Evaluation of Medial Retrotympanum by High-Resolution Computed Tomography and Endoscopy - A Descriptive Study.

The aim of this study was to determine and compare the capability of the High-Resolution Computed Tomography (HRCT) and endoscope in detecting hidden areas of medial retrotympanum in cases with chronic otitis media (COM). Per-operative endoscopic evaluation of structures in medial retrotympanum was done in 74 patients suffering from COM and was compared with pre-operative HRCT of the temporal bone in 50 patients. HRCT revealed type-A Sinus Tympani (ST) in 61.2%, type-B in 34.7%, and type-C in 4.1% of the patients; endoscope could reveal type-A in 71.6%, type-B in 25.7% and type-C in 1.4% of the patients. Ponticulus was discovered in 84.1%, subiculum in 100%, finiculus in 97.3% and sinus subtympanicus (SST) in 100% of the cases using endoscope. HRCT could detect ponticulus in 38.6% and subiculum in 4.0% of the cases. HRCT could not very clearly detect finiculus and SST. HRCT could not differentiate the content of the ST as compared with endoscopy. HRCT is a useful diagnostic tool in predicting the presence and type of ST, but its accuracy in detecting SST, finer bony ridges of ponticulus, subiculum, and finiculus and the contents is poorer than endoscope.

Radiologic evaluation and clinical assessment of facial sinus in adults and children - computed tomography study.

OBJECTIVE: The facial sinus is a recess of the lateral retrotympanum located between the chorda tympani (ChT) and facial nerve (FN). Chronic otitis media with cholesteatoma often spreads from the pars flaccida to the facial sinus (FS). In stapedotomy, if an unfavorable ChT type is encountered, there is a need for removal of bone between the ChT and FN. The aim of the study was to assess FSs in adults and children according to Alicandri-Ciufelli classification, to measure FS width and depth in computed tomography scans, evaluate the correlation between measurements and different types of facial sinuses, and provide a clinical context of these findings. METHODS: Cone Beam Computed Tomography (CBCT) of 130 adults and High Resolution Computed Tomography of 140 children were reviewed. The type of facial sinus was assessed according to Alicardi-Ciufelli's classification in different age groups. Width of entrance to facial sinus (FSW) and depth of FS (FSD) were evaluated among age groups. RESULTS: Type A of FS is dominant in both adult and children populations included in the study. The average depth of FS was 2.31±1.43 mm and 2.01±0.90 in children and adults respectively. The width of FS was 3.99±0.69 and 3.39±0.98 in children and adults respectively. The depth of FS (FSD) presented significant deviations (ANOVA, p<0.05) among all three types and age groups. In 116/540 (21.5%) cases the value of FSD was below 1 mm. CONCLUSION: The qualitative classification of facial sinuses into types A, B and C, introduced by Alicandri-Ciufelli and al. is justified by statistically significant differences of depth between individual types of tympanic sinuses. Type A sinuses may be extremely shallow (<1 mm - As) or normal (>1 mm - An). Preoperative assessment of CT scans of the temporal bones gives crucial information about type and size of facial sinus. It may increase the safety of surgeries in this area and play a role in choosing an optimal approach and surgical tools.

Surgical anatomy of posterior tympanotomy: influence of the retrotympanum on round window exposure.

OBJECTIVES: To describe how the retrotympanic structures could influence the visibility of the round window niche and the round window membrane during cochlear implant surgery, and to investigate if a round window approach is possible even in cases with unfavourable anatomy. METHODS: Video recordings from 37 patients who underwent cochlear implantation were reviewed. The visibility of the round window niche and round window membrane at different timepoints was assessed according to a modified version of the Saint Thomas Hospital classification. The structures that concealed the round window niche and round window membrane were evaluated. RESULTS: After posterior tympanotomy, 54 per cent of cases had limited exposure (classes IIa, IIb and III) of the round window niche. After remodelling the retrotympanum, round window niche visibility significantly increased, with 100 per cent class I and IIa cases. Following remodelling of the round window niche, visibility of more than 50 per cent of the round window membrane surface was achieved in 100 per cent of cases. CONCLUSION: Remodelling the retrotympanum and the round window niche significantly increased exposure of the round window niche and round window membrane respectively, allowing round window insertion in all cases.

Accuracy of High-Resolution Computed Tomography Compared to High-Definition Ear Endoscopy to Assess Cholesteatoma Extension.

OBJECTIVE: To correlate radiographic evidence of cholesteatoma in the retrotympanum with intraoperative endoscopic findings in cholesteatoma patients and to evaluate the clinical relevance of radiographic evidence of cholesteatoma in the retrotympanum. STUDY DESIGN: Case series with chart review. SETTING: Tertiary referral center. METHODS: Seventy-six consecutive cases undergoing surgical cholesteatoma removal with preoperative high-resolution computed tomography (HRCT) were enrolled in this study. A retrospective analysis of the medical records was conducted. The extension of cholesteatoma regarding different middle ear subspaces, into the antrum and mastoid were reviewed radiologically in preoperative HRCT and endoscopically from surgical videos. Additionally, facial nerve canal dehiscence, infiltration of the middle cranial fossa, and inner ear involvement were documented. RESULTS: Comparison of radiological and endoscopic cholesteatoma extension revealed statistically highly significant overestimation of radiological cholesteatoma extension for all retrotympanic regions (sinus tympani 61.8% vs 19.7%, facial recess 69.7% vs 43.4%, subtympanic sinus 59.2% vs 7.9%, and posterior sinus 72.4% vs 4.0%) and statistically significant overestimation for mesotympanum (82.9% vs 56.6%), hypotympanum (39.5% vs 9.2%), and protympanum (23.7% vs 6.6%). No statistically significant differences were found for epitympanum (98.7% vs 90.8%), antrum (64.5% vs 52.6%), and mastoid (26.3% vs 32.9%). Statistically significant radiological overestimation of facial nerve canal dehiscence (54.0% vs 25.0%) and invasion of tegmen tympani (39.5% vs 19.7%) is reported. CONCLUSION: Radiologic cholesteatoma extension in different middle ear subspaces is overestimated compared to the intraoperative extension. The preoperative relevance of radiological retrotympanic extension might be limited in the choice of approach and transcanal endoscopic approach is always recommended first.

Variability of the retrotympanum and its association with mastoid pneumatization in cholesteatoma patients.

PURPOSE: This study aimed to investigate the variability of the retrotympanum in patients undergoing surgical treatment for cholesteatoma. METHODS: We included 59 ears of patients undergoing middle ear surgery for cholesteatoma who had preoperative computed tomography scans. A retrospective analysis of the medical records was conducted. The sinus tympani (ST), subtympanic sinus (STS) and facial recess (FR) were classified into types A-C based on the relationship of their extension to the facial nerve. The mastoid and petrous apex were assessed and categorized as normal pneumatized or sclerotic. RESULTS: Type A extension was the most frequently found in all sinuses (ST 64%, FR 77%, STS 69%), Type B extension was found more often in ST (34%) and STS (24%) than in FR (15%). A very deep extension was found only rarely (ST 2%, FR 8%, STS 7%). A sclerotic mastoid was found in 67% of cases. Those cases showed a statistically significant difference regarding retrotympanum pneumatization when compared with normal mastoid. CONCLUSION: The most frequent variant of retrotympanic pneumatization in relation to the facial nerve was type A in all subsites in cholesteatoma patients. The variability among patients with cholesteatoma is different to previously published results in healthy subjects. Moreover, the pneumatization of the retrotympanum is associated with mastoid pneumatization.

A micro-computed tomography study of the sinus tympani variation in humans.

BACKGROUND: The posterior part of the tympanic cavity comprises a depression called the sinus tympani (ST). The said structure is of outmost importance, e.g. in surgical procedures involving the middle ear, as a pathology (microbial biofilm or cholesteatoma) present in this difficult to access location might hinder its effective treatment. The aim of the study was to evaluate anatomical variants of the ST in human adult petrous bones. For this purpose, three-dimensional (3D) models of the ST were recreated from micro-computed tomography (CT) scans of 44 dry petrous bone samples (19 female, 25 male), applying 3D Slicer, Meshmixer and MeshLab software. MATERIALS AND METHODS: Anatomical variants of the ST were classified in terms of both shape and surface configuration. The internal configuration of the ST was classified as heterogeneous - containing small bony trabeculae and crests up to 1.0 mm in size, contrasting to homogeneous ST that characterizes a relatively smooth interior, or mere presence of minor depressions and mild folds. Female STs were more bowl-shaped (57.9%) than saccular (42.1%), and had heterogeneous surface configuration (52.6%) compared to homogeneous (47.4%). On the contrary, male STs were more saccular (52.0%) rather than bowl-shaped (48.0%), and predominantly had a heterogeneous surface (84.0%) over homogeneous (16.0%). RESULTS AND CONCLUSIONS: A complex combination of ST features comprised of a saccular shape and heterogeneous surface occurred in 52.0% of males and in 15.8% of females (a statistically significant difference; p = 0.0254, Fisher's exact test) seems to be clinically important because of its potential negative implication on health outcomes after surgery in the case of, for example, cholesteatoma, and it may also favour chronic pathological processes.

On the radiologic anatomy of pediatric sinus tympani: HRCT study.

OBJECTIVE: Sinus tympani (ST) is considered the most constant among retrotympanic recesses but it is of great anatomical variability in shape and relation to mastoid portion of facial nerve. ST is difficult to access when clearing the cholesteatoma or serving as a window for cochlear implantation. The objective was to describe morphology of ST and assess feasibility of retrofacial approach in children under 5 years old. METHODS: HRCT images of 150 children were reviewed. The type of sinus tympani was assessed according to Marchioni's classification. Width of entrance to sinus tympani (STW), depth of ST (STD), distance between the posterior semicircular canal and facial nerve (F-PSC), distance between the latter plane to the floor of ST at the right angle (P-ST) were measured. Width (HS-SS) and length (ML) of mastoid process were also measured. RESULTS: From 300 temporal bones analyzed, the most common type of ST was type B (59.3%), followed by type C (34.3%) and type A (6.3%). The average depth of ST was 3.38±1.04 mm (1.32-8.24 mm) and mean value of F-PSC (width of retrofacial approach) was 4.91±0.75. The depth of ST (STD) presented significant deviations (ANOVA, p<0.05) among all three types. The value of ML increased with age (very high correlation). CONCLUSION: Deep tympanic sinus (type C) is more frequent in children than in adult populations and it may suggest that pneumatization may affect the development of tympanic sinus final shape. Retrofacial approach can be used in selected pediatric patients after HRCT analysis.

Endoscopic Ear Surgery: Redefining Middle Ear Anatomy and Physiology.

Middle ear anatomy and physiology is highly complex, yet familiarity is important to perform middle ear surgery and understand surgically relevant ventilation pathways of the ear compartments. The middle ear is divided into five subspaces: the mesotympanum, the retrotympanum posteriorly, the epitympanum superiorly, the protympanum anteriorly, and the hypotympanum inferiorly. The Eustachian tube plays a crucial role in maintaining middle ear aeration and atmospheric pressure. There are two independent aeration routes of the epitympanum. Thanks to the advent of the endoscope, this anatomic and physiologic knowledge has allowed one to understand the pathophysiology of ear diseases, improving surgical concepts.

Microsurgical anatomy of the stapedius muscle in adult cadavers.

This study aimed to establish an extended morphometric dataset regarding the stapedius muscle for anatomists and otologists. The tympanic cavity of ten cadavers (five females, five males) aged with 75.70 ± 13.75 years was bilaterally dissected. Morphometric properties of the stapedius muscle (i.e., its muscular belly and tendon) and its relationship with the neighborhood structures including the facial nerve was evaluated. The length of the entire stapedius muscle was found as 4.80 ± 1.13 mm. The depth between the entrance of the external auditory canal and stapedius muscle was measured as 18.23 ± 2.30 mm. The incudostapedial joint and stapedial tendon were found to be 1.66 ± 0.25 mm and 1.18 ± 0.19 mm away from the facial nerve, respectively. The stapedial tendon length was standardized as five types: Type 1, extremely short tendon (under 0.5 mm), 5% of cases; Type 2, short tendon (between 0.5 and 1 mm), 30% of cases; Type 3, normal tendon (between 1 and 2 mm), 55% of cases; Type 4, long tendon (between 2 and 2.5 mm), 10% of cases; and Type 5, extremely long tendon (above 2.5 mm), no cases. Our findings showed that the stapedius tendon size in adults was quite similar to fetuses. Therefore, probably entire muscle dimension does not alter after birth. Considering the concordance between direct anatomic (our findings) and radiologic measurements (literature findings) of the stapedius muscle, preoperative radiological evaluation may be important for otologists in terms of the choice of surgical tools such as diamond burr sizes. Due to the lack of standardization regarding the evaluation of the stapedius tendon size (i.e., extremely short or extremely long), we defined the tendons below 0.5 mm as extremely short (Type 1) and above 2.5 mm as extremely long (Type 5).

Endoscopic evaluation of middle ear anatomic variations in autopsy series: analyses of 204 ears / Avaliação endoscópica das variações anatômicas da orelha média em uma série de autópsias: análise de 204 orelhas

Abstract Introduction Microsurgery of the ear requires complete evaluation of middle ear surgical anatomy, especially the posterior tympanic cavity anatomy. Preoperative assessment of the middle ear cavity is limited by the permeability of eardrum and temporal bone density. Therefore, middle ear exploration is an extremely useful method to identify structural abnormalities and anatomical variations. Objective The aim of this study is to determine anatomic variations of the middle ear in an autopsy series. Methods All evaluations were performed in the Forensic Medicine Institute Morgue Department. The cases over 18 years of age, with no temporal bone trauma and history of otologic surgery included in this study. Results One hundred and two cadavers were included in the study. The mean age was 49.08 ± 17.76 years. Anterior wall prominence of the external auditory canal was present in 27 of all cadavers (26.4%). The tympanic membrane was normal in 192 ears (94%) while several eardrum pathologies were detected in 12 ears (6%). Agenesis of the pyramidal eminence and stapedial tendon was found in 3 ears. While the ponticulus was bony ridge-shaped in 156 of 204 ears (76.4%), it was bridge-shaped in 25 ears (12.3%). The ponticulus was absent in 23 ears (11.3%). While complete subiculum was present in 136 of all ears (66.7%), incomplete subiculum was present in 21 ears (10.3%). Subiculum was absent in 47 ears (23%). Facial dehiscence was found in 32 ears and the round window niche was covered by a pseudomembrane in 85 ears (41.6%). A fixed footplate was present in 7.4% of all ears, and no persistent stapedial artery was seen in any cases. Conclusion The pseudomembrane frequency covering the round window niche was found different from reports in the literature. In addition, the frequency of the external auditory canal wall prominence has been reported for the first time.

Resumo Introdução A otomicrocirurgia requer avaliação completa da anatomia cirúrgica da orelha média, especialmente da anatomia da cavidade timpânica posterior. A avaliação pré-operatória da cavidade timpânica é limitada pela permeabilidade do tímpano e densidade do osso temporal. Portanto, a exploração da orelha média é um método extremamente útil para identificar anormalidades estruturais e variações anatômicas. Objetivo Determinar as variações anatômicas da orelha média em uma série de autópsias. Método Todas as avaliações foram realizadas no necrotério do Instituto Médico-Legal. Os casos com mais de 18 anos, sem trauma do osso temporal e história de cirurgia otológica foram incluídos neste estudo. Resultados Cento e dois cadáveres foram incluídos no estudo. A média de idade foi de 49,08 ± 17,76 anos. A proeminência da parede anterior do conduto auditivo externo estava presente em 27 de todos os cadáveres (26,4%). A membrana timpânica era normal em 192 orelhas (94%), enquanto várias alterações do tímpano foram detectadas em 12 orelhas (6%). Agenesia da eminência piramidal e do tendão do estapédio foi encontrada em 3 orelhas. Enquanto o pontículo tinha formato de crista óssea em 156 das 204 orelhas (76,4%), tinha o formato de ponte em 25 orelhas (12,3%). O pontículo estava ausente em 23 orelhas (11,3%). Enquanto o subículo completo estava presente em 136 de todas as orelhas (66,7%), encontrava-se incompleto em 21 orelhas (10,3%). O subículo estava ausente em 47 orelhas (23%). Deiscência facial foi encontrada em 32 orelhas e o nicho da janela redonda estava coberto por uma pseudomembrana em 85 orelhas (41,6%). A platina fixa foi observada em 7,4% de todas as orelhas e a artéria estapediana persistente não foi vista. Conclusão A frequência da pseudomembrana que cobre o nicho da janela redonda foi diferente daquela encontrada na literatura. Além disso, a frequência da proeminência da parede do canal auditivo externo foi relatada pela primeira vez.

Endoscopic evaluation of middle ear anatomic variations in autopsy series: analyses of 204 ears.

INTRODUCTION: Microsurgery of the ear requires complete evaluation of middle ear surgical anatomy, especially the posterior tympanic cavity anatomy. Preoperative assessment of the middle ear cavity is limited by the permeability of eardrum and temporal bone density. Therefore, middle ear exploration is an extremely useful method to identify structural abnormalities and anatomical variations. OBJECTIVE: The aim of this study is to determine anatomic variations of the middle ear in an autopsy series. METHODS: All evaluations were performed in the Forensic Medicine Institute Morgue Department. The cases over 18 years of age, with no temporal bone trauma and history of otologic surgery included in this study. RESULTS: One hundred and two cadavers were included in the study. The mean age was 49.08±17.76 years. Anterior wall prominence of the external auditory canal was present in 27 of all cadavers (26.4%). The tympanic membrane was normal in 192 ears (94%) while several eardrum pathologies were detected in 12 ears (6%). Agenesis of the pyramidal eminence and stapedial tendon was found in 3 ears. While the ponticulus was bony ridge-shaped in 156 of 204 ears (76.4%), it was bridge-shaped in 25 ears (12.3%). The ponticulus was absent in 23 ears (11.3%). While complete subiculum was present in 136 of all ears (66.7%), incomplete subiculum was present in 21 ears (10.3%). Subiculum was absent in 47 ears (23%). Facial dehiscence was found in 32 ears and the round window niche was covered by a pseudomembrane in 85 ears (41.6%). A fixed footplate was present in 7.4% of all ears, and no persistent stapedial artery was seen in any cases. CONCLUSION: The pseudomembrane frequency covering the round window niche was found different from reports in the literature. In addition, the frequency of the external auditory canal wall prominence has been reported for the first time.

Microtomographic morphometry of the stapedius muscle and its tendon.

The aim of this study was to evaluate the morphology of the stapedius muscle and its tendon with the use of microCT and to describe their anatomic relationship with facial nerve and incudostapedial joint. The study was performed on 16 fresh cadaveric temporal bones scanned in microtomography (microCT). Stapedius muscle and its tendon were identified in each set of images. The length of the medial and lateral border of the stapedius tendon (STL-med, STL-lat), width at the insertion to stapes (STW-s), at the point it emerges from the pyramidal eminence (STW-p) and in the half way from the pyramidal eminence to stapes (STW-m), and the length and the width of the belly of stapedius muscle (BSML and BSMW) were measured in modified axial plane. The shortest distance between the facial canal and incudostapedial joint (FN-isj), and between the facial canal and stapedius tendon (FN-st) were measured in the Pöschl plane. The average values of all distances measured were: STL-lat 1.29 ± 0.50 mm, STL-med 1.27 ± 0.44 mm, BSML 2.98 ± 0.51 mm, STW-s 0.47 ± 0.10 mm, STW-p 0.46 ± 0.12 mm, STW-m 0.35 ± 0.12 mm, BSMW 1.26 ± 0.29 mm, FN-isj 1.72 ± 0.33 mm, FN-st 1.35 ± 0.30 mm. The stapedius muscle complex consists of the tendon and the belly, and the border between them in microCT scans is not always evident. The distance between the facial nerve and the incudostapedial joint is greater than the distance between the facial nerve and the stapedius muscle tendon.

Assessment of Middle Ear Anatomy Teaching Methodologies Using Microscopy versus Endoscopy: A Randomized Comparative Study.

Teaching methodologies for the anatomy of the middle ear have not been investigated greatly due to the middle ear's highly complex structure and hidden location inside of the temporal bone. The aim of this randomized study was to quantitatively compare the suitability of using microscope- and endoscope-based methods for teaching the anatomy of the middle ear. We hypothesize that the endoscopic approach will be more efficient compared to the microscopic approach. To answer the study questions, 33 sixth-year medical students, residents and otorhinolaryngology specialists were randomized either into the endoscopy or the microscopy group. Their anatomical knowledge was assessed using a structured anatomical knowledge test before and after each session. Each participant received tutoring on a human cadaveric specimen using one of the two methods. They then performed a hands-on dissection. After 2-4 weeks, the same educational curriculum was repeated using the other technique. The mean gains in anatomical knowledge for the specialists, residents, and medical students were +19.0%, +34.6%, and +23.4%, respectively. Multivariate analyses identified a statistically significant increase in performance for the endoscopic method compared to the microscopic technique (P < 0.001). For the recall of anatomical structures during dissection, the endoscopic method outperformed the microscopic technique independently of the randomization or the prior training level of the attendees (P < 0.001). In conclusion, the endoscopic approach to middle ear anatomy education is associated to an improved gain in knowledge as compared to the microscopic approach. The participants subjectively preferred the endoscope for educational purposes.

Novel Surgical and Radiologic Classification of the Subtympanic Sinus: Implications for Endoscopic Ear Surgery.

Objective The aim of this study is to describe the endoscopic anatomy of the subtympanic sinus (STS), establish a classification according to its extension regarding the level of the facial nerve (FN), and assess the feasibility of the transcanal endoscopic approach to the STS. Study Design Experimental anatomic research. Setting Temporal bone laboratory. Methods We performed endoscopic dissection of 34 human whole head and ear block specimens. Of those, 29 underwent high-resolution computed tomography. The STS was classified according to its extension regarding the level of the FN: type A, no extension medial to the FN; type B, extension to the medial limit of the FN; type C, extension of the sinus medially and posteriorly from the FN into the mastoid cavity. Results The majority of cases (n = 21, 72%) showed a shallow type A STS. We observed a deep type B configuration in 6 cases (21%) and a type C in 2 cases (7%). The STS was completely exposable with a 0° endoscope in 44% of the specimens. Using a 45° endoscope, we gained complete insight in 79%. However, in 21% of the cases, the posteromedial extension of the STS was too deep to be completely explored by an endoscopic transcanal approach. Conclusion The majority of the STS is shallow and does not extend medially from the FN. This morphologic variant allows complete transcanal endoscopic visualization. In more excavated STS, a complete endoscopic exploration is not achievable, and a retrofacial approach may be adopted to completely access the STS.

Facial sinus endoscopic evaluation, radiologic assessment, and classification.

OBJECTIVES: To describe facial sinus anatomy from an endoscopic perspective and present a radiologic classification. METHODS: Facial sinus was studied by endoscopy and high-resolution computed tomography (HRCT) scan in 39 temporal bones that underwent exclusive transcanal endoscopic approach. A radiomorphologic classification based on the relationship between the facial sinus and the mastoid portion of the facial nerve is created as follows. In type A facial sinus, the pneumatization of the facial sinus did not extend medially or posteriorly to the mastoid portion of the facial nerve. In type B facial sinus, the pneumatization extended posteriorly to the mastoid portion of the facial nerve. In type C facial sinus, the pneumatization extended posteriorly and medially to the mastoid portion of the facial nerve. RESULTS: In all the specimens that underwent HRCT (n = 31), facial sinus could be identified, and its depth classified, in relation to the facial nerve. In this group, 58% type A, 29% type B, and 13% type C facial sinuses were identified. In all the specimens (n = 39), the facial sinus could be assessed by means of an exclusive endoscopic transcanal approach, and anatomical variants of the chordiculus, previously known as chordal ridge, could be described: ridge (39%), bridge (18%), incomplete (15%), and absent (28%). CONCLUSION: Endoscopic exploration of the retrotympanum guarantees a very good exposure of the facial sinus, allowing detailed anatomic descriptions of its conformation and relationships with other structures. Improvement in our knowledge of its anatomy might decrease the possibility of residual disease during cholesteatoma surgery. Angled endoscopes (e.g. 45 °, 70 °) can guarantee a better view of the facial sinus. LEVEL OF EVIDENCE: NA. Laryngoscope, 128:2397-2402, 2018.

The variants of the retro- and hypotympanum: an endoscopic anatomical study.

The retro- and hypotympanum are hidden areas of the middle ear, only poorly recognized. Nevertheless, this region is of relevant clinical significance, since it is regularly affected by disease such as cholesteatoma. The aim of this study is to explore and describe the anatomical variants of the hypo- and retrotympanum by the means of transcanal endoscopy. We hypothesize a significant variability of this hidden region of the middle ear. Moreover, we believe that the minimal invasive, endoscopic access is suitable since angled scopes may be used to explore the region. To this end a total of 125 middle ears (83 cadaveric dissections, 42 surgical cases) were explored by the means of 3 mm straight and angled scopes. The variants were documented photographically and tabularized. The bony crests ponticulus, subiculum and finiculus were most frequently represented as ridges. The ponticulus showed the highest variability with 38% ridge, 35% bridge and 27% incomplete presentation. The subiculum was bridge-shaped only in 8% of the cases, the finiculus in 17%. The sinus tympani had a normal configuration in 66%. A subcochlear canaliculus was detectable in 50%. The retro- and hypotympanum were classified, respectively, to the present bony crests and sinus in a novel classification type I-IV. In conclusion, we found abundant variability of the bony structures in the retro- and hypotympanum. The endoscopic access is suitable and offers thorough understanding and panoramic views of these hidden areas.