Postnatal development of the subarcuate fossa and subarcuate canaliculus-a computed tomographic study.

PURPOSE: The subarcuate fossa (SF) is an anatomical structure situated on posterior wall of the petrous part of the temporal bone. In older children and adults, SF is a shallow depression and the subarcuate canaliculus starts within it. Awareness of postnatal changing morphology of this region is important especially for otosurgeon. The aim of this paper is to characterize both SF and SC by means of anatomical and radiological methods. METHODS: The study was carried out on CT scans of 101 children, aged 1-60 months. Length of the pyramid (PL), the distance between the anterior semicircular canal (ASC) and the pyramidal apex (PLM), the outer diameter of ASC (ASCD), width under ASC (SFWM), the distance between the fundus of SF and ASC (SFLL), the maximal width of SF lateral to ASC (SFWL), the distance between the fundus of SF and posterior surface of the pyramid (SFL) were measured. RESULTS: Average value of all measured distances: PL 52.14 ± 6.32 mm and PLM 25.73 ± 3.47 mm (raised with age); ASCD 8.63 ± 0.67 mm; SFWM 0.95 ± 1.24 mm; SFLL 1.07 ± 1.63 mm; SFWL 0.76 ± 1.19 mm; SFL 3.60 ± 2.50 mm. CONCLUSIONS: Petrous part of the temporal bone grows with age up to 5 years old, whereas ASC does not. SF diminishes with age: lateral to ASC is well developed in newborns and infants (up to first year), rapidly diminishes in children aged 1-2 years and is totally absent in children > 2 years. SF medial to ASC is constant and diminishes with age. In children older than 3 years morphology of SF is similar to adult.

The developing temporal bone: computed tomography measurements and assessment of suture closure from birth to 18 years of age.

PURPOSE: To describe the normal CT appearance of the developing temporal bone in children from birth to 18 years of age. METHODS: Two hundred and six temporal bone CTs of children from 0.14 to 18.95 years were retrospectively selected and reviewed. Temporal bones were measured in a standardized slice orientation using the length of the basal turn of the cochlea, the length and width of the petrous bone, the coronal extent, trailing edge and anterior-posterior dimension of the temporal bone and the angle between petrous bone's length and the midsagittal line in the axial plane showing the basal turn of the cochlea in its greatest extent. Two sutures, two synchondroses and three fissures of the temporal bone were evaluated and graded. RESULTS: Chosen measurements and calculations demonstrate an increase of values from 0 to 18 years with the greatest increase occurring during the first 2 years of life. The angle between the basal turn of the cochlea and the midsagittal line shows a large variability. Logarithmic trend lines illustrate larger measurements of males as compared to females. The ratio of the basal turn of the cochlea and the length of the petrous bone is about 1:4.1 (f/m) during the first year of life and about 1:6.1 (f)/1:6.8 (m) from 17 years onwards. Results of suture closure are described using box-and-whisker plots. CONCLUSIONS: The developing temporal bone grows the most during the first 2 years of life. Knowledge of changing proportions and suture closure is essential for evaluation of temporal bone CT of children.

Prenatal growth stages show the development of the ruminant bony labyrinth and petrosal bone.

Foetuses are a source of scientific information to understand the development and evolution of anatomical structures. The bony labyrinth, surrounding the organ of balance and hearing, is a phylogenetically and ecologically informative structure for which still little concerning growth and shape variability is known in many groups of vertebrates. Except in humans, it is poorly known in many other placentals and its prenatal growth has almost never been studied. Ruminants are a diversified group of placentals and represent an interesting case study to understand the prenatal growth of the ear region. We computed tomography -scanned five cow foetuses and an adult petrosal bone (Bos taurus, Artiodactyla, Mammalia), and describe the bony labyrinth when already ossified. The foetuses encompass the second half of the 9.3-month-long gestation period of the cow. They were sampled at different ontogenetic stages to understand how and when the petrosal bone and bony labyrinth ossify in ruminants. The petrosal bone and bony labyrinth ossify within about 20 days in the fourth month of gestation. The bony labyrinth is already fully ossified at least in the 6th month, while only the cochlea, most of the vestibule and the common crus are already ossified at the beginning of the 4th month. The pars canalicularis of the petrosal thus ossifies at last. The size and volume of the bony labyrinth stay similar from the 6th month (possibly even from the 5th). From the end of the 4th month of gestation, a progressive lengthening of the cochlear aqueduct and endolymphatic sac occurs, culminating in the adult form and partly explaining the larger volume of the later. The inner ear in the cow ossifies quickly during the gestation period, being fully ossified around mid-gestation time, as in humans. The adult size and most of its volume are reached by mid-gestation time while the petrosal bone and skull still grow. A negative ontogenetic allometry between the bony labyrinth and the petrosal bone and skull is thus observed. It matches the evolutionary negative allometry of the structure observed in earlier studies. Few changes occur after ossification is achieved; only open structures (i.e. cochlear aqueduct and endolymphatic sac) continue to grow after birth and reflect size increase of the petrosal bone.

Age classes and sex differences in the skull of the Mediterranean monk seal, Monachus monachus (Hermann, 1779). A study based on bone shape and density.

This study analyzes morphometrically 17 skulls of the Mediterranean monk seal Monachus monachus housed in different Italian Museums and collections. We considered several morphometric variables (31 linear, 1 volumetric and 1 surface area measurements). In addition, we identified, measured and compared two nonmorphometric variables, namely, the bone densities of selected areas obtained using a dual-energy X-ray absorptiometry (DXA) device. The high correlation coefficient of all variables indicated continuous growth with the onset of age. The ranking of the hierarchical cluster analysis identified the presence of three main groups containing individuals of similar sizes: lactating pups and yearlings; subadult individuals and adult females; and adult males. Smaller groups were identified within these clusters, and their respective allocations into two subgroups were argued on the basis of skull development and other factors. The discriminant analysis of the three main groups indicated a discriminant diagnostic key, based on condilobasilar length (CBlr-L); maximum mandibular branch height (MB-H); and surface area of the bulla tympanica. The proposed diagnostic key is useful to classify monk seal skulls of unidentified age and sex. The data reported here suggest that in this species certain adult skull growth features (enhanced tympanic bullae surface area extension, occipital bone density) are sexually dimorphic and possibly related to specific anatomical functions. These functions may include an enhanced auditory capacity; an increased development of the cranial musculature capable of supporting a large skull and guaranteeing the mandibular strength necessary for mastication; and male to male social interactions.

Petrous carotid canal dehiscence: an anatomic and radiographic study.

HYPOTHESIS: Development of the osseous petrous carotid canal is frequently incomplete. BACKGROUND: Although dehiscence of the carotid canal has been observed in previous studies, the frequency and extent of bony dehiscence have not been quantified. Inadvertent internal carotid artery injury occurs in 3 to 5% of skull base procedures, with an additional 1.9% of patients having carotid artery vasospasm. Documentation of the incidence of petrous apex carotid canal dehiscence is therefore warranted. METHODS: Ninety-nine cadaveric skulls were evaluated physically and by computed tomographic scan. RESULTS: Incidence of dorsal (endocranial) dehiscence of the petrous carotid canal was identified in 82.83% of the left side and 88.89% of the right side. Average dimensions for left dorsal dehiscence measured 10.81 mm longitudinally by 4.10 mm transversely. Dimensions for the right averaged 11.59 mm longitudinally by 4.29 mm transversely. Incidence of ventral (exocranial) dehiscence was less frequent: 37.37% on the left and 34.34% on the right. Ventral dehiscence was classified into major (absence of bone) and minor (fissure) types. Major dehiscence was observed in 8.08% and 6.06% of specimens for left and right sides, respectively; minor ventral dehiscence was present in 29.29% and 28.28% for left and right sides, respectively. CONCLUSION: Dorsal petrous carotid canal dehiscence is more common than previously recognized. Dehiscence of the dorsal carotid canal is a frequent finding with significant implications in advanced skull base approaches to the petrous apex, clivus, and lateral sellar compartment. Ventral dehiscence is a frequent finding that will become increasingly relevant as the scope of endoscopic skull base procedures.

Assessing age-related ossification of the petro-occipital fissure: laying the foundation for understanding the clinicopathologies of the cranial base.

The petro-occipital fissure (POF) lies within a critical interface of cranial growth and development in the posterior cranial fossa. The relationships between skeletal and soft tissues make this region especially important for examining biomechanical and basic biologic forces that may mold the cranial base and contribute to significant clinicopathologies associated with the structures located near the POF. Therefore, this study investigates the POF in adults in both preserved human cadavers and dried crania in order to determine if developmental changes can be observed and, if so, their value in age assessment as a model system for describing normal morphogenesis of the POF. This study demonstrates that tissue within the POF undergoes characteristic changes in ossification with age, the onset of which is considerably later than that of other synchondroses of the cranial base. Statistically, there is a moderate to strong correlation between age and stage of ossification within the POF. Further, male crania were observed to reach greater degrees of ossification at a younger age than female crania and that individual asymmetry in ossification of the tissue within the POF was not uncommon. An understanding of the basic temporal biological processes of the POF may yield insight into the development of clinicopathologies in this region of the cranial base.

The effect of neurocranial surgery on basicranial morphology in isolated sagittal craniosynostosis.

OBJECTIVE: Isolated sagittal craniosynostosis produces a scaphocephalic neurocranium associated with abnormal basicranial morphology, providing additional evidence of the developmental relationship of the neurocranium and basicranium. Corrective surgical procedures vary, but the immediate impact of the surgical procedure is restricted to the neurocranium. This study addresses the secondary effects of neurocranial surgery on the cranial base. DESIGN: Three-dimensional (3-D) computed tomography (CT) scans were obtained for preoperative (n = 25) and postoperative (n = 12) patients with isolated sagittal synostosis. Landmark data from 14 landmarks on and around the cranial base were collected from 3-D CT reconstructions and analyzed using Euclidean distance matrix analysis. Subsamples of age-matched patients were used to identify basicranial differences in pre- and postoperative patients and to compare postoperative growth patterns identified in longitudinal data with preoperative growth patterns characterized in cross-sectional data. RESULTS: Statistically significant differences (p < or = 0.10) were found in the morphology of the cranial base in preoperative and postoperative patients. The relative positions of the landmarks nasion, right asterion, and left asterion are similar in preoperative and postoperative patients. However, the position of these landmarks relative to the cranial base is different in the two groups, being positioned relatively more anteriorly in postoperative patients. In addition, we found that the cranial base angle, on average, neither increases nor decreases in the first postoperative year. These morphological differences are associated with divergent growth trajectories in the operated and unoperated cranial base. CONCLUSION: Regardless of specific procedure, neurocranial surgery in sagittal synostosis patients affects growth patterns of the cranial base. The lack of change in the postoperative cranial base angle suggests that neurocranial surgery alleviates the occipital rotation and decreased cranial base angle described in the sagittal synostosis basicranium.

[Computed tomographic findings of the development of the bone around the vestibular aqueduct in Meniere's disease].

OBJECTIVE: To study the development of the bone around the vestibular aqueduct (VA) in Meniere's disease (MD) by CT. METHOD: The experiment consisted of three groups; normal ear group, non-MD vertigo group and MD group. VA in each group was examined by CT, and the minimum distance between the posterior semicircular canal and the posterior petrous surface where contain the endolymphatic sac. RESULT: VA visualization rate in MD was low, P-P distance in MD group was shorter than that of normal ear group and non-MD vertigo group. CONCLUSION: It is the fundamental pathological anatomy in MD that VA and the bone around VA are maldeveloped.

Imaging findings of the developing temporal bone in fetal specimens.

PURPOSE: To trace the development of the normal fetal temporal bone by means of plain radiography, MR, and CT. METHODS: Eighteen formalin-fixed fetal specimens, 13.5 to 24.4 weeks' gestational age, were examined with a mammographic plain film technique, CT, and MR imaging at 1.5 T. Temporal bone development and ossification were assessed. RESULTS: The membranous labyrinth grows with amazing rapidity and attains adult size by the middle of the gestation period. The cochlea, vestibule, and semicircular canals are very prominent and easily recognized on MR images. The otic capsule develops from a cartilage model. Ossification of the otic capsule proceeds rapidly between 18 and 24 weeks from multiple ossification centers that replace the cartilaginous framework. The mastoid, internal auditory canal, vestibular aqueduct, and external auditory canal continue to grow after birth. CONCLUSION: The study of fetal developmental anatomy may lead to a better understanding of congenital disorders of the ear. Faster MR scanning techniques may provide a method for in utero evaluation of the fetal temporal bone.

[Developmental studies on the petrous part of the human temporal bone--special references to the morphogenesis of the facial nerve canal].

Development and formation of the petrous bone was examined in total of 343 Japanese skulls. The materials used consisted of 310 skulls of Japanese fetuses ranging from the fourth to tenth month, 19 skulls of Japanese juveniles from the third month to 7 years of age, and 20 temporal bones obtained from 14 adult cadavers. A total of six group of ossification centers appear in the petrous part during 5th fetal month, and they form the petrous bone at 6th fetal month. The firstly-appeared ossification center is just above the round window, and the second is on the ampulla of anterior semicircular canal. Other ossifications are observed between the cochlea and semicircular canals, on the brim of internal acoustic porus, on the superior surface of the petrous apex, and on the summit of posterior semicircular canal. The ossification of the facial canal starts at 6th fetal month, though the geniculate part and tympanic part do not complete until one year old after birth. Even in adults, the facial canal dehiscence are found at more than 10% of cases, mainly locating in the tympanic part. On the basis of these results, formation of the petrous bone including facial canal and other bony structures was discussed from the viewpoints of the ossification and pre- and postnatal middle ear development.

Suture closure in the human chondrocranium: CT assessment.

PURPOSE: To chronicle the development of ossification centers, sutures, and synchondroses in the chondrocranium throughout childhood by using computed tomography (CT). MATERIALS AND METHODS: One hundred eighty-nine children (age range, newborn to 18 years; median age, 4.0 years) without skull base deformity were referred for cranial CT. The closure of 18 sutures and synchondroses was graded. RESULTS: In the occipital bone at birth, six components were identified. The Kerckring ossicle rapidly fused to the supraoccipital bone within the 1st month. At age 1-3 years, the posterior and anterior intraoccipital synchondroses began to fuse. The occipitomastoidal, petro-occipital, and spheno-occipital synchondroses remained partially open into the teenage years. In the sphenoid bone at birth, 13 ossification centers were identified; most assimilated into the sphenoidal body during the first 2 years. Pneumatization of the sphenoid sinus appeared at age 1-2 years and advanced posteriorly over the next 3-5 years. CONCLUSION: The complex process of skull base development is chronicled, which provides CT standards for judgment of the patterns and timing of sutural or synchondrosal closure.

Postnatal development of the internal auditory canal studied by computer-aided three-dimensional reconstruction and measurement.

Postnatal development of the internal auditory canal (IAC) was investigated in 20 normal human temporal bones obtained from individuals 1 month to 72 years old. Computer-aided three-dimensional reconstruction and measurement of bones showed that the superior, inferior, anterior, and posterior walls of the IAC lengthen significantly from birth until about 10 years of age, with development mainly attributable to lengthening of the part of the IAC medial to the foramen singulare. The lengths of the part of the IAC lateral to the foramen singulare and of the transverse crest and Bill's bar did not appear to develop postnatally. The IAC diameter increased slightly at the porus for about the first year after birth, but not at the fundus or the middle portion of the canal. This finding was confirmed by studying the shape of the IAC. Postnatal increases in the volume of the IAC followed patterns similar to that of increases in length of studying the shape of the IAC. Postnatal increases in the volume of the IAC followed patterns similar to that of increases in length of the IAC walls. These results show that postnatally the IAC increases significantly in length until about 10 years of age and slightly in diameter until about 1 year of age, especially medial to the foramen singulare. This concentration of growth of the IAC medially implies that its postnatal development is mainly due to growth of the bone around the otic capsule, which has implications for IAC surgery.

Postnatal development of the vestibular aqueduct in relation to the internal auditory canal. Computer-aided three-dimensional reconstruction and measurement study.

To investigate a possible developmental relationship between the internal auditory canal (IAC) and the vestibular aqueduct (VA), we made the following measurements in 10 normal temporal bones from individuals 4 months to 70 years of age at death, using a computer-aided three-dimensional reconstruction and measurement method: the volume of the VA, the length of the IAC, and the distance between the IAC and the external aperture of the VA. The degree of periaqueductal pneumatization was also assessed qualitatively by means of a light microscope. The three parameters increased postnatally in parallel with the development of the periaqueductal air cells, and all pairwise comparisons of these parameters showed a statistically significant correlation. Our results indicate that the IAC and VA develop synchronously and in parallel with the development of the periaqueductal air cells. We believe that an understanding of this relationship will be of help during surgery involving the IAC and VA, and may shed some light on the morphological features of Meniere's disease.

[Anatomical study on the sphenoidal sinus and petrous apex cells].

Morphological relation between the sphenoidal sinus and the petrous apex cell was studied using HRCT images obtained by 339 adults and 43 infants. The adults were classified into normal group (without chronic otitis media or its surgery) 237 cases, and otitis group (chronic otitis media or its post. op.), 102 cases. The posterior extent of the sphenoidal sinus was evaluated in reference to the carotid canal, and the petrous apex cells were evaluated by their mode of distribution in the apex. In the normal adults, no evident relation was seen between the posterior extent and the mode of distribution. Although adult normal female showed statistically significant better development of the posterior extent, sinus-cell relation was similar between both sexes. The adult normal group and otitis group behave similarly by sinus-cell relation, i.e., no evident relation, although inhibited mode of distribution was seen by otitis group. When the adult and infant were compared, the sinus-cell relation was similar and the posterior extent suffered underdevelopment by infant. The distance, between the posterior extension of the sphenoidal sinus and the apex cell at the medial-anterior tip of the petrous bone, is between 8-16 mm and the contact of the both separated by thin bony wall (less than 0.5 mm) was seen in 3 adult cases (0.9%). Both the sphenoidal sinus and the petrous apex cells are under genetic influence of variable degree, separate genes seem to be at work, thus effecting no evident relation between the two. Apart from the internal or genetic influence, environmental or outer influence also affects the development of the two, less than the genetic.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of the cranial base in craniosynostosis.

The configuration of the neurocranium has long been used as a diagnostic tool in assessing infants with abnormal head shape. In the case of craniosynostosis, a characteristic shape is caused by a constraint placed on growth of the neurocranium by prematurely closed sutures and secondary accommodation to that constraint. This investigation is a preliminary test of our hypotheses of growth of the cranial base under these constraints. Three dimensional landmark coordinate data were collected from pre-, peri-, and postoperative CT scans of eleven patients from The Cleft Palate and Craniofacial Deformities Institute, St. Louis, MO. These data were used in two sets of analytical comparisons. Comparisons of preoperative and perioperative morphology were taken to represent preoperative growth, while comparisons of perioperative to postoperative CT scans represent postoperative growth. Finite-element scaling analysis (FESA) and Euclidean distance matrix analysis (EDMA) were used to make these comparisons. Our results show that in cases involving premature closure of the metopic, sagittal, and bilateral coronary sutures, predictions about growth of the cranial base made prior to analysis prove correct. In these forms of craniosynostosis there are characteristic and consistent changes in the cranial base in both pre- and postoperative growth. Preoperative and postoperative growth in patients diagnosed with unicoronal synostosis show a greater degree of individual variability and do not follow a predictable pattern.

Petrous apex and subarcuate fossa maturation.

During the first year of life, the bone of the petrous apex grows rapidly. At birth, only 5 mm of bone separates the cochlea from Dorello's canal as compared to 2 cm in the adult. More than half this growth occurs during the first year of life. The subarcuate fossa is a cavity within the superior semicircular canal which reaches from the posterior fossa to the future mastoid in fetuses and nearly to the mastoid antrum in newborns. During the second year of left it is nearly obliterated to form a shallow depression or slit on the posterior aspect of the temporal bone and the variable petromastoid canal which contains the subarcuate artery and vein. Clinical petrositis of infants less that 1 year of age is rare, and provides a challenge for surgery. A case is reported and discussed.

[Postnatal developmental changes in the posterior cranial fossa area. I. Facies posterior partis petrosae (porus et meatus acusticus internus, fossa subarcuata, apertura externa aqueductus vestibuli, apertura externa canaliculi cochleae)]. / Uber postnatale Wachstumsveränderungen im Bereich der Fossa cranialis posterior. I. Facies posterior partis petrosae (Porus et Meatus acusticus internus, Fossa subarcuata, Apertura externa aqueductus vestibuli, Apertura externa canaliculi cochleae).

1. In the newborn the lateral edge of the internal acoustic pore is located about 13.3 mm, in the 2-year-old about 22.5 mm and in the adults about 28.5 (22 to 34) mm from the paramedian plane of the skull. Also the mean distance from the lateral wall of the skull increases from about 13 to 30 mm in the postnatal period. 2. Without the postnatal development of height and width of the internal acoustic pore the postnatal extension (from a mean value of 5 mm in the newborn to about 10 mm in the 15- to 17-year-old) also the postnatal development of height and width of the internal acoustic meatus were measured. 3. Size, width and position of the subarcuata fossa, the external aperture of the aqueduct of the vestibulum just as the external aperture of the cochlear canaliculus were determined. The results were discussed in detail with the datas of former investigators.