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 dis- tance 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. Keywords Subarcuate fossa · Subarcuate canaliculus · Petromastoid canal Introduction chimpanzee, orangutan) and in human, the volume of adult form of SF has been highly reduced . The subarcuate fossa (SF) in adults is a shallow depression The bottom of SF usually gives an origin to the subarcu- on the posterior surface of petrous part of the temporal bone. ate canaliculus (SC), also known as petromastoid canal or It is situated superior and lateral to the internal acoustic antrocerebellar canal of Chatellier . It connects the pos- meatus. It has a shape of real fossa in most of the mammals. terior cranial fossa with periantral mastoid cells. Both SF In tree climbing animals, such as small apes (prosimians, and SC house the dura mater and subarcuate blood vessels macaques), it is of relatively large volume and houses the that supply surrounding tissues and mastoid cells . One petrosal lobule of the cerebellar paraflocculus. On the other of these vessels, the subarcuate artery, usually originates hand, in greater apes, living mostly on the ground (gorilla, from the anterior inferior cerebellar artery or from the laby- rinthine artery, whereas the subarcuate vein drains into the superior petrosal sinus or directly into the sigmoid sinus [11, 13]. The role of SF and SC has not been clearly explained * Mateusz Maślanka in the literature. Some reports provide the hypothesis that firstname.lastname@example.org the SC can be a potential route for infection from the middle ear to the posterior cranial fossa—even 3.2% of cerebellar Department of Descriptive and Clinical Anatomy, The Medical University of Warsaw, 5 Chalubinskiego St., abscesses can have such origin . 02004 Warsaw, Poland The reason of above may be explained by developmental Department of Pediatric Neurosurgery, Bogdanowicz characteristics of SF. Throughout the intrauterine period, Memorial Hospital for Children, 4/24 Nieklanska St., SF develops together with the membranous labyrinth under 03924 Warsaw, Poland Vol.:(0123456789) 1 3 1112 Surgical and Radiologic Anatomy (2018) 40:1111–1117 the arch of the anterior semicircular canal (ASC). It may be study. Patients with congenital or acquired malformations of distinguished in 11 Hbd human fetuses—as a hollow pouch the head or the history of such in their medical records, the of 2 mm diameter, which normally begins to ossify after scans containing fractures of the middle or posterior cranial 15th week of gestation  and attains the greatest dimen- fossa or inflammatory disease of the temporal bone were not sions between the 24 and 28 weeks. After this stage, the SF included in the study. Finally, the studied group consisted of slowly but constantly decreases in size, although it is still 101 cases (43 female, 59 male). relatively big after birth . Some authors hypothesize that For a better clarity of results, the studied sample was the size of FS in early stages of postnatal development may divided into three age groups: A (from 0 to 12 months, 32 promote spreading infections into the cranial cavity. On the cases), B (from 13 to 30 months, 37 cases) and C (from 31 other hand, the dimensions of SF may also serve as impor- to 60 months, 32 cases). tant landmarks for the purposes of planning the implantation To describe relations between SF and petrous part of of cochlear implants in the youngest children . the temporal bone, several parameters were measured: (1) Subarcuate fossa was described several times by other the length of the pyramid (PL), (2) the distance between authors and the differences in SF anatomy between the popu- the anterior semicircular canal (ASC) and the pyramidal lation younger and older than 5 years have been described apex (PLM) and (3) the outer diameter of ASC (ASCD) [5–8]. However, anatomical descriptions of SF in individu- (see Table 1; Fig. 1). The changing morphology of SF was als younger than 5 years given in the literature are usually described by: (4) its width under ASC (SFWM), (5) the dis- incomplete, due to a fact that this period is characterized by tance between the fundus of SF and ASC (SFLL), (6) the the greatest intensiveness of the development of the petrous maximal width of SF lateral to ASC (SFWL), and (7) the part of the temporal bone. Therefore, the aim of this paper is to characterize both SF and SC by means of anatomical and radiological methods. Materials and methods The study was carried out on anonymized CT scans (bone window) of children of both sexes collected retrospectively at the Bogdanowicz Memorial Hospital for Children, War- saw, between February 2011 and January 2012. All the scans were made due to clinical indications with CT scan- ner Siemens Somatom Emotion (slice thickness from 0.75 to 3 mm, the exposition performed with source voltage of 270 kV and current of 100 mA). Only the scans of patients Fig. 1 CT scan of a 4-month-old infant. MA mastoid antrum, PL, aged 1 month–5 years (60 months) were included in the PLM, ASCD—parameters described in the text and Table 1 Table 1 Description of parameters used in the study Parameter (all meas- Description ured in horizontal plane) PL Length of the petrous part of TB measured from the apex to the external table of TB. The measurement was perpen- dicular to ASCD PLM Length of the petrous part of TB medial to the ASC measured from the apex to the ASCD. The measurement was perpendicular to ASCD ASCD Outer diameter of ASC measured between the most distal points of the lumen of ASC SFWM Width of SF under ASC (width of medial part of SF) SFWL Maximal width of lateral part of SF measured laterally to ASC SFLL Distance between the fundus of SF and ASC (length of the lateral part of SF). The measurement was perpendicular to ASCD SFL Distance between the fundus of SF and posterior surface of the pyramid (length of the whole SF). Measured in hori- zontal axis TB temporal bone, ASC anterior semicircular canal, SF subarcuate fossa 1 3 Surgical and Radiologic Anatomy (2018) 40:1111–1117 1113 distance between the fundus of SF and posterior surface of the pyramid (SFL) (see Table 1; Fig. 2). The presence of the SC was noted in every case. It was identified as a bony canal of a diameter less than 2 mm, emerging from the fundus of SF below ASC and connecting the posterior cranial fossa with mastoid air cells (Fig. 3). All the measurements were obtained with the use of software provided and calibrated by the manufacturer. The parameter values were noted in a database designed for the purpose of this study. Obtained data were analyzed statisti- cally with the use of StatSoft Statistica 13.1 software. We used parametric tests (t test and Pearson correlation coef- ficient) due to normal distribution of our data. Results Obtained data showed that both PL and PLM constantly Fig. 3 CT scan of a 5-year-old child. Arrowheads indicate subarcu- increase with age (Fig. 4a). Within the studied period of ate canaliculus, ASC anterior semicircular canal, MCF middle cranial 60 months, the length of the pyramid ranged from 35.1 fossa, MA mastoid antrum, PCF posterior cranial fossa, SS sphenoid sinus to 63.9 mm and the PLM distance increased from 16.5 to 32.3 mm (Fig. 4b). Both these parameters revealed a strong positive correlation with age (PL Pearson’s r = 0.74, bones in group B (78.4%) and in 55 out of 64 temporal bones p < 0.05; PLM Pearson’s r = 0.73, p < 0.05). On the other hand, the ASCD showed no correlation with age; its value in group C (85.9%). All the measured parameters are pre- sented in Table 2. was more constant throughout age groups and ranged from 6.7 to 10.5 mm (Table 2). The morphology of SF revealed a strong relation to the measured parameters: its portion located lateral to the ASC Discussion decreased rapidly in all measured dimensions and was totally absent in children older than 18 months (Fig. 5). The dynam- The petrous part of the temporal bone is characterized by ics of the reduction of SF volume can be precisely followed based on the changes in SFL (Fig. 6). In group A, the aver- a complex growth pattern. The descriptions of such can be found in numerous papers [2, 5, 10]. The computed tomog- age depth of SF was the greatest, in group B it decreased to almost total absence in group C. As shown in Fig. 6, this raphy seems to be an accurate method for assessment of the temporal bone development, as it shows age-specific stages parameter attains a constant average adult depth of 1 mm after 36 months of life. of internal bone organization and, therefore, allows a precise estimation of appropriate timeline for each stage [5–8, 10, The subarcuate canaliculus was identified in 13 out of 64 temporal bones in group A (20.3%), in 58 out of 74 temporal 13]. Fig. 2 CT scan of a 2-month- old infant. ASC anterior semicir- cular canal, MCF middle cranial fossa, MA mastoid antrum, PCF posterior cranial fossa. SFLL, SFWM, SFW, SFL—parameters described in the text and Table 1 1 3 1114 Surgical and Radiologic Anatomy (2018) 40:1111–1117 Fig. 4 Chart of correlation between the length of petrous part of the temporal bone and age. PL, PLM—parameters described in the text and Table 1 Table 2 Descriptive statistics Parameter (mm) Group A (0–12 months) Group B (13–30 months) Group C (31–60 months) of direct parameters used in the study Avg SD Min Max Avg SD Min Max Avg SD Min Max PL 45.44 5.27 35.10 55.80 53.81 3.90 40.10 61.20 56.83 3.20 48.20 63.90 PLM 21.94 2.72 16.50 28.10 26.82 1.96 21.50 31.20 28.20 2.08 23.40 32.30 ASCD 8.60 0.72 6.80 10.50 8.64 0.66 6.70 9.60 8.65 0.63 7.10 10.20 SFWM 2.43 0.88 0.70 4.20 0.51 0.82 0.00 2.40 0.00 0.00 0.00 0.00 SFWL 3.13 1.25 0.00 5.70 0.23 0.72 0.00 3.60 0.00 0.00 0.00 0.00 SFLL 6.61 1.27 2.90 9.60 3.03 1.60 0.90 7.60 1.32 0.64 0.80 4.50 SFL 2.16 1.12 0.00 5.30 0.22 0.57 0.00 2.30 0.00 0.00 0.00 0.00 Avg average value 1 3 Surgical and Radiologic Anatomy (2018) 40:1111–1117 1115 Fig. 5 Morphological changes of SF with age. a SF of 2-month-old SF and SC, ASC anterior semicircular canal, MCF middle cranial infant (group A), b SF of 18-month-old child (group B), c morpho- fossa, MA mastoid antrum logical transformation of SF into SC (group C). Arrowheads indicate Fig. 6 Chart of correlation between the length of SF (SFL) and age. Group A (from 0 to 12 months), group B (from 13 to 30 months) and group C (from 31 to 60 months) A decrease of SF after birth remains a fact and the dif- interesting that the ASC can serve as a marker of the sym- ferences between children up to 5 years and older have been metry of the temporal bone development—based on its posi- well established [6–9, 13]. Proctor indicates that SF nar- tion the growth of the petrous part splits into two alternative rows into the canal before the 5th year of life and the adult pathways. The portion of the pyramid medial to ASC grows morphology of SF is attained in the 5th year of life. Migirov as a solid bone, by increasing in all the dimensions, whereas and Kronenberg support the findings of Proctor and do not the portion lateral to ASC gains its size by the enlargement find significant differences in SF morphology between older of pneumatic areas. Meanwhile, the bony labyrinth seems to children and adults. However, the postnatal developmental be unaffected by the growth of surrounding structures [2 , 5]. pattern of SF in children below the age of 5 years is more In our study, in children younger than 12 months the vol- complex and, in our opinion, should be described more ume of SF is the greatest in postanatal life. The appearance precisely. of SF in group A refers to type IV of SC by Migirov and After birth, the petrous part of the temporal bone grows Kronenberg [7, 8]. Our distinction of SF into two portions rapidly during the first 2 years of life, especially in long located on both sides of the ASC allows to describe the axis, and this pattern of growth promotes ASC (together decreasing of SF in a more precise manner. In our sample, with SF) to take the central position in the pyramid. It seems the portion lateral to ASC is well developed in newborns 1 3 1116 Surgical and Radiologic Anatomy (2018) 40:1111–1117 [6, 12]. As in other papers, all the recognized SC had a form of a single canal [7, 8, 13]. Regarding this problem, it seems that a targeted study using more accurate imaging techniques would be most appropriate to evaluate this structure. Since experimental configuration of CT scanner raises ethical con- cerns, in our opinion further study might be possible with the comparable population of pediatric cadaveric specimens and the use of CT scanner of a greater accuracy (i.e. cone- beam CT). Developmental morphology of SF and SC contributes to broadening of clinical experience. The anatomy of these two subarcuate structures and their radiological appearance are essential in recognizing the lines of temporal bone fracture in case of padiatric head trauma [1, 6]. The knowledge about them is crucial in diagnostics of cerebrospinal fluid fistulas, that may originate from SF [3, 13], especially as a poten- tial complication of cerebellopontine angle surgery. Other complications, such as unintended damage to the subarcuate artery, might be prevented with a detailed CT-based preop- Fig. 7 Morphological changes of pneumatization of petrous part of erative planning, which would also benefit from this study. the temporal bone with age. a Temporal bone of 3-month-old infant, Finally, the morphology of SF and SC seems to prove that b temporal bone of 5-year-old child. Arrowheads indicate pneumati- infections can spread from the tympanic cavity or mastoid zation of temporal bone, ASC anterior semicircular canal, MCF mid- air cells, especially in the first year of life. Hilding in his dle cranial fossa, PCF posterior cranial fossa, MA mastoid antrum, IAM internal acoustic meatus paper indicates that the infection on its way can affect only soft tissue without destroying the bone . The results of our study seem to concur with this opinion. The width of and infants, reaching its maximal depth in the first month of the canal and its contents may promote the transmission of life. It decreases throughout the first half of the second year pathogens with the easiest route being probably through the to finally disappear about the 18th month. This observation sinusoidal, low-pressure-type, petromastoid vein . correlates with the paper of Hilding . Contrarily, the por- tion of SF medial to ASC seems to decrease less rapidly, as it is still present throughout the second year of life and attains the adult depth (about 1 mm) in the third year of postnatal Conclusions life (group C, Fig. 6), which is earlier than about 5 years, stated in other papers [8, 9]. The SF in newborns and infants is a relatively wide depres- The postnatal development of SF may result in problems sion that narrows into the subarcuate canaliculus, connecting with its proper description, especially in terms of distinction the mastoid air cells with the posterior cranial fossa. After between the SF and SC. This may be one of the limitations the 12th month of postnatal life, its portion lateral to ASC of this study. It seems that SF decreases and narrows into starts to decrease, by gradually losing its previous dimen- SC. This transformation starts laterally and is related to the sions to the complete absence in the 18th month. The portion pneumatization of the mastoid process (Figs. 5, 7) [7, 8, of SF located medial to ASC remains present but is reduced 14]. It is important to note that a standard calibration of to adult size in the third year of life. CT scanners used for clinical purposes does not allow exact Author contribution MM (Neurosurgery Resident, Lecturer in Depart- measurements of the subarcuate canaliculus, as it is limited ment of Descriptive and Clinical Anatomy)—project development, data to ossified portions of the structures described in this study. collection, data analysis, manuscript writing, approval of the manu- Therefore, we decided to apply a criterion of the width of script. TS (Neurosurgeon, Senior Lecturer in Department of Descrip- bony canal to differentiate the SF from SC. The structure tive and Clinical Anatomy)—protocol development, data analysis, manuscript writing, approval of the manuscript. BC (Neurosurgeon, wider than 2 mm was identified as the SF, whereas the canal Head of Department of Descriptive and Clinical Anatomy)—data narrower than 2 mm was considered the SC. This is coher- analysis, approval of the manuscript. ent with other reports as well as requires the use of slices of appropriate thickness. As shown in other papers, a 1-mm Funding This research did not receive any specific grant from fund- slice is appropriate to visualize SC in all cases, whereas the ing agencies in the public, commercial, or not-for-profit sectors. The authors declare that this manuscript has not been published elsewhere thickness above 2 mm may be insufficient for this purpose 1 3 Surgical and Radiologic Anatomy (2018) 40:1111–1117 1117 and is not under consideration by another journal. The authors declare skull–brain interface. Am J Phys Anthropol 77:143–164. https :// that the study complies with the current law in Poland.doi.org/10.1002/ajpa.13307 70202 5. Hilding DA (1987) Petrous apex and subarcuate fossa maturation. Laryngoscope 97:1129–1135 Compliance with ethical standards 6. Krombach GA, Schmitz-Rode T, Prescher A, DiMartino E, Wei- dner J, Günther RW (2002) The petromastoid canal on computed Conflict of interest The authors declare that they have no conflict of tomography. Eur Radiol 12:2770–2775. https ://doi.org/10.1007/ interest. s0033 0-002-1306-5 7. Migirov L, Kronenberg J (2006) Radiology of the petromastoid Open Access This article is distributed under the terms of the Crea- canal. Otol Neurotol 27:410–413 tive Commons Attribution 4.0 International License (http://creat iveco 8. Migirov L, Kronenberg J (2009) Petromastoid canal and cochlear mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- aqueduct in cochlear implant candidates. Otolaryngol Head Neck tion, and reproduction in any medium, provided you give appropriate Surg 140:419–422. https ://doi.org/10.1016/j.otohn s.2008.11.017 credit to the original author(s) and the source, provide a link to the 9. Proctor B (1983) The petromastoid canal. 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