Ana Cisneros

Fetal Development of the Human Tympanic Ossicular Chain Articulations

Objectives: To obtain further knowledge on the morphogenesis of the articulations in the tympanic ossicular chain in humans. Material and Methods: In 25 temporal bones of human fetuses the structural development of incudomallear, incudostapedial and stapediovestibular articulations was studied. The chronological ages were between the 7th week (21 mm) and the 29th week (270 mm). Results and Discussion: Incudomallear articulation showed diarthrosis and sellar joint characteristics. It showed a homogenous interzone in the 7th week of development, a three-layered interzone in the 8th week, the first cavitation signs in the 9th week and the presence of an articular cavity in the 10th week. The presence of a hyaline cartilage covering articular surfaces was observed starting in the 20th week of development. Incudostapedial articulation showed typical characteristics of a diarthrosis and spheroidal joint with a homogenous interzone at the 7th week, showing similar characteristics for 12 weeks, and completed its cavitation at the 16th week. We observed hyaline cartilage on articular surfaces from 29 weeks. Stapediovestibular articulation showed typical characteristics of syndesmosis. The annular ligament primordium derived from cartilage differentiation, both from stapedial footplate and from the surrounding otic capsule, into mesenchyme and its subsequent transformation into fibrous tissue, reaching definitive characteristics from the 12th week.

Influencia de la existencia de una dehiscencia en un canal semicircular en el espesor óseo de los canales contralaterales

OBJECTIVES Our objective was to determine if the existence of dehiscence in the superior or posterior semicircular canal was associated with the thinning of the bone roof in the rest of the vertical canals (superior or posterior). METHODS The thickness of the superior and posterior semicircular canals contralateral to a dehiscence was studied using computerized tomography and compared statistically. RESULTS When a superior semicircular canal had a dehiscence, the contralateral canal showed a significant mean decrease in its thickness of 0.5mm (SD: 0.3 mm). This was not the case if the dehiscence was in the posterior semicircular canal, where the thickness of 2.1 mm remained unchanged (SD: 1.2 mm; P=.49). When a posterior semicircular canal showed dehiscence, no significant thinning was shown in the superior semicircular (1 mm; SD: 0.4) or in the posterior contralateral (1.3 mm; SD: 0.3) canals. CONCLUSION The existence of a dehiscence in the superior semicircular canal is associated with bone thinning in the canal on the opposite side, but not with the posterior semicircular canal. In contrast, if the dehiscence is in the posterior semicircular canal, contralateral and superior canal thickness is not modified.

Association Between Tegmen Tympani Status and Superior Semicircular Canal Pattern.

Objective: Detecting and quantifying the possible association between tegmen tympani (TT) status and superior semicircular canal (SSC) pattern. Design: Observational study. Setting: Study conducted in three tertiary Spanish hospitals. Patients: Nonselected consecutive patients of all ages (607 temporal bones). Interventions: Thin-section multidetector row computed axial tomography (CAT scan) of the temporal bones. Main Outcome Measure: Thickness of SSC bone coverture adjacent to the middle fossa, and TT status as a dichotomous variable: dehiscence (TTD) or integrity (TTI). Results: The observed SSC patterns were dehiscence (3.79%), papyraceous or thin (11.20%), normal (76.77%), thick (4.94%), and pneumatized (3.29%). The observed TT statuses were TTD (10.87%) and TTI (89.13%). TTD was associated with SSCD and papyraceous patterns, and TTI percentages were higher in normal and thick patterns (&khgr;2 = 11.102; p = 0.001). The TTD probability was estimated as a function of SSC pattern and age by a multivariate binary logistics regression model (&khgr;2 = 45.939; p < 0.001). Conclusion: SSC pattern was significantly associated with TT status. Age influenced this association. The risk for TTD increased by 4.1% per each year of increasing age, did not differ significantly for normal and thick patterns, and increased 12 times and 20 times for papyraceous and SSCD patterns, respectively.

Congenital dehiscence in the posterior semicircular canal.

Hypothesis Posterior semicircular canal dehiscence (PSCD) may be of congenital origin. Background PSCD is characterized by the lack of bone coverage, which results in its lumen being exposed to the meninges of the posterior cranial fossa or to the gulf of the jugular vein. It has an incidence of 0.2%. Its presence has been associated with several well-defined entities, although a congenital origin has not been proven. Methods We have analyzed, from a macroscopic, microscopic, and radiologic (computed tomography) viewpoint, the right temporal bone of a 32-week-old human fetus that presented a defect in the bone coverage located in the rear. Results The macroscopic study showed a solution of continuity in the posterior semicircular canal, with elliptic morphology and smooth edges. This defect was 3.4 mm long with a width that varied between 0.67 mm in its apical portion and 1.42 in the basal portion. The radiologic study (computed tomography) showed the absence of bone coverage of the posterior semicircular canal, which was open to the intracranial space in the posterior fossa. Its histologic study showed good bone coverage of this canal at the expense of compact bone tissue. However, at the medial end, there is a lack of bone coverage, resulting in the lumen of the canal being open to the intracranial space. The bone edges of the defect did not present any osteoclast activity. Conclusion The lack of bone coverage (dehiscence) of the posterior semicircular canal in a 32-week-old fetus suggests a congenital component of bony dehiscences of this canal. Even so, this single finding does not conclusively prove the congenital component, and the dehiscence is a finding that can be part of and not by itself a syndrome.

Tympanic Ossicles and Pharyngeal Arches

We have performed a study on 11 human embryos regarding the development of the tympanic ossicles and their relationship with the first pharyngeal arch. After performing measurements to date the embryos and foetuses chronologically, we performed a meticulous dissection of the temporal bones. Subsequently, they were fixed in 10% formol, decalcified with 2% nitric acid, embedded in Paraplast, sectioned in 7‐mm sequences and stained with Martin’s trichrome technique. In the 21‐ and 24‐mm cranium‐raquis (CR) length human embryos, we have observed the head of the malleus and the body of the incus close to Meckel’s cartilage, in addition to the handle of the malleus, the long limb of the incus and the stapes. Between them there was a mesenchymal band inside the primordium of the tympanic cavity. In the 27‐mm CR embryo, the various components of the malleus and incus were fusing, and in the 30‐mm CR embryo the union was complete. From our observations, we can conclude that the malleus and the incus are derived from the first and second pharyngeal arches.

Peculiaridades en el desarrollo del canal semicircular superior

OBJECTIVE Our objective was to study the ontogeny of the superior semicircular canal in order to describe its peculiarities. METHODS We analyzed 76 series of human embryos aged between 32 days (6mm) and newborns. The samples were cut serially and stained using Martins trichrome technique. RESULTS In semicircular canal development there were a number of peculiarities, such as: a defined chronological sequence of osteogenesis with a variable rate of ossification; the fact that each nucleus of ossification was involved in the formation of one of its covers (the upper in the superficial and the lower in the deep); the appearance of transitory dehiscence; and canal closure by means of bone with laminar pattern, with a minimum thickness of 0.1mm. CONCLUSION The peculiarities in canal development could explain the origin of pathological dehiscence in the canal, whether congenital or acquired.

Defecto de cobertura del canal semicircular superior y su implicación clínica

INTRODUCTION AND OBJECTIVE The aetiology of the superior semicircular canal dehiscence is currently unknown. Our objective was to analyse and discuss different hypotheses about the origin of this pathology. METHODS In this study performed on 295 temporal bones, one case of partial alteration of the bony roof in the right superior semicircular canal was described from the anatomical and radiological points of view, and compared with the temporal bone on the other side. RESULTS Macroscopically, the superior semicircular canal shows deterioration in the bony roof, which consists exclusively of the inner or endosteal layer that separates the canal from the superior semicircular conduct. The Pöschl plane reconstruction showed a whole bony roof, but its thickness decreased from the canal curvature to the defect (from 0.6 to 0.3mm). CONCLUSION The presence of partial defects in the bony roof of the superior semicircular canal with absence of the external and middle layers, besides its lesser thickness, makes the canal susceptible to suffering a second event. This could produce its fracture and a dehiscence.

Explicación ontogénica para la asociación entre dehiscencia del tegmen tympani y dehiscencia del canal semicircular superior

OBJECTIVES To analyze the ontogeny of the superior semicircular canal and tegmen tympani and determine if there are common embryological factors explaining both associated dehiscence. METHODS We analyzed 77 human embryological series aged between 6 weeks and newborn. Preparations were serially cut and stained with Massons trichrome technique. RESULTS The tegmental prolongation of tegmen tympani and superior semicircular canal originate from the same structure, the otic capsule, and have the same type of endochondral ossification; while the extension of the squamous prolongation of tegmen tympani runs from the temporal squama and ossification is directly of intramembranous type. The nuclei of ossification of the superior and external semicircular canals and accessory of tegmen collaborate in the ossification of the tegmental extension and by growth extend to the tegmental prolongation. This fact plus the fact that both structures share a common layer of external periosteum could explain the coexistence of lack of bone coverage in tegmen and superior semicircular canal. CONCLUSION The development of the semicircular canal and tegmen tympani could explain the causes of the association of both dehiscences.

Peculiaridades Anatómicas del Canal Semicircular Superior y su Posible Implicancia Clínica

El objetivo fue estudiar las peculiaridades en la morfologia apical del canal semicircular superior, a nivel de la eminencia arcuata con la finalidad de obtener conclusiones aplicativas. Se estudiaron 48 cabezas de cadaveres humanos (96 huesos temporales), con la intencion de identificar la presencia de adelgazamiento o dehiscencia del canal semicircular superior, asi como la existencia de surcos vasculares de la eminencia acuata que, discurriendo sobre el techo del canal, pudieran afectar a su integridad anatomica. El estudio incluye un analisis histologico (Tricromico de Martins) y radiologico (Tomografia Computarizada) de los hallazgos positivos (dehiscencias y adelgazamientos), asi como estudio tomografico de los canales con surcos vasculares visibles. En un caso (1,04 %) hemos observado como el canal presentaba un defecto oseo completo (dehiscencia), en tres (3,12%) el canal presentaba una pared muy delgada cuyo grosor no excedia de 0,2 mm. En 12 casos (12,5%) la eminencia arcuata estaba recorrida por surcos por el que discurrian vasos colaterales meningeos, que determinaron una concavidad entre 0,1 y 0,2 mm, mientras que el grosor medio de dicha pared en estos casos fue de 1,2 mm. De las tres peculiaridades estudiadas, la falta de cobertura osea es la que produce el sindrome de dehiscencia del canal semicircular superior. Los canales que presentaban una cubierta adelgazada pueden estar predispuestos a una rotura y por lo tanto causar patologia en el canal. En cambio la presencia de surcos vasculares que recorren la superficie apical del canal, no parece tener consecuencias al disminuir minimamente su grosor.

Development of ossification in the vertical semicircular canals: tomographic study

PurposeTo describe the ontogeny of vertical semicircular canals using computed tomography.Materials and methodsWe have studied 39 human fetuses aged between 17 and 38 weeks of development through multi-helicoidal CT.ResultsThe first signs of ossification in the semicircular canals, superior and posterior, are from 19 weeks of development, through two primary ossification centers in each canal, which will take part in the formation of the outer cover oriented towards the middle and posterior brain fossae, respectively. In this process it must be added the intervention of the common branch. Internal bone covers are formed by ossification of the fossa subarcuata in the superior semicircular canal, and from the compact center of the labyrinthine capsule into the posterior canal. The tomographic study has allowed us to demonstrate how ossification follows a variable rate, establishing a period between 21 and 26 weeks where there are completely closed canals with others still open to the brain fossae.ConclusionsThe tomographic study of the semicircular canals has enabled us to establish a critical period in its ossification that could explain the etiology of the congenital-type dehiscence.