Superior Canal Dehiscence Research Articles

Superior semicircular canal dehiscence syndrome.

Superior semicircular canal dehiscence syndrome is a condition with troubling ear symptoms and vertigo caused by a defect in the bone between the inner ear and the middle cranial fossa. The disease is not dangerous, and for many patients it is sufficient to provide a thorough explanation for the symptoms and advice about coping strategies, balance exercises and, if necessary, use of assisted hearing devices. Surgical treatment may be appropriate for patients with severe symptoms.

A “Double” Third Window Syndrome: The Case of Semicircular Canal Dehiscence in Twin Sisters

A “Double” Third Window Syndrome: The Case of Semicircular Canal Dehiscence in Twin Sisters

Post-traumatic peripheral vestibular disorders (excluding positional vertigo) in workers following head injury

Benign paroxysmal positional vertigo has typically been reported to be the most common cause of post-traumatic dizziness. There is however paucity in the literature about other peripheral vestibular disorders post-head injury. This article provides an overview of other causes of non-positional dizziness post-head trauma from our large institutional experience. The UHN WSIB Neurotology database (n = 4291) between 1998 and 2018 was retrospectively studied for those head-injured workers presenting with non-positional peripheral vestibular disorders. All subjects had a detailed neurotological history and examination and vestibular testing including video nystagmography, video head impulse testing (or a magnetic scleral search coil study), vestibular-evoked myogenic potentials, and audiometry. Imaging studies included routine brain and high-resolution temporal bone CT scans and/or brain MRI. Based on a database of 4291 head-injured workers with dizziness, 244 were diagnosed with non-positional peripheral vertigo. Recurrent vestibulopathy (RV) was the most common cause of non-positional post-traumatic vertigo. The incidence of Meniere’s disease in the post-traumatic setting did not appear greater than found in the general population. The clinical spectrum pertaining to recurrent vestibulopathy, Meniere’s disease, delayed endolymphatic hydrops, drop attacks, superior semicircular canal dehiscence syndrome, and uncompensated peripheral vestibular loss are discussed.

Superior semi-circular canal dehiscence syndrome: quantifying the effectiveness of treatment from the patient's perspective

Superior semi-circular canal dehiscence syndrome is a disorder characterised by auditory and vestibular symptoms that can significantly impact quality of life, and yet it has no disease-specific quality of life instrument. Thirty-six patients who underwent transmastoid superior semicircular canal resurfacing and plugging were included from an initial cohort of 60 surgically managed patients. A sub-cohort of 19 consecutive patients completed validated symptom and quality of life questionnaires before and after surgery. Of the 36 patients, 31 participated in a telephone semi-structured interview post-operatively. Following surgery, there was a statistically significant improvement in autophony index score (p = 0.02), symptom severity score (p < 0.001) and sound hypersensitivity (p = 0.01). Thematic analysis of telephone interviews suggested three main symptom themes: auditory hypersensitivity, dysequilibrium, headache and concentration difficulties. Dysequilibrium was found to persist post-operatively. Surgery improves overall symptoms and quality of life. However, important symptom themes may be overlooked using the outcome measures that are currently available. A unified disease-specific outcome measure is urgently required to better understand the impact of symptoms and measure treatment effects.

Usefulness of Cervical Vestibular-Evoked Myogenic Potentials for Diagnosing Patients With Superior Canal Dehiscence Syndrome: A Meta-Analysis.

To compare the diagnostic accuracy of cervical vestibular-evoked myogenic potential (cVEMP) for detecting superior canal dehiscence (SCD) syndrome to that of computed tomography (CT) and surgical findings. PubMed, SCOPUS, Embase, Web of Science, and the Cochrane database. Databases were searched up to July 2021. True positives, true negatives, false positives, and false negatives were extracted. Methodological quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. Our search yielded nine studies with 721 patients. Including all cVEMP thresholds, the diagnostic odds ratio (DOR) was 32.8483 (95% confidence interval [CI]: 19.6577, 54.8900; I2 = 49.9%). The area under the summary receiver operating characteristic curve (AUC) was 0.879. Sensitivity and specificity were 0.8278 (95% CI: 0.7517, 0.8842; I2 = 76.4%) and 0.8824 (95% CI: 0.7859, 0.9387; I2 = 92.8%), respectively. However, there was a high degree of heterogeneity (I2 ≥ 70%) due to the different VEMP threshold values used among the studies. In subgroup analysis, higher cVEMP threshold values showed higher sensitivity (threshold ≤ 85: 0.9568; threshold ≤ 65: 0.7691) but lower specificity (threshold ≤ 85: 0.5879; threshold ≤ 65: 0.8913). The threshold ≤75 subgroup showed moderate sensitivity of 0.7455, high specificity of 0.9526, and the highest DOR of 38.9062. The AUC of this subgroup was 0.894. cVEMP is a reliable adjunctive tool for the clinical diagnosis of SCD. Taking the balance between sensitivity and specificity into consideration, a cVEMP threshold value of 75 showed good diagnostic accuracy.

Outcomes of Stapedotomy in Patients With Concomitant Otosclerosis and Superior Semicircular Canal Dehiscence: Should a Radiographic Third-Window Be a Contraindication to Stapes Surgery?

Review surgical outcomes of stapedotomy in patients with concomitant otosclerosis and superior semicircular canal dehiscence. Retrospective case review. Tertiary referral center. Patients with otosclerosis and radiographic superior semicircular canal dehiscence undergoing stapedotomy between 2008 and 2020. Stapedotomy. Pre- and postoperative hearing and unmasking of third-window symptoms. Hearing was measured by air conduction (AC) and bone conduction (BC) pure-tone averages (PTA), air-bone gap (ABG), and word recognition scores (WRS). Third-window symptoms included hyperacusis, autophony, sound- or pressure-induced vertigo, imbalance, or oscillopsia. Twenty patients with otosclerosis and radiographic superior semicircular canal dehiscence underwent stapedotomy, 13 primary and 7 revision. Mean AC PTA was 49.3 dB preoperatively and 35.6 dB postoperatively (p = 0.0077), while the ABG improved on average from 23.9 to 9.68 dB (p < 0.0001). The ABG improved to ≤10 dB in 12/20 patients (60%), and ≤20 dB in 18/20 patients (90%). There was no significant difference in BC PTA or WRS postoperatively. Two patients (10%) experienced potential transient unmasking of third-window symptoms-hyperacusis and prolonged imbalance-which both resolved. There were no other complications. There was no significant difference in audiologic outcomes or unmasking of third window symptoms between primary or revision cases. Persistent conductive hearing loss is common following stapedotomy for otosclerosis in patients with concomitant superior semicircular canal dehiscence. However, a majority of patients can achieve excellent hearing outcomes, while unmasking of third window symptoms appears to be rare. Radiographic superior semicircular canal dehiscence may not be an absolute contraindication to stapes surgery for otosclerosis.

Surgical treatments of superior semicircular canal dehiscence: A single-centre experience in 63 cases.

abstractObjectiveDifferent procedures have been described to treat superior canal dehiscence. The present study aims to describe the results obtained with middle fossa approach, transmastoid approach, and round window reinforcement in a large series of patients.Methods and DesignIn this single‐center retrospective study, we report the results of the procedures performed between 2006 and 2019 using the three main surgical approaches, middle fossa approach (MFA), transmastoid approach (TMA), and round window reinforcement (RWR). The outcome on cardinal cochlear and vestibular symptoms, audiometric results, and changes in cervical vestibular evoked myogenic potentials (cVEMPs) were analyzed. The patients were also interviewed 12 months to 13 years post‐treatment to establish their overall satisfaction following surgery.ResultsSixty‐three patients were divided into three groups: 42 MFA; 12 RWR; 9 TMA. Postsurgical control rates exceeded 80% for the majority of symptoms in the MFA and TMA groups, and ranged from 11.1% to 83.3% for the RWR group. Over 90% of MFA or TMA patients and 60% of the RWR cohort were satisfied overall with their treatment. Hearing thresholds were intact following surgery in the MFA and TMA groups. There was one case of profound postoperative deafness in the RWR group.ConclusionMFA and TMA are both safe and effective techniques in the treatment of disabling SSCD. Since MFA is the more invasive technique, we suggest that TMA should be proposed as first‐line treatment, temporal bone anatomy permitting. RWR outcomes are more variable in term of symptomatic control, and this option could be offered to patients at risk under general anesthesia. level of evidenceLevel 4 evidence.

Investigation of the Relationship Between Idiopathic Intracranial Hypertension and Superior Semicircular Canal Dehiscence

Purpose: The etiology of superior semicircular canal dehiscence (SSCD) is not yet clear; however, several theories implicate cumulative erosive changes. Here, using thin-section temporal bone CT images, we aimed to investigate the relationship between the bone roof thickness overlying the SSC and idiopathic intracranial hypertension (IIH) which may cause repetitive microtrauma. Materıals and methods: Between January 2017-December 2019, temporal bone CT scans from 18 patients with a diagnosis of IIH, and 21 age- and sex-matched controls were analyzed retrospectively. Multiplanar reformatted images (Pöschl and Stenver) were reconstructed from the scans and the roof thickness of the SSC bone was measured and SSCD was classified in 4 grades. Results: A total of 78 thin-section temporal bone CT scans were evaluated. Although grade-II dehiscence was most frequent in both groups, grade-IV was only observed in both temporal bones of one patient in the IIH group. Grade-III and grade-IV dehiscence rates were significantly higher in the IIH group (p=0.006). There was a significant difference between IIH and control groups in terms of SSC bone roof thickness (p=0.03). Conclusıon: Increased CSF pressure in patients with IIH may cause chronic, progressive, and irreversible damage to the bone that covers the superior semicircular canal, and may play a role as a predisposing factor for SSCD.

Low accuracy of 1.5 Tesla magnetic resonance imaging in identification of the bony defect in patients with superior semi-circular canal dehiscence syndrome: case-control study.

To determine the accuracy of 1.5 Tesla magnetic resonance imaging in identifying the bony defect in superior semi-circular canal dehiscence syndrome. A retrospective case-control study was conducted in tertiary university settings. The study included 12 patients with a definite diagnosis of superior semi-circular canal dehiscence syndrome and a control group comprising 12 non-superior semi-circular canal dehiscence syndrome patients, all with available magnetic resonance imaging data. The imaging scans were anonymised, and reviewed blindly and independently by three experienced radiologists. There was low sensitivity and specificity, with average values of 47 per cent (range, 16.7-66.7 per cent) and 69 per cent (range, 66.7-75 per cent) respectively. Cohen's kappa was 0.75, indicating substantial inter-rater reliability. Given the low accuracy of 1.5T magnetic resonance imaging in identifying the bony defect in superior semi-circular canal dehiscence syndrome, despite its value in inner-ear imaging, computed tomography or equivalent should be used when superior semi-circular canal dehiscence syndrome is suspected.

Peripheric smell regions in patients with semicircular canal dehiscence: An MRI evaluation

ObjectivesWe investigated the peripheric smell regions in patients with semicircular canal dehiscence (SCD) by cranial MRI. MethodsIn this retrospective study, cranial MRI images of 186 adult patients were included. Group 1 consisted of 83 adult patients with SCD. The control group (Group 2) consisted of 83 healthy subjects without central vertigo. Olfactory bulb (OB) volume and olfactory sulcus (OS) depth were measured in all groups. ResultsIn group 1, SCD was detected on the right (33.7%), left (26.5%) sides and bilateral (39.8%). Localization of dehiscence was at superior SC (75.9%), posterior SC (21.7%), lateral SC (1.2%), and posterior + superior SCs (1.2%). OB volumes of the SCD group were significantly lower than the control group bilaterally (p < 0.05). There were no significant differences between OS depths of groups 1 and 2 (p > 0.05). In SCD group, there were positive correlations between OB volumes; OS depths; and OB volumes and OS depths (p < 0.05). In older patients, bilateral OS depth values got lower (p < 0.05). In females, left OB volume values were lower than males (p < 0.05). In right SCD (+) patients, left OS depth values got lower (p < 0.05). ConclusionWe concluded that possible changes in CSF dynamics may cause the development of SCD at thin bone segments; and a decrease in the OB volume. CSF leaks into the perineural sheet of the olfactory bulb (OB) maybe responsible for the decrease in the OB volume. In addition, minor trauma, infection, and inflammation may also be responsible for both coexistences of SCD development and OB volume decrease.

Superior semi-circular canal dehiscence syndrome: quantifying the effectiveness of treatment from the patient's perspective.

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Relationship Between Clinical Features and the Arc and Length of Dehiscence in SCDS: A Single Center Review of 42 Cases.

Superior canal dehiscence syndrome (SCDS) is a rare disorder characterized by an array of audiovestibular symptoms due to a dehiscence of bone overlying the superior semicircular canal (SSC). In the presence of debilitating symptoms, surgical management, to plug or resurface the SCC is performed. Although computed tomography (CT) may overestimate the size or presence of a dehiscence due to a partial volume effect, it remains an invaluable diagnostic tool. To assess for correlation between the arc and length of dehiscence and clinical symptomology. A single-center, single-operator retrospective analysis of 42 patients who underwent trans mastoid plugging of SCC with confirmed radiological dehiscence of their SSC between January 2008 and July 2019 was undertaken. Patients were assessed based on seven predefined clinical symptoms. Length and arc of dehiscence's were evaluated by means of high resolution (0.5 mm) CT (HRCT), using multiplanar reconstruction (MPR). Receiver operating characteristics (ROC), and more specifically the area under the ROC curve (AUROC) were used to assess for statistical significance. Our results demonstrate overall very little correlation between the arc and size of the dehiscence and symptoms. The only statistically significant correlation we found was between length of dehiscence and the presence of aural fullness. SCDS is a debilitating condition with an array of symptoms on presentation. While dehiscence length demonstrated a correlation with aural fullness, no other symptomology in patients with radiologically evident SCDS demonstrated a statistically significant correlation either against the length or arc of dehiscence.

Superior semicircular canal dehiscence: The neglected pathology

Superior semicircular canal dehiscence: The neglected pathology

Superior semicircular canal dehiscence: a narrative review.

Described just over 20 years ago, superior semicircular canal dehiscence remains a relatively unknown and easily missed cause of dizziness and auditory symptoms. This review focused on the origin, presenting symptoms and underlying pathophysiology of superior semicircular canal dehiscence, and the available treatment options. The bony dehiscence acts as a 'third window', affecting inner-ear homeostasis, and resulting in hypersensitivity and a vestibular response to lower sound level stimuli. The third window effect explains the pressure- and sound-induced vertigo, oscillopsia, and nystagmus, as well as autophony, conductive hyperacusis and tinnitus. The origin of superior semicircular canal dehiscence is linked to the combination of a congenital or developmental factor, and a 'second event' like head trauma, rapid pressure changes or age-related factors. Computed tomography of the temporal bone and reduced vestibular-evoked myogenic potential thresholds can confirm the diagnosis. Despite only retrospective cohorts, surgery is considered a safe treatment option, targeting mainly vestibular but also auditory symptoms, with transmastoid approaches gaining popularity.

Diagnosing Pulsatile Tinnitus: A Review of 251 Patients.

To analyze the underlying etiologies, presenting characteristics, and diagnostic workup of patients with pulsatile tinnitus (PT). Retrospective review. Tertiary referral center. All patients who received a diagnostic workup for PT from January 01, 2015 and May 31, 2020. Diagnostic rate of imaging studies. Among 251 patients with PT, the most common etiologies included neoplasms (16%), arteriopathies (14%), venopathies (8.5%), middle/inner ear pathology (9.0%), or idiopathic (50%). Patients with identifiable etiologies of PT more often had hypertension, obesity, vision changes, ipsilateral asymmetric hearing loss, or an abnormal otologic examination. Only 18.5% of patients without those characteristics had an identifiable etiology of PT. The most commonly ordered diagnostic studies were magnetic resonance imaging with contrast (n = 146), MR angiography (MRA) (n = 105), CT angiography (CTA) (n = 84), computed tomography (CT) without contrast (n = 76), and MR Venogram (MRV) (n = 62). Magnetic resonance imaging with contrast and CT without contrast preferentially identified patients with nonvascular etiologies of PT, while MRA and CTA identified patients with vascular etiologies of PT. MRV did not demonstrate high diagnostic rate for either type of PT. No difference in diagnostic rate was found between MR-based or CT-based imaging. Patients who lack a history of hypertension, obesity, vision changes, ipsilateral asymmetric hearing loss, or an abnormal otologic examination are less likely to have an identifiable cause for PT. In cases where a specific etiology was identified, MR-based imaging (MRI with contrast and MRA) or CT-based imaging (CT without contrast and CTA) were equally efficacious in identifying that etiology. MR-based imaging is preferred for neoplasms, while CT-based imaging is preferred for semicircular canal dehiscence.

The Relationship Between the Third Window Abnormalities and Inner Ear Malformations in Children with Hearing Loss.

OBJECTIVE: To evaluate the relationship between the third window abnormalities and congenital inner ear malformations in pediatric patients with different types of hearing loss. If such a relationship should exist, it would be important to take it into account, in order to diagnose and treat pediatric hearing loss cases more accurately.Methods:Two hundred twenty-one children with hearing loss who had temporal bone computed tomography (CT) examination and were identified from 2013 to 2018 were retrospectively evaluated. The types of hearing loss were grouped as sensorineural hearing loss (SNHL), conductive hearing loss (CHL), and mixed hearing loss (MHL). Third window abnormalities included superior semicircular canal (SC) dehiscence, posterior SC dehiscence, enlarged vestibular aqueduct (EVA), X-linked stapes gusher, perilymph fistula, and bone dyscrasias. Congenital inner ear malformations included cochleovestibular, SC, and internal acoustic canal malformations. The relationships were analyzed with chi-square and Fisher’s exact tests.Results: In the study, 40 patients had unilateral hearing loss and 181 had bilateral hearing loss. In 402 ears, the rates of SNHL, CHL, and MHL were 88.5%, 6.9%, and 4.4%, respectively. EVA was the most common third window abnormality (41/402; 9.7%), and SC malformations were the most common inner ear malformations (53/402; 13.2%). In the SNHL group, superior and posterior SC dehiscence were associated with cochleovestibular malformations (P = .035 and.020, respectively). In the CHL group, there was a relationship between EVA and SC malformations (P = .041). No relationships were found in the MHL group. Conclusion: Third window abnormalities and congenital inner ear malformations may be encountered simultaneously in children with SNHL and CHL.

A Cohort Study Comparing Importance of Clinical Factors in Determining Diagnosis and Treatment for Superior Semicircular Canal Dehiscence Syndrome.

To determine which clinical factors have the strongest impact on determining diagnosis and decision for surgical repair for superior semicircular canal dehiscence syndrome (SCDS). A total of 81 patients presented with a suspicion for SCDS between October 2017 and October 2018. 38 patients ultimately were diagnosed with SCDS, and 28 chose surgical repair. Clinical factors of subjective patient symptoms (autophony, sensitivity to loud sounds, vertigo induced by loud sounds, dizziness, hearing their own heartbeats or other visceral organs) and audiogram findings (low frequency conductive hearing loss [CHL], bone-conduction hyperacusis, low cVEMP threshold [<80 db nHL], increased oVEMP [>17 μV] amplitudes) were analyzed with logistic regression to identify factors that predicted those who would ultimately be diagnosed with SCDS and those who would have surgical repair. Preoperative high-resolution CT imaging was performed on all patients. Significant predictors of presence of SCDS from logistic regression included low frequency CHL and increased oVEMP amplitude (p = 0.002 [OR 40, 95%CI 3.8-413], p = 0.001 [OR 93, 95%CI 6.8-1267], respectively). These were also significant predictors of individuals who chose to have surgical repair (p = 0.004 [OR 47, 95%CI 3.5-620], p = 0.001 [OR 126, 95%CI 8.2-1941], respectively). Area under the receiver operating characteristic curve (ROC curve) for these two variables are 93% for diagnosing SCDS and 94% for predicting choice for surgical repair. Low frequency CHL and increased oVEMP amplitude are the strongest predictive factors for making a diagnosis of SCDS and for choosing surgical repair.

Auditory Outcomes Following Transmastoid and Middle Cranial Fossa Approaches for Superior Semicircular Canal Dehiscence Repair.

To describe postoperative hearing outcomes following transmastoid (TM) and middle cranial fossa (MCF) approaches for semicircular canal dehiscence (SSCD) repair. Retrospective review. Academic, tertiary referral center. Adults with SSCD who underwent repair between 2005 and 2019. Pure tone audiometry pre- and postoperatively after SSCD repair. Change in air-bone gap (ABG) at 250 and 500 Hz, pure tone average (PTA), bone conduction (BC), and air conduction (AC) thresholds at 500, 1000, 2000, and 4000 Hz for patients undergoing TM and MCF approaches for SSCD repair. The average change in BC PTA for patients undergoing TM (n = 26) and MCF (n = 24) SSCD repair was not significantly different between the two groups. The first and final postoperative PTAs were recorded an average of 1.7 (range 0.30-3.0) and 29.1 (range 3.5-154) months postoperatively. For patients who underwent MCF repair, the average BC PTAs increased (+) by 2.2 dB HL (p 0.43) and 0.57 dB HL (p 0.88) at the first and final audiograms respectively compared to +1.27 dB HL (p 0.53) and a decrease (-) of 0.57 dB HL (p 0.63) for the TM group. The average changes in low frequency ABG for patients undergoing MCF repair were -4.7 dB (p 0.08) and -6.9 dB (p 0.15) at first and final audiograms respectively compared to -4.9 dB (p 0.06) and -4.1 dB (p 0.36) for patients who underwent TM repair. There was a high frequency hearing loss noted at 8000 Hz for the MCF (30.0 dB ± 18.7 preop; 41.7 dB ± 21.7 postop; p 0.01) and TM (32.1 dB ± 23.2 preop; 44.3 dB ± 29.6 postop; p 0.001) groups which persisted on long term follow up. Both TM and MCF approaches to SSCD repair can be performed with long-term preservation of hearing. ABGs were reduced in each treatment group but did not reach significance. A high frequency hearing loss (8000 Hz) may be expected with either approach.

Superior Semicircular Canal Dehiscence Revision Surgery Outcomes: A Single Institution's Experience

Superior semicircular canal dehiscence (SSCD) is an abnormality of the otic capsule, which normally overlies the superior semicircular canal. Surgical management is indicated in patients with persistent and debilitating symptoms. Given the complexity of the disease, there are patients who experience less favorable surgical outcomes and require revision surgery. The purpose of this study was to report to the rate of postoperative symptomatic improvement in patients who required revision surgery. A retrospective analysis of patients undergoing SSCD surgical repair at a single institution was performed. Information on patient demographics, primary and secondary surgical approaches, surgical outcomes, and follow-up length was collected. Seventeen patients underwent 20 revision surgeries. There were eleven (65%) females and six (35%) males. Mean age of the cohorts was 50 years (range 30-68 years), and mean follow-up length was 6.8 months (range 0.1-31.1 months). Cerebrospinal fluid leak was noted in 67% of cases. The greatest postoperative symptomatic resolution was reported in oscillopsia (100%), headache (100%), and internal sound amplification (71%), while the least postoperative symptomatic resolution was reported in tinnitus (42%), aural fullness (40%), and dizziness (29%). Revision surgery can provide symptomatic improvement in select SSCD patients; however, patients should be cautioned about the possibility of less favorable outcomes than in index surgery. Revision surgeries are associated with a considerably higher rate of perioperative cerebrospinal fluid leak.

Relationship Between Superior Semicircular Canal Dehiscence Volume with Clinical Symptoms: Case Series

Superior semicircular canal dehiscence (SSCD) is an osseous defect of the arcuate eminence of the petrosal temporal bone. Patients typically present with auditory and vestibular symptoms, such as hearing loss and disequilibrium. Using advanced imaging segmentation techniques, we evaluated whether the volume of SSCD correlated with preoperative symptoms and postoperative outcomes. Our laboratory previously described a novel method of quantifying the size of an SSCD via manual segmentation. High-resolution computed tomography images of the temporal bones were imported into a specialized segmentation software. The volume of the dehiscence was outlined on consecutive slices of the coronal and axial planes via a single-pixel-thick paintbrush tool and was then calculated according to the number of nonzero image voxels. This study included 111 patients (70 women and 41 men; mean age, 55.1 years; age range, 24-87 years) with a total of 164 SSCDs. Mean postoperative follow-up time was 5.2 months (range, 0.03-59.5 months). The most common preoperative and postoperative symptoms were tinnitus (n= 85) and dizziness (n= 45), respectively. Surgery resulted in improvement of symptoms in most patients. The average volume of 164 SSCDs was 1.3 mm3. SSCD volume was not significantly associated with either preoperative symptoms or postoperative outcomes. Advances in imaging techniques have allowed increased visualization of SSCD. Further research will be necessary to evaluate the potential correlation of volume of the dehiscence with clinical variables.