turning the head to the right induced right otalgia and tinnitus. The patient denied hearing loss, vertigo, exposure to loud noise, feeling of fullness in ear, otorrhea, facial weakness, numbness, dysphagia, changes in smell or taste, and problems with the jaw or temporomandibular joint. The focused neurological examination and head and neck examination were within normal limits. The patient had normal hearing on audiometry. T1-weighted, T2-spin-echo, T2-FLAIR, and diffusion-weighted magnetic resonance imaging sequences were obtained, revealing a right cerebellopontine angle arachnoid cyst. After arachnoid cyst marsupialization, the patient's tinnitus and otalgia resolved. CONCLUSIONS This case highlights the importance of suspecting identifiable nonauditory system disorders as causes of tinnitus in children. Thorough analysis of clinical findings and timely use of imaging is critical to prevent delay in diagnosis and treatment of children with bothersome tinnitus caused by rare medical conditions.

A Combined Image- and Coordinate-Based Meta-Analysis of Whole-Brain Voxel-Based Morphometry Studies Investigating Subjective Tinnitus

Previous voxel-based morphometry (VBM) studies investigating tinnitus have reported structural differences in a variety of spatially distinct gray matter regions. However, the results have been highly inconsistent and sometimes contradictory. In the current study, we conducted a combined image- and coordinate-based meta-analysis of VBM studies investigating tinnitus to identify robust gray matter differences associated with tinnitus, as well as examine the possible effects of hearing loss on the outcome of the meta-analysis. The PubMed and Web of Science databases were searched for studies published up to August 2021. Additional manual searches were conducted for studies published up to December 2021. A whole-brain meta-analysis was performed using Seed-Based d Mapping with Permutation of Subject Images (SDM-PSI). Fifteen studies comprising 423 individuals with tinnitus and either normal hearing or hearing loss (mean age 50.94 years; 173 females) and 508 individuals without tinnitus and either normal hearing or hearing loss (mean age 51.59 years; 234 females) met the inclusion criteria. We found a small but significant reduction in gray matter in the left inferior temporal gyrus for groups of normal hearing individuals with tinnitus compared to groups of hearing-matched individuals without tinnitus. In sharp contrast, in groups with hearing loss, tinnitus was associated with increased gray matter levels in the bilateral lingual gyrus and the bilateral precuneus. Those results were dependent upon matching the hearing levels between the groups with or without tinnitus. The current investigation suggests that hearing loss is the driving force of changes in cortical gray matter across individuals with and without tinnitus. Future studies should carefully account for confounders, including hearing loss, hyperacusis, anxiety, and depression, to identify gray matter changes specifically related to tinnitus. Ultimately, the aggregation of standardized individual datasets with both anatomical and useful phenotypical information will permit a better understanding of tinnitus-related gray matter differences, the effects of potential comorbidities, and their interactions with tinnitus.