Torus Tubarius Research Articles

The effect of torus tubarius size on upper airway aerodynamics in children: a computational fluid dynamics study.

Some children with sleep-disordered breathing (SDB) continue to experience symptoms after adenotonsillectomy. One possible cause is the excessive size of the torus tubarius. In this study, the relationship between torus tubarius size and surgical outcome in 24 children with SDB who underwent adenotonsillectomy was retrospectively analyzed based on cone beam computed tomography (CBCT) imaging measurements and medical records. A computational fluid dynamics (CFD) approach was used to quantitatively compare the effects of different torus tubarius sizes on upper airway (UA) aerodynamics in children. The percentage of UA area occupied by the torus tubarius (TTA%) was significantly different between the excellent and poor groups (10.4 ± 3.58% vs. 17.71 ± 4.7%, p < 0.001). The results of CFD simulation showed that the mean airflow velocity, wall shear stress (WSS) and pressure drop (ΔP) in the nasopharynx significantly increased when the TTA% was > 15%. Our study confirmed the effect of round pillow size on the aerodynamics of the UA in children. When the TTA% exceeds 15%, it causes change in aerodynamics, which may affect the outcome of children with SDB.

CLINICAL AND MORPHOLOGICAL CHARACTERISTICS AND EVALUATION OF TORUS TUBARIUS IN CHILDREN WITH PHARYNGEAL TONSIL HYPERTROPHY

Introduction: Among children with hypertrophy of pharyngeal tonsils undergoing adenoidectomy, 31.3% of cases show hypertrophy of the torus tubarius, even in the absence of middle ear pathology. However, the nature of the changes in this anatomical area in these children has not been described.&#x0D; The aim of the study: to investigate and evaluate morphological changes of pharyngeal tonsil and torus tubarius in children with hypertrophy of pharyngeal tonsil.&#x0D; Materials and methods: histological investigation and scanning electron microscopy were performed on fragments of pharyngeal tonsil and torus tubarius, obtained during adenoidectomy of 12 children with nasal breathing disturbances (Group 1) and 13 children with concomitant inflammatory diseases of the upper respiratory tract (Group 2).&#x0D; Results: In patients of Group 2, changes in the pharyngeal tonsil were more pronounced, showing inflammatory alterations such as infiltration by polymorphonuclear leukocytes in the covering epithelium and subepithelial layer, as well as lymphocytes in the covering epithelium, along with the presence of fibrosis compared to patients of Group 1. Additionally, samples covered by biofilms were significantly more frequently identified in Group 2 compared to Group 1 (53.8% vs. 16.6%, p&lt;0.05). The mucosal changes in the torus tubarius corresponded to the nature of the changes observed in the pharyngeal tonsil in the respective group. Biofilms in the torus tubarius samples were found in 38.5% of cases in Group 2 and 8.3% of cases in Group 1 (p&lt;0.05).&#x0D; Conclusions: 1. In children with hypertrophy of pharyngeal tonsil and torus tubarius, the morphological characteristics of the mucous membrane of torus tubarius are similar to those observed in the mucous membrane of pharyngeal tonsil of the respective group. 2. Biofilms were reliably more frequently identified on the surface of pharyngeal tonsil and torus tubarius in children with upper respiratory tract infections than in patients with nasal breathing disturbances. 3. The detected changes provide a basis for revising the therapeutic approach to hypertrophic torus tubarius in children with pharyngeal tonsil hypertrophy.

Long-term clinical results of power-assisted adenoidectomy with torus tubarius correction

In patients with hypertrophy of the pharyngeal tonsil, hypertrophy of the lymphoid tissue of the torus tubarius is often observed. The application of power-assisted technologies allows for precise correction of the torus tubarius simultaneously with adenoidectomy. The purpose of the study was to investigate the clinical effectiveness of power-assisted endoscopic adenoidectomy with additional correction of the torus tubarius in the presence of its hypertrophy, based on postoperative survey results. For this purpose, we surveyed of 209 patients who underwent endoscopic power-assisted adenoidectomy. In 107 of them additional correction of torus tubarius hypertrophy was performed in case of its presence (main group), while in 102, only adenoidectomy was performed in all patients (control group). The prevalence of main group complaints before adenoidectomy and their dynamics were assessed based on a survey 12–24 months post-intervention. It was found that the additional removal of hypertrophied torus tuba­rius in children during power-assisted endoscopic adenoidectomy significantly reduces the risk of frequent upper respiratory tract infections and acute otitis media. The proportion of individuals who assessed the adenoidectomy effect as "significant improvement" in terms of "frequent upper respiratory tract infections" in the main group was 20.4% higher, and for "frequent acute otitis media" it was 41.3% higher. Conclusion: Endoscopic power-assisted adenoidectomy with torus tubarius correction is an effective and safe method for children with hypertrophy of the pharyngeal tonsil in combination with torus tubarius hypertrophy, especially in cases where indications for intervention include frequent upper respiratory tract infections and acute otitis media. Keywords: scoring system, tonsils hypertrophy, tonsil pharingeal, hypertrophy, otitis, inflammatory diseases of the nose and paranasal sinuses.

Assessment the impact of the torus tubarius correction by power-assisted technique on the equipressor eustachian tube function

Purpose of the research is to evaluate the impact of the torus tubarius correction by microdebrider technique on the eustachian tube function in children without middle ear pathology. Materials and methods. 115 children aged 3 to 12 years participated in the study. All children underwent endoscopic modified microdebridement adenotomy for the first time, which, in the case of tubal hypertrophy (we analyzed the frequency of this phenomenon), was combined with its correction by the microdebridement method. For the next stage of the research, we selected 19 children, who had preoperative intratympanic pressure monitoring results more than -100 daPa and who hadn’t concomitant tonsil hypertrophy (19 children). Control measurement was done on days 1 and 8-10 after the intervention. Depending on the presence/absence of concomitant hypertrophy of the torus tubarius, patients were divided into the main (11 patients) and control (8 patients) groups. The analysis was carried out using the STATISTICA program. Results. 36 patients were diagnosed with torus tubarius hypertrophy. When comparing intratympanic pressure on the 1st day after the intervention in patients of the main and control groups, a significant difference in values was found (-144.37±41.09/-95.00±27.90 daPa). On day 8-10, the intratympanic pressure data in patients of both groups did not differ from each other (-39.15±14.85 daPa in the main and -33.87±19.57 daPa in the control groups) and preoperative values in both groups. Conclusions. Hypertrophy of the torus tubarius is noted in 31.3% of patients with primary adenotomy. The microdebrider technique method of torus tubarius correction is safe in view of the equipressor function of the auditory tube. The research was carried out in accordance with the principles of the Declaration of Helsinki. The research protocol was approved by the Local Ethics Committee of the institution mentioned in the work. Informed consent of parents or their guardians was obtained for conducting research. No conflict of interests was declared by the authors.

Using Geometric Morphometric Analysis of Magnetic Resonance Imaging to Assess the Anatomy of the Eustachian Tube in Children with and without Otitis Media.

Otitis media (OM) is among the most common of childhood illnesses. It has long been hypothesized that children under age two are predisposed to OM due to differences in the anatomy of the Eustachian tube (ET), including the angle of the ET. OM in later childhood is less common but does occur, begging the question, are there shape differences in the ET that persist underlying later occurrences of OM? To answer this question, a novel method, which applied geometric and morphometric shape analysis to landmarks obtained from MRI data, was used. MRI scans were performed on 16 children (5 control, 3 cOME, and 8 rAOM) between 2011 and 2015. Sixteen landmarks representing the shape of the ET, cranial base, and palate were analyzed. The results of a Procrustes ANOVA indicate that the shape of the ET varies significantly (p < 0.01) between the OM and control groups. The shape differences between the OM group and the control are a medial and low attachment site of the tensor veli palatini (TVP) muscle, a posterior and high torus tubarius, and an anteriorly projected palate. These results support previous findings that a relatively horizontal ET is associated with a predisposition for OM. This study used a novel approach to examine anatomical differences in children with and without OM. First, the data set is unique in that it includes MRI scans of children with a confirmed OM diagnosis. Second, the use of MRI scans in craniofacial anatomy OM research is novel and allows for the collection of soft tissue landmarks and the visualization of soft tissue structures. Third, geometric morphometric shape analysis is a statistical method that captures shape differences, offering a more universal picture of nuanced changes within the entire set of landmarks, in contrast to more traditional linear and angular measurements used in prior OM studies examining craniofacial anatomy.

Torus Tubarius Hypertrophy After Adenoidectomy.

Backgrounds: Adenoidectomy is widely used to cure sleep-disordered breathing symptoms in children, torus tubarius hypertrophy (TTH) after adenoidectomy causing recurred snoring, sleep apnea, nasal obstruction, or mouth breathing was rarely reported, and the causes of TTH are still unclear. Objectives: To report a rare complication TTH after adenoidectomy, and the features of TTH. Material and Methods: A total of 36 pediatric patients with TTH diagnosed by our hospital from January 2017 to 2023 were included in this study. All children were treated conservatively for a month at first, and 13 patients underwent partial resection of TTH. The influencing factors (sex, age, allergic rhinitis [AR], and first operation way) were analyzed. Results: There were 36 patients with TTH: 27 boys and 9 girls. The age of the first operation ranged from 20 to 63 months, and the interval time of TTH after operation ranged from 3 to 55 months. Thirteen patients underwent partial resection of TTH. Thirteen children had definite symptoms and signs of AR. Conclusions and Significance: TTH is a rare complication after adenoidectomy, which is common in male children (75.0%) and in patients who took adenoidectomy before the age of 5 years (94.4%). TTH can occur as early as 3 months after adenoidectomy. AR and the operation way might have relationships with TTH.

Objective Tinnitus of Nasopharyngeal Origin.

We report a rare case of objective tinnitus induced by nasopharyngeal muscle constriction. A 49-year-old female patient presented at the clinic with unintentional sounds coming from the nasal cavity while talking or swallowing, which were similar to the lip-smacking sound. Physical examination revealed a hypertrophic posterior nasopharyngeal wall and torus tubarius at rest. With voluntary effort, the posterior pharyngeal wall protruded prominently and collided with the torus tubarius on either side, generating a sound when they were separated. Botox injection was recommended but the patient refused. The diagnosis and treatment of objective tinnitus are well established, but in some cases, it may occur under unexpected conditions. We report a novel type of objective tinnitus. A thorough physical examination for tinnitus could reveal the cause.

Application of virtual endoscopy in the diagnosis of adenoid hypertrophy and the morphologic classification of adenoid

Objective:To discuss the application of virtual endoscopy in the diagnosis of adenoid hypertrophy and the morphologic classification of adenoid. Methods:The clinical data of 97 children with adenoid hypertrophy admitted to Department of Otorhinolaryngology Head and Neck Surgery, Shenzhen University General Hospital from July 2022 to December 2022 were collected. The virtual endoscopic reconstruction of the nasopharynx was performed by cone beam computed tomography. The results of virtual endoscopic adenoid size measurement were compared with the results of nasopharyngeal CT median sagittal position and nasopharyngeal endoscopy. Virtual endoscopic classification of adenoid based on the size of the adenoids and their relationship with the torus tubarius. Results:The t-test results of the size of adenoids measured by virtual endoscopy and nasopharyngeal CT were t=1.699 and P=0.093, and the results of intra-group correlation coefficient（ICC） analysis were ICC=0.921 and P<0.01. The proportion of adenoids measured by virtual endoscopy and nasopharyngeal CT was highly consistent. The t-test results of the size of adenoids measured virtual endoscopy and nasopharyngeal endoscopy were t=1.543 and P=0.15, and the results of intra-group correlation coefficient（ICC） analysis were ICC=0.900 and P<0.01. The proportion of adenoids measured by virtual endoscopy and nasopharyngeal endoscopy was highly consistent. Among the 97 children, the morphological classification results of adenoids were 48 cases of overall hypertrophy type, 47 cases of central bulge type, and 2 cases of flat thickening type. Conclusion:The diagnosis of adenoid hypertrophy by virtual endoscopy has high accuracy, which not only avoids the invasive operation of traditional nasopharyngeal endoscopy, but also can observe the adenoid condition and its relationship with the torus tubarius from multiple angles. And, the morphological classification of adenoids using virtual endoscopy has guiding significance for perioperative preparation.

Tubarial Salivary Gland – The New Member of Nasopharynx

Tubarial Salivary Gland – The New Member of Nasopharynx

Unilateral hearing loss: case report on the insidious consequence of nasopharyngeal tuberculosis

BackgroundNasopharyngeal tuberculosis constitutes 1% of the head and neck manifestation of extra-pulmonary tuberculosis. The rarity of the disease along with its non-specific presentation may pose a challenge in diagnosis.Case presentationWe present a case of a 33-year-old patient who presented with a gradual onset of unilateral hearing loss. Endoscopic examination revealed leukoplakic lesions over the bilateral torus tubarius with audiological assessment revealing a mixed hearing loss in the left ear. Patient completed a 6-month course of anti-tuberculous therapy with a complete resolution of nasopharyngeal lesions and hearing loss.ConclusionWe hypothesize that tuberculosis of the nasopharynx may not only lead to impaired middle ear ventilation but also damage to the ossicular chain and inner ear structures.

Concurrent Occurrence of Nasopharyngeal and Disseminated Cutaneous Rhinosporidiosis: A Rare Presentation.

Concurrent Occurrence of Nasopharyngeal and Disseminated Cutaneous Rhinosporidiosis: A Rare Presentation.

Transnasal Endoscopic Resection of Torus Tubarius Pleomorphic Adenoma

Pleomorphic adenoma is the most common benign tumor of the salivary glands. Pleomorphic adenoma mainly occurs in the major salivary glands and less in the minor salivary gland. If pleomorphic adenoma occurs in the minor salivary glands, the most commonly found site is the palate. In addition, it can be developed from lip/cheek, tongue, nasal cavity, larynx and the nasopharynx. Pleomorphic adenoma rarely occurs in the nasopharynx, especially torus tubarius. We present a rare case of pleomorphic adenoma originating from torus tubarius in the nasopharyngeal cavity treated successfully via transnasal endoscopic resection.

Tubarial gland involvement in IgG4-related diseases

Background Tubarial glands (TGs) are a collection of unidentified salivary glands overlying the torus tubarius in the nasopharyngeal wall. Immunoglobulin G4-related disease (IgG4-RD) is a chronic fibroinflammatory state that often has multiple organ involvement. Involvement of the head and neck, especially the salivary glands, is common in IgG4-RD. Aims/objectives This study aimed to elucidate the clinical significance of TGs in IgG4-RD. Materials and methods We investigated the local findings of TGs in ten patients with IgG4-RD. Results Nasopharyngeal endoscopic examination revealed oedematous swelling of the nasopharyngeal wall surrounding the TGs, which improved after steroid treatment. Moreover, sonotubometry showed a stenotic pattern in three out of seven patients with IgG4-RD. Conclusions and significance TGs may be involved in IgG4-RD. The swollen TGs may be responsible for obstructive Eustachian tube dysfunction. Further studies are required to clarify the clinical significance and physiological roles of TGs in IgG4-RD.

Histologic Investigation of the Salpingopharyngeus.

The purpose of this study was to characterize the histologic contents of the salpingopharyngeal fold. The primary objective was to observe the presence of salpingopharyngeus (SP) muscle fibers, particularly at the section near the muscle origin at the torus tubarius (TT). Histologic samples of the salpingopharyngeal fold from 10 cadavers (six females and four males) were analyzed. Following a head bisection, a tissue sample measuring 5 mm in length along the course of the salpingopharyngeal fold was collected from one side (i.e., right or left). The tissue sample was taken from the estimated base of the TT to a point 5 mm inferiorly. Slides were prepared using a standard histological approach and basic pathological staining and analyzed via bright-field microscopy. Skeletal muscle fibers were identified in eight of the 10 tissue blocks of the salpingopharyngeal fold, with dense connective tissue identified in the remaining two tissue blocks. Glandular material was also identified in all 10 tissue blocks. Skeletal muscle fibers and/or dense connective tissue can be consistently identified in the section of the salpingopharyngeal fold near the TT. Glandular material is also consistently present in this same region of the salpingopharyngeal fold. These findings are discussed in relation to possible functional roles of the salpingopharyngeal fold contents, including the SP muscle.

Nasopharyngeal morphology contributes to understanding the "muddle in the middle" of the Pleistocene hominin fossil record.

The late archeologist Glynn Isaac first applied the term "muddle in the middle" to a poorly understood period in the Middle Pleistocene human fossil record. This study uses the nasopharyngeal boundaries as a source of traits that may inform this unclear period of human evolution. The nasopharynx lies at the nexus of several vital physiological systems, yet relatively little is known about its importance in human evolution. We analyzed a geographically diverse contemporary Homo sapiens growth series (n= 180 adults, 237 nonadults), Homo neanderthalensis (La Chapelle aux Saints 1, La Ferrassie 1, Forbes Quarry 1, Monte Circeo 1, and Saccopastore 1), mid-Pleistocene Homo (Atapuerca 5, Kabwe 1, Petralona 1, and Steinheim 1), and two Homo erectus sensu lato (KNM-ER 3733 and Sangiran 17). Methods include traditional (Analysis 1) and 3D geometric morphometric analysis (Analysis 2). H. erectus exhibited tall, narrow nasopharyngeal shape, a robust, ancestral morphology. Kabwe 1 and Petralona 1 plotted among H. sapiens in Analysis 2, exhibiting relatively shorter and vertical cartilaginous Eustachian tubes and vertical medial pterygoid plates. Atapuerca 5 and Steinheim 1 exhibited horizontal vomeral orientation similar to H. neanderthalensis, indicating greater relative soft palate length and anteroposterior nasopharynx expansion. They may exhibit synapomorphies with H. neanderthalensis, supporting the accretionary hypothesis. Species-level differences were found among H. sapiens and H. neanderthalensis, including relatively longer dilator tubae muscles and extreme facial airorhynchy among Neanderthals. Furthermore, H. neanderthalensis were autapomorphic in exhibiting horizontal pterygoid plate orientation similar to human infants, suggesting that they may have had inferiorly low placement of the torus tubarius and Eustachian tube orifice on the lateral nasopharyngeal wall in life. This study supports use of osseous nasopharyngeal boundaries both for morphological characters and understanding evolution of otitis media susceptibility in living humans.

Primary nasopharyngeal amyloidosis with nasal polyposis: Case report of a diagnostic challenge.

BackgroundPrimary nasopharyngeal amyloidosis is a rare entity of localised amyloidosis. Patients usually present with symptoms that mimic other common nasal diseases. We report an unusual case of nasopharyngeal amyloidosis that co-exist with nasal polyposis at the same time.Case presentationWe described a 72-year-old gentleman who presented with left-sided nasal obstruction, rhinorrhoea and hyposmia and right-sided hearing loss. Examination revealed bilateral intranasal polyposis with right lobular swelling at torus tubarius and right sided middle ear effusion. Biopsy revealed inflammatory nasal polyps with nasopharyngeal amyloidosis. Patient was treated successfully with functional endoscopic sinus surgery (FESS) for nasal polyposis and an en bloc wide local excision of the torus tubarius with no signs of recurrence at one year follow-up.ConclusionClinicians should have raised index of suspicion of a possible primary nasopharyngeal amyloidosis in patients presenting with nasopharyngeal mass with co-existing nasal polyposis to avoid delay in diagnosis and treatment.

Preliminary experience of surgical treatment for torus tubarius hypertrophy in children

Objective: To assess the incidence of symptomatic torus tubarius hypertrophy (TTH) in recurred OSA in children, and to explore the preliminary experience of partial resection of TTH assisted with radiofrequency ablation. Methods: From January 2004 to February 2020, 4 922 children, who diagnosed as OSA and received adenotonsillectomy at the Department of Otolaryngology, The 4th Medical Center of the PLA General Hospital, were retrospectively reviewed. There were 3 266 males and 1 656 females, the age ranged from 1 to 14 years old(median age of 5.0 years). Twenty-two cases were identified with recurrence of OSA syndrome, and the clinical data, including sex, age of primary operation, age of recurrence and presentation, and opertation methods were analyzed. Follow-up was carried out by outpatient visit or telephone. Graphpad prism 5.0 software was used for statistical analysis. Results: Twenty-two cases were identified as recurred OSA and received revised surgery in 4 922 cases. Among these 22 cases, 11 cases were diagnosed as TTH resulting in an incidence of 2.23‰(11/4 922), 1 case was cicatricial adhesion on tubal torus (0.20‰, 1/4 922), 10 cases were residual adenoid combined with tubal tonsil hypertrophy (2.03‰, 10/4 922). Median age of primary operation was 3.0 years (range:2.4 to 6.0 years) in 11 TTH cases. Recurrent interval varied from 2 months to 5.5 years (2.4±1.9 years) after first operation. Age of revised partial resection of TTH was 7.0±2.7 years (range: 4.0 to 12.0 years). Average time interval between primary operation and revised operation was 3.5±2.1 years (range: 0.5 to 6.0 years). Individualized treatments were carried out based on partial resection of TTH assisted with radiofrequency ablation. All of 11 cases received satisfied therapeutic results without nasopharyngeal stenosis occured. Twenty-two cases were followed up for 1.6 to 13 years (median follow-up time was 6.2 years). Conclusions: TTH contributed to recurred OSA in child. TTH might be misdiagnosed as tubal tonsil hypertrophy. Partial resection of TTH assisted with radiofrequency ablation was a safty and effective treatment.

THE ANATOMICAL AND MEASUREMENT STUDY OF ROSENMÜLLER FOSSA AND OROPHARYNGEAL STRUCTURES USING CONE BEAM COMPUTED TOMOGRAPHY.

The objective of this study was to assess Rosenmüller fossa (RF) anatomy and neighboring structures using cone beam computed tomography (CBCT). A total of 1000 patients were analyzed using CBCT. The reference points were based on the spina nasalis posterior (Snp) and basion. The length between RF and neighboring structures were measured.The mean distance from Snp to the posterior pharyngeal wall was 17.7 mm. The mean distance from right to left torus levatorius was 25.69 mm. The mean depth of right RF was 5.54 mm while the mean depth of left RF was 5.26 mm. RF, also described as the lateral pharyngeal recess, is a source location of nasopharyngeal carcinoma development. Its location is on the lateral pharyngeal wall posterior to the cartilaginous part of the eustachian tube, the torus tubarius. The knowledge of RF is important to diagnose and perform treatment planning of nasopharyngeal carcinoma.

Classification, diagnosis and treatment of Eustachian tube dysfunction literature review

&lt;b&gt; Introduction:&lt;/b&gt; The Eustachian tube (ET) is the anatomical structure that connects the middle ear with the nasopharynx. It is part of a system that, in addition to the already mentioned elements, also includes the soft palate. The functions of ET are pressure equalization, clearance of secretions and protection of the middle ear from sounds and reflux of secretions from the nasopharynx. Dysfunctions of ET are multifactorial, and the diagnostics is difficult due to lack of defined standards for assessing its function prior and post treatment. &lt;/br&gt;&lt;/br&gt; &lt;b&gt;Aim:&lt;/b&gt; The aim of the study is the review of the publications concerning actual definitions and classification of ET dysfunctions, efforts of adopting unified criteria and methods of assessing its functions and ways of treatment. &lt;/br&gt;&lt;/br&gt; &lt;b&gt; Material and methods:&lt;/b&gt; In the year 2015 classification was adopted which distinguish three subtypes of ET dysfunction: (1) dilatory ET dysfunction, (2) baro-challenge-induced, (3) patulous ET. Dilatory ET dysfunctions were further divided as follows: functional obstruction (most common), dynamic dysfunction and anatomical obstruction. The Eustachian Tube Dysfunction Questionnaire (ETDQ-7) enables the systematization of symptoms. Clinical assessment of the patient with ET dysfunction should include otoscopy or otomicroscopy, tympanometry, Rinnes and Webers tuning fork tests or pure tone audiometry, nasopharyngoscopy with visualization of ET orifice and opening. Other tests of assessment of ET functions like tubomanometry, sonotubomanometry and pressure chamber tests are useful research tools. Endoscopic evaluation of ET orifice should encompass the assessment of mucosa of the torus tubarius and ET as well as dynamic process of ET opening. In surgical treatment of functional obstructions of ET, the most common method is balloon dilatation tuboplasty. Several studies showed that this is safe and in high percentage of cases successful method of treatment, however the indications for this type of surgery are not yet universally accepted.

Unilateral Tubarial Oncocytic Papillary Cystadenoma Presenting with Epistaxis.

Oncocytic papillary cystadenoma (OPC) is a relatively rare benign tumor of the salivary glands, frequently seen in minor salivary glands, and occasionally in major salivary glands, such as the parotid gland. Patients only become symptomatic upon progression of the swelling, causing obstructive symptoms depending on its location. To our knowledge, there are no reports of presentation with bleeding tumor. Herein, we report a case of an OPC of the right torus tubarius in a 54-year-old man who presented with recurrent epistaxis.